manufacturing yogurt and fermented milks 2006 chandan

Manufacturing Yogurtand Fermented Milks

Manufacturing Yogurtand Fermented Milks

EditorRamesh C. Chandan

Associate EditorsCharles H. White

Arun KilaraY. H. Hui

Ramesh C. Chandan, Ph.D., is a consultant in dairyscience and technology with special expertise in themanufacture of yogurt and fermented milks. He hasmore than 40 years experience with various food com-panies, including Unilever, Land OLakes and GeneralMills. He served on the faculty of the Department ofFood Science and Human Nutrition, Michigan StateUniversity, East Lansing from 1976–82.

Charles H. White, Ph.D., is professor and formerHead of the Department of Food Science, Nutritionand Health Promotion at Mississippi State University.

Arun Kilara, Ph.D., is a food industry consultant spe-cializing in dairy foods, ingredient functionality, prod-uct development, and training. He has served on thefaculty of Penn State University for more than 20 years.

Y.H. Hui, Ph.D., is a food industry consultant and hasserved as the author, editor, or editor-in-chief of numer-ous books in food science, technology, engineering,and law.

C© 2006 Blackwell PublishingAll rights reserved

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First edition, 2006

Library of Congress Cataloging-in-Publication Data

Manufacturing yogurt and fermented milks /editor, Ramesh C. Chandan ; associate editors,Charles H. White, Arun Kilara, Y. H. Hui.—1st ed.

p. cm.Includes bibliographical references and index.ISBN-13: 978-0-8138-2304-1 (alk. paper)ISBN-10: 0-8138-2304-8 (alk. paper)1. Yogurt. 2. Fermented milk. 3. Dairy

processing. 4. Food industry and trade.I. Chandan, Ramesh C.

SF275.Y6M36 2006637′.1476—dc22

2005017248

The last digit is the print number: 9 8 7 6 5 4 3 2 1

Contents

Contributors, vii

Preface, ix

Part I Basic Background1. History and Consumption Trends, 3

Ramesh C. Chandan2. Milk Composition, Physical and Processing Characteristics, 17

Ramesh C. Chandan3. Regulatory Requirements for Milk Production, Transportation, and Processing, 41

Cary P. Frye4. Regulations for Product Standards and Labeling, 57

Cary P. Frye5. Basic Dairy Processing Principles, 73

Arun Kilara6. Starter Cultures for Yogurt and Fermented Milks, 89

Ebenezer R.Vedamuthu7. Laboratory Analysis of Fermented Milks, 117

Robert T. Marshall8. Fermented Dairy Packaging Materials, 129

Aaron L. Brody

Part II Manufacture of Yogurt9. Yogurt: Fruit Preparations and Flavoring Materials, 151

Kevin R. O’Rell and Ramesh C. Chandan10. Milk and Milk-Based Dairy Ingredients, 167

Isabelle Sodini and Phillip S. Tong11. Ingredients for Yogurt Manufacture, 179

Ramesh C. Chandan and Kevin R. O’Rell12. Principles of Yogurt Processing, 195

Ramesh C. Chandan and Kevin R. O’Rell13. Manufacture of Various Types of Yogurt, 211

Ramesh C. Chandan and Kevin R. O’Rell14. Plant Cleaning and Sanitizing, 237

Dennis Bogart

v

vi Contents

15. Yogurt Plant: Quality Assurance, 247Ramesh C. Chandan and Kevin R. O’Rell

16. Sensory Analysis of Yogurt, 265Yonca Karagul-Yuceer and MaryAnne Drake

Part III Manufacture of Fermented Milks17. Cultured Buttermilk, 279

Charles H. White18. Cultured/Sour Cream, 285

Bill Born19. Other Fermented and Culture-Containing Milks, 295

Ebenezer R. Vedamuthu

Part IV Health Benefits20. Functional Foods and Disease Prevention, 311

Ramesh C. Chandan and Nagendra P. Shah21. Health Benefits of Yogurt and Fermented Milks, 327

Nagendra P. Shah22. Probiotics and Fermented Milks, 341

Nagendra P. Shah

Index, 355

Contributors

Dennis Bogart (Chapter 14)Randolph Associates Inc.3820 3rd Avenue South, Suite 100Birmingham, AL 35222 USAPhone: 205-595-6455Fax: 205-595-6450E-mail: dennis [email protected]

Bill Born (Chapter 18)Dairy Consultant (Retired from DeanFoods Company)7254, South MainRockford, IL 61102 USAPhone: 815-965-2505Fax: 815-968-9280E-mail: [email protected]

Aaron L. Brody, Ph.D. (Chapter 8)President & CEOPackaging/Brody, Inc.PO Box 956187Duluth, GA 30095-9504 USAPhone: 770-613-0991Fax: 770-613-0992E-mail: [email protected]

Ramesh C. Chandan, Ph.D.(Editor, Chapters 1, 2, 9, 11–13, 15, 20)Consultant1364, 126th Avenue, NWCoon Rapids, MN 55448-4004 USAPhone: 763-862-4768Fax: 763-862-4768E-mail: [email protected]

MaryAnne Drake, Ph.D. (Chapter 16)Department of Food ScienceNorth Carolina State UniversityPO Box 7624Raleigh, NC 27695 USAPhone: 919-513-4598Fax: 919-513-0014E-mail: [email protected]: (919) 515-4598; F: (919) 515-7124

Cary P. Frye (Chapters 3, 4)Vice President Regulatory AffairsInternational Dairy Foods Association1250 H Street, N.W., Suite 900Washington, DC 20005 USAPhone: 202-737-4332Fax: 202-331-7820E-mail: [email protected]

Y. H. Hui, Ph.D (Associate Editor)Senior ScientistScience Technology SystemP.O. Box 1374West Sacramento, CA 95691, USAPhone: 916-372-2655Fax: 916-372-2690E-mail: [email protected]

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viii Contributors

Arun Kilara, Ph.D. (Associate Editor, Chapter 5)PrincipalArun Kilara Worldwide(An affiliate of Stratecon International Consultants)516 Copperline DriveChapel Hill, NC 27516Phone: 919-968-9322Home: 919-370-9684Cell: 603-491-5045www.akilara.comwww.stratecon-intl.comE-mail: [email protected]

Robert T. Marshall, Ph.D. (Chapter 7)Professor EmeritusDepartment of Food ScienceUniversity of Missouri122 Eckles HallColumbia, MO 65211 USAPhone: 573-882-7355Fax: 573-882-0596E-mail: [email protected]

Kevin R. O’Rell (Chapters 9, 11–13, 15)Vice President, R&D/QAHorizon Organic6311, Horizon LaneLongmont, CO 80503 USAPhone 303-530-2711, ext 175Fax: 303-516-7252Cell: 303-579-4507E-mail: [email protected]

Nagendra P. Shah, Ph.D. (Chapters 20–22)Professor of Food Science and TechnologySchool of Molecular SciencesVictoria UniversityPO Box 14428Melbourne City Mail CentreVictoria 8001, AustraliaPhone: 61 3 9919 8289Fax: 61 3 9919 8284E-mail: [email protected]

Isabelle Sodini, Ph.D. (Chapter 10)Portocork America560, Technology WayNapa, CA 94558-6722, USAPhone: 707-258-3930Fax: 707-258-3935E-mail: [email protected]

Phillip S. Tong, Ph.D. (Chapter 10)Director, Dairy Products Technology CenterCalifornia Polytechnic State UniversitySan Luis Obispo., CA 93407 USAPhone: 805-756-6102Fax: 805-756-2998E-mail: [email protected]

Ebenezer R. Vedamuthu, Ph.D. (Chapters 6, 19)332 NE Carmen PlaceCorvallis, OR 97330 USAPhone: 541-745-5206E-mail: [email protected]

Charles H. White, Ph.D.(Associate Editor, Chapter 17)Mississippi State UniversityDepartment of Food Science, Nutrition andHealth PromotionPO Box 9805Mississippi State, MS 39762-9805 USAPhone: (662)325-2473Fax: (662)325-8728E-mail: [email protected]

Yonca Karagul-Yuceer, Ph.D. (Chapter 16)Assistant ProfessorCanakkale Onsekiz Mart UniversityDepartment of Food EngineeringTerzioglu Campus17020 Canakkale, TurkeyE-mail: [email protected]: +90 (0) 286 218 00 18, Ext. 1729Fax: +90 (0) 286 218 05 41

Preface

Fermented dairy products other than cheeses havebeen consumed around the world for thousands ofyears. Nevertheless, their industrial production is rel-atively a new innovation. Yogurt has emerged as anoutstanding new product of recent times. It has oc-cupied a very significant position of consumer ac-ceptance and growth in North America and through-out the world. In the United States, yogurt, butter-milk, sour cream, and probiotic drinks have become amulti-billion-dollar industry. The yogurt market con-tinues to grow on an annual basis.

The literature on yogurt and fermented milks isvast and diverse. It encompasses the basic and fun-damental aspects as well as the applied and practi-cal facets of the industry. This book is intended todisseminate the applied and practical aspects. Somebasic science is included only to facilitate under-standing of the practice of manufacturing yogurt andfermented milks. Overall, our objective is not to pro-vide fundamental information. Instead, attempts havebeen made to deal with the application of the sci-ence of yogurt and fermented milks to their manu-facture and emphasize the practices in vogue in theindustry.

As mentioned above, this book is dedicated to themanufacture of yogurt and fermented milks. In viewof the multidisciplinary nature and continued fast de-velopments in the technology and packaging of fer-mented milks including yogurt, the book has multi-ple authors. The authors drawn from the industry andacademia are acknowledged as experts in their re-spective fields. Many authors have utilized their life-long experience in the product development, qualityassurance, and manufacture of yogurt and fermentedmilks in their contributed chapters. Their contributionto the writing of the book makes this book unique andfirst of its kind in the literature. From comprehension

and readability standpoint, an effort has been madeto make the book reader- friendly.

The book is organized into twenty-two chaptersand divided into four parts. Part I covers the basicbackground with eight chapters. The objective is toprepare the reader for the manufacturing of yogurtand fermented milks by providing relevant informa-tion on product trends, regulatory aspects, dairy pro-cessing technologies, packaging techniques, startercultures use, and laboratory analysis.

Part II is devoted to the manufacture of yogurt. Thispart also consists of eight chapters. It includes rawmaterials, namely dairy and dairy-based ingredients,fruits and flavors, stabilizers, sweeteners (nutritiveand high intensity), principles of yogurt processing,types of yogurt products on the market and their man-ufacturing techniques, quality control procedures,sensory evaluation of yogurt, and plant cleaning andsanitizing programs. The formulation, regulatory as-pects, labeling, processing equipment, and packagingoperations of various products have been included.

Part III contains three chapters detailing the man-ufacturing technology of cultured buttermilk, sourcream, and miscellaneous fermented milks popularthroughout the major regions of the world. It also in-cludes culture-containing milks that are not culturedand retain the sensory characteristics of milk but con-comitantly provide beneficial probiotic cultures to theconsumer.

Part IV deals with the overall health benefits ofyogurt and fermented milks. This topic has assumedmuch interest in view of consumer perception ofhealth promotion attributed to functional foods likeyogurt and fermented milks. This part brings to thereader a brief review of our understanding of bothperceived and real benefits. A concise account of thescientific and clinical evidence associated with the

ix

x Preface

benefits of consuming yogurt and milks containingprobiotic cultures, prebiotics, and synbiotics has beenreviewed. This is a timely subject because new prod-ucts with health claims are increasingly appearing inthe market. We feel that this is the direction for fu-ture growth of the industry engaged in yogurt andfermented milks manufacture.

This book is the culmination of efforts to providea systematic and relatively simplified version of theinformation available on significant aspects of man-ufacturing yogurt and fermented milks. It is intendedas a textbook to be used by upper undergraduate uni-versity students of dairy and food science to learntheory and practice of technology associated with themanufacture of yogurt and fermented milks. Gradu-ate students should find the book useful as a refer-ence book to obtain information on applied scienceand technology of yogurt and fermented milks. Theindustrial bias of the book should appeal to the practi-tioners of food science and technology in the food in-dustry. In this case, it would provide a ready reference

material for plant operators, personnel performingfunctions in quality control/assurance, and researchand development. The book should also be helpfulfor food industry personnel engaged in taking pur-chasing decisions. Since the book conveys collatedpractical information on yogurt and fermented milksin entirety, it should be useful as a textbook to theinstructors and participants of the industry-orientedshort courses on cultured dairy products.

We acknowledge the worldwide contribution of allthe scientists, technologists, and engineers who haveestablished modern principles for the manufacture ofyogurt and fermented milks to provide the consumerwith a truly functional family of foods that furnishvital dairy nutrients as well as unique, wholesome,and healthy products.

Ramesh C. Chandan, Minneapolis, MNCharles H. White, Mississippi State, MS

Arun Kilara, Chapel Hill, NCY. H. Hui, Sacramento, CA

Part IBasic Background

Manufacturing Yogurt and Fermented MilksEdited by Ramesh C. Chandan

Copyright © 2006 by Blackwell Publishing

1History and Consumption Trends

Ramesh C. Chandan

Overview of the World Dairy IndustryMilk Production in the United StatesProduction of Dairy Foods in the United StatesFermented/Cultured Dairy ProductsOccurrence and Consumption of

Fermented Milks in Various RegionsMilk of Various SpeciesCultures for Production of Fermented MilksForms of Fermented Milks

Major Commercial Fermented MilksFermented Milks of ScandinaviaFermented Milks of Russia and East EuropeFermented Milks of Middle EastFermented Milks of South AsiaReferencesBibliography

OVERVIEW OF THE WORLDDAIRY INDUSTRYThe world production of cow’s milk in the year 2003was 398 million metric tons (see Table 1.1). Thedocumented number of cows was 125,490 thousandheads. Individual cow milk yield varies widely in theworld. Japan was the most efficient milk producerwith a yield of 8.71 t/cow, followed by the UnitedStates with a yield of 8.50 t/cow.

MILK PRODUCTION IN THEUNITED STATESDuring the last decades, the trend indicates decreasein dairy cow population (Table 1.2). Currently, nearlynine million cows produce 77.25 million metric tons(170,312 million pounds) of milk (USDA, 2004). Asindicated in Table 1.2, there is a steady increase inmilk production per cow. Approximately 20% of the

world’s milk is produced in the United States. TheAmerican dairy farmer has been able to achieve thecurrent milk output by applying scientific and mana-gement advancements in milk production. On thedairy farm, selection of dairy cows, their breeding,and judicious use of balanced feed rations have beeninstrumental in increasing milk output per cow. Inthe year 2003, milk production per cow increasedto 8,507 kg (18,749 lb). As a result of continuousefficiencies in milk production at the farm, milk pro-duction per cow has doubled in the last 30 years.

PRODUCTION OF DAIRY FOODSIN THE UNITED STATESModern milking and milk-handling equipment, in-cluding automated milking systems, have improvedthe speed of cleaning, sanitizing, cooling, and deliv-ering good quality raw milk to processing plants. TheUnited States has the distinction of being the largestprocessor of milk and dairy products in the world.Advanced processing and packaging technologiesensure efficient delivery and shelf life of high-qualitymilk products, including yogurt and fermented milks.Currently, there are 800 dairy processing plants in theUnited States, where milk is transformed into morethan 300 varieties and styles of cheese, 100 flavors ofice cream and frozen yogurt, and 75 flavors of sev-eral types of refrigerated yogurt. Dairy plants alsoproduce an array of flavored and white milks rang-ing from fat-free to full fat, butter, sweetened con-densed milk, evaporated milk, dry milk, lactose, andwhey products, as well as cultured products such assour cream and dips, buttermilk, yogurt, and yogurtdrinks. More recently, the industry has introducedpackaging and marketing innovations to compete

3



4 Part I: Basic Background

Table 1.1. Milk Production in the World in 2003

Country Milk Cows (1000 head) Milk Yield/Cow-(t) Total Milk Produced (1000 t)

Canada 1,065 7.30 7,778Mexico 6,800 1.00 9,784United States 9,084 8.50 77,253Argentina 2,000 3.98 7,950Brazil 15,300 1.49 22,860Peru 630 1.95 1,226European Union 24,690 5.35 132,044Romania 1,684 3.21 5,400Russia 11,700 2.82 33,000Ukraine 4,715 2.84 13,400India 36,500 1.00 36,500China 4,466 3.91 17,463Japan 964 8.71 8,400Australia 2,050 5.19 10,636New Zealand 3,842 3.73 14,346

Total selected countries 125,490 – 398,040Source: USDA, Service, FAS/CMP/DLP December, 2004.http//www.fas usda.gov/dlp/circular2004/64-12Dairy/cowprod.pdf

aggressively for consumer food dollar share. Table1.3 lists the products manufactured and their volumesduring 1997–2002.

Dairy farmers and dairy processors alike abide bystrict state and federal sanitary standards. Grade APasteurized Milk Ordinance (PMO) regulations arethe recommendations of the Public Health Service ofthe Food and Drug Administration of United StatesDepartment of Health and Human Services (DHHS,1999). The PMO is meant for voluntary adoption,but its importance in ensuring the quality and safetyof milk supply in the country is recognized by thedairy industry as well as by the state regulatory

and sanitation officials. The PMO is a constantlyevolving set of regulations to accommodate advance-ments and developments in science and technologyrelated to milk production, processing, packaging,and distribution. From time to time, modifications inthe regulations are adopted following an agreementamong the representatives of government, industry(milk producers, processors, equipment manufactur-ers, and suppliers), and academic and research in-stitutions. To conform to the PMO, dairy farms anddairy plants are visited regularly by representatives ofgovernment regulatory agencies, who conduct qual-ity assurance and safety inspections at the farms

Table 1.2. Milk Production in the United States

Milk Cows Total Milk ProductionYear (1000 head) Production/Cow (lb) (million pounds)

1994 9,494 16,179 153,6021995 9,466 16,405 155,2921996 9,372 16,433 154,0061997 9,252 16,871 156,0911998 9,154 17,189 157,3481999 9,156 17,772 162,7162000 9,206 18,201 167,5592001 9,114 18,159 165,4972002 9,139 18,608 170,0632003 9,084 18,749 170,312Source: http//usda.mannlib.cornell.edu/reorts/nassr/dairy/pmp-bb/2004/mkpr0204.txt.

1 History and Consumption Trends 5

Table 1.3. Production of Dairy Products in the United States During 1997–2002

Production Volume (millions of pounds)

Product 1997 1998 1999 2000 2001 2002

Butter 1,151 1,168 1,277 1,251 1,236 1,237Natural cheese 7,330 7,492 7,941 8,258 8,260 8,599Processed cheese, 2,210 2,278 2,425 2,288 2,207 2,155

foods and spreadsFrozen dessertsa 1,569 1,624 1,623 1,068 1,571 1,576Ice creamsa

Regular 914 935 972 980 981 989Low fat 387 407 381 373 407 362Nonfat 41 43 40 31 21 –

Cottage cheeseCreamed 360 367 361 371 372 372Low fat 347 361 359 364 371 370Curd 458 466 465 461 454 –

PlainWhole milk 18,413 18,147 18,467 18,448 18,007 17,960Reduced and 23,709 23,449 23,571 23,649 23,630 23,610low fat milkNonfat milk 9,139 9,203 8,985 8,435 8,225 8,030

Flavored milk and drinks 2,830 3,044 3,216 3,336 3,526 4,040Half and half 883 895 960 1,008 1,146 1,140Light cream 119 134 168 168 – –Heavy cream 504 515 555 743 797 720Eggnog 102 102 109 93 105 127Refrigerated yogurt 1,574 1,639 1,717 1,837 2,003 2,135Frozen yogurt∗ 92 97 91 94 71 73Sour cream and dips 794 817 841 914 990 1,031Buttermilk 691 676 668 622 592 576

a Millions of gallons.Source: IDFA, 2003.

and processing plants. These inspectors confirm herdhealth, oversee veterinary practices, monitor sanita-tion of the facilities and milking equipment, and ver-ify that the milk is being rapidly cooled and properlystored until delivered to processing facilities. Theyalso ensure that the processing of milk is in accor-dance with the state and federal food laws. In someinstances, the state standards differ and may be evenmore stringent than the federal standards. The stateand in some cases local communities have jurisdic-tion for standards for milk in their own market.

The PMO defines Grade A specifications and stan-dards for milk and milk products to facilitate move-ment of milk across state lines. Market milk, cream,yogurt, cultured buttermilk, and sour cream are gov-erned by the Grade A standards. Reciprocity rightsmaintain that milk conforming to the PMO sani-tary standards in one state would not require further

inspections for acceptance by another state (seeChapter 3 for a detailed discussion on this topic).

The industry has consolidated and continued tomake large investments in new, state-of-the-art dairymanufacturing facilities. During the past decade,such developments have enabled a 45% reduction inthe number of manufacturing facilities while the totalmilk output has increased by 4–5% annually. Contin-ued investment will mean still lower processing costsand higher milk output.

FERMENTED/CULTUREDDAIRY PRODUCTSFermented dairy foods have constituted a vital part ofhuman diet in many regions of the world since timesimmemorial. They have been consumed ever sincehumans domesticated animals. Evidence showing


the use of fermented milks has been found in arche-ological research associated with the Sumerians andBabylonians of Mesopotamia, the Pharoes of north-east Africa, and Indo-Aryans of the Indian subconti-nent (Chandan, 1982, 2002; Tamime and Robinson,1999). Ancient Indian scriptures, the Vedas, datingback some 5,000 years, mention dadhi (modern dahi)and buttermilk. Also, the ancient Ayurvedic system ofmedicine cites fermented milk (dadhi) for its health-giving and disease-fighting properties (Aneja et al.,2002).

Historically, products derived from fermentationof milk of various domesticated animals resulted inconservation of valuable nutrients, which otherwisewould deteriorate rapidly under high ambienttemperatures prevailing in South Asia and MiddleEast. Thus, the process permitted consumption ofmilk constituents for a period of time significantlylonger than possible for milk itself. Concomitantly,conversion of milk to fermented milks resulted in thegeneration of distinctive viscous consistency, smoothtexture, and unmistakable flavor. Furthermore, fer-mentation provided food safety, portability, andnovelty for the consumer. Accordingly, fermenteddairy foods evolved into the cultural and dietaryethos of the people residing in the regions of theworld where they owe their origin.

Milk is a normal habitat of a number of lactic acidbacteria, which cause spontaneous souring of milkheld at bacterial growth temperatures for appropri-ate length of time. Depending on the type of lacticacid bacteria gaining entry from the environmentalsources (air, utensils, milking equipment, milkers,cows, feed, etc.), the sour milk attains characteris-tic flavor and texture.

Approximately 400 diverse products derived fromfermentation of milk are consumed around theworld. Fermentation conserves the vital nutrients ofthe milk. Simultaneously, it modifies certain milkconstituents enhancing their nutritional status andfurnishes to the consumer live and active culturesin significant numbers, which provide distinct healthbenefits beyond conventional nutrition. Fermentedmilk products may be termed as “functional foods.”They represent a significant and critical sector of thehuman diet. These products fit into the cultural andreligious traditions and dietary pattern of many popu-lations. In addition to the main ingredient, milk, otherfood ingredients are also used in the fermented milksto innovate a range of nutritional profiles, flavors,textures, and mouth feel, thereby offering an array ofchoices for the consumer. Fermented foods and their

derivatives may constitute a staple meal, or may beconsumed as an accompaniment to the meal. Theymay be also used as a snack, drink, dessert, condi-ment, or spread as well as an ingredient of cookeddishes.

Diversity of fermented milks may be ascribed to anumber of factors: (a) Use of milk obtained from var-ious domesticated animals, (b) application of diversemicro flora, (c) addition of sugar, condiments, grains,fruits, etc., to create a variety of flavors and textures,and (d) application of additional preservation meth-ods, e.g., freezing, concentrating, and drying.

OCCURRENCE ANDCONSUMPTION OF FERMENTEDMILKS IN VARIOUS REGIONSThere is a diversity of fermented milks in the variousregions of the world (see Table 1.4). As shown inTable 1.5, the 1998 annual per capita consumptionof various fermented fluid milks in various countrieshas been reported to range from 0.2 to 45 kg.

This variety of fermented milks in the world maybe ascribed to various factors.

Milk of various species

Milk of various domesticated animals differs in com-position and produces fermented milk with a charac-teristic texture and flavor (Table 1.6). The milk of var-ious mammals exhibits significant differences in totalsolid, fat, mineral, and protein content. The viscosityand texture characteristics of yogurt are primarily re-lated to its moisture content and protein level. Apartfrom quantitative levels, protein fractions and theirratios play a significant role in gel formation andstrength. Milk proteins, further, consist of caseinsand whey proteins, which have distinct functionalproperties. Caseins, in turn consist of �s1-, �-, and �-caseins. The ratio of casein fractions and the ratio ofcaseins to whey proteins differ widely in the milks ofvarious milch animals. Furthermore, pretreatment ofmilk of different species, prior to fermentation, pro-duces varying magnitudes of protein denaturation.These factors have a profound effect on the rheo-logical characteristics of fermented milks, leading tobodies and textures ranging from drinkable fluid tofirm curd. Fermentation of the milk of buffalo, sheep,and yak produces a well-defined custard-like bodyand firm curd, while the milk of other animals tendsto generate a soft gel consistency.

Cow’s milk is used for the production of fermentedmilks, including yogurt, in a majority of the countries


Table 1.4. Major Fermented Dairy Foods Consumed in the Different Regions of the World

Product Name Major Country/Region

Acidophilus milk United States, RussiaAyran/eyran/jugurt TurkeyBusa TurkestanChal TurkmenistanCieddu ItalyCultured buttermilk United StatesDahi/dudhee/dahee Indian subcontinentDonskaya/varenetes/kurugna/ryzhenka/guslyanka RussiaDough/abdoogh/mast Afghanistan, IranErgo EthiopiaFilmjolk/fillbunke/fillbunk/surmelk/taettemjolk/tettemelk Sweden, Norway, ScandinaviaGioddu SardiniaGruzovina YugoslaviaIogurte Brazil, PortugalJugurt/eyran/ayran TurkeyKatyk TranscaucasiaKefir, Koumiss/Kumys Russia, Central AsiaKissel maleka/naja/yaourt/urgotnic BalkansKurunga Western AsiaLeben/laban/laban rayeb Lebanon, Syria, JordanMazun/matzoon/matsun/matsoni/madzoon ArmeniaMezzoradu SicilyPitkapiima FinlandRoba/rob IraqShosim/sho/thara NepalShrikhand IndiaSkyr IcelandTarag MongoliaTarho/taho HungaryViili FinlandYakult JapanYiaourti GreeceYmer DenmarkZabady/zabade Egypt, SudanAdapted from Chandan, 2002; Tamime and Robinson, 1999.

around the world. In the Indian subcontinent, buffalomilk and blends of buffalo and cow milk are usedwidely for dahi preparation, using mixed mesophiliccultures (Aneja et al., 2002). In certain countries, buf-falo milk is the base for making yogurt, using ther-mophilic cultures. Sheep, goat, or camel milk is thestarting material of choice for fermented milks inseveral Middle Eastern countries.

Cultures for productionof fermented milks

Various microorganisms characterize the diversity offermented milks around the world. In general, lactic

fermentation by bacteria transforms milk into themajority of products. A combination of lactic startersand yeasts are used for some products and in a fewcases lactic fermentation combined with molds makeup the flora (Table 1.7).

Forms of fermented milks

Fermented milks may be mixed with water to make arefreshing beverage. Salt, sugar, spices, or fruits maybe added to enhance the taste. Liquid yogurt is a primeexample. Spoonable yogurt has significant commer-cial importance all over the world. It is availablein cups and tubes. To enhance its health appeal, the


Table 1.5. Consumption of Fermented Milksin Certain Countries in 1998

Country Per Capita (kg)

Netherlands 45.0Finland 38.8Sweden 30.0Denmark 27.3France 26.9Iceland 25.3Germany 25.0Israel 24.8Norway 19.3Bulgaria 15.6Austria 14.7Spain 14.5Czech Republic 10.0Portugal 9.8a

Hungary 9.4Poland 7.4Slovakia 7.4U.S.A. 7.4b

Australia 6.4Argentina 6.0Canada 3.6Ukraine 3.4South Africa 3.1China 0.2

a In 1997.b In 2003.

Source: IDF, 1999, with permission.

trend now is to deliver prebiotics as well as probioticorganisms through conventional yogurt. In manycountries, probiotic yogurt and fermented milks areavailable. They are made with defined cultures thathave been scientifically documented to display cer-tain health benefits.

Yogurt/buttermilk may be concentrated through aprocess that removes whey by straining through clothor by mechanical centrifugation to generate a cheese-like product. The concentrate may be mixed withherbs, fruit, sugar, or flavorings to yield shrikhandin India, Quarg/tvorog/topfen/taho/kwarg in centralEurope, and fromaige frais in France. Similarly,cream cheese and Neufchatel cheese are obtainedfrom sour cream and buttermilk.

To enhance the shelf life, fermented milks and yo-gurt may be sun-dried or spray-dried to get a powderform. Leben zeer of Egypt and than/tan of Armeniaare examples of concentrated yogurt without whey re-moval. In Lebanon, the concentrated yogurt is salted,compressed into balls, sun-dried, and preserved inoil. Another way to preserve yogurt is the processof smoking and dipping in oil. Labneh anbaris andshanklish are partially dried yogurt products pre-served in oil. Spices are added to shanklish and theballs made from this are kept in oil. In Iran, Iraq,Lebanon, Syria, and Turkey, concentrated yogurt ismixed with wheat products and sun-dried to get kishk.Frozen yogurt is available in the United States andCanada as well as in several other countries.

MAJOR COMMERCIALFERMENTED MILKSYogurt represents a very significant dairy productaround the world in recent times. It is a semisolid fer-mented product made from a heat-treated standard-ized milk mix by the activity of a symbiotic blend ofStreptococcus thermophilus and Lactobacillus del-brueckii subsp. bulgaricus. In certain countries, thenomenclature yogurt is restricted to the product madeexclusively from the two cultures, whereas in othercountries it is possible to label the product yogurt

Table 1.6. Proximate Composition of Milk of Mammals Used for Fermented Milks

Total Total WheySolids (%) Fat (%) Protein (%) Casein (%) Protein (%) Lactose (%) Ash (%)

Cow 12.2 3.4 3.4 2.8 0.6 4.7 0.7Cow, zebu 13.8 4.6 3.3 2.6 0.7 4.4 0.7Buffalo 16.3 6.7 4.5 3.6 0.9 4.5 0.8Goat 13.2 4.5 2.9 2.5 0.4 4.1 0.8Sheep 19.3 7.3 5.5 4.6 0.9 4.8 1.0Camel 13.6 4.5 3.6 2.7 0.9 5.0 0.7Mare 11.2 1.9 2.5 1.3 1.2 6.2 0.5Donkey 8.5 0.6 1.4 0.7 0.7 6.1 0.4Yak 17.3 6.5 5.8 – – 4.6 0.9Adapted from Chandan and Shahani, 1993; Chandan, 2002.

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Yogurt: U.S. per capita sales

1982 1987 1992 1997 1998 1999 2000 2001 2002Figure 1.1. Trends in the per capita sales ofyogurt in the United States.

made with yogurt cultures and adjunct probioticcultures. The more common adjunct cultures areLactobacillus acidophilus, Bifidobacterium spp.,Lactobacillus reuteri, Lactobacillus casei, and Lac-tobacillus rhamnosus GG, Lactobacillus gasseri,and Lactobacillus johnsonii LA1 (Chandan, 1999).

Yogurt is produced from the milk of cow, buffalo,goat, sheep, yak, and other mammals. In industrialproduction of yogurt, cow’s milk is the predominantstarting material. To get a custard-like consistency,cow’s milk is generally fortified with nonfat drymilk, milk protein concentrate, or condensed skimmilk. Varieties of yogurt available include plain, fruitflavored, whipped, drinking type, smoked, dried,strained, and frozen. Details of yogurt technologyare given in various texts (Chandan and Shahani,1993; Chandan, 1997; Tamime and Robinson, 1999;Mistry, 2001; Robinson et al., 2002). This subject isdetailed in chapters 9–16 in this book.

The popularity of yogurt has increased due toits perceived health benefits. Health-promotingattributes of consuming yogurt containing live andactive cultures are well documented (Chandan, 1989;Chandan and Shahani, 1993; Fernandes et al., 1992).The current trend of using prebiotics and probioticcultures in the manufacture of fermented milksand yogurt products is supported by clinical trials(Chandan, 1999; Ouwehand et al., 1999; Hirahara,2002; Salminen and Ouwehand, 2003). The bene-ficial effects documented in the numerous studiesand reviews include prevention of cancer, reductionin diarrhea associated with travel, antibiotic therapy,and rotavirus, improvement of gastrointestinalhealth, enhancement of immunity of the host, ame-lioration of lactose intolerance symptoms, protection

from infections caused by food-borne microorgan-isms, control of vaginitis, and vaccine adjuvanteffects.

Following world trends in increased consumptionof fermented milks, the per capita sales of yogurt inthe United States has also shown enormous growth.The past two decades has witnessed a dramatic risein per capita yogurt consumption from nearly 2.5 to7.4 lbs (Fig. 1.1). The increase in yogurt consumptionmay be attributed to yogurt’s perceived natural andhealthy image along with providing to the consumerconvenience, taste, and wholesomeness attributes.

In the year 2003, yogurt sales in the United Statesexceeded $2.7 billion. The total sales volume was2,387 million pounds. From 1995 to 2002, as a snackand lunchtime meal, yogurt consumption grew by60%. As a breakfast food, yogurt consumption in-creased by 75% during the same period.

It is interesting to note that the sale of culturedbuttermilk is on the decline (Fig. 1.2), while thesales of yogurt and sour cream and dips are regis-tering a significant growth. Buttermilk sales declinedfrom 1,039 million pounds in 1987 to 592 millionpounds in 2002. Yogurt drinks, on the other hand, areexhibiting significant growth. Sour cream and dipssales have grown from 694 million pounds in 1987to 1,031 million pounds in 2002. The recent popu-larity of Mexican cuisine has, in part, enhanced theconsumption of sour cream.

The rise in yogurt consumption is also related tothe choices available in the marketplace. Besides thevarieties of flavors, diversification in yogurt marketincludes variety of textures, packaging innovations tofulfill consumer expectations of health food trends,convenience, portability plus a magnitude of eating


Sour cream

Buttermilk

01980 1985 1990 1995 2000 2005

200

400

600

800

1000

1200

Year

Sal

es, m

illio

n po

unds

Figure 1.2. Trends in the total sales ofbuttermilk and sour cream and dips in theUnited States.

occasions. Figure 1.3 illustrates segmentation andvarious forms of yogurt available in the U.S. market.

Cultured buttermilk is an important fermentedmilk of the United States. It is obtained frompasteurized skim or part skim milk cultured with lac-tococci and aroma-producing bacteria leuconostoc.

Generally, milk is standardized to 9–10% milksolids-not-fat and <0.5% fat and heat-treated at85◦C for 30 minutes or at 88–91◦C for 2.5–5minutes. After homogenization at 137 kPa (2,000psi), it is inoculated with lactic starter and ripenedfor 14–16 hours at 22◦C. When the pH reaches 4.5,

Yogurtwith

ProbioticCultures

FruitflavoredYogurtWhipped

/ AeratedYogurt

MildYogurt

YogurtDrink/Smoothie

LongLife

Yogurt Yogurtfor

Toddlers

Yogurtfor

Breakfast

Hard andSoft

Frozen

Lowcalorie/ LightYogurt

PLAINYOGURT

Figure 1.3. Segmentation of yogurt market.


the coagulum is broken and blended with 0.18% saltand butter flakes while cooling to 4◦C. The productis bottled in paper/plastic containers.

Buttermilk is primarily consumed as a beverage.In addition, it is used in cooking, especially bakeryitems (see Chapter 17 for a detailed discussion oncultured buttermilk).

Sour/cultured cream is a significant fermentedmilk product in North America. It is manufacturedby culturing pasteurized cream with lactococci andaroma-producing bacteria, leuconostoc (Table 1.7).It has a butter-like aroma and flavor. Cream is stan-dardized to 18% fat, 9% milk solids-not-fat, and 0.3%stabilizer to get stable acid gel. The blend is heat-treated at 72◦C for 20 minutes and homogenized at172 kPa (2,500 psi) at 72◦C, single stage, two times.It is cooled to 22◦C, inoculated with 2–5% of thestarter, and cultured for 16–18 hours at 22◦C or untilpH drops to 4.7. It is packaged in cartons and cooledto 4◦C so that it develops thick consistency. Individ-ual serving cups and packages are also available. Inthis case, fermentation is carried out by filling seededbase, followed by packaging and cooling.

Creme fraiche is popular in France and otherEuropean countries. This product resembles sourcream, except that it contains up to 50% fat as com-pared to 18% fat in sour cream and has a higher pHof 6.2–6.3.

Cultured cream is used as a topping on vegetables,salads, fish, meats, and fruits and as an accompani-ment to Mexican meals. It is also used as a dip, as afilling in cakes, in soups, and in cookery items. Chap-ter 18 contains a detailed discussion on sour/culturedcream.

Culture-containing milks are seeded but are unfer-mented milks delivering significant doses of probi-otic microorganisms. In this case, the growth of theculture is intentionally avoided to preserve the freshtaste of milk. Accordingly, the product is stored atrefrigeration temperatures at all times. In the past,acidophilus milk was marketed by fermenting steril-ized milk with Lb. acidophilus. The inoculated basewas incubated at 37◦C for 24 hours. The plain productdeveloped titratable acidity of 1–2%. Consequently,it had a very harsh acidic flavor. Its popularity de-clined rapidly as sweetened yogurt with fruit flavorsbegan to dominate the market. However, Lb. aci-dophilus does have a strong consumer appeal. Mostof the yogurts now sold in the United States containLb. acidophilus, which is either added after cultur-ing with yogurt culture or is cocultured with yogurtculture.

Sweet acidophilus milk is an acceptable substitutefor acidophilus milk of the past era. The product ismade from pasteurized and chilled low-fat milk towhich a concentrate of Lb. acidophilus culture hasbeen incorporated to deliver a minimum of one mil-lion organisms per milliliter. It is sold in refrigeratedform and has a shelf life of 2–3 weeks. For more de-tails see Chapter 19. More recently, additional probi-otic organisms have been included to enhance healthyconnotation of the product. Among the additional cul-tures are Bifidobacteria, Lb. delbrueckii subsp. bul-garicus, S. thermophilus, and Lb. casei. Additionaldetails are given in chapters 20, 21 and 22.

FERMENTED MILKSOF SCANDINAVIAAs shown in Table 1.6, the Scandinavians have a highper capita consumption of fermented milks. The fer-mented milks of Scandinavia are distinctive in flavorand texture. They are generally characterized by aropy and viscous body, and include viili, ymer, skyr,langfil, keldermilk, and several local products.

viili, a fermented milk of Finland, is sold plainas well as fruit-flavored. Its fat content ranges from2% to 12%. Milk standardized to required fat levelis heat-treated at 82–83◦C and held at this tempera-ture for 20–25 minutes. Homogenization is avoided.It is then cooled to 20◦C and inoculated with 4%starter consisting of diacetyl producing Lactococ-cus lactis subsp. lactis, Leuconostoc mesenteroidessubsp. cremoris, and a fungus Geotrichum candidum.Following packaging in individual cups, the productis incubated at 20◦C for 24 hours, which results inacid development (0.9% titratable acidity) and creamlayer on the top. The cream layer traps the fungusgiving a typical musty odor to the product (Mistry,2001). The fermentation process also elaborates mu-copolysaccharides imparting ropiness and viscosityto the product.

Ymer is a Danish product with characteristic highprotein (5–6%) and pleasant acidic flavor with butteryaroma. Protein enrichment is achieved by ultrafiltra-tion technology prior to fermentation. Alternatively,the traditional process involves removal of whey bydraining curd after fermentation or by inducing sep-aration of whey by first heating the curd followed byremoving the whey. The standardized milk base isheated to 90–95◦C for 3 minutes and cooled to 20◦C.It is then inoculated with mesophilic culture consist-ing of a blend of Lc. lactis subsp. lactis biovar. di-acetylactis and Leuc. mesenteroides subsp. cremoris.


After incubation at 20◦C for 18–24 hours, the productis cooled and packaged.

Skyr is another Scandinavian product. In Iceland,this product is obtained by fermenting skim milkwith yogurt culture and a lactose-fermenting yeast.A small amount of rennet may be used to developheavier body. The milk base is cultured at 40◦C untila pH of 4.6 is achieved in 4–6 hours. It is then allowedto cool to 18–20◦C and held for additional 18 hoursfor further acidification to pH 4.0. Following pasteur-ization, the mass is centrifuged using a clarifier-typeseparator at 35–40◦C to concentrate the solids andachieve a protein level of around 13%. Skyr has typi-cal flavor compounds consisting of lactic acid, aceticacid, diacetyl, acetaldehyde, and ethanol.

FERMENTED MILKS OF RUSSIAAND EAST EUROPEKefir is relatively the most popular of fermented milksin Russia, Eastern Europe, and certain Asian coun-tries. In addition to lactic fermentation, this productemploys yeast fermentation as well. Thus, a percep-tible yeast aroma and alcohol content characterizethese products. Also, a fizz is noticed due to theproduction of carbon dioxide as a result of yeastgrowth. Kefir preparation involves natural fermenta-tion of cow’s milk with kefir grains. Kefir grains area curd-like material, which are filtered-off after eachuse and reused for inoculation of the next batch. Kefirgrains contain polysaccharides and milk residue em-bedded with bacteria Lb. kefir, Lb. kefirogranum, andspecies of leuconostocs, lactococci, and lactobacilli.Along with bacteria, the grains contain yeasts includ-ing Saccharomyces kefir, Candida kefir, and Torulaspecies. Milk is heated to 85◦C for 30 minutes, cooledto 22◦C, and incubated with kefir grains for 12–16hours to obtain traditional kefir. Typical flavor com-pounds in kefir are lactic acid, acetaldehyde, diacetyl,ethanol, and acetone.

In the United States, kefir is appearing in somemarkets. It varies from traditional kefir in that it isfermented with a blend of species of lactococci andlactobaclli. Some yeast is used to give only tracesof alcohol. The commercial product is blended withsugar and fruit juices/flavors.

Koumiss is obtained from mare’s milk or cow’smilk, using a more defined culture containing Lb.delbrueckii subsp. bulgaricus, Lb. acidophilus, andtorula yeasts. This therapeutic product has per-ceived health benefits and is recommended for all

consumers, especially those with gastrointestinalproblems, allergy, and hypertension and ischemicheart diseases (Mistry, 2001). Since mare’s milk hasonly 2% protein, no curdling is seen in the product.It contains 1–1.8% lactic acid, 1–2.5% ethanol, andenough carbon dioxide to give a frothy appearance tothe product (more detailed discussion on this topic isgiven in Chapter 19).

FERMENTED MILKSOF MIDDLE EASTFermented milks and their products have been his-torically associated with the Middle East.

Laban rayeb is prepared at home by pouring rawwhole milk in clay pots and allowing the fat to rise atroom temperature. The top cream layer is removedand partially skimmed milk is allowed to undergospontaneous fermentation. Some variations of theproduct exist. One of these is laban khad, which is fer-mented in a goat pelt. The other is laban zeer, which isdistinctly fermented in earthenware pots. The organ-isms responsible for fermentation are thermophiliclactobacilli in summer season and mesophilic lacto-cocci in winter season (Mistry, 2001).

Kishk is obtained from laban zeer. Wheat grainsare soaked, boiled, sun-dried, and ground to pow-der form. The blend of wheat and laban zeer is al-lowed to ferment further for another 24 hours andportioned into small lumps and sun-dried. The driedkishk has 8% moisture and 1.85% lactic acid. Af-ter proper packaging, its shelf life is of the order ofseveral years. Kishk may contain spices.

Labneh is prepared by concentrating fermentedmilk, after fermentation process is completed. Milk isfermented with yogurt culture and then concentratedusing Quarg separator. This product contains 7–10%fat.

Zabady is an Egyptian product obtained by fer-menting milk that has been concentrated by boilingand then fermented with yogurt culture. Further con-centration of milk solids is achieved by heating it andseparating the whey.

FERMENTED MILKSOF SOUTH ASIAThe fermented milks discussed below and the prod-ucts derived from these are of commercial impor-tance in India, Pakistan, and Bangladesh (Aneja et al.,2002; Mathur, 2002).


Dahi, also called curd, is a semisolid product ob-tained from pasteurized or boiled buffalo or a mixtureof cow and buffalo milk by souring natural, or oth-erwise, by a harmless lactic acid or other bacterialculture. Dahi may contain cane sugar. It should haveat minimum the same percentage of fat and solids-not-fat as the milk from which it is prepared (Anejaet al., 2002).

To prepare good quality of dahi, right type of cul-ture is essential. A mixed culture containing Lc. lactissubsp. lactis, Lc. lactis subsp. diacetilactis, or Leuc.species, Lc. lactis subsp. cremoris in the ratio of 1:1:1may be used. In addition, S. thermophilus may be acomponent of dahi culture or a culture composed ofLc. lactis subsp. lactis and Lc. lactis subsp. diaceti-lactis may be employed.

Mild dahi is made from mesophilic lactococci.Leuconostocs may be adjunct organisms for addedbuttery aroma and flavor. Sour dahi contains ad-ditional cultures belonging to thermophilic group,which are generally employed in the manufacture ofyogurt.These thermophilic organisms grow rapidlyat 37–45◦C, producing dahi in less than 4 hours.

Mishti doi is a fermented milk product, havingcream to light brown color, firm consistency, smoothtexture, and pleasant aroma. It contains 2–9% fat,10–14% solids-not-fat, and 17–19% sugar. The mostcommon sweetener used is cane sugar. In some spe-cial varieties of mishti doi fresh palm jaggery is usedas a sweetener. Typically, a mix comprising 71.26%milk (3% fat, 9% solids-not-fat), 5.32% cream (35%fat), 5.42% nonfat dry milk, and 18% crystallinesugar is blended. Caramel (0.1%) may be added asa flavor. This mix is heat-treated at 85–90◦C for 15min and homogenized. The heating process developslight brown color in the mix. The mixture is cooledto 42◦C. The starter is added at 1% level. Followingdispersion of the starter, mishti doi mix is dispensedinto sanitized cups and lids are heat-sealed to makethe packaging airtight as well as to prevent leakage ofthe mix. The sealed cups are then incubated at 42 ±1◦C for about 6–8 hours until the acidity develops to0.7–0.8%. The product is moved to a cold room (4◦C)with minimum disturbance because at this stage theproduct has a weak body and unstable top layer. Ex-cessive shaking may result in undesirable cracks onthe top layer or in the curd mass. Mishti doi is usedas a dessert and snack in India and Bangladesh.

Shrikhand is a dahi-based product. The culturedmilk or dahi is separated from whey to get chakka,which is blended with sugar, color, flavor, andspices to reach a desired level of composition andconsistency. The final product contains 8.5% fat, 10%

protein, 42% sugar, and 60% total solids. The acidityof the product is usually between 1.10% and 1.20%,expressed as lactic acid. Skim milk (9% solids-not-fat, 0.05% fat) is heated to 90◦C for 10 seconds ina High-Temperature Short-Time pasteurizer, cooledto 30◦C, and inoculated with 0.25–0.50% dahi cul-ture. After 8 hours of incubation period or titratableacidity of 0.8%, the curd is ready for further process-ing. Chakka is prepared by separating the whey fromdahi employing a basket centrifuge or a desludgingcentrifuge. Shrikhand is prepared by adding sugar atthe rate of 80% of the amount of chakka and mixed ina planetary mixer. Predetermined amount of plasticcream (80% fat) is added along with sugar and fla-vorings/spices to chakka to obtain at least 8.5% fatin the finished product. Shrikhand is used primarilyas a snack and dessert.

Lassi is a refreshing beverage derived from dahi.It is a popular drink of India, especially North India.Significant advancements have been made towardthe industrial production of lassi through applicationof ultra high temperature (UHT) technology (Anejaet al., 2002). Standardized milk (9–10% solids-not-fat and 0.5–1.0% milk fat) is heated to 85◦C for 30minutes or at 91◦C for 2.5–5 minutes, cooled to 25◦C,and cultured with dahi starter. It is then fermented at25◦C to lower the pH to 4.5. The set curd is brokenwith the help of a stirrer and at the same time 30%sugar solution is added to get 8–12% sugar concentra-tion in the blend. In some variations, fruit flavor maybe incorporated. Lassi is then homogenized at 13.7kPa (2000 psi) and UHT processed at 135–145◦Cfor 1–5 seconds and packaged aseptically employingstandard equipment. See Chapter 13 for details onLassi.

Chapter 19 in this book contains a detailed dis-cussion on various fermented milks available in theworld.

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2002. Technology of Indian Milk Products. DairyIndia Yearbook, New Delhi, India, pp. 158–182.

Chandan RC. 1982. Fermented dairy products. In: G.Reed (Ed), Prescott and Dunn’s IndustrialMicrobiology, 4th ed. AVI Publ, Westport, CT,pp. 113–184.

Chandan RC (Ed). 1989. Yogurt: Nutritional andHealth Properties. National Yogurt Association,McLean, VA.

Chandan RC. 1997. Dairy-Based Ingredients. EaganPress, St. Paul, MN.


Chandan RC. 1999. Enhancing market value of milkby adding cultures. J. Dairy Sci. 82:2245–2256.

Chandan RC. 2002. Benefits of live fermented milks:Present diversity of products. In: Proceedings ofInternational Dairy Congress, Paris, France.[Available in CD-ROM.]

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Fernandes CF, Chandan RC, Shahani KM. 1992.Fermented dairy products and health. In: BJB Wood(Ed), The Lactic Acid Bacteria, Vol. 1. Elsevier,New York, pp. 279–339.

Hassan A, Frank JF. 2001. Starter cultures and theiruse. In: EH Marth, JL Steele (Eds), AppliedMicrobiology, 2nd ed. Marcel Dekker, New York,pp. 151–205.

Hirahara T. 2002. Trend and evolution of fermentedmilk. In: Proceedings of International DairyCongress, Paris, France. [Available in CD-ROM.]

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International Dairy Foods Association (IDFA). 2003.Dairy Facts. IDFA, Washington, DC.

Mathur BN. 2002. Using microflora in traditional milkproducts processing. In: Proceedings ofInternational Dairy Congress, Paris, France.[Available in CD-ROM.]

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Microbiology, 2nd ed. Marcel Dekker, New York,pp. 301–325.

Ouwehand AC, Kirjavainen PV, Srortt C, Salminen S.1999. Probiotics: Mechanisms and establishedeffects. Int. Dairy J. 9:43–52.

Robinson RK, Tamime AY, Wszolek M. 2002.Microbiology of fermented milks. In: RK Robinson(Ed), Dairy Microbiology Handbook. John Wiley,New York, pp. 367–430.

Salminen S, Ouwehand AC. 2003. Probiotics,applications in dairy products. In: Encyclopedia ofDairy Sciences, Vol. 4. Academic Press, London,pp. 2315–2322.

Tamime AY, Robinson RK. 1999. Yogurt Science andTechnology, 2nd ed. Woodhead Publ, Cambridge,England, and CRC Press, Boca Raton, FL.

U.S. Department of Health and Human Services(DHHS). 1999. Grade ”A” Pasteurized MilkOrdinance, 1999 revision. Publication No. 229. U.S.Department of Public Health, U.S. DHHS, Food andDrug Administration, Washington, DC.

BIBLIOGRAPHYInternational Dairy Federation. 2003. Yogurt:

Enumeration of Characteristic Organisms—ColonyCount Technique at 37◦C. IDF Standard No.117/ISO 7889 Standard IDF, Brussels, Belgium.

Tamime AY. 2002. Microbiology of starter cultures. In:RK Robinson (Ed), Dairy Microbiology Handbook.Wiley-Interscience, pp. 261–366.

U.S. Department of Agriculture (USDA). 2003.National Agricultural Statistics Service. Dairy andPoultry Statistics. USDA, Washington, DC, Ch 8.

2Milk Composition, Physical and

Processing Characteristics∗Ramesh C. Chandan

IntroductionDefinition of MilkMilk Composition

Factors Affecting Composition of MilkPhysical StructureConstituents of Milk

Major ConstituentsMilk Fat GlobuleProteinsMilk EnzymesFunctional Attributes of Major Milk ProteinsLactoseMineralsVitamins and Some Other Minor Constituents

Physical Characteristics of MilkOptical PropertiesFlavorAcidity and pHBuffering CapacityElectrochemical PropertiesThermal PropertiesDensity and Specific GravityViscositySurface ActivityCurd TensionColligative Properties

ReferencesBibliography

INTRODUCTIONFrom a physiological standpoint, milk is a unique bi-ological secretion of the mammary gland endowedby nature to fulfill the entire nutritional needs of

∗The information in this chapter has been derived from Handbook of Fermented Foods, published by Science TechnologySystems, West Sacramento, CA, C©2004. Used with permission.

the neonate. Following parturition, milk is the secre-tion of normally functioning mammary gland of thefemales of all mammals. The yield and compositionof milk vary among various species to entirely meetpostnatal growth requirements of the offspring. Milk,therefore, contains all the chemicals in the form ofsix major nutrients, viz., water, fat, proteins, carbohy-drates, minerals, and vitamins that are ideal for nour-ishment. Milk and milk products are used as compo-nents of many food products around the world.

Milk is an integral part of fermented milks, in-cluding yogurt, and considered by many as an idealvehicle to deliver beneficial cultures as well as pro-biotics and ingredients known to stimulate activityof the benefical cultures and the microflora of thehuman gastrointestinal tract. The conversion of milkinto fermented milks augments the nutritional valueof inherent milk constituents. Additionally, the fer-mentation process generates metabolic and cellularcompounds that have positive physiological benefitsfor the consumer.

This chapter provides basic information relative tomilk composition that is relevant to the processing ofyogurt and fermented milks. For detailed discussions,the reader is referred to Wong et al., 1988; Jensen,1995; Swaisgood, 1996; Fox and McSweeney, 1998;and Walstra et al., 1999.

DEFINITION OF MILKChemically speaking, milk is a complex fluid inwhich more than 100,000 separate molecules and

17




chemical entities have been found, the levels of whichvary with the species. In terms of physical chemistry,milk is an opaque, white heterogeneous fluid in whichvarious constituents are held in multidispersed phasesof emulsion, colloidal suspension, or solution.

Worldwide, milk from cows, water buffaloes,goats, sheep, camel, mare, and other mammals is usedfor human consumption. However, cow’s milk entailsby far the most important commercial significance.

According to the Food and Drug Administration(FDA) of the United States, milk refers to cow’s milk.Milk from other species must be labeled to indicatethe species. For instance, milk from goats must becalled goat’s milk. Milk is the whole, clean lactealsecretion of one or more healthy cows properly fedand kept, excluding that obtained within 15 days be-fore calving and 3–5 days after. This would excludecolostrum, the milk secreted immediately after giv-ing birth. The definition of Grade A milk as per FDAstandards of identity is “the lacteal secretion practi-cally free of colostrum, obtained by complete milk-ing of one or more healthy cows, which contains notless than 8.25% milk solids not fat and not less than3.25% milk fat.”

MILK COMPOSITIONThe chemical makeup of milk and its physicochemi-cal behavior provide scientific basis for the basic pro-cessing of milk and the manufacture of products. Thecomposition of milk is generally described in termsof its commercially important constituents, milk fatand nonfat solids or milk solids not fat (MSNF). TheMSNF consists of protein, lactose, and minerals.These solids are also referred to as “serum solids.”The term “total solids” refers to the serum solids plusthe milk fat. The major constituents of milk are givenin Table 2.1.

The ash content is not quite equivalent to the saltlevel in milk. In the determination of mineral con-tent, some salts like chlorides and organic salts arevolatilized or destroyed as a result of high temper-ature exposure during routine mineral analysis bythe ash method. The data given in Table 2.1 referto all major breeds of cows in North America. Milk

from Jersey and Guernsey breeds would be closer toa higher fat and protein range.

Factors Affecting Compositionof Milk

Apart from the differences due to the breed, certainadditional factors also influence the gross composi-tion of milk: (a) individuality of animal, (b) stagesof milking, (c) intervals of milking, (d) completenessof milking, (e) frequency of milking, (f) irregular-ity of milking, (g) portion of milking, (h) differentquarters of udder, (i) lactation period, (j) yield ofmilk, (k) season, (l) feed, (m) nutritional level, (n) en-vironmental temperature, (o) health status, (p) age,(q) weather, (r) oestrum or heat, (s) gestation period,(t) exercise, (u) excitement, and (v) administrationof drugs and hormones. In general, these variablestend to average out in commercial pooled milk usedby dairy processors, but they do display an inter-esting seasonal pattern. The seasonal variations inprotein and mineral content have an important im-pact on viscosity and gel structure of yogurt and fer-mented products. During late spring and early sum-mer months, milk in some areas of the United Statesregisters low protein and calcium content resultingin poor viscosity in finished yogurt. During thesemonths of low-protein milk, it is necessary to com-pensate by raising the solids-not-fat (SNF) contentof yogurt mix by 0.25–0.50%. However, because ofthe current widespread use of stabilizers (modifiedstarch and gelatin) in yogurt mix, the seasonal vari-ations in protein content do not impact viscosity andtexture to the extent it does in natural yogurt in whichno stabilizers are used.

PHYSICAL STRUCTUREVarious interactive forces between the chemical con-stituents of milk determine the technological behav-ior of milk. Milk has well-defined physical equilib-ria between various constituents that exist mainly inthree forms, viz., emulsion, colloidal solution, andtrue solution. Milk lipids are present as an “oil-in-water” type of emulsion in the form of microscopic

Table 2.1. Composition of Bovine Milk

Water Fat Protein Lactose Ash

Average, % 86.6 4.1 3.6 5.0 0.7Range, average % 84.5–87.7 3.4–5.1 3.3–3.9 4.9–5.0 0.68–0.74Source: Adapted from Swaisgood, 1996.

2 Milk Composition, Physical and Processing Characteristics 19

Table 2.2. Physical State and Particle Size Distribution in Milk

Compartment Size, Diameter (nm) Type of Particles

Emulsion 2,000–6,000 Fat globulesColloidal dispersion 50–300 Casein–calcium phosphate

4–6 Whey proteinsTrue solution 0.5 Lactose, salts, and other substances

globules varying from 0.1 to 22 �m in diameter.The colloidal phase contains casein micelles, calciumphosphates, and globular proteins. Whey proteins arein colloidal solution and the casein is in colloidalsuspension. Lactose, vitamins, acids, enzymes, andsome inorganic salts are present as true solutions.Table 2.2 gives the relative sizes of these particles inmilk.

Certain factors tend to influence the physical equi-librium of milk that exists between colloidal dis-persion and salts. These factors are (a) addition ofpolyvalent ionizable salts, (b) concentration of serumsolids, (c) changes in pH, (d) heat treatment (whichmay alter the surface charges or unfold proteins), and(e) addition of alcohols (which reduces bound waterassociated with the colloidal constituents). All thesefactors tend to destabilize colloidal systems and thusinfluence the technological behavior of milk duringproduct manufacture. In the production of culturedmilks, as the fermentation proceeds, the colloidal cal-cium phosphate gets progressively converted to ionicform as the pH drops from 6.6 in milk to less than4.6 in yogurt and fermented milks. Casein and theinteracted whey proteins coagulate at the isoelectricpoint at pH 4.6, forming a gelled structure.

Certain terms related to milk structure need clearunderstanding. Milk plasma is the fluid portion ofmilk minus fat globules, being almost similar to skimmilk.

Milk serum is milk plasma minus milk fat and ca-sein micelles. Removal of casein micelles from skimmilk by clotting with rennet yields the liquid calledwhey. It is different from milk serum because it con-tains some polypeptides cleaved from casein by ren-net.

CONSTITUENTS OF MILKMajor Constituents

Water

Water is the medium in which all the other com-ponents of milk (total solids) are dissolved or

suspended. Water content varies from 85.4% to87.7% in different species of cows (Table 2.1). Asmall percentage of the water in milk is hydrated tothe lactose and salts and some is bound with the pro-teins.

Fat

Milk fat, though quite bland in taste, imparts rich-ness/smoothness to fat-containing dairy products.Milk fat in freshly secreted milk occurs as micro-scopic globular emulsion of liquid fat in aqueousphase of milk plasma. Fat content of milk varies from3.4% to 5.1%, depending on the breed of the cow.Most of the milk used for yogurt production typi-cally contains an average of 3.5–3.6% fat. Variabilityof milk fat also depends upon the individuality of an-imal, stage of lactation, feed, environmental factors,and stage of milking. The composition of milk fat isgiven in Table 2.3.

The milk fat of cows consists chiefly of triglyc-erides of fatty acids, which make up 95–96% of milkfat. The remaining milk fat is composed of diglyce-rides, monoglycerides, free fatty acids, phospho-lipids, and cholesterol, as shown in Table 2.3.

Table 2.3. Composition of Bovine MilkFat/Lipids

Lipid Fraction g/l in Milk Weight %

Triacylglycerols/triglycerides

30.7 95.80

Diacylglycerols/diglycerides

0.72 2.30

Monoacylglycerols/monglycerides

0.03 0.08

Free fatty acids 0.09 0.28Phospholipids 0.36 1.11Cholesterol 0.15 0.46Cholesterol esters 0.006 0.02

Total 32.056 100.05


Table 2.4. Fatty Acid Profile of Milk Fat

Fatty Acids Common Name Weight %

C4:0 Butryic 3.8C6:0 Caproic 2.4C8:0 Caprylic 1.4C10:0 Capric 3.5C12:0 Lauric 4.6C14:0 Myristic 12.8C14:1 Myristoleic 1.6C15:0 – 1.1C16:0(branched) – 0.30C16:0 Palmitic 43.7C16:1 Palmitoleic 2.6C17:0 – 0.34C18:0(branched) – 0.35C18:0 Stearic 11.3C18:1 Oleic 27.42C18:2 Linoleic 1.5C18:3 Linolenic 0.59

The functional properties of milk fat are attributedto its fatty acid makeup. More than 400 distinct fattyacids have been detected in milk. Typical milk fatconsists of 62% saturated, 29% monounsaturated,and 4% polyunsaturated fatty acids. It contains 7–8%short-chain fatty acids (C4—C8), which is a uniquecharacteristic of milk fat. The major fatty acids ofmilk fat are given in Table 2.4.

Milk fat functions as a concentrated source of en-ergy as well as a source of fat-soluble vitamins A,D, E, and K and essential fatty acids, linoleic acids,and arachidonic acids. The essential fatty acids arenot synthesized by the human body. They must besupplied by the diet. Arachidonic acid with four dou-ble bonds is present in traces. Its precursor is linoleicacid. Omega-3-linoleic acid and its products, eicos-apentaenoic acid (EPA) and docosahexaenoic acid(DHA), are also present in trace, but significant,amounts. The positional location of individual fattyacids in the triglycerides is not random. In fact, thesyn-1 and syn-2 positions on the glycerol moleculeare mainly occupied by myristic (C14:0), palmitic(C16:0), stearic (C18:0), or oleic acids (C18:1). Thesyn-3 positions contain butanoic (C4:0), hexanoic(C6:0), or oleic (C18:1) acids.

Saturated fatty acids are solid at ambient temper-ature, while unsaturated fatty acids are liquid. Theirratio in milk fat has a profound effect on the hardnessand spreadability of butter at low temperatures. Thebalance between C4 and C18 fatty acids keeps milk fatliquid at body temperature (Otter, 2003). The origin

of fatty acids is either blood plasma lipids or they aresynthesized in the mammary gland. There is a cor-relation between the fatty acid composition of feedlipids and butter hardness. A seasonal effect is seenas well. A softer butter is observed when the cow ison summer pasture or when the ration includes oilsliquid at ambient temperature.

Cholesterol

The cholesterol content of milk is significantly af-fected by the species, breed, feed, stage of lactation,and season of the year. Cholesterol content is gener-ally lowest in the beginning of lactation period andprogressively rises throughout the lactation period,being highest toward the end of the lactation. Thecholesterol content of colostrum is relatively high(570–1950 mg per 100 g fat) for the first milking af-ter parturition and progressively declines to normallevels during subsequent milking.

In general, typical cholesterol content of wholemilk (3.25% fat) is 10.4 mg/100 ml or 24.4 mg perserving of 8 fl. oz. It corresponds to 3–4 mg/g fat.Fat reduction in dairy products is accompanied bycholesterol reduction. By separating fat from milk, an80% reduction in cholesterol content can be achievedin skim milk. Thus, nonfat milk/skim milk showsresidual cholesterol level of 4.9 mg/8 oz serving. Yo-gurt and fermented milks, therefore, contain choles-terol content depending on the milk fat and SNF con-tent of the product.

Phospholipids

A number of factors influence the unique phospho-lipid content of milk. The total phospholipid contentof cow’s milk is approximately 36 mg/100 ml.

Milk Fat Globule

Milk fat occurs in milk as an emulsion of fat particlessuspended in aqueous phase. The spherical particlesare called fat globules (Fig. 2.1).

The average size of fat globules in raw cow milkvaries from 3.4 to 4.5 �m, depending on the breed ofthe cow. Jersey milk fat globules tend to have largerdiameters than Holstein milk fat globules. Milk lipidglobules fall into three overlapping size distributions.These are shown in Table 2.5.

The use of a separator in dairy plants permits frac-tionation of whole milk into skim/low-fat milk andcream. Fat globules are lighter (less dense) than the


Figure 2.1. Electron micrograph of freeze-etched fatglobule of Jersey cow milk. Note the surface is smoothas well as uneven, and some particle-like materialprotrudes out on the surface as depicted by arrows.From: Henson et al., with permission.

surrounding water phase and rise to the surface whenmilk is left undisturbed, as per Stoke’s law.

V = 2r2(density of serum − density of fat) × g

Viscosity of milk × 9

(2.1)

where V is velocity of rise of fat globules, g is thegravitational force, and r is the radius of the fat glob-ule. From the equation, it follows that V is directlyproportional to g. If g is increased by centrifugalforce, fat globules can be separated in a relativelyshort time. Also, g is inversely proportional to theviscosity of milk, which decreases as the tempera-ture goes up, converting the fat into liquid state. Ac-cordingly, V is increased. Thus, separation is moreefficient at warmer temperatures. Skim milk shouldcontain 0.05% fat or less, if the separator is function-ing properly.

Processed milk products, namely homogenizedmilk, ultra-high temperature (UHT) milk, ice cream,yogurt, light cream, half and half, evaporated milk,and condensed milk, which have undergone homoge-nization have diameters of their globules of the order

Figure 2.2. Electron micrograph of freeze-etched fatglobule membrane isolated from the globules of Jerseycow milk. Note the membrane as depicted by arrows.From: Henson et al., with permission.

of 0.3–0.7 �m. The fat globules of unhomogenizedproducts like whipping cream show an average diam-eter of 4.0 �m. Skim milk has smaller fat globulesleft over as a result of separator action and their di-ameter is around 1.3 �m. Cream layer is observed inproducts with relatively large fat globules, while thehomogenized dairy products show virtually no creamlayer during the shelf life of such products.

The fat globules are stabilized by a very thin mem-brane, closely resembling plasma membrane, only5–10 nm thick (Fig. 2.2).

Table 2.5. Size Distribution of Milk Lipid Globules

Proportion of the Total Fraction of TotalClass Diameter (�m) Globule Population (%) Milk Lipid (%)

Small Below 2 70–90 <5Intermediate 3–5 10–30 90Large 8–10 0.01 1–4


Table 2.6. Proximate Composition of BovineMilk Fat Globule Membrane

Component % (w/w) of Total Membrane

Protein 41Phospholipids 27Neutral glycerides 14Water 13Cerebrosides 3Cholesterol 2Source: Adapted from Fox and McSweeney, 1998.

The fat globule membrane consists of proteins,lipids, lipoproteins, phospholipids, cerebrosides, nu-cleic acids, enzymes, trace elements, and bound wa-ter, details of which are given in Table 2.6.

The membrane is important in keeping the fat fromseparating as free oil when it is subjected to physicalabrasion during handling/processing of milk. It alsoprotects milk lipids against the action of enzymes, no-tably lipase, in development of rancidity. Certain en-zymes such as alkaline phosphatase and xanthine oxi-dase as well as certain important minerals such as ironand copper are preferentially attached to the fat glob-ule membrane. The membrane contains 5–25% ofthe total copper and 30–60% of the total iron contentof milk. Other elements associated with membraneare cobalt, calcium, sodium, potassium, magnesium,manganese, molybdenum, and zinc. Molybdenum isassociated with the enzyme xanthine oxidase. Activ-ity of nearly all the enzymes of milk has been detectedin the membrane.

The proteins of membrane are unique and are notfound in skim milk phase. Because of damage of theglobule or as a result of homogenization, the mem-brane proteins contain skim milk proteins (casein andwhey proteins). A hydrophobic protein, butyrophilin,has been isolated from the membrane, which showsextraordinary affinity for association with lipids.

The lipid fraction of the membrane constitutesabout 1% of the total milk lipids. It contains phos-pholipids and neutral lipids in the ratio of 2:1.The phospholipids are phosphatidyl choline (34% oftotal lipid phosphorus), phosphatidyl ethanolamine(28%), sphingomyelin (22%), phosphatidyl inosi-tol (10%), and phosphatidyl serine (6%) (Fox andMcSweeney, 1998). The major fatty acid content ofphospholipids is 5% C14:0, 25% C16:0, 14% C18:0,25% C18:1, 9% C18:2, 3% C22:0, and 3% C24:0. Ac-cordingly, the unsaturated content of the membranelipids is different from the rest of the milk lipids interms of their high unsaturated fatty acid level. Thus,they are more susceptible to oxidative deterioration.

The neutral lipids of the membrane consist of ap-proximately 83–88% triglycerides, 5–14% diglyc-erides, and 1–5% free fatty acids. The fatty acidscontained therein are largely long chain. In order oftheir preponderance, they are palmitic, stearic, myris-tic, oleic, and lauric acids.

The sterols, Vitamin A, carotenoids, and squaleneare largely located in the fat core of the globule.

Proteins

Milk contains hundreds of proteins and most of themoccur in trace amounts. The major proteins of milkare broadly classified as caseins and whey proteins.Caseins are defined as the proteins that are insolubi-lized and precipitate at or above 20% when the pHof milk is lowered to 4.6. The soluble fraction at pH4.6 is termed as whey proteins. In addition, milk con-tains degradation products produced by plasmin, aninherent proteolytic enzyme. Thus, � -casein and pro-teose peptones owe their origin to the proteolysis of�-casein. Also, proteins derived from milk fat glob-ule membrane are present. The membrane proteinsare spilled into the milk system following mechan-ical disruption of the fat globule, such as churningand homogenization processing. Milk also containsnumerous enzymes and biologically active proteins.Nonprotein nitrogen compounds like urea, uric acid,creatine, creatinine, orotic acid, and hippuric acid arealso found.

Casein, the principal milk protein, makes up 80%of the total, while whey proteins make up the re-maining 20%. These fractions have been shownto be heterogeneous, consisting of several proteins(Table 2.7).

Caseins

Typical of milk proteins, caseins display distinctivestructure, charge, physical and biological properties,as well as a nutritional role. The interaction of vari-ous caseins and calcium phosphate contributes to theformation of large colloidal complex particles calledcasein micelles. The whitish color of milk is ascribedto the light scattering effect of colloidal micelles. Themicelles are rough-surfaced spherical particles vary-ing in size from 50 to 500 nm. Electron microscopicpicture analysis has shown that the micelles are com-posed of smaller particles or submicelles of 20 nmdiameter or less. Hydrophobic interactions with cal-cium phosphate and submicelles seem to be involvedin the formation of micelles. Micelle compositionconsists of 63% moisture and the dry matter consists


Table 2.7. Concentration of Various Proteinsand Polypeptides in Milk

Concentration in MilkProtein/Polypeptide (g/100 ml)

Caseins 2.4–2.8�S1-Casein 1.2–1.5�S2-Casein 0.3–0.4�-Casein 0.9–1.1�-Casein 0.3–0.4Casein fragments 0.2–0.35� -Casein 0.1–0.2Whey proteins 0.5–0.7�-Lactoglobulins 0.2–0.4�-Lactalbumins 0.1–0.17Serum albumins 0.02–0.04Immunoglobulins 0.05–0.18Proteose peptone 0.06–0.17Milk Fat GlobuleMembrane Protein 0.04Enzymes –

of 92–94% protein and 6–8% colloidal calcium phos-phate. Other associated salts are magnesium and cit-rate. Micelles have a porous structure with large volu-minosity (approximately 4 ml/g of casein). They areconsiderably hydrated, showing 3.7 g water/g casein.

Caseins are further divided into �S1-, �S2-, �-, and�-fractions (Table 2.7), which along with whey pro-teins, �-lactglobulin, and �-lactalbumin are gene-derived proteins synthesized in the mammary gland.All these proteins are heterogeneous and exhibitgenetic polymorphs. There are two to eight geneticvariants differing from each other in 1–14 aminoacids. The variants may have impact on the proteinconcentration and processing properties of milk. The� -fraction is derived from the breakdown of �-caseinby the native proteolytic enzymes of milk.

The caseins are phosphorylated proteins, contain-ing 1–13 phosphoserine residues. �-Casein existsin as many as nine glycosylated forms. It containstwo cysteine molecules per molecule. As a result of

disulfide bond formation, it can exist as polymersof two to eight units. Similarly, �S2-casein also con-tains two cysteines and exists in a dimeric form. Thecomposition and size of various caseins are shown inTable 2.8.

Casein micelles contain �S1-, �S2-,�-, and �-caseinin the ratio of 3:1:3:1. Most of the fractions �S1-, �S2-,and �-casein are located in the interior of micelles,with �-casein predominantly wrapped around the sur-face of the micelle. Casein fractions in the interior ofmicelle are sensitive to calcium and become insolublein the presence of calcium. However, �-casein is notsensitive to calcium and thereby keeps the micellescontaining calcium-sensitive caseins intact and sus-pended in aqueous phase. �-Casein is a protein withhydrophilic carbohydrate moiety (sialic acid) that ex-tends into aqueous phase. This arrangement furtherlends stability to the micelle. Casein micelles are sta-ble under most heating, homogenization, and otherdairy processing conditions.

Caseins possess certain distinctive amino acidmakeup that impacts their processing and functionalproperties. They are rich in apolar and hydropho-bic amino acids, namely valine, leucine, isoleucine,phenylalanine, tyrosine, and proline. The apolaramino acids normally are insoluble in water, buttheir nature is balanced by phosphate groups sothat caseins exhibit some solubility. Methionine andcysteine, the sulfur-containing amino acids, are rel-atively low in caseins. This fact impacts their nu-tritional deficiency. On the other hand, the essentialamino acid lysine content is high. In human diet, thehigh lysine content is helpful in complementing andbalancing the low-lysine plant proteins. The ε-aminogroup of lysine present in caseins interacts with thealdehyde group of lactose at elevated temperature,leading to the formation of brown pigments (Mail-lard reaction). This also explains browning of heat-sterilized milk and nonfat dry milk during extendedstorage.

The high prolene content results in low �-helixand �-sheet in their secondary structure, giving them

Table 2.8. Composition and Some Characteristics of Caseins

Approx. % of No. of Amino Phosphate Approx. Mol.Casein Total Casein Acid Residues Groups Wt. (Da) Isoelectric pH

�S1-Casein 38 199 8 23,164 4.1�S2-Casein 10 207 10–13 25,388 4.1�-Casein 35 209 5 23,983 4.5–5.3�-Casein 13 169 1 19,038 4.1–4.5Source: Adapted from Spreer, 1998; Fox, 2003; Otter, 2003.


ability for more proteolytic degradation and en-hanced digestion (Otter, 2003).

Caseins possess limited secondary and tertiarystructures. Accordingly, their molecular conforma-tion is fairly flexible, and open. The polar and apolaramino acids in the primary structure of caseins con-tribute to hydrophilic and hydrophobic regions. Thisconfers surface activity and contributes to emulsify-ing and foam-forming characteristics of caseins.

Caseins are very heat-stable under normal proteinlevels, environmental pH, and ionic concentrations.Moderate heat has little or no effect on caseinmolecules since they exist naturally in an open andextended state. However, heating of milk at elevatedtemperature for an appreciable length of time couldresult in hydrolytic cleavage of peptide and phosphatebond, which affects the stability of the complex, con-tributing to coagulation of milk.

Coagulation of milk is primarily a manifestationof micellar casein precipitation. This temperature-dependent phenomenon is critical in the manufac-ture of yogurt and fermented milks as well as incheese making. The precipitation/coagulation mech-anism consists of the following types:

Isoelectric Precipitation. Factors such as the pHstrongly influence the electrostatic interactions in ca-sein. Casein becomes insoluble and precipitates outwhen the milk is acidified and the pH is reduced to4.6 at or above 20◦C. At low temperature (4◦C), novisible precipitation is observed. As the temperatureis raised, coagulation is observed at or above 20◦C.The proteins remaining in solution are whey proteins.The destabilization of micellar casein by added acidor by lactic acid produced during fermentation bylactic acid bacteria starts at pH 4.9 when colloidalcalcium phosphate becomes soluble and changes toionic form. As the pH reaches 4.6, calcium phos-phate is cleaved in entirety from the micelle. At thesame time, the isoelectric point of casein is reachedand the micelle has no longer any charge to keep itsuspended by repelling forces. The result is aggrega-tion of casein micelles leading to dense coagulum.This type of coagulation is relevant in all fermenteddairy products including cottage cheese and creamcheese. Many textural attributes are controlled by thetemperature, quiescent conditions, pH, and rate ofacidification of milk.

Rennet Coagulation. In the production of mostcheese varieties, the mechanism of coagulation is

not acid-based but is caused by enzymatic attack byacid proteinase, chymosin contained in rennet. Thiscoagulation occurs at normal pH of milk. The spe-cific cleavage of �-casein molecule occurs at aminoacid 105 (phenyl alanine) and 106 (methionine) toform para-�-casein and a macropeptide called gly-comacropeptide (GMP). The GMP contains carbo-hydrate residues. Being hydrophilic, it is soluble andends up in the whey fraction. Since the micellesare stabilized by calcium-insensitive �-casein, theirhydrolysis by chymosin results in the exposure ofcalcium-sensitive �S-casein and �-casein to serumcalcium; the overall effect is coagulum formationby aggregation of the micelles. Further hydropho-bic interactions result in the expulsion of moisturefrom the coagulated micelles, causing syneresis andcurd shrinkage. This coagulum is the basis of cheesecurd formation. para-�-Casein is further degradedduring cheese ripening to produce numerous flavorcompounds and textural components.

Polyvalent Ion Precipitation. Because of its disor-dered molecular structure, casein fractions also pre-cipitate out in the presence of di- and polyvalent ionsof various salts.

Alcohol Precipitation. Casein micelles becomeunstable at 40% alcohol concentration at normal milkpH. At lower pH, the stability becomes even less andlower alcohol levels can precipitate milk. Dehydra-tion of casein micelles appears to be the major causeof this type of precipitation.

Heat Coagulation. Severe and extensive heatingof milk can cleave the calcium phosphate complexeswith casein micelle, resulting in destabilization, ag-gregation, and precipitation. Casein can withstandnormal heating processes in dairy plants; interactionsdo occur with the whey proteins.

Among the minor caseins of milk, � -casein isthe C-terminal fragment of �-casein, a product ofattack by natural proteolytic enzyme plasmin. TheN-terminal residue is the proteose–peptone fraction.These hydrolytic products of �-casein occur at arange of 3–10% of the total casein content of milk.The stage of lactation and the health status of the cowaffect their concentration.

Peptides derived from caseins are biologically ac-tive and display significant extra nutritional attributesfor maintaining normalcy of physiological functionsin human subjects.


Table 2.9. Composition and Some Characteristics of Whey Proteins

Approx. % of No. ofTotal Whey Amino acid Approx. Mol.

Whey Protein Protein Residues Wt. (Da) Isoelectric pH

�-Lactoglobulin 7–12 162 18,277 5.2�-Lactalbumin 2–5 123 14,175 5.1Bovine serum albumin 0.7–1.3 582 69,000 4.8Immunoglobulins 1.9–3.3 – 150,000–1,000,000 4.6–6.0Proteose peptone 2–6 – 4,000–40,000 3.7Source: Adapted from Spreer, 1998; Fox, 2003; Otter, 2003.

Whey/Serum Proteins

Whey proteins consist of �-lactoglobulin and �-lactalbumin, bovine serum albumin, immunoglob-ulins (mainly IgG1, IgG2, and IgM), lactoferrin,proteose–peptone, and a number of diverse enzymes.Table 2.9 shows some characteristics of whey pro-teins.

Compared to caseins, whey proteins have a rela-tively more ordered globular structure, which con-tains disulfide linkages. Accordingly, unlike caseins,they are soluble and not vulnerable to precipitationunder acidic conditions or by polyvalent ions. Likeother globular proteins, they are very heat-labile andcan be denatured at 90◦C, resulting in gel forma-tion. �-Lactoglobulin complexes with �-casein inmilk when subjected to rigorous heat treatment. Allthe whey proteins are superior in biological value ascompared to caseins and compare with the quality ofegg albumins. Major differences in the behavior ofcaseins and whey proteins are summarized in Table2.10.

�-Lactoglobulin. This major whey protein ofmilk displays the presence of four genetic vari-ants. Besides the two genetic variants namely Aand B, variants C and D have also been re-ported. �-Lactoglobulin is rich in sulfur amino acids,

containing five cysteine residues. It exists as a dim-mer linked by 1-3 disulfide bonds. It is a fairly heat-labile protein. Heat treatment of 60◦C results in par-tial denaturation. Differential scanning calorimetryresults show a peak maximum of denaturation at80◦C and formation of reactive sulfhydryl groups thatcan interact with �-casein and/or �-lactalbumin bydisulfide linkages. Further heating liberates hydro-gen sulfide, which is associated with “cooked” favor.�-Lactoglobulin stimulates lipolysis and generationof rancidity. It also acts as a carrier of vitamin A.The large numbers of lysine residues can result inlactosylation and accompanying changes in physicalproperties of the protein.

�-Lactalbumin. �-Lactalbumin is the major pro-tein of human milk, but in cow milk it is secondin preponderance to �-lactoglobulin. Three geneticvariants are reported, but Western cow contains vari-ant B only. This protein is rich in tryptophan andsulfur amino acids cysteine and methionine. Thereare four disulfides in the molecule and it exists asa monomer. �-Lactalbumin has 54 amino acid link-ages identical to the enzyme lysozyme. It is a gly-coprotein as well as a metalloprotein. One mole ofcalcium is bound to each protein molecule, whichconfers heat stability on �-lactalbumin. This protein

Table 2.10. Major Differences in Physical and Chemical Properties of Casein and Whey Protein

Casein Whey Protein

Strong hydrophobic regions Both hydrophobic and hydrophilic regionsPhosphate residues No phosphate residuesLittle cysteine content Both cysteine and cystine contentRandom coil structure Globular structure and helical structureVery heat–stable Heat-denatured and precipitatesPrecipitates at pH 4.6 Soluble at pH 4.6Precipitates with di- and polyvalent ions Relatively resistant to the ionsSource: Adapted from Chandan, 1997.


has been shown to possess a physiological role inthe synthesis of lactose in the mammary gland. It isa component of lactose synthetase along with uri-dine diphosphate-galactosyl transferase, catalyzingthe transfer of galactose to glucose to form lactose.

Immunoglobulins. There are five major classes ofimmunoglobulins, viz., IgA, IgD, IgE, IgG, and IgM.Their concentration is very high (100g/l) in first twoto three milkings after calf birth, but falls to 0.6–1 g/lsoon after. Immunoglobulins are antibodies synthe-sized in response to stimulation by specific antigens.These offer nonspecific humoral response to Gram-negative enteric and aerobic bacteria. Accordingly,they provide passive immune protection to the newlyborn calf. The basic structure of all immunoglob-ulins is similar, which is composed of two identi-cal light chains (23,000 Da) and two identical heavychains (53,000 Da). The four chains are joined to-gether by disulfide bonds. The complete moleculehas a molecular weight of about 180,000 Da. Theantigenic sites are located at the NH2-terminal of therespective chain. Of the five immunoglobulin classes,IgG is the predominant fraction of milk, comprisingabout 90% of the total colostral immunoglobulins.Relatively smaller concentrations of IgM and IgA arealso present in progressively decreasing amounts.

Bovine Serum Albumin. As the name indicates,this protein originated from blood and during synthe-sis in the udder spills into milk. It is a large moleculewith binding ability for fatty acids and metals.

Lactoferrin/Lactotransferrin. This is a glyco-protein that displays a strong tendency to bind ioniciron because of the presence of two metal bindingsites. The average lactoferrin content of 0.32 mg/mlhas been found for cow milk. The molecular weightof lactoferrin varies between 73,700 and 74,000 Da.Lactoferrin displays a very strong chelating tendencyfor ionic iron and forms a salmon red color pigment.Lactoferrin is a single peptide chain, with two lobes,each of which is capable of binding iron. Iron-freeform of lactoferrin is known as apolactotransferrin,which is colorless in appearance. Lactoferrin displaysa strong inhibitory effect toward Gram-negative en-teropathogenic bacteria by virtue of its ability to bindfree ionic iron, which is essentially required for thegrowth of enteropathogenic microorganisms. Apartfrom the antibacterial effect in the gut of calf, a nutri-tional role in iron metabolism has also been ascribedto lactoferrin.

Biologically Active Proteins and Peptides

A number of proteins and peptides derived from milkproteins have physiological activity. They are (1)immunoglobulins, lactoperoxidase, lactoferrin, andfolate-binding protein; (2) insulin-like growth factors(IGF-1 and IGF-2), mammary-derived growth fac-tors (MDGF-I and MDGF-II), transforming growthfactors (TGF�1, TGF�2, TGF�), fibroblast growthfactors, platelet-derived growth factors, bombesin,and bifidus factors; (3) peptides derived from milkproteins, such as glycomacropeptides from �-casein,phosphopeptides from caseins, caseinomorphins,immunomodulating peptides, platelet-modifyingpeptides, angiotensin-converting enzyme (ACE) in-hibitor that lowers blood pressure, calmodulin-binding peptides, and bactericidal peptides from lac-totransferrin (Otter, 2003).

Milk Enzymes

Milk is a repository of a variety of enzymes. Over60 indigenous enzymes have been reported in cowmilk. They are associated either with milk fat glob-ule membrane (xanthine oxidase, sulfhydryl oxi-dase, and � -glutamyltransferase) or with skim milkserum (catalase, superoxide dismutase) or with mi-celles of casein (plasmin and lipoprotein lipase).The partition and distribution of these enzymes isaffected by the processing and storage conditionsof milk. Other enzymes present are lactate dehy-drogenase, malate dehydrogenase, lactoperoxidase,galactosyl transferase, alkaline phosphatase, phos-phoprotein phosphatase, ribonuclease, lysozyme,fructose biphosphate aldolase, and glucose phosphateisomerase. The enzymes in milk come either from thecow’s udder (original enzymes) or from bacteria (bac-terial enzymes). Several of the enzymes in milk areutilized for quality testing and control. Some of theenzymes, which are important from the processingpoint of view, are described below:

Alkaline Phosphatase

This enzyme has assumed significance because ofthe association with the temperature at which it is in-activated and the temperature employed for pasteur-ization of milk. The basis of pasteurization is thatthe spore-forming pathogens, which may be presentin milk, are completely destroyed by heat treatmentdesignated in the pasteurization process. In turn, al-kaline phosphatase activity is also destroyed by the


pasteurization heat treatment. Thus, efficiently pas-teurized milk should be safe from pathogens, andconcomitantly, should not display any alkaline phos-phatase activity. Contamination of pasteurized milkwith raw milk can also be detected by positive phos-phatase activity in milk. Alkaline phosphatase is dis-tributed through milk. Its concentration is higher inthe cream fraction. The optimum pH for the action ofalkaline phosphatase on p-nitrophenylphosphate is9.5. The Km value for this substrate is 6.6 × 10−4 Mfor skim milk enzymes, whereas for the cream al-kaline phosphatase the corresponding value is 3.6 ×10−4 M. For details of the test, see Chapter 7.

Lipoprotein Lipase

This enzyme brings about hydrolytic cleavage ofglycerides, liberating free fatty acids and glycerol.The volatile short-chain free fatty acids generate un-desirable rancid flavor in milk. Thus, the activity ofthis enzyme can result in rancid flavor defects indairy products. Lipase is activated by homogeniza-tion of fat globule membrane in raw milk. Similarly,lipase can degrade milk fat and develop off-flavorin a short storage period, if raw milk accidentallygets mixed with homogenized milk. The optimumpH for the enzymatic activity ranges from 8.4 to 9.0,while optimum temperature for enzymatic activityis 37◦C. Sodium chloride and magnesium chloridehave a stimulatory effect on these enzymes whereascalcium chloride and manganese chloride have an in-hibitory effect. Residual activity of lipase remainingin processed milk or milk products tends to reducetheir shelf life.

Protease/Plasmin

This enzyme is responsible for the hydrolytic degra-dation of proteins. The optimum activity is observedat a temperature of 37◦C and a pH of 8.0. Nearly 82%of proteolytic activity is lost when milk is pasteurized.Native proteases of milk are more heat-labile com-pared to the microbial proteases, which tend to sur-vive even UHT processing treatment. Residual pro-teolytic activity in processed milk and milk productsleads to decrease in shelf life.

Lactoperoxidase

This enzyme catalyzes oxidation of substrate in thepresence of an oxygen donor such as hydrogen per-oxide. It displays optimum activity at pH of 6.0 and

is stable over a wide pH range of 5.0–10.0. This en-zyme has gained significance in view of its supportiverole for the preservation of raw milk by employingthe lactoperoxidase (LP) system under ambient con-ditions.

Lysozyme

This is a relatively small, single peptide chain protein.The variant found in bovine milk has 129–130 aminoacid residues, with molecular weight of 14,000Da.The lysozyme cleaves the glycosidic linkage betweenN -acetylmuramic acid and N -acetylglucosamine ofthe bacterial cell wall. Gram-positive bacteria aregenerally more susceptible because they have a sim-pler cell wall providing greater accessibility of thesubstrate compared to the Gram-negative bacteria.Cow milk contains about 13 �g /100 ml of lysozyme.More recently, emphasis has been focused on theantibacterial role of lysozyme as a natural defensein milk. During mastitis, lysozyme levels in milktend to increase considerably, being in the range of100–200 �g/100 ml. It has also been suggested thatlysozyme may have an indirect effect on the defensesystems as an immunomodulator through the stimula-tion of the breakdown products of the peptidoglucanon the immunosystem.

Functional Attributes of MajorMilk Proteins

Milk proteins are used in various foods to impart de-sirable effects. Table 2.11 shows such characteristicsof milk proteins that are helpful in their use as func-tional ingredients.

Lactose

The major carbohydrate of milk, lactose monohy-drate, ranges from 4.8% to 5.2%. Lactose contentof milk is relatively constant. In colostrum and mas-titic milk, its concentration is significantly lower. Itconstitutes 52% of MSNF, nonfat dry milk, and 34%whey protein concentrate, and 70% of whey solids.It is a disaccharide of one residue each of d-glucoseand d-galactose. Structurally, lactose is 4-O-�-d-galactpyranosyl-d-glucopyranose. Fresh milk con-tains small amounts of glucose (100 mg/100 ml),galactose (100 mg/100 ml), and oligisaccharides(10mg/100 ml). It is a reducing sugar and extensiveheating of milk results in Maillard reaction betweenlactose and proteins, creating brown pigments and abrownish color of milk.


Table 2.11. Functional Properties of Milk Proteins

Functionality Casein or Caseinates Whey Proteins

Water binding Very high, minimum at pH 4.6 Water-binding capacity increases withdenaturation of the protein

Solubility Insoluble at pH 4.6 Soluble at all pH levels. If denatured,insoluble at pH 5

Viscosity High at or above pH 4.6 Low for native protein. Higher, if denaturedGelation No thermal gelation except in the

presence of Ca+2Heat gelation at 70◦C (158◦F) or higher and

influenced by pH and saltsMicelles gel with rennin

Emulsification Excellent at neutral and basic pH Good except at pH 4–5, if heat-denaturedFoaming Good overrun. �-Casein best

followed by �- and �S1-caseins.Poor foam stability

Good foam/overrun. �-Lactoglobulin betterthan �-lactalbumin

Flavor binding Good Retention varies with degree of denaturationSource: Adapted from Fox, 2003; Chandan, 1997.

In isolated form, lactose exists in either of the twocrystalline forms, �-hydrate and anhydrous-�, or asamorphous “glass” mixture of �- and �-lactose. In so-lution both the forms exist in equilibrium with a ratioof (� to �) 1.68 at 20◦C. Lactose has an asymmetriccarbon and therefore displays optical activity. Lac-tose anomers rotate plane-polarized light and theirconcentration can be assayed by polarimetric mea-surements. The �-lactose anomer is more dextroro-tatory than the �-lactose anomer. If lactose crystal-lizes from a solution like milk or whey below 93.5◦C,�-lactose is usually formed, while above 93.5◦C,�-lactose is usually formed. During crystallization,the �-form mutarotates to �-lactose. Crystals of �-lactose monohydrate are shaped like a tomahawk andother shapes arise as a result of cocrystallization onthe face of lactose crystals. The rate of crystallization,size, and shape of lactose crystals depend on the de-gree of supersaturation of lactose solution and theinhibitor (�-form) level.

The �-form is less soluble (70 g/l at 15◦C) than the�-form. Crystallization of lactose when milk is con-centrated is of importance in regard to the texture. Anequilibrium mixture of �- and �-lactose, formed bymutarotation, exhibits a solubility of about 155 g/l at10◦C and 119 g/l of water at 0◦C. The relatively poorsolubility at low temperatures (4◦C or below) con-tributes to sandy texture in high milk solids ice cream,processed cheese products, and condensed milk prod-ucts. As a general rule, a concentration of lactose ex-ceeding 13 g/100 ml water in a dairy product tendsto promote crystallization of �-lactose monohydrateand accompanying sandy texture defect. In the manu-facture of nonhygroscopic dry milk and whey, lactose

crystallization plays an important role. In rapid dry-ing conditions, lactose glass (amorphous lactose) isformed. This form of lactose is very hygroscopic andcauses caking in dried products containing moisturelevels of 8% or more. Under such conditions, theconversion of lactose glass to �-lactose monohydratecrystals is responsible for binding powder particlestogether as a “cake.”

In sweetening power, lactose is only 16–33% assweet as sucrose. This makes lactose uniquely suit-able for certain food applications. Toppings, icing,and various types of fillings are examples of usewhere its inclusion in the formulations can improvethe quality. The pharmaceutical industry has used lac-tose for many years for tablet or pill formation. Be-ing a reducing sugar, it reacts with proteins to form ahighly flavored golden brown substance, commonlyfound on the crust of baked foods. Lactose contributessignificantly to the flavor, texture, appearance, shelflife, and toasting qualities of baked foods.

A compound formed from lactose in heated milkproducts is lactulose. It stimulates the growth ofBifidobacterium bifidum and is thus beneficial in es-tablishing useful microflora in the gut.

The role of lactose in yogurt and fermented milksis extremely important because the culture nutrition-ally requires it as a substrate for growth. It is a sourceof carbon and after fermentation about 30% of thelactose content is converted to lactic acid. Lactose iseasily hydrolyzed by �-d-galactosidase or lactase en-zyme of the culture to glucose and galactose. Glucoseis readily metabolized by the Embden–Meyerhof–Parnas pathway, while galactose tends to accumu-late. One molecule of lactose gives one molecule of


galactose and two molecules of lactic acid. Energy isgenerated in this reaction. The acid production lowersthe pH enough so that the fermented food is safe frommost pathogens. The shelf life of fermented milks issignificantly increased because many spoilage organ-isms cannot grow at their low pH.

Digestion of lactose presents a problem in someindividuals. These individuals lack the enzyme �-d-galactosidase in their gastrointestinal tract. Con-sequently, dietary lactose is not hydrolyzed and itreaches the colon intact where it is metabolized bycolonic bacteria forming gases like methane and hy-drogen. It leads to discomfort caused by bloating anddiarrhea. This lactose malabsorption is alleviated byyogurt containing live cultures, because the culturefurnishes the lactose-hydrolyzing enzyme and nor-mal digestion pattern is restored.

Minerals

Average normal milk is considered to contain 0.70%ash and this amount represents a salt content of about

0.90%. The percentage of salt and ash in milk varieswith the breed, feed, season, and stage of lactationand disease. The white residue after incineration ofa given weight of milk is used as a measure of themineral content of milk. Ash content is not identicalto milk mineral level because of decomposition andvolatilization of certain minerals as a result of heat.The ash contains substances derived from both the or-ganic and inorganic compounds in the milk. The CO2

of the carbonates is formed mostly from the organiccomponents; the SO3 of the sulfates is consideredto be a decomposition product of the proteins. Partof the P2O5 arises from the casein, since this pro-tein contains phosphorus equivalent to about 1.62%P2O5. Citric acid is completely lost. Chloride is partlylost (45–50%) by the high temperature employed forashing. This loss can be minimized by keeping thetemperature below 600◦C. The mineral content ofmilk is shown in Table 2.12.

Mineral makeup of milk is crucial to the stabil-ity of the physicochemical equilibrium in milk. Theminerals of milk exist in colloidal and soluble form.

Table 2.12. Typical Mineral Content of Cow’s Milk

Mean (mg/100 ml) Range (mg/100 ml)

Major MineralCalcium, total 121 114–130Calcium, ionic 8 6–16Citrate 181 171–198Chloride 100 90–110Magnesium 12 9–14Phosphorus, inorganic 65 53–72Potassium 144 116–176Sodium 58 35–90

Mean (�g/100 g of milk) Range (�g/100g of milk)Trace ElementsBoron 27 –Chromium 1 0.8–1.3Cobalt 0.1 0.05–0.13Copper 20 10–60Fluoride 12 3–22Iodine 26 –Iron 45 30–60Manganese 3 2–5Molybdenum 7 2–12Nickel 2.5 0–5Selenium 12 5–67Silicon 260 75–700Zinc 390 200–600Source: Adapted from Swaisgood, 1996; Fox, 2003.


Table 2.13. Partition of Major Minerals inColloidal and Solution Phases

Percent of Total Mineral as

Major Mineral Colloidal Dissolved

Calcium 67 33Magnesium 36 64Sodium 4 96Potassium 6 94Phosphate 55 45Citrate 6 94Chloride 0 100Sulfate 0 100

Table 2.13 shows approximate phase compositionsof the minerals.

They are present in a complex equilibrium con-sisting of colloidal state and soluble state. The sol-uble state exists in both ionic and nonionic form,and their ratio is influenced by the pH of milk. Theirconcentration is less than 1% in milk but the techno-logical behavior of milk is affected a great deal bythem. For instance, the following characteristics areinfluenced:

� Heat stability and alcohol coagulation of rawmilk.

� Preparation, quality, and storage stability ofproducts like concentrated/condensed, evaporatedmilk products.

� Clumping of fat globules upon homogenization ofcream.

� The calcium content of milk influences thefirmness of curd during cheese making and theviscosity of fermented milks. From a nutritionalstandpoint, milk is an excellent source of calciumand phosphorus. Their ratio in milk is optimal forbone formation and bone health.

Sodium, potassium, and chloride are almost com-pletely (95–96%) present in true solution and in ionicform and therefore diffuse freely across the mem-brane during ultrafiltration and electrodialysis of milkand whey. Calcium and magnesium, phosphate andcitrate are partly in solution and partly in colloidalsuspension, depending on the pH of milk. Approx-imately 20–30% of diffusible Ca and Mg exist asfree ions and the remainder as salts of citrate andphosphate. As the pH of milk drops in manufactur-ing yogurt and fermented milks, the colloidal formis converted progressively to the ionic form. At pH4.4 most of the minerals are in ionic, soluble, anddiffusible form.

Vitamins and Some Other MinorConstituents

The concentrations of fat-soluble vitamins A, D, E,and K, water-soluble vitamins B and C, and minorconstituents of milk are given in Table 2.14.

Milk contains both fat-soluble (A, D, E, and K) andseveral water-soluble vitamins. In the production oflow-fat and skim milk, the fat-soluble vitamins getconcentrated in the cream fraction. Whole milk is agood source of vitamin A but the separation processleads to low vitamin A content in low-fat and skimmilk. The FDA regulations require fortification oflow-fat and skim milk to restore and to make the vi-

Table 2.14. Vitamins and Some MinorComponents of Milk

Per 100 g of milk

VitaminsA 40 �g RED 4 IUE 100 �gK 5 �gB1 45 �gB2 175 �gNiacin 90 �gB6 50 �gPantothenic acid 350 �gBiotin 3.5 �gFolic acid 5.5 �gB12 0.45 �gC 2 mg

Nonprotein Nitrogen (NPN) CompoundsTotal NPN 23–31 mgUrea N 8–13 mgCreatine N 0.6–2 mgUric acid N 0.5–0.8 mgOrotic acid N 1.2 mgPeptides N 3.2 mgAmmonia N 4–5 mgCholine 4–28 mgCarnitine 1–1.7 mgN -Acetyl neuraminic acid 12–27 mg

Miscellaneous CompoundsNucleic acids and nucleotides 56 mgPhosphoric esters 30 mgEthanol 0.3 mgLactic acid 3.5–10 mgCitric acid 175 mgAcetic acid 0.3–5 mgFormic acid 1–8.5 mgSource: Adapted from Goff and Hill, 1992.


tamin A content of low-fat and skim milk equivalentto that of whole milk. The regulations require 2,000IU of vitamin A per quart of milk. The objective isto insure essentially the same dietary vitamin A con-tribution of all fluid milk beverages. Natural vitaminA activity in milk is due to retinol and the pigment�-carotene. Their levels as well as those of vitamin Dand E vary in milk according to the season and feedprofile. Vitamin D is important in bone health andvitamin E is an antioxidant. Vitamin K is present inmilk but its dietary nutritional role is minor.

Milk is an important source of dietary B vitamins.They are stable to various heating and processingconditions milk is normally subjected to. Riboflavinis vulnerable to light (wavelength <610 nm), gener-ating a sunlight flavor defect in milk. Ascorbic acid(vitamin C) content of milk is very low and not sig-nificant. Also, it is inactivated by heat processing.

As shown in Table 2.14, some nonprotein nitrogencompounds and several miscellaneous compoundsare also detected in milk.

PHYSICAL CHARACTERISTICSOF MILKThe reader is referred to excellent reviews on thesubject by McCarthy (2003), Goff and Hill (1993),and Fox and McSweeney (1998).

Optical Properties

Color

The color and appearance of milk has significancebecause the consumers perceive it as a parameter ofquality. The opaque, white or turbid color of milk isdue to the scattering of light by the dispersed phaseof fat globules, casein micelles, and the colloidal cal-cium phosphate. The intensity of color is directly pro-portional to the size and number of these particles.The smaller particles scatter light of shorter wave-length. The creamy color of whole milk is due toits �-carotene content. Some breeds (for example,Guernsey cows) have more of this pigment and theircolor is yellowish/golden. In cases of goat milk andwater buffalo milk, the pigment content is very low.�-Carotene is a precursor of vitamin A and in themilks of goats and water buffaloes, it is inherentlyconverted to vitamin A. Accordingly, their milk haswhite color as opposed to the creamy color of cow’smilk.

Extended heating imparts a slightly brown color tomilk as a result of Maillard’s reaction between lactoseand proteins.

Homogenization increases the number and totalvolume of fat globules. This results in whiter colorof homogenized products than their unhomogenizedcounterparts. Lack of fat globules and the presenceof water-soluble pigment riboflavin produces a bluishgreen tint in skim milk. In the absence of fat globules,light scattering is primarily by casein micelles, whichscatter more blue (short wavelengths of light) thanred. The color thus becomes distinctly green in wheyafter removal of casein particles from skim milk. Theyellow color of cow milk fat in butter and cream is dueto the presence of the fat-soluble pigments caroteneand xanthophyll.

Refractivity

The refraction of light by a solution is a function of themolecular concentration of the solute in the solution.Each solute maintains its own refractivity, and the re-fractive index of a mixture is that of the total of therefractive indices of the substances plus that of thesolvent. The components of milk contributing to itsrefractive index in descending order of importanceare water, proteins, lactose, and minor constituents.Specific refractive increments (in ml/g) in water atwavelength 589.3 nm and temperature 20◦C for ca-sein complex, whey proteins, lactose, and other dis-solved substances are 0.207, 0.187, 0.140, and 0.170,respectively. The fat globules do not contribute to therefractive index of milk because refraction occurs atthe interface of plasma and air.

Refractive index of a substance varies with thewavelength of the light and the temperature at whichthe measurement was taken. It is generally measuredat 20◦C with D line of sodium spectrum (wavelength589.3 nm) and represented as n20d. The value of n20dof cow milk generally falls in the range of 1.3440–1.3485. Refractive indices of human and goat milkshave slightly higher values. The refractive index ofmilk fat ranges from 1.4537 to 1.4552 at 40◦C and isused for verification of its authenticity.

Flavor

Taste and aroma are critical to the assessment of milk.Flavor is a critical criterion of quality for the con-sumer. It is a sensory property in which odor and tasteinteract. The sweet taste of lactose is balanced againstthe salty taste of chloride, and both are somewhatmoderated by proteins. This balance is maintainedover a fairly wide range of milk composition evenwhen the chloride ion level varies from 0.06% to0.12%. Saltiness can be detected by sensory tests in


Table 2.15. Off-Flavors in Milk Caused by Absorption from the Feed and Environment

Off-Flavor Description Possible Cause

Feed Aromatic, onion, garlic Cows fed 0.5–3 hours before milkingCowy Chemical after-taste, cow’s breath odor Cows with ketosis/acetonemiaBarny Unclean, reminiscent of barn, silage Poor ventilation, buildup of aromatic

silage/barn odors

samples containing 0.12% or more of chloride ionsand becomes marked in samples containing 0.15%.Some workers attribute the characteristic rich flavorof dairy products to the lactones, methylketones, cer-tain aldehydes, dimethyl sulfide, and certain short-chain fatty acids.

Although milk has a clean, pleasantly sweet flavor,it is quite bland, and therefore, any off-flavors arereadily discernible. Off-flavors result when the bal-ance of flavor compounds is altered because of themicrobiological activity or processing treatments, orchemical or biochemical reactions. The fat globuleshave a large surface area and tend to adsorb aromaticodors (for example, onion and garlic) readily.

Some off-flavors in milk are shown in Tables 2.15–2.18.

Acidity and pH

Freshly drawn milk shows a certain acidity as de-termined by titration with an alkali (sodium hydrox-ide) in the presence of an indicator phenolphthalein(equivalent to pH 8.3). This acidity, also called titrat-able acidity, as determined by titration, is known as“natural” or “apparent” acidity. It is caused by thepresence of casein, acid-phosphates, citrates, etc., inmilk. The natural acidity of individual milk variesconsiderably depending on species, breed, individ-uality, stage of lactation, physiological conditionof the udder, etc., but the natural acidity of fresh,herd/pooled milk is much more uniform. The higherthe SNF content in milk, the higher the natural acidity

and vice versa. The titratable acidity of individualcow milk varies from 0.12% to 0.18%, but in com-mercial pooled milk the range is only 0.14–0.16%.“Developed” or “real” acidity is due to lactic acid,formed as a result of bacterial action on lactose inmilk. Hence, the titratable acidity of stored milk isequal to the sum of natural acidity and developedacidity. The titratable acidity is usually expressed asa “percentage of lactic acid.” The higher the serumsolids, the higher is the titratable acidity. But the pHremains relatively the same. The titratable acidity (orpH measurement) is a critical parameter in yogurtand fermented milk production. It determines the endpoint of the fermentation process. Measuring the pHis preferable because unlike titratable acidity, it doesnot vary with the total MSNF in yogurt mix.

The pH of normal, fresh, sweet milk usually variesbetween 6.6 and 6.8. Higher pH values for fresh milkindicate udder infection (mastitis) and lower valuesindicate bacterial action. Skimming and dilution withwater raise the pH of milk while sterilization usuallylowers it.

Buffering Capacity

The pH is a measure of acidity or inverse of the loga-rithm of the hydrogen ion concentration in milk. Therelationship of hydrogen ion concentration and pH isshown by the following equation. A weak acid (HA)dissociates as follows:

Ka � (H+)(A−)

(HA)(2.2)

Table 2.16. Milk Off-Flavors of Microbiological Origin


Malty Grape nut-like, caramelized burnt Unsanitary equipment, insufficient cooling andstorage at >10◦C

Bitter/unclean Musty, spoiled, stale, dirty, bitter Exposure to warm temperature, dirty utensils, weedsFruity/fermented Odor resembling fruits like

apple/pineappleOld milk, too long storage of raw milk

Sour Tingling acidic taste Growth of lactic and other organisms


Table 2.17. Off-Flavors in Milk of Biochemical Origin


Rancid Bitter, soapy, foul odor, unclean Homogenized raw milk stored too long,mixture of pasteurized and raw milk,raw milk agitated vigorously

Oxidized/light-induced Medicinal chemical taste, reminiscentof burnt feather or tallow

Milk in transparent plastic/glass bottlesexposed to sunlight or UV light inrefrigerated cases

Here, Ka is dissociation constant, (H+) is hydrogenion concentration, and (A−) is the concentration ofthe anion and (HA) is the concentration of the acidHA.

pH = log1

(H+)= pKa + log

(A−)

(HA)(2.3)

Here pKa equals –log10 Ka.When the pH equals pKa,the weak acid is 50% dissociated and the buffering ca-pacity is maximum. Proteins contain many basic andacid groups in their molecule. Generally, their max-imum buffering capacity is at their isoelectric point.For milk, maximum buffering capacity is aroundpH 5.1.

Milk displays innate ability to resist the changes inthe pH or exhibits buffering capacity (dB/dpH). Thisis mainly due to the presence of amino acid residuesof caseins and whey proteins, and colloidal salts (cal-cium phosphate complex, citrates, etc.). Caseins dis-play maximum buffering capacity at their isoelectricpH of 4.6 and phosphates at around pH 7.0. Whey pro-teins show maximum buffering capacity at pH 4–5.The buffer index of milk is defined as the amount ofacid or alkali (mol/l) required in changing the pH of1 liter of milk by one unit. Buffering capacity hassome significance in the survival of live cultures inthe stomach where high acid conditions are delete-rious to the survival of yogurt cultures. Since pH ofyogurt is close to its isoelectric point, the milk pro-teins of yogurt exercise maximum buffering capacity.Accordingly, the impact of acidic conditions on the

culture cells is somewhat moderated for better sur-vival rates in the stomach.

Electrochemical Properties

Oxidation Reduction Potential

The oxidation–reduction (Eh) potential of milk is ex-pressed in volts. It is measured relative to the po-tential of the standard hydrogen electrode, which isassigned 0 V at pH 0. Eh is due to the presence ofseveral soluble constituents capable of yielding or ac-cepting electrons. In milk, Eh is controlled by factorssuch as dissolved oxygen, ascorbic acid, riboflavin,cystine–cysteine transformation, and pH value. Freshcow milk displays values of +0.2 to +0.3 V at 30◦C.It is due largely to dissolved oxygen, ascorbic acid,and riboflavin. Bacterial growth reduces the oxygentension. Methylene blue reduction test, used for as-sessing the microbial quality of milk, is based on thisphenomenon. The ascorbic acid oxidation in storedmilk leads to the formation of singlet oxygen, whichin turn is involved in lipid oxidative deterioration. Ri-boflavin in milk exposed to light near 450 nm assistsin photooxidation of methionine residues of wheyproteins to produce methional, the principal cause ofsunlight flavor defect. Heating of milk increases thereducing capacity of milk and heating above 70◦Calso causes noticeable decrease in the Eh because ofthe liberation of −SH groups from whey proteins.The increase in the reducing capacity of yogurt mix

Table 2.18. Off-Flavors Arising from Processing Conditions


Cooked Sulfur-like odor, caramelized, scorched Too high pasteurization temperature and holdingtime too long, Excessive heat treatment

Foreign Non-milk-like odor/flavor Contamination with sanitizers, cleaningcompounds

Flat Watery Too low milk solids, watered milk


after heat treatment is significant in promoting thegrowth of yogurt bacteria, which are microaerophilicin nature.

Electrical Conductivity

Current passes through milk by virtue of the activ-ity of its ionic mineral constituents, of which chlorideions carry 60–68% of the current. There is, therefore,a close correlation between the electrical conductiv-ity of milk and its chloride content. The specific elec-trical conductivity of milk at 25◦C ranges between0.004 �−1 cm−1 and 0.0055 �−1 cm−1, correspond-ing to that of approximately 0.25% NaCl solution(w/w). Higher values usually represent mastitic in-fections. Sodium, potassium, and chloride ions arethe major contributors to electrical conductance ofmilk. Whey and permeate from ultrafiltration havehigher conductivity than skim milk. The presence offat tends to decrease the specific conductance. Con-ductivity of milk may be used to detect added neu-tralizers.

The development of acidity by bacterial action dur-ing fermentation of milk increases its conductancebecause of conversion of calcium and magnesium toionic forms. Thus, measuring their electrical conduc-tance can follow the progress of fermentation dur-ing manufacture of yogurt and other fermented dairyproducts. Electrical conductance can also be used tofollow demineralization of whey, leading to loss ofionic minerals during the manufacture of whey pro-tein concentrates. Electrical conductance is directlyproportional to temperature. Conductance of milk in-creases by about 0.0001 �−1 cm−1 C−1.

Thermal Properties

Thermal Expansion

When warmed the volume of milk increases whichaffects the design considerations for storage and flowrates through processing treatments. The coefficientof thermal expansion of fresh milk (4% fat, 8.95%SNF) is approximately 0.335 cm3/kg/◦C at a temper-ature range of 5–40◦C. (Goff and Hill, 1993).

Heat Capacity

Heat capacity of milk and milk products, a functionof total solids of the sample, decreases with their in-creasing contents. Heat capacity expressed in SI units

equates to 1/4186 cal/g/◦C in cgs units. Heat capac-ity increases linearly with increase in temperature inskim milk from 3906 J/kg/K at 50◦C to 4218 J/kg/Kat 140◦C, according to the following equation (Goffand Hill, 1993):

Heat capacity = 2.814 × temperature in ◦C + 3824

The heat capacity of milk and cream depends stronglyupon fat content. Milk fat has a heat capacity of 2177J/kg/K. The heat of fusion is 8.37 J/g. The heat capac-ity of milk in the range of 50–140◦C can be estimatedaccording to the equation

Heat capacity of milk = 2.976 × temperature ◦C

+3692

Specific Heat

Specific heat is the ratio between the amount of heatnecessary to raise a given weight of a substance toa specified temperature and the amount of heat nec-essary to raise an equal weight of water to the sametemperature. It is nearly identical to the heat capac-ity figure as the heat capacity of water (1 cal/g/◦Cor 4186 J/kg/K) is fairly constant over the range of0–100◦C. It is important in processing for determin-ing the amount of heat or refrigeration necessary tochange the temperature of milk. Fat content influ-ences the specific heat of the product.

Specific heat of skim milk and whole milk is ap-proximately 4.052 and 3.931 kj/kg/k, respectively at80◦C. The value for non fat dry milk ranges from1.172–1.340 kj/kg/k at 18–30◦C while for milk fat itis 2.177 kj/kg/k.

Thermal Conductivity

Thermal conductivity determines how fast milk iscooled or heated. It is the rate of heat transfer by con-duction in J/m/s/K. Thermal conductivity increases astemperature increases. It decreases as the concentra-tion level increases, and for a given temperature andconcentration, the higher the fat content, the lowerthe thermal conductivity. The thermal conductivityfor milk at 20◦C is 0.53 J/m/s/K, and 0.61 J/m/s/Kat 80◦C. There is a marked decrease in the thermalconductivity with increase in either fat or total solids.

Effects of Heat

Dairy plants routinely use heat processes to makemilk safe from pathogenic organisms and to extend


the shelf life of milk and milk products. The pas-teurization and sterilization temperatures and hold-ing times employed in such treatments have profoundeffects on milk proteins, enzymes, fat globule mem-brane, some vitamins, and physical state of mineralsand other constituents. Caseins of milk are relativelystable to moderate heating regimes under conditionsof normal pH and ionic balance. The serum pro-teins are globular proteins. They are more prone todenaturation to heat. At 60–65◦C, �-lactoglobulinmolecules begins to uncoil themselves and start inter-action with �-casein located in casein micelle form-ing disulfide linkages. The denaturation process iscomplete at 90–95◦C when milk is held for 5 minutes.Under this heat treatment, �-lactalbumin is relativelyless vulnerable to heat, undergoing reversible denat-uration. However, the immunoglobulins are fully de-natured. In the manufacture of yogurt, this heatingtreatment is beneficial in increasing water-holdingcapacity and in reducing syneresis of the coagulum.Also, the resultant viscosity increase assists in opti-mizing the texture of yogurt. High heat treatment isdeleterious to rennin curd formation, and should beavoided in cheese manufacture.

Normal pasteurization treatment causes “creamplug phenomenon” in which some fat globules breakdown to free fat that sticks to other fat globules giv-ing rise to the plug. On homogenization, the plugis broken down. Exposure to higher temperatures(>135◦C) results in partial aggregation of proteins ofmilk fat globule membrane and a more dense mem-brane that is less permeable.

Severe heat treatment above 100◦C gives rise tobrown pigments (melanoidin polymers) in milk. TheMaillard reaction between the ε-amino group of ly-sine residue of proteins and carbonyl group of lactosegives a brown color to milk. Such heat treatment alsoresults in nutritional compromise. Cooked flavor re-sults from the production of sulfhydryl groups arisingfrom the breakdown of disulfide linkages.

Heat Stability

In the manufacture of certain high heat-treated/concentrated milk products, heat stability of milkplays a significant role. A number of factors interactin a complex manner, which ultimately determinesthe heat coagulation of milk. On the basis of signif-icant findings, the role of various interacting factorsmay be summarized as follows:

Protein composition: Various genetic variants ofthe casein fractions display variable heat stability.The heat coagulation of milk is related to the ratiobetween �-casein and �-lactoglobulin. Higher heatcoagulation temperature is observed at higher levelsof �-lactoglobulin.

Mineral balance: The heat stability of milk ismainly determined by the makeup of proteins aswell as the relative concentration of various saltspresent in colloidal and ionic states. The molar ra-tios between various cations and anions (both mono-valent/polyvalent) strongly impact the physical equi-libria of milk and the heat stability. Heat stability ismaximum at the optimum salt equilibria defined bythe relative concentration of Ca+2, Mg+2, citrate−3,and phosphates−3.

The molar ratio between cations and anions mainlydetermines whether milk will be stable at certain tem-perature and pH employed for processing. When milkis heated, salts of calcium and magnesium display aninverse solubility curve manifested by progressivetransition of calcium and manganese from the col-loidal state to the ionic state. However, the solubilityof the salts of sodium and potassium increases withthe rise in processing temperature.

pH: The pH plays a critical role in determining theheat stability of milk. The pH effects both the molec-ular disassociation of casein components and theformation of aggregated protein complexes throughprotein–protein interactions. Further, pH strongly af-fects the salt equilibrium between the colloidal andionic states of the minerals of milk. Maximum heatstability is observed between pH 6.6–6.8.

Concentration of milk solids: In general, the heatstability of milk decreases progressively as milk isconcentrated to higher levels of total solids. This isaccompanied by concomitant shift of salt from theionic state to the colloidal state as well as drop in thepH values.

Homogenization: Although fat itself does not af-fect heat stability of milk, homogenization of milkbrings about certain significant changes in the phys-ical equilibria of milk. During homogenization ofmilk, the original fat globule is disrupted and sur-face area increases by many folds. Resurfacing ofthe newly formed fat globules takes place instantly,predominantly by the adsorption of micellar casein.A shift in the colloidal state because of the adsorptionof caseins affects the equilibria between the colloidaland ionic states, which ultimately reduces the heatstability, although only marginally.


Density and Specific Gravity

The density of milk (mass/volume) is the sum total ofthe densities of its constituents, their concentration,and state at a particular temperature. The densityof milk is a useful parameter to convert volumet-ric measurements to gravimetric measurements andvice versa. Milk is purchased on weight basis andis sold in volumetric packages. Yogurt is sold inavoirdupois/weight units, while fermented milks arepackaged in volumetric units. Most of the dairy plantsprocess milk and other products in gallons, a volu-metric measure. Density is also useful in estimatingdegree of concentration during condensed milk man-ufacture by a simple hydrometer reading.

Milk density at 20◦C ranges from 1.027 to 1.033with an average of 1.030 g/cm−3. Accordingly, theweight of 1 liter of milk would range from 1.027to 1.033 kg. The density of milk at 15.5◦C can beestimated according to the following formula (Otter,2003):

d15.5◦C = 100

F/0.93 + SNF/1.608 + Water %g / cm−3

(2.4)

Here, d represents density, F = % fat, SNF = %solids-not-fat, and Water % = 100 – F – SNF.

The densities of some fluid milk products are givenin Table 2.19.

The specific gravity of milk is the ratio of den-sity of milk to that of water at a given temperature.Yogurt mix and other dairy mixes containing sugarand added milk solids exhibit higher densities andspecific gravities than milk. For instance, the spe-cific gravity of ice cream mix is in the range 1.0544–1.1232, while that of fresh whole milk lies in therange 1.030–1.035, with an average of 1.032. Milkfat, MSNF, skim milk, and evaporated whole milk, at15.5◦C, have specific gravity of 0.93, 1.614, 1.036,

and 1.066, respectively. The specific gravity of milkis influenced by the proportion of its constituents,each of which has a different specific gravity approx-imately, as follows: water, 1.000; fat, 0.930; protein,1.346; lactose, 1.666; salts, 4.120; and SNF, 1.616.As the milk fat is the lightest constituent, the morethere is of it, the lower the specific gravity will beand vice versa. Determination of the density of milkis carried out by first warming the milk to 40◦C to al-low melting of fat and then adjusting the temperaturedown to the desired working temperature.

The percentage of total solids or SNF in milk canbe roughly estimated by the following formula:

%TS = 0.25D + 1.22F + 0.72

%SNF = 0.25D + 0.22F + 0.72

where D = 1000 (d− 1) is the density of sample ofmilk at 20◦C and F is the fat percentage of sample.

The empirical formulas given above lack the accu-racy of laboratory analysis but in field conditions areuseful as quick estimates.

Viscosity

The viscosity of milk and cream creates the im-pression of “richness” to the consumer. From anorganoleptic standpoint, viscosity contributes tomouth feel and flavor release. Fluidity is the inverse ofviscosity. It has a bearing on fat separation/creaming,rate of heat transfer, and flow conditions during pro-cessing of milk. Assuming laminar flow with parallelstream lines, viscosity may be defined as the ratio ofshearing stress (force per unit area) to shear rate (ve-locity difference divided by distance, in reciprocalseconds). In dairy industry, the common units arecentipoise (cP) or (poise × 10−2).

Viscosity of milk and dairy products depends onthe temperature and on concentration and state of

Table 2.19. Density of Fluid Milk Products at Various Temperatures

Density (kg/cm3) at Various Temperatures

Product 4.4◦C 10◦C 20◦C 38.9◦C

Raw milk, 4% fat 1.035 1.033 1.030 1.023Homogenized milk, 3.6% fat 1.033 1.032 1.029 1.022Skim milk, 8.9% SNF 1.036 1.035 1.033 1.0026Half and half, 12.25% fat 1.027 1.025 1.020 1.010Light cream, 20% fat 1.021 1.018 1.012 1.000Whipping cream, 36.6% fat 1.008 1.005 0.994 0.978Source: Adapted from Goff and Hill, 1993.


casein micelles and fat globules. Representative val-ues at 20◦C for various products are as follows:whole milk, 1.9 cP; skim milk, 1.5 cP; and whey,1.2 cP. Viscosity of milk and cream increases withhomogenization and the increase is proportional tothe homogenization pressure. Increase in viscositycan be attributed to the fine state of fat globules andthe formation of a coat of plasma proteins on them.

The casein micelles of milk contribute more to theviscosity of milk than does any other constituent. Vis-cosity varies not only with changes in physical na-ture of fat but also with the hydration of proteins.Alterations in the size of any dispersed constituentsresult in viscosity changes. The fat contributes lessthan caseins but more than whey proteins. When fatglobules are greatly subdivided by homogenization,an increase in viscosity is observed. The viscosity ofskim milk decreases on heating to 62◦C after whichit increases apparently because of changes in pro-tein hydration. An increase in temperature causes amarked reduction in viscosity. For example at 20◦C,milk is about half as viscous as at 0◦C, and at 40◦C,is approximately one third of the value at 0◦C.

Viscosity is critical in the texture development ofyogurt and cultured milks. It is a crucial attributein defining mouth feel, flavor release, and refresh-ing quality of the product. It forms an important pa-rameter in quality control programs of culture dairyplants. In yogurt, the viscosity is of the order of15,000–25,000 cP.

Surface Activity

Surface activity is involved in adsorption phenom-ena and the formation and stability of emulsions. Itis relevant to creaming, fat globule membrane func-tion, foaming, and emulsifier use in dairy products.Normal cow milk has an inherent surface activity.Its surface tension approximates 70% of that of wa-ter (72 dynes/cm). The surface tension of cow wholemilk ranges from 50 to 52 dynes/cm, and for skimmilk, 55–60 dynes/cm at 20◦C. For cream it is ap-proximately 46–47 dynes/cm. Casein, along with theproteolysis products protease–peptones, is largelyresponsible for the surface activity. Whey proteinsmake little contribution. Fat reduces surface tensionby a physical effect. Lactose and most of the saltstend to raise it when they are present in true solution.

Surface tension decreases as milk temperaturerises. Processing treatments such as heating, ster-ilization, homogenization, and shear tend to in-crease surface tension. However, homogenization of

imperfectly pasteurized milk or contamination of ho-mogenized pasteurized milk with raw milk causespartial hydrolysis of milk fat, resulting in low sur-face tension, bitter flavor, and rancidity of milk.

Foaming

Milk and milk products high in milk fat and/or milkproteins interact frequently with air and form foams.Sometimes the process is desirable as in whippingof cream and sometimes it has a nuisance value asin handling of skim milk. Fat globules and free fatmake foam less stable. Heating of milk to such anextent that whey proteins are denatured yields morevoluminous and more stable foam on heating. How-ever, sterilization diminishes its foaming capacity. Aconcentrate of 30% total milk solids that has beenvigorously homogenized forms very stable foam.

Foaming of milk is minimum at 30–35◦C. At 60◦C,the foam volume is independent of the fat content.Below 20◦C and above 30◦C, the foaming tendencyappears to increase. Fat tends to stabilize the foamformed below 20◦C, for instance, during churningfor butter production. Skim milk produces slightlymore stable foam above 30◦C than does whole milkor light cream.

The formation of stable foam depends upon twomain factors. First, the lowering of the surface tensionallows the gathering and spreading of the surface-active components into thin films. Second, the filmsmust be sufficiently elastic and stable to prevent thecoalescence of the gas cells. Stable foam is thusformed when the surface tension of the liquid is notgreat enough to withdraw the film from between thegas cells and when the stabilizing agent has greatinternal viscosity.

Foaming properties affect handling of milk prod-ucts and how dairy-based ingredients are used inother products. Foam formation and its stability con-stitute important factors in getting the necessary over-run and texture in frozen dairy desserts, includingfrozen yogurt and whipped yogurt. Many yogurtplants use antifoaming agents as processing aid tocontrol foam formation during the preparation ofyogurt mix. Foam control is also necessary from aproper pasteurization standpoint because organismssuspended in foam are resistant to common heat pas-teurization time–temperature regime.

Curd Tension

This property is considered important in relationto the cheese making characteristics as well as the


digestibility of milk. The curd tension of milk is28–54 g. Heat treatment of milk causes a reduction ofcurd tension, as does the homogenization treatment.Addition of some of the salts such as the sodium cit-rate and sodium hexametaphosphate tend to reducethe curd tension of milk.

Colligative Properties

Osmotic Pressure

The number of molecules or particles, not theweight of solute, control osmotic pressure; thus 100molecules of size 10 will have 10 times the osmoticpressure of 10 molecules of size 100. It follows thatfor a given weight, the smaller the molecules, thehigher the osmotic pressure.

Milk is formed from blood, the two being sepa-rated by a permeable membrane; hence they havethe same osmotic pressure. In other words, milk isisotonic with blood. The osmotic pressure of bloodis remarkably constant although the composition, asfar as pigment, protein, etc. are concerned, may vary.The osmotic pressure is basically a function of saltbalance and lactose content of milk.

Freezing Point

Pure water freezes at 0◦C. Milk freezes at a tempera-ture slightly lower than water because of the presenceof soluble constituents such as lactose and solublesalts. The freezing point of milk depends on molarconcentration of its soluble, low molecular weightcompounds. Lactose, potassium, sodium, and chlo-ride are the principal milk constituents responsiblefor 75–80% of the entire freezing point depression(FPD). Since it is a fairly constant property of milk, itis routinely used for detecting adulteration of incom-ing milk with water, using a cryoscope. Adulterationof milk with water lowers the molal concentrationof lactose and salts, and thus increases the freez-ing point. Earlier work was done with the Hortvetcryoscope using a mercury-in-glass thermometer andresults on freezing point were based on the Hortvetscale. More recent work with thermistor measuringdevices has shown that the Celsius and Hortvet scalesare not identical. The following relationship has beenreported (Harding, 1995):

◦C = 0.96418◦H + 0.00085

◦H = 1.03711◦C − 0.00085

Accordingly, −0.540◦H is actually −0.521◦C. Mostof the industry data is reported in ◦H. Freezing point

is expressed in negative numbers whereas FPD is thepositive version of freezing point. Accordingly,freezing point depression of 0.540◦H is equivalentto freezing point of −0.540◦H. On adulteration withwater, zero degree being the reference point, FPDdecreases, while freezing point registers an increase.Milks from individual cows show a narrow range intheir FPD (0.530–0.525), but pooled milk has av-erage of 0.543◦H. It is generally agreed that milkof FPD higher than 0.535◦H may be presumed tobe water-free. But readings between 0.530◦H and0.534◦H warrant a letter to the suppliers for a checkon their plant operation. When FPD readings are be-tween 0.525◦H and 0.529◦H, there is a strong sus-picion of added water to the milk. Any time, if thereading is 0.525◦H or less, assumption of extraneouswater in milk is justified.

We will now illustrate how the freezing pointmethod detects the adulteration of milk with extrane-ous water. Let us assume milk with no added waterfreezes at −0.540◦C. When 10% water is added, itsfreezing point should be in the range of −0.478◦C. Ingeneral, the percentage of added water is calculatedas follows:

% added water = 0.540 − FPD

0.540(2.5)

×(100 − total milk solids)

As little as 3% water added to milk can be detectedby this method. Fermented milks show significant in-crease in FPD because of the conversion of lactoseto lactic acid and the transformation of minerals tothe ionic form. The freezing point of cream, skimmilk, and whey are identical with that of the milkfrom which they are prepared. Therefore, the freez-ing point test does not detect the addition of skimmilk or removal of fat from milk samples. More-over, watered milk, which has soured, may pass thetest because souring results in increase of the FPDas a result of an increase in the amount of solublemolecules. Hence, the freezing point should be deter-mined in fresh samples (having no developed acidity)for greatest accuracy.

Boiling Point

A solution boils at a higher temperature than doesthe pure solvent, according to the concentration of thedissolved substance. The milk constituents in true so-lution are mainly responsible for the elevation of theboiling point above 100◦C. Elevation of the boilingpoint is based on the same principles as the depression


of freezing point. However, for detecting added wa-ter, the freezing point method is far superior on thegrounds of accuracy and convenience. The boilingpoint of milk is 100.17◦C.

REFERENCESFox PF, McSweeney PLH. 1998. Dairy Chemistry and

Biochemistry. Blackie Academic and Professional,New York, p. 95.

Goff HD, Hill AR. 1993. Chemistry and physics. In:YH Hui (Ed), Dairy Science and TechnologyHandbook, Vol. 1: Principles and Properties. VCHPublishers, New York, pp. 1–62.

Harding F. 1995. Adulteration of milk. In: MilkQuality. Blackie Academic and Professional, NewYork, pp. 60–67.

Henson AF, Holdsworth G, Chandan RC. 1971.Physico-chemical analysis of the bovine milk fatglobule membrane. J. Dairy Sci., 54:1752–1763.

Jensen RG (Ed). 1995. Handbook of MilkComposition. Academic Press, New York.

McCarthy, DJ. 2003. Milk: Physical and physics.Chemical properties. In: H. Roginski, JW Fuquay,PF Fox (Eds). Encyclopedia of Dairy Sciences.Academic Press, New York, pp. 1812–1821.

Otter D. 2003. Milk: Physical and chemical properties.In: B Cabellero, LC Trugo, PM Finglas (Eds),Encyclopedia of Food Sciences and Nutrition, 2nded. Academic Press, New York, pp. 3957–3963.

Swaisgood HE. 1996. Characteristics of milk. In: O.Fennema (Ed), Food Chemistry. Marcel Dekker,New York, pp. 841–878.

Walstra P, Geurts TJ, Noomen A, Jellema A, vanBoekel MAJS. 1999. Dairy Technology: Principlesof Milk, Properties and Processes. Marcel Dekker,New York.

Wong NP, Jenness R, Keeney M, Marth EH (Eds).1988. Fundamentals of Dairy Chemistry. VanNostrand Reinhold, New York.

BIBLIOGRAPHYBylund G. 1995. Dairy Processing Handbook. Tetra

Pak Processing System, Lund.Chandan R. 1997. Dairy-Based Ingredients. Eagan

Press, St. Paul, MN, p. 5.Fox PF. 2003. The major constituents of milk. In:

G Smit (Ed), Dairy Processing. Improving Quality.CRC Press, Boca Raton, FL, pp. 6–41.

Spreer E. 1998. Milk and Dairy Product Technology.Marcel Dekker, New York, p. 21.

3Regulatory Requirements for

Milk Production, Transportation,and Processing

Cary P. Frye

History of Milk SafetyUnited States Public Health Grade “A” Milk Safety Program

Inspection of Milk SafetyFarm RequirementsMilk TransportationProcessing PlantHACCPStandards and Regulations

ImportsEquipments Standards

The 3-A Sanitary Standards SymbolMilk Pricing—U.S. Federal Milk Marketing Orders

Background of Federal OrdersClassified PricingProducer PricesMilk Pricing for Fermented Milk Products

GlossaryReferences

HISTORY OF MILK SAFETYMilk, the primary ingredient used for yogurt and fer-mented milk products, is rich in nutrients but also hasthe properties to readily support microbial growth andpotentially pathogenic organisms. Milk cows on thefarm are exposed to many sources of potential con-tamination. Some of these may be the water, feedsources, exposure to manure, insects, contact withdiseased animals in housing or corral areas, injuriesto the udder, and poor milking practices.

Early studies implicate milk as the carrier for manycommunicable diseases to the consumer. Some ofthe most notable outbreaks were tuberculosis, bru-cellosis, salmonaelliosis, diptheria, scarlet fever, sep-tic sore throat, and dysenteries of the food infectiontype. Recent outbreaks of salmonaelliosis, listeriosis,yerisnia, and camplhylobacter have been responsible

for milk-related human illness. Coxiella burnetti wasalso noted as one of the pathogens responsible formilk-borne outbreaks of Q fever and the impositionof more stringent pasteurization requirements (US-DHHS PMO, 2003).

The incidence of milk-borne illness in the UnitedStates has been sharply reduced. In 1938, milk-borneoutbreaks constituted 25% of all disease outbreaks,because of infected foods and contaminated water.Recent information reveals that milk and fluid milkproducts continue to be associated with less than1% of such reported outbreaks. Many groups havecontributed to this commendable achievement, in-cluding public health and agricultural agencies, dairyand related industries, several interested professionalgroups, educational institutions, and the consumingpublic.

The responsibility for insuring the ready availabil-ity and safe supply of milk and milk products, includ-ing yogurt and fermented milks, is the cooperativeeffort of all engaged, including government regula-tors and the industry.

UNITED STATES PUBLICHEALTH GRADE “A” MILKSAFETY PROGRAMThe U.S. Public Health Service (USPHS) branch ofFDA is a division of the Federal Health and HumanServices under the Food and Drug Administration(FDA), which has broad authority of overseeing thehealth and safety of food. USPHS oversight began atthe turn of the century with studies on the role thatmilk plays in the spread of diseases. The findingsindicated that effective public health control of milk-borne disease requires the application of sanitation

41




measures throughout the production, handling, pas-teurization, and distribution of milk and milk prod-ucts. These studies were followed by research to iden-tify and evaluate sanitary measures that might be usedto control milk-borne disease, including studies thatled to the improvement of the pasteurization process.

To assist states and municipalities in initiating andmaintaining effective programs for the prevention ofmilk-borne disease, the USPHS developed a modelregulation known as the Standard Milk Ordinancefor voluntary adoption by State and Local Milk Con-trol Agencies in 1924. An accompanying Code waspublished in 1927 to provide a uniform interpretationof this Ordinance and to establish administrative andtechnical details as to satisfactory compliance. Thismodel milk regulation is still used today, though nowtitled the Grade “A” Pasteurized Milk Ordinance(Grade “A” PMO), 2003 Revision. This regulationincorporates the provisions governing the process-ing, packaging, and sale of Grade “A” milk and milkproducts, including yogurt, fermented milk prod-ucts, whey, whey products, and condensed and drymilk products. The 25th revision of the Grade “A”PMO incorporates new knowledge into public healthpractices.

The USPHS alone did not produce the Grade “A”PMO. As with preceding editions, it was developedwith the assistance of Milk Regulatory and RatingAgencies at every level of federal, state, and localgovernments. All segments of the dairy industry, in-cluding health and agriculture regulators, producers,milk plant operators, equipment manufacturers, as-sociations, and educational and research institutionsassisted in producing the Grade “A” PMO.

The Grade “A” PMO is the basic standard usedin the voluntary Cooperative State–USPHS Programfor the Conference of Interstate Milk Shipments, aprogram participated in by all 50 states, the Dis-trict of Columbia, and the U.S. Trust Territories. TheNational Conference on Interstate Milk Shipments(NCIMS), in accordance with the “Memorandum ofUnderstanding” with the FDA, recommends changesand modifications to the Grade “A” PMO at its bien-nial conferences.

The Grade “A” PMO is incorporated by referencein Federal specifications for procurement of milk andmilk products. It is used as the sanitary regulation formilk and milk products served on interstate carriersand is recognized by the Public Health Agencies, themilk industry, and many others as the national stan-dard for milk sanitation.

The USPHS has legal jurisdiction for the enforce-ment of milk sanitation standards, in the case ofinterstate commerce. It also serves in an advisoryand simulative capacity and is designed primarily toassist state and local regulatory agencies.

Inspection of Milk Safety

State and local regulatory agencies are responsiblefor the enforcement of sanitation requirements ondairy farms, in milk hauling receiving and transferstations, and in processing plants. The FDA’s primaryfunction under the Federal/State Milk Safety Coop-erative Program is to provide technical assistance tothe states in the implementation and enforcement oftheir regulations. This assistance is provided throughdistrict and regional milk specialists and the Cen-ter for Food Safety and Nutrition’s (CFSAN) MilkSafety Team. The inspection program is carried outby the state regulatory agency under the requirementsof the Cooperative Program of the National Confer-ence on Interstate Milk Shipments (NCIMS). As aresult, there is a greater degree of reciprocity betweenstates on acceptance of inspections. The NCIMS Pro-cedures document contains information for establish-ing milk sanitation standards, rating procedures, sam-pling procedures, laboratory evaluation, and samplecollector procedures (USDHHS Procedures, 2003).

The Procedures requires that producer farms andprocessing facilities are inspected by the state regu-latory agencies on a routine basis at a minimum oftwice a year, with many state regulatory agencies in-specting on a four-per-year schedule. These farmsand dairy plants are also inspected under the Inter-state Milk Shipper (IMS) Program to determine the“rating” of all plants electing to participate in the IMSprogram. State or local ratings must be conducted bya certified USPHS representative. These ratings areconducted no less than once every 24 months (butno more than 15 days) and are based on compliancewith the Grade “A” PMO requirements. The ratingsprovide an assessment of state and local sanitarians’activities regarding public health control and milkquality control. Rating inspections are expressedin terms of percentage compliance. For example,if the milk plant and dairy farms comply with allrequirements of the Grade “A” PMO, the SanitationCompliance Rating of the pasteurized milk supplywould be 100%. However, if the plant of some of thedairy farms fails to satisfy one or more of these re-quirements, the Sanitation Compliance Rating would

3 Regulatory Requirements for Milk Production, Transportation, and Processing 43

be reduced in proportion to the amount of milk andmilk products involved in the violation, and to therelative public health significance of the violateditem(s).

Additionally, the USPHS is obligated to conductperiodic “check ratings” to assure validity and uni-formity with each state’s ratings (USDHHS Methods,2003).

Farm Requirements

The Grade “A” PMO sections on raw milk establishedthe requirements and standards for milk productionand farm conditions. These require that milking ani-mals are disease-free and do not show signs of secre-tion of abnormal milk such as blood or mastitis. Milkfrom cows that have been treated with medications orantibiotics must be properly separated. The milkingbarn, stable, or parlor must be properly constructedwith floors that are concrete or impervious so as toeasily maintain cleanliness. Walls and ceilings shouldbe smooth, painted, or finished, making it dust-tightin order to reduce the likelihood of dust and extrane-ous material from getting into the milk. There mustbe sufficient light during the day and night, as wellas good air circulation to prevent condensation andexcess odors.

Milking barns must be kept clean and the cowyard should be graded for proper drainage to preventstanding water or excess accumulation of organicwaste. The milk house should be of sufficient sizeand provide proper cooling, handling, and storageof milk. It should include proper facilities to wash,sanitize, and store milk containers and utensils. Milkhouses must have tight-fitting doors to the milkingbarn and water that is piped under pressure, withan adequate supply of hot water. The milk coolingmust be monitored by accurate accessible tempera-ture recording devices installed in the milk line, andmilk must be cooled to below 7◦C (45◦F). The milkhouse must be kept clean to reduce the likelihood ofcontamination of the milk. Every dairy farm shouldhave at least one conveniently located toilet. Waterfor the milk house must be from a supply properlylocated and protected to provide safe and sanitarywater quality.

Milking equipment and utensils for handling andstorage of milk on the farm must be made of smooth,nonabsorbent, corrosion-resistant, and nontoxic ma-terial and must be constructed in such a way so thatthey can be easily cleaned. Multiuse woven mate-

rial is not allowed for straining milk. Strainers, ifused, must be of a perforated design or constructedto utilize a single-use strainer media such as paperor cloth. Details for plans of mechanically cleanedmilk pipeline systems must be submitted to thestate regulatory agency for written approval prior toinstallation.

Utensils and equipment used for milk handling,storage, or transportation must be cleaned after eachuse, sanitized before reusing, and stored to assurecomplete drainage and protection from contamina-tion. Additionally, effective measures must be inplace to prevent contamination by insects, rodents,and the chemicals used to control these pests.

Milking must be done in the milking barn, stable,or parlor. The cows’ flanks, udders, bellies, and tailsmust be free from visible dirt. Udders and teats shouldbe cleaned and dried before milking. Teats should betreated with a sanitizing solution just prior to the timeof milking and dried before milking. However, alter-native udder preparation methods may be allowedonce they are evaluated and approved by the FDA.

Milking house operations, equipment, and facili-ties should be conducted to prevent any contamina-tion of milk, equipment, containers, or utensils. Ve-hicles used to transport the milk from the dairy farmto the milk plant, receiving station, or transfer stationshould be constructed in such a way so as to protectthe milk from sunlight, freezing, and contamination.Cleaners and sanitizers used on the farm should beproperly identified. Animal drugs must be properlylabeled and segregated for their use on nonlactatinganimals. Unapproved drugs should not be used. Per-sonal cleanliness of the farm employees is impor-tant, and therefore hand-washing facilities must beprovided.

Furthermore, the dairy farm is responsible for as-suring that the raw milk for pasteurization is cooledto 10◦C (50◦F) or less within 4 hours or less ofthe commencement of the first milking, and to 7◦C(45◦F) or less within 2 hours after the completion ofmilking provided that the blend temperature after thefirst milking and subsequent milking does not exceed10◦C (50◦F).

Milk Transportation

The sanitary requirements for transportation of rawmilk from the farms to the processing plant arealso detailed in the Grade “A” PMO. These policiesmay be found under the sections on raw milk and


regulations pertaining to raw milk receiving stationsand transfer stations.

Milk is collected and stored at the farms in acooled bulk tank and then picked up daily or everyother day by bulk milk transportation trucks. Thesetrucks must be made of smooth, nonabsorbent,corrosion-resistant, nontoxic, material that can beeasily cleaned, and constructed in a way to protectthe milk from dust or airborne contamination.

The bulk milk hauler is often responsible for col-lecting official milk samples as well as transportingraw milk from a farm to a receiving station, transferstation, or a milk processing plant. The bulk milkhauler is required to have training and pass an ex-amination with a score of 70% or greater related tosanitation, sampling, and weighing procedures, in-cluding proper use and cleaning of equipment, andrecord-keeping requirements. The bulk milk hauleris issued a permit upon successful completion of theexamination. The state regulatory agency must ob-serve the techniques of the bulk milk hauler at one ormore farms every 24 months for the permit to remainvalid.

Bulk milk tank trucks are also permitted and in-spected by the state regulatory agency annually. Ifconstruction or repair defects are noted, the milk tanktruck must be removed for service until repairs andsufficient cleaning are verified. The milk tank truckstandards encompass the following areas: properlyconstructed equipment to hold milk at correct temper-atures of 7◦C (45◦F) or less, adequate milk samplingequipment, and a tag affixed to the truck’s outlet valveto verify washing and sanitizing records. When bulkmilk haulers are responsible for obtaining and trans-porting milk samples for official laboratory analysis,they must complete records verifying the chain-of-custody for the samples.

Bulk raw milk from farms may be transported di-rectly to the milk or yogurt processing plants or itmay be held at a transfer station where it is pooledwith other raw bulk milk loads. The transfer stationunloads smaller bulk milk trucks into holding silosand then reloads the commingled raw milk into largerover-the-road tanker trucks for delivery to processingplants.

All vehicles and milk tank trucks containing milkor milk products should be legibly marked with thename and address of the milk plant or hauler in pos-session of the contents.

Milk tank trucks transporting raw, heat-treated, orpasteurized milk and milk products to a milk plantfrom another milk plant, receiving station, or transfer

station are required to be marked with the name andaddress of the milk plant or hauler and should besealed. Additionally, a statement should be preparedfor each shipment containing at least the followinginformation:

� Shipper’s name, address, and permit number.Each milk tank truck containing milk shouldinclude the IMS Bulk Tank Unit (BTU)identification number(s) or the IMS Listed MilkPlant Number (for farm groups listed with a milkplant) on the weight ticket or manifest

� Permit identification of hauler, if not an employeeof the shipper

� Point of origin of shipment� Tanker identification number� Name of product� Weight of product� Temperature of product when loaded� Date of shipment� Name of supervising regulatory agency at the

point of origin of shipment� Whether the contents are raw or pasteurized, or in

the case of cream, low-fat, or skim milk, whetherit has been heat-treated

� Seal number on inlet, outlet, wash connections,and vents

� Grade of product

Processing Plant

Manufacturing plants that process yogurt and fer-mented milk products are subject to the food safetyrequirements in the Grade “A” PMO section on Stan-dards for Grade “A” pasteurized, ultra-pasteurized,and aseptically processed milk and milk products.These requirements dictate the construction of floors,walls, ceilings, doors, and windows as well as properlighting and ventilation. Floors in all rooms of theprocessing facility where milk products are handled,processed, and sorted or in which milk containers,utensils, and equipment are washed must be con-structed of concrete or other equally impervious andeasily cleanable material. The floor must be properlysloped with trapped drains. Storage rooms for dry in-gredients need not have drains and may have floorsconstructed of wood. Walls and ceilings should besmooth, light-colored, washable, and in good repair.Doors and windows should prevent access to insectsand rodents and all openings to the outside must havesolid doors or glazed windows. However, other meth-ods of effectively protecting openings to the outer air


such as screening, fans, air curtains, and properlyconstructed flaps may be used provided the entranceof insects and rodents are prevented.

The processing plant must be designed so that sep-arate rooms are provided for each of the followingoperations:

� The pasteurizing, processing, cooling,reconstitution, condensing, drying, and packagingof milk and milk products.

� Packaging of dry milk or milk products.� The cleaning of milk cans, containers, bottles,

cases, and dry milk or milk product containers.� The fabrication of containers and closures for

milk and milk products.� Cleaning and sanitizing facilities for milk tank

trucks in milk plants receiving milk or whey.� Receiving cans of milk and milk products in milk

plants receiving such cans.

Every milk processing plant should have toilet andhand-washing facilities with hot and cold running wa-ter, soap, and individual sanitary towels or approvedhand-drying devices. The water supply must be ade-quate, safe, and of sanitary quality. The water supplymay be approved as safe from the State Water ControlAuthority, or in the case of individual water systems(wells), comply with construction specifications andbacteriological standards.

The processing facility should be kept clean, neat,and free of evidence of insects and rodents in orderto reduce the likelihood of contamination of the milkor milk products. All piping, floors, walls, ceilings,fans, shelves, tables, and nonproduct contact surfacesshould be clean. Trash and solid waste must be keptin covered containers.

All sanitary piping, fittings, connections, mul-tiuse containers, and equipment that come in con-tact with milk and milk products should be smooth,impervious, corrosion-resistant, nontoxic, and easilycleanable material that is approved for food contactsurfaces. All sanitary piping, connections, and fit-tings must meet the following requirements:

� They must be made from either of the following:a. Stainless steel of the AISI 300 seriesb. Equally corrosion-resistant metal that is

nontoxic and nonabsorbentc. Heat-resistant glassd. Plastic or rubber and rubber-like materials that

are relatively inert and resistant to scratching,scoring, decomposition, crazing, chipping, and

distortion under normal use conditions; must benontoxic, fat-resistant, relatively nonabsorbent,not impart flavor or odor to the milk or milkproducts, and maintain their original propertiesunder repeated use conditions

� They must be designed to permit easy cleaning,maintained in good repair, free of breaks orcorrosion, and must contain no dead ends ofpiping in which milk or milk products maycollect.

Equipment, containers, and utensils should havejoints that are flush and have a smooth finish. Allopenings to tanks, vats, and separators are pro-tected by raised edges to prevent the entrance of sur-face drainage and thus condensation-diverting apronsshould be provided. There must not be threaded fit-tings in milk contact areas. Strainers, if used, shouldbe of a perforated design or constructed to utilize asingle-use strainer media, such as cloth or paper. Wo-ven material may be used only where it is impracticalto use perforated strainers. However, woven strainersmust be thoroughly mechanically cleaned.

All single-service containers, closures, gaskets,and other articles that contact milk must be nontoxicand should be manufactured, packaged, transported,and handled in a sanitary manner and may not bereused.

One of the most critical food safety proceduresis proper cleaning and sanitation of containers andequipment that are used for processing, culturing, fill-ing, packaging, and storage of milk and fermentedmilk products. All multiuse containers and uten-sils such as tanks, lines, vessels, pasteurizers, andfilling equipment must be cleaned at least once aday. Storage tanks should be cleaned when emp-tied at least every 72 hours and records must bereadily available to verify storage times. Cleaningfrequencies beyond these requirements are allowedafter review and acceptance of specific informa-tion by the state regulatory agency in consultationwith FDA. Pipelines and equipment designed formechanical cleaning (cleaning-in-place [CIP]) mustmeet specific requirements of being equipped witha temperature recording device that provides a con-tinuous record of the time and temperature, clean-ing solution velocity, and the presence, strength, orcleaning solution chemicals. For manual washingthere must be a two-compartment wash-and-rinsevat. After cleaning, milk product containers, utensils,and equipment should be stored to assure completedrainage and protection from contamination.


Single-service caps, cap stock, containers, gaskets,and other articles for use in direct contact with milkand milk products must be stored in sanitary wrap-ping or cartons and kept in a clean, dry place untilused. This category also includes the containers andlids used for yogurt and fermented milk packages.

Throughout the milk processing plant, ingredientsin process product, packaging, and finished prod-ucts must be protected from contamination. This in-cludes discarding spilled, overflowed, or leaked milkand milk products. All poisonous or toxic materialsshould be properly labeled and stored in a separatearea and used to preclude contamination. All productcontact surfaces must be covered or otherwise pro-tected to prevent the exposure to insect, dust, con-densation, and other contamination. Many openings,including valves, piping attached to milk storage,milk tank trucks, pumps, and vats should be cappedor properly protected. Air must be free of oil, rust,excessive moisture, extraneous materials, and odorwhen air pressure is used for agitation or the move-ment of milk. The use of steam in contact with milkrequires it to be of culinary quality.

During processing, pipelines and equipment usedto contain or conduct milk and milk products shouldbe effectively separated from tanks or circuits con-taining cleaning and/or sanitizing solutions. This canbe accomplished by physically disconnecting all con-nection points, by separation with two automaticallycontrolled valves or by a single-bodied double seatvalve, with a drainable opening between tanks andcircuits containing cleaning and/or sanitizing solu-tions from pipelines and equipment used for milkor milk products. Additionally, there should be nophysical connection between water, nondairy prod-ucts, unpasteurized dairy product, with pasteurizedmilk and milk products.

Pasteurization is the only practical, commercialmeasure that, if properly applied to all milk, will de-stroy all milk-borne disease organisms. It has beendemonstrated that the time–temperature combina-tions specified by this Grade “A” PMO, if appliedto every particle of milk or milk products, will kill allmilk-borne pathogens. Although pasteurization de-stroys the organisms, it does not destroy the tox-ins that may be formed in milk and milk prod-ucts when certain staphylococci bacteria are present.Staph toxin can result from udder infections andwhen the milk or milk products are not properlyrefrigerated before pasteurization. Such toxins maycause severe illness. The temperature requirementsfor milk pasteurization are given in Tables 3.1 and3.2.

Table 3.1. Pasteurization Temperature vs.Time

Temperature Time

63◦C (145◦F)a 30 minutes72◦C (161◦F)a 15 seconds89◦C (191◦F) 1.0 second90◦C (194◦F) 0.5 seconds94◦C (201◦F) 0.1 seconds96◦C (204◦F) 0.05 seconds100◦C (212◦F) 0.01 seconds

aIf the fat content of the milk product is 10% or more, or ifit contains added sweeteners, or is concentrated (condensed),the specified temperature shall be increased by 3◦C (5◦F).

Detailed information about the design, installation,and operation of the milk pasteurizing equipment isalso dictated by the Grade “A” PMO. The oversee-ing regulatory agency performs specific tests on thepasteurizer’s critical instruments and devices uponinitial installation and at least once every 3 months,and then applies seals to specific equipment that reg-ulate the temperature or flow rate. All temperatureand flow rate pasteurization records are required tobe preserved for a period of 3 years.

Maintaining milk at proper temperatures to avoidbacterial growth and spoilage is critical to productquality and safety. All raw milk and milk productsshould be maintained at 7◦C (45◦F) or less until pro-cessed. All pasteurized milk and milk products, ex-cept those to be cultured, should be cooled imme-diately prior to filling or packaging in an approvedequipment, at a temperature of 7◦C (45◦F). This ex-emption for higher temperature during culturing hasalso been applied to fermentation that occurs in thefinal package, such as cup-set yogurt. All pasteurizedmilk and milk products should be stored at a temper-ature of 7◦C (45◦F) or less until further processed. Toverify proper refrigeration, every refrigerated roomor tank in which milk or milk products are storedshould be equipped with an accurate indicating ther-mometer. On delivery vehicles, the temperature ofmilk and milk products should not exceed 7◦C (45◦F).However, aseptically processed milk and milk

Table 3.2. Eggnog PasteurizationTemperature vs. Time

Temperature Time

69◦C (155◦F) 30 minutes80◦C (175◦F) 25 seconds83◦C (180◦F) 15 seconds


products to be packaged in hermetically sealed con-tainers are exempt from these cooling requirements.

Filling, packaging, and capping of pasteurizedmilk products must be done at the place of pasteur-ization in a sanitary manner by approved mechani-cal equipment. The packaging equipment and sup-ply lines must be equipped with covers to preventcontamination from reaching the inside of the fillerbowl and drip deflectors must be designed to divertcondensation away from open containers. Containerin-feed conveyors to automatic bottling or packagingmachines should have overhead shields to protect thebottles or packaging from contamination. Caps andclosures must be applied in a manner where they can-not be removed without detection, help to provide as-surance to the consumer that the milk and milk prod-ucts have not been contaminated after packaging. Allpackaging must be handled in a sanitary manner.

Employees working in the milk processing plantmust maintain a high degree of personal cleanliness.Hands must be thoroughly washed before commenc-ing plant functions or resuming work after visitingthe toilet, eating, or smoking. Employees must wearclean outer garments and adequate hair coverings.No persons affected with any disease capable of be-ing transmitted to others through the contaminationof food are not allowed to work at a milk plant in anycapacity that brings them into direct contact with pas-teurized milk or aseptically processed milk or milkproduct contact surfaces.

All vehicles used to transport pasteurized milk andmilk products should be constructed and operated insuch a way so that the milk and milk products aremaintained at 7◦C (45◦F) or less and are protectedfrom contamination. Milk tank cars, milk tank trucks,and portable shipping bins should not be used totransport or contain any substances that may be toxicor harmful to humans.

The surroundings of a milk plant should be keptneat and clean to prevent attracting rodents, flies, andother insects that may contaminate the milk or milkproducts. Insecticides and rodenticides must be ap-proved for use in milk plants and used in accordancewith label recommendations.

HACCP

History of HACCP

The use of the Hazard Analysis and Critical Con-trol Point (HACCP) System is not new to the dairyindustry. HACCP is a logical, simple, effective, andhighly structured system of food safety control. The

HACCP System was introduced to the food industryas a spin-off of the space program during the 1960s.The National Aeronautics and Space Administration(NASA) used HACCP to provide assurance of thehighest quality available for components of space ve-hicles. This program, to develop assurance of productreliability, was carried over into the development offoods for astronauts.

Background

HACCP is a management tool that provides a struc-tured and scientific approach to the control of identi-fied hazards. HACCP is a logical basis for better deci-sion making with respect to product safety. HACCPis internationally recognized as an effective meansof controlling food safety hazards and is endorsedas such by the joint Food and Agriculture Organiza-tion (FAO) of the World Health Organization CodexAlimentarius Commission. The U.S. National Ad-visory Committee on Microbiological Criteria forFoods (NACMCF) has also endorsed it.

The HACCP concept enables those operating andregulating under an HACCP Plan to move to apreventive approach, whereby potential hazards areidentified and controlled in the manufacturing envi-ronment, i.e., prevention of product failure. HACCPallows for a preventive systematic approach to foodsafety.

Voluntary Participation

The NCIMS HACCP Program is a voluntary alterna-tive to the traditional inspection system. Milk plants,receiving stations, or transfer stations can partici-pate in the voluntary NCIMS HACCP Program onlywhen the state regulatory agency responsible for theoversight of the facility agrees to participate withthem in the program. Management responsible forboth the state and dairy plants, receiving stations,or transfer stations must be willing to provide theresources needed to develop and implement a suc-cessful HACCP System. Both parties must providewritten commitment to each other that the necessaryresources to support participation in the NCIMSHACCP Program will be made available.

HACCP Principles

Following are the seven HACCP principles to be in-cluded in an HACCP Plan:

� Conduct a hazard analysis� Determine the critical control points


� Establish critical limits� Establish monitoring procedures� Establish corrective actions� Establish verification procedures� Establish record-keeping and documentation

procedures

Prerequisite Programs

Prior to the implementation of a HACCP Plan, thereis a requirement for dairy plants, receiving stations,and transfer stations to develop, document, and im-plement written prerequisite programs (PPs). Theseprovide the basic environment and operating condi-tions that are necessary for the production of safe,wholesome food. Many of the conditions and prac-tices are specified in federal and state regulations andguidelines.

The seven principles of HACCP are also called theHACCP Plan. When combined with the PPs, theyconstitute an HACCP System. The NCIMS HACCPProgram combines the HACCP System and other pre-scribed Grade “A” PMO criteria, such as drug residuetesting and trace back, use of milk only from suppliesthat have been awarded a milk sanitation compliancerating of at least 90% or from an acceptable IMSHACCP listed source, and labeling requirements.When properly implemented, the HACCP Programwill provide assurance of milk and milk productsafety that is equivalent to that provided under thetraditional inspection system.

Standards and Regulations

Standards for Containers and Closures

Single-service containers and closures, such as plas-tic jugs, plastic-coated paperboard milk containers,plastic tubs, lids, and aluminum aerosol cans, areused by the dairy industry for packing milk and milkproducts. Industry-applied quality assurance controlsfor manufacturing and handling of the materials havemade it possible for these products to reach the pointof use in a sanitary condition free from toxic ma-terials that may migrate into milk or milk products.Standards set forth in the Grade “A” PMO, AppendixJ ensure the production of sanitary containers andclosures for milk and milk products. The standardsinclude the bacterial requirements, fabrication plant,equipment, processing, and packaging standards aswell as materials, waxes, adhesives, sealants, and inksthat can be used. Approval of certified single-service

containers and closures plants is published in the In-terstate Milk Shipper List quarterly.

Labeling

Labeling of bottles, containers, and packages con-taining milk or milk products such as yogurt andfermented milk are defined in applicable require-ments of the Federal Food Drug and Cosmetic Act(FFDCA), the Nutrition Labeling and Education Act(NLEA) of 1990, and regulations developed there un-der the Federal Code of Regulations Title 21. Moredetailed information on FDA labeling regulations canbe found in Chapter 4. However, in addition to federalrequirements, the Grade “A” PMO requires additionallabeling as follows:

All bottles, containers, and packages containingmilk or milk products, except milk tank trucks, stor-age tanks, and cans of raw milk from individual dairyfarms, should be conspicuously marked with thefollowing:

1. The identity of the milk plant where the milk waspasteurized, ultra-pasteurized, aseptically pro-cessed, condensed, or dried. This may be accom-plished by printing on the container the companyname and its location (listing the city and state)or the unique identification number, which is the“IMS Listed Milk Plant Number,” assigned by thestate to each plant.

2. The words “keep refrigerated after opening” inthe case of aseptically processed milk and milkproducts.

3. The common name of the hooved mammal pro-ducing the milk should precede the name of themilk or milk product when the product is or ismade from milk other than cow’s milk, for exam-ple, “Goat,” “Sheep,” “Water Buffalo,” or “OtherHooved Mammal” milk or milk products.

4. The words Grade “A” on the exterior surface. Ac-ceptable locations should include the principal dis-play panel, the secondary or informational panel,or the cap/cover. The term Grade “A” may notsolely appear in the ingredient statement.

5. The word “reconstituted” or “recombined” if theproduct is made by milk subject to reconstitution,recombined milk, or milk ingredients.

All labeling terms must be truthful and notmisleading as dictated by the FFDCA. Gradedesignations, such as Grade “AA” Pasteurized,Selected Grade “A” Pasteurized, Special Grade “A”Pasteurized, etc., give the consumer the impression


that such a grade is significantly safer than Grade “A.”Such an implication is false because the Ordinancerequirements for Grade “A” pasteurized, ultra-pasteurized, or aseptically processed milk whenproperly enforced will ensure that this grade of milkwill be as safe as milk can practically be made.Descriptive labeling terms must not be false and mis-leading and should not be used in conjunction withthe Grade “A” designation or the name of the milkor milk product. If descriptive terms are used in con-junction with attributes of the product other than milksafety, i.e., “special select strawberries” for straw-berry yogurt or “rich creamy texture,” these labelingterms should not be in a location immediately preced-ing or following the name of the food. Creating phys-ical distance and employing graphic enhancementssuch as distinctive type styles, bursts, and other tech-niques generally are effective ways of distinguishingoptional information from the required information(USDHHS PMO, 2003).

Examination of Milk Products

In order to verify the quality and safety of the milk andmilk products to the Grade “A” PMO, it is requiredthat raw milk, commingled milk in the silos intendedfor processing, and finished products be sampled andtested by state regulatory agencies at a specific fre-quency. The products must meet chemical, bacterio-logical, and temperature standards, which are givenin Table 3.3.

It is required that the state regulatory agency collectand test official samples of at least four times duringany consecutive 6 months. However, many state reg-ulatory agencies sample and test monthly. The sam-ples must include each fat level and both plain andflavored products for finished milk and milk products.Therefore, if a plant produces plain low-fat yogurt,flavored low-fat yogurt, and flavored nonfat yogurt,all three products must be sampled. It is not necessaryto sample each flavor monthly, but usually differentflavors are chosen each time the product is sampled.

Testing of official samples must be done in labo-ratories that are certified under the Interstate MilkShippers Program and by technicians that havebeen certified to perform the specific required tests.Requirements for laboratories are governed by theEvaluation of Milk Laboratories (EML). Samplingprocedures and required laboratory tests must be incompliance with the most current edition of Stan-dard Methods for the Examination of Dairy Products(SMEDP) of the American Public Health Association

and the most current edition of Official Methods ofAnalysis of AOAC INTERNATIONAL (OMA).

IMPORTSTraditional fermented milk such as yogurt, culturedbutter milk, lactobacillus acidophilus milks, and evensome of the newer fermented milk products suchas drinkable yogurt are defined and regulated bythe Grade “A” PMO.This regulatory system relieson a complex oversight and inspection of raw milkproduction, milk transportation, and processing de-scribed previously in this chapter.

The United States is a signatory of the World TradeOrganization (WTO) agreement, which allows coun-tries to establish measures to ensure safety of foodwithin their countries. The measures, however, mustbe applied in a manner so that they do not arbitrarilydiscriminate between products from different coun-tries or treat domestic products more favorably thanimported products without justification. The deter-mination of equivalence is made by the importingcountry based on whether the exporting country’smeasures meet the level of protection deemed ap-propriate by the importing country as provided by itsown measures.

The FDA and the NCIMS have identified and mu-tually accepted three options that are consistent withNCIMS Procedures and allow states to receive PMOdefined Grade “A” products produced outside of theUnited States.

These options are as follows:

1. A dairy firm outside of the United States couldcontract with any current NCIMS member’s regu-latory agency to provide the Grade “A” milk safetyprogram in total. This would include the regula-tory licensing, dairy farm and milk plant inspec-tion, sampling, pasteurization equipment tests,laboratory certification, and rating/NCIMS listingcertification. To use this option, the firm would berequired to abide by all applicable NCIMS reg-ulatory and rating requirements and the regula-tory/rating agency would have to agree to treat thefirm as if it were located within its jurisdictionfor all purposes including inspection and enforce-ment. Ratings of the firm would be check-rated bythe FDA.

2. The importing country may become a full memberof the NCIMS subject to all NCIMS rules and en-joying all privileges of a U.S. state. This would re-quire, among other things, that the milk regulatory

Table 3.3. Chemical, Physical, Bacteriological, and Temperature Standards

Grade “A” raw milk andmilk products forpasteurization,ultra-pasteurization,or aseptic processing

Temperature................ Cooled to 10◦C (50◦F) or less within4 hours or less of the commencementof the first milking, and to 7◦C (45◦F)or less within 2 hours after thecompletion of milking, provided thatthe blend temperature after the firstmilking and subsequent milkings doesnot exceed 10◦C (50◦F).

Bacterial limits.......... Individual producer milk not to exceed100,000 per milliliter prior tocommingling with other producer milk.

Not to exceed 300,000 per milliliter ascommingled milk prior topasteurization.

Drugs...................... No positive results on drug residuedetection methods as referenced inSection 6—Laboratory Techniques.

Somatic cell counta ........ Individual producer milk not to exceed750,000 per milliliter.

Grade “A” pasteurized milkand milk products andbulk shipped heat-treatedmilk products

Temperature................ Cooled to 7◦C (45◦F) or less andmaintained thereat.

Bacterial limitsb. . . ........ 20,000 per milliliter or grams.c

Coliformd ............... Not to exceed 10 per milliliter. But in thecase of bulk milk, transport tankshipments shall not exceed 100 permilliliter.

Phosphatasee........... Less than 350 milliunits/liter for fluidproducts and other milk products by theFluorometer or Charm ALP orequivalent.

Drugsb.................. . . .. No positive results on drug residuedetection methods as referenced inSection 6—Laboratory Techniques thathave been found to be acceptable foruse with pasteurized and heat-treatedmilk and milk products.

Grade “A” pasteurizedconcentrated(condensed)

Temperature..................... Cooled to 7◦C (45◦F) or less andmaintained thereat unless drying iscommenced immediately aftercondensing.

milk and milk products Coliform.......................... Not to exceed 10 per gram. But in the caseof bulk milk transport tank shipmentsshall not exceed 100 per milliliter.

Grade “A” aseptically Temperature................ Noneprocessed milk and milk Bacterial limits........... Refer to 21 CFR 113.3(e)(1) f

products Drugsb.................... No positive results on drug residuedetection methods as referenced inSection 6—Laboratory Techniques thathave been found to be acceptable foruse with aseptically processed milk andmilk products.

(Continued)

50


Table 3.3. Continued

Grade “A” nonfat dry milk No more than:Butterfat.................. 1.25%Moisture................... 4.00%Titratable acidity......... 0.15%Solubility index........... 1.25 mlBacterial estimate......... 30,000 per gramColiform................... 10 per gramScorched particles disc B................ 15.0 per gram

Grade “A” whey forcondensing

Temperature................ Maintained at a temperature of 7◦C(45◦F) or less, or 63◦C (145◦F) orgreater, except for acid-type wheywith a titratable acidity of 0.40%or above, or a pH of 4.6 or below.

Grade “A” pasteurizedcondensed whey and whey

Temperature. . . . . . . . . . . . ............ Cooled to 7◦C (45◦F) or less duringcrystallization, within 48 hours ofcondensing.

products Coliform limit. . . . . . . . . .......... Not to exceed 10 per gramGrade “A” dry whey, Grade “A”

dry whey products, Grade“A” dry buttermilk, andGrade “A” dry buttermilkproducts

Coliform limit. . . . . . . . . .. Not to exceed 10 per gram

aGoat milk 1,000,000 per milliliter.bNot applicable to acidified or cultured products.cResults of the analysis of dairy products that are weighed in order to be analyzed will be reported in # per grams. (Refer to

the current edition of the SMEDP.)d Not applicable to bulk shipped heat-treated milk products.eNot applicable to bulk shipped heat-treated milk products; UP products that have been thermally processed at or above

138◦C (280◦F) for at least 2 seconds to produce a product that has an extended shelf life (ESL) under refrigerated conditions;and condensed products.

f 21 CFR 113.3(e) (1) contains the definition of “commercial sterility.”Source: USDHHS PM0, 2003.

agencies of the importing countries adopt and en-force rules and regulations that are the same asthose required in the United States and abide byall applicable NCIMS regulatory and rating re-quirements. Their ratings would be check-rated byFDA in the same way as state ratings. The FDAwould certify their rating, sampling surveillance,and laboratory evaluation officers.

3. The FDA can evaluate the importing country’ssystem of assuring the safety of dairy productsand compare the effect of that system with theeffect of the U.S. system on the safety of dairyproducts produced domestically. The NCIMS hasadopted a procedure to accept FDA findings ofequivalence and to allow NCIMS member statesto accept products produced within the scope ofsuch a finding.

Additionally, Grade “A” milk products have re-strictions in the use of imported dairy ingredients un-less the foreign ingredient facility has meet the U.S.grade “A” requirements by using one of the threeoptions listed above. As specified in the Grade “A”PMO, Grade “A” dairy products must use only Grade“A” dairy ingredients, except that small amounts offunctional ingredients (total of all such ingredientsshould not exceed 5% by weight of the finished blend)that are not Grade “A” are allowed in Grade “A” whenthe finished ingredient is not available in Grade “A”form, i.e., sodium caseinate (USDHHS PMO, 2003).

EQUIPMENTS STANDARDSThe specific requirements for milking equipment,milk transportation, storage, and processing are


explained in the Grade “A” PMO. To comply withthe sanitary design and construction standards of thePMO, equipment manufactured in conformity withthe 3-A Sanitary Standards must be evaluated bythe state regulatory agency prior to installation. The3-Sanitary Standards for dairy equipment are promul-gated jointly by the Sanitary Standards Subcommit-tee of the Dairy Industry Committee, the Committeeon Sanitary Procedure of the International Associa-tion for Food Protection (IAFP), and the FDA MilkSafety Branch.

The 3-A Sanitary Standards Symbol

The 3-A Symbol was introduced in 1927 and is usedto identify equipment that meets 3-A Sanitary Stan-dards for design and fabrication. Use of the 3-ASymbol is governed by 3-A Sanitary Standards, Inc.(3-A SSI).

Once a 3-A Sanitary Standard has been developedand becomes effective, manufacturers may receiveauthorization from the 3-A Symbol Council to use thesymbol. Voluntary use of the 3-A Symbol on dairyand food equipment serves three important purposes:

� Assures processors that equipment meets sanitarystandards;

� Provides accepted criteria to equipment manufac-turers for sanitary design; and

� Establishes guidelines for uniform evaluation andcompliance by sanitarians.

3-A SSI formulates standards and practices for thesanitary design, fabrication, installation, and clean-ability of dairy and food equipment or systems usedto handle, process, and package consumable prod-ucts where a high degree of sanitation is required.These standards and practices are developed throughthe cooperative efforts of industry experts. Its ulti-mate goal is to protect consumable products fromcontamination and to ensure that all product surfacescan be mechanically cleaned-in-place (CIP) or easilydismantled for manual cleaning.

3-A Accepted Practices cover a system, which isdefined as a set of connected equipment and machin-ery that forms as a whole or works together. In ad-dition to the criteria for equipment, a practice mayalso provide specifications for sanitary installationand legal controls.

3-A Sanitary Standards provide material specifica-tions, design criteria, and other necessary informationfor equipment types to satisfy public health concerns.3-A Standards are available for more than 70 equip-ment types, from fittings, centrifugal pumps, heat

exchangers, valves, membranes, CIP spray devicesto silo tanks.

3-A criteria are universally accepted by equip-ment manufacturers, fabricators, users, and sanitari-ans. The 3-A Symbol, where authorized by 3-A SSI,is used by equipment manufacturers and fabricatorsto indicate conformance to 3-A Standards.

In order for dairy and food equipment manufactur-ers to use the 3-A Symbol, they must file an applica-tion with the 3-A Symbol Council office signifyingthat the equipment is compliant with all provisions ofthat standard. A statement of quality controls in placemust be submitted along with drawings or picturesof the equipment. The Council may also request ad-ditional materials to ensure compliance on complexsubassemblies. The Council reviews the applicationand, if all areas are in compliance under that specific3-A Standard, the manufacturer is permitted to usethe 3-A Symbol.

Equipment manufacturers are required to placethe serial number of the 3-A Standard with whichit complies adjacent with the 3-A Symbol on theirequipment.

A listing of authorized holders of 3-A symbol cer-tification can be found on the 3-A Sanitary StandardsWeb site (http://www.3-a.org). The listing is orga-nized by standards for each type of equipment andprovides the manufacturing company’s informationand if relevant, the model number of the piece ofequipment that has received authorization.

MILK PRICING—U.S. FEDERALMILK MARKETING ORDERSBackground of Federal Orders

The Federal Milk Marketing Orders system is a regu-latory function administered by the United States De-partment of Agriculture (USDA). The Federal Ordershave evolved significantly since their first legislativeintroduction in 1937. The objective of the FederalOrders is to stabilize markets by placing certain re-quirements on the pricing and handling of milk in thearea it covers, and ultimately, assure that an adequatesupply of wholesome milk is available and will con-tinue to be available at a reasonable price to con-sumers. There are 10 regions in the United Statesthat are regulated by a Federal Order (see Fig. 3.1).Regions that are not subject to a Federal Order havea state milk marketing order such as in Califor-nia where the pricing system is akin to the FederalOrders, or they may be unregulated (USDA, 2004).


ARIZONA -LAS VEGAS

UPPERMIDWEST

CENTRAL

SOUTHWEST

SOUTHEAST

FLORIDA

APPALACHIAN

MIDEAST

NORTHEAST

PACIFICNORTHWEST

ConsolidatedFederal Milk Marketing Order Areas

USDAAgricultural Marketing ServiceDairy Programs

DIFFERENCES IN SHADING MERELY SERVE TODIFFERENTIATE BETWEEN MARKETING AREAS

Figure 3.1. Consolidated Federal Milk Marketing Orders areas.

The Federal Milk Marketing Orders are concernedprimarily with orderly marketing of raw Grade “A”milk from producer to processor. Classified pricingand pooling are the two key elements for the FederalMilk Orders which set minimum prices for more than70% of the Grade “A” milk produced in the UnitedStates. A major function of the Federal Orders is com-puting minimum prices for raw Grade “A” milk thathandlers must pay to dairy farmers. The Federal MilkMarketing Orders system has been developed to poolthe proceeds of all qualified milk sales in order to en-sure that all producers in an area receive a uniformprice for their milk—regardless of how their milk wasused.

Classified Pricing

The Federal Milk Marketing Orders program usesproduct price formulas to determine milk componentvalues that are combined to calculate monthly classprices. The factors in the formulas are dairy productprices, which change monthly, and make allowancesand product yields, which are set in the formulas. Thedairy product prices are those collected by USDA

from weekly surveys of dairy product manufacturersthat sell specific products on a bulk, wholesale basis(Jesse and Cropp, 2004).

Federal orders define the following four classesof milk, from highest to lowest value (under mostcircumstances):

1. Class I is milk used for beverage products. Thisincludes “white” whole, low-fat, and skim milk inall container sizes, chocolate and other flavoredmilks, liquid buttermilk, and eggnog.

2. Class II is milk used for soft manufactured prod-ucts like yogurt and cultured dairy products, sourcream, ice cream, and other frozen dairy desserts,cottage cheese, and creams.

3. Class III is milk used to manufacture cream cheeseand hard cheeses.

4. Class IV is milk used to make butter and dry milkproducts—principally nonfat dry milk.

Producer Prices

The Federal Orders requires milk handlers in a mar-keting area to pay dairy farmers (producers) no less


than certain minimum prices for fluid milk. The pricefor class II, III, and IV milk is the same under allFederal Orders. Class II prices are computed eachmonth for each marketing area and are based onNational Agricultural Statistics Service (NASS) re-leased prices for milk used in manufactured products.The Federal Orders also require that a plant’s usagevalue for milk be combined with other plants usagevalue (pooled) and each producer (or cooperative) bepaid on the basis of a uniform/blend/average price.This blend price represents an average of the value ofmilk in all uses (fluid milk, cottage cheese, ice cream,cheese, butter, etc.).

With federal order pooling, producers receive acommon price for their milk components regardlessof how their milk is used. Total producer milk valueunder the order is the sum of the following elements:

� Total hundredweight milk × Producer PriceDifferential (at locations)

� Protein pounds × Protein Price

� Other Solids pounds × Other Solids Price� Butterfat pounds × Butterfat Price� Total hundredweight milk × Somatic Cell

Adjustment

Expressed in terms of hundredweights of milk,producer prices will differ according to milk compo-sition, milk quality, and the location of the receivingplant.

Milk Pricing for FermentedMilk Products

Milk pricing for fermented milk and milk productsis dependent on whether the final product will beconsumed as a beverage, on the level of fat, andon milk solids. Products similar to spoonable yogurtand sour cream are considered as class II under theFederal Milk Marketing Orders system. Drinkablefermented products, such as cultured buttermilk, aci-dophilus milk, kefir, and yogurt drinks that have 6.5%

Fluid milkproduct

Begin Here

no

yes

Beverage no

yes

Less than 9%butterfat

Infant feeding ordietary use

(meal replacement)

no

yes

no

no

yes

yes

Class I Class II

Hermeticallysealed container

Class IIidentification

no

no

no

no

no

no

yes

yes

yesyes

yes

yes

Less than6.5% NFMS

Distributed in less thanone-half gallon package

Class III or Class IV

Used in soft or semisolid form(except for spreadable

cheese which are utilized in class II)

Distributed in larger thanone gallon package

Commercialfood

processingestablishment

Figure 3.2. Flow diagram used to determine milk classification pricing for a product.Source: IDFA Milk Procurement Workbook, 2005.


or greater milk solids nonfat and less than 9% milk fatwill be priced as class I. The flow chart in Figure 3.2can be used to determine whether a product will beconsidered as class I or class II.

GLOSSARYAISI 300—A quality specification for stainless steel

from the American Iron and Steel Institute.BULK TANK UNIT—A dairy farm or a group of dairy

farms from which raw milk is collected.CIP (CLEANING-IN-PLACE)—A method of clean-

ing lines and tanks without disassembly by purgingwater and cleaning chemicals.

CLASSIFIED PRICING—A system used to price rawmilk sold for processing based on the intended use ina specific dairy product.

COLIFORM—A group of microorganisms found inthe intestinal tract; their presence indicates contami-nation with fecal matter.

FDA—U.S. Food and Drug Administration.FFD&CA (FEDERAL FOOD DRUG AND COS-

METIC ACT)—An act of the U.S. Congress thatspecified the basis for food safety standards.

GRADE “A” PMO (PASTEURIZED MILKORDINANCE)—Model milk regulations used forthe inspection of milk production and processingfacilities.

HACCP (HAZARD ANALYSIS AND CRITICALCONTROL POINTS)—A system of steps for estab-lishing a food safety program through identificationand prevention of problems.

IMS (INTERSTATE MILK SHIPPERS) LISTED—A publication that provides a listing of farms andplants that have successfully passed a sanitary inspec-tion.

NCIMS—National Conference on Interstate Milk Ship-ments.

PASTEURIZATION—A process of heating fluid milkproducts to render them safe for human consump-tion by destroying the disease-producing organisms(pathogens). The process inactivates approximately95% of all microorganisms in milk.

PHOSPHATE—An enzyme that is deactivated in milkat normal pasteurization temperatures; its presence in

pasteurized milk indicates the milk has not been prop-erly heated or was mixed with unpasteurized milk.

SINGLE-SERVICE CONTAINERS—A containerused in the storage, handling, or packaging of milkor milk products intended for only one use.

SNF—Solids-not-fat portion of the milk.SOMATIC CELL COUNT—A numeric count of the

dead epithelial cell and leucocytes (white blood cells)that migrate into milk from the udder of a cow.

UHT (ULTRA-HIGH TEMPERATURE)—Heattreatment at a temperature of 135–150◦C for aholding time of 4–15 seconds that sterilizes theproduct for aseptic packaging to permit storage atambient temperatures.

USDA—United States Department of Agriculture.

REFERENCESCFSAN (Center for Food Safety and Applied

Nutrition). 2004. National Conference on InterstateMilk Shipments Model Documents—Milk SafetyReferences [Online]. Available at http://www.cfsan.fda.gov/∼ear/p-nci.html.

Jesse E, Cropp R. 2004. Basic Milk Pricing Conceptsfor Dairy Farmers. University of Wisconsin—Extension, Cooperative Extension, Madison, WI.

USDA (U.S. Department of Agriculture). 2004.Agriculture Marketing Services Dairy Programs.Federal Milk Marketing Orders [Online]. Availableat http://www.ams.usda.gov/dairy/orders.htm.

USDHHS PMO (U.S. Department of Health andHuman Services). 2003. Grade “A” Pasteurized MilkOrdinance, 2003 Revision, Department of PublicHealth, USDHHS, Food and Drug Administration,Washington, DC.

USDHHS Procedures. 2003. Procedures Governingthe Cooperative State-Public Health Service/Foodand Drug Administration Program of the NationalConference on Interstate Milk Shipment, 2003Revision, Department of Public Health, USDHHS,Food and Drug Administration, Washington, DC.

USDHHS Methods. 2003. Methods of MakingSanitation Ratings of Milk Shippers, 2003 Revision,Department of Public Health, USDHHS, Food andDrug Administration, Washington, DC.

4Regulations for Product Standards

and LabelingCary P. Frye

U.S. Code of Federal RegulationsU.S. Product Standards of Identity

Fermented Milk and Milk ProductsGeneral DefinitionsStayed ProvisionsProposed Changes to U.S. Standards for Yogurt and

Fermented MilksFood Additives and Packaging

LabelingGeneral RequirementsNomenclatureFlavor LabelingIngredient DeclarationNutrition Facts PanelSpecial Labeling Requirements

Codex Standards and Definitions for Fermented MilkProducts

GlossaryReferences

U.S. CODE OF FEDERALREGULATIONSThe U.S. Code of Federal Regulations (CFR) pub-lished by the U.S. government is a set of com-prehensive documents containing all Federal Reg-ulations. Each branch of government is assigned adifferent numerical title. The regulations for Food andDrugs are published in Title 21. These publicationsare revised and issued yearly. The current versioncan also be found online. The Title 21 Code of Fed-eral Regulations Parts 1—199 lays out FDA’s regula-tions for current good manufacturing practices, foodlabeling, standards of identity, and approved foodadditives.

U.S. PRODUCT STANDARDSOF IDENTITYFood standards were established to promote fair com-petition among manufacturers and to eliminate con-sumer confusion. Currently there are 97 federal stan-dards of identity for various dairy products out of atotal of 262 standards for all foods including dairy.Many states have also promulgated standards of iden-tity for dairy products. The Nutrition Labeling Edu-cation Act (NLEA) of 1990 established that wherefederal and state standards exist simultaneously, thefederal standard preempts the state regulation. How-ever, in the event if no federal standard exists for aspecific dairy product and a state standard has beenpromulgated, the state standard is in effect. In terms ofdetailed presentation, this section only addresses fed-eral standards of identity. For the most part, standardsof identity dictate the processing procedure, compo-sition, and allowed ingredients of the product andoften cover public safety concerns and product label-ing. All federal standards of identity for dairy prod-ucts are referenced in Title 21 CFR, Parts 130–135.The Grade “A” Pasteurized Milk Ordinance (PMO), amodel regulation for milk sanitation, adopts by refer-ence the federal standards of identity. These standardsof identity apply to products that are manufacturedfor sale in the United States including both domesti-cally produced and imported products.

Fermented Milk and Milk Products

The milk and cream standards are found in 21 CFRpart 131, which include definitions of milk ingredi-ents and specific requirements for fermented milk

57




products such as cultured milk, sour cream, and yo-gurts, which are listed below.

General Definitions

In addition to the standards of identity listed below,the CFR also provides definitions of milk and creamas ingredients in fermented milk products:

Milk. Milk is the lacteal secretion, free from colos-trum, obtained by milking one or more healthy cows.Milk fat and milk solids nonfat (MSNF) may be “ad-justed” by removing the milk fat or adding cream,concentrated milk, dry whole milk, skim milk, con-centrated skim milk, or nonfat dry milk. Composi-tionally, it must have a minimum of 8.25% MSNFand a minimum of 3.25% milk fat.

Cream. Cream means the liquid milk product highin fat separated from milk, which may have beenadjusted by adding to it milk, concentrated milk, drywhole milk, skim milk, concentrated skim milk, ornonfat dry milk. Cream contains not less than 18%milk fat.

Cultured Milk—21 CFR §131.112

Description of Process

� Prepared by culturing with characterizingmicrobial organisms with one or more of thefollowing: cream, milk, partially skimmed milk,and skim milk.

� Must be pasteurized or ultra-pasteurized prior tothe addition of the microbial culture and may behomogenized.

� May contain other optional ingredients (listedlater below).

Composition

� Minimum of 3.25% of milk fat� Minimum of 8.25% MSNF� Minimum of 0.5% titratable acidity (expressed as

lactic acid)� 2000 IU of vitamin A/qt (optional)� 400 IU of vitamin D/qt (optional)

Other Ingredients

� Acidifying ingredients such as acetic acid, adipicacid, citric acid, fumaric acid, glucono-delta-lactone, hydrochloric acid, lactic acid, malicacid, phosphoric acid, succinic acid, or tartaricacid.

� Optional dairy ingredients include concentratedskim milk, nonfat dry milk, buttermilk, whey,lactose, lactalbumins, lactoglobulins, and whey(modified by partial or complete removal oflactose and/or minerals).

The provision in the standard of identity forcultured milk limiting the sources of optionaldairy ingredients has been stayed, pending theoutcome of a public hearing. Other milk-derivedingredients (e.g., caseinates) may be used toincrease the nonfat solids content in culturedmilk.

� Nutritive carbohydrate sweeteners such as beet orcane sugar (sucrose), inverted sugar (paste orsyrup), brown sugar, refiner’s sugar, molasses (notblackstrap), high fructose corn syrup, fructose,fructose syrup, maltose, maltose syrup, driedmaltose syrup, malt extract, dried malt extract,honey, maple sugar, dextrose anhydrous, dextrosemonohydrate, glucose syrup, dried glucosesyrup, lactose, cane syrup, maple syrup, andsorghum.

� Flavoring.� Color additives may be added, except that those

that impart butterfat or milk fat color may not beadded directly to the fluid product so that it givesthe appearance that the product contains moremilk fat than it actually does.

� Stabilizers.� Butterfat or milk fat in the form of granules or

flakes (which may or may not contain coloradditives).

� Aroma and flavor producing microbial culture.� Salt.� Flavor precursors (citric acid 0.15% maximum of

milk or equal the amount of sodium citrate).

Nomenclature. The name of the food is “culturedmilk.”

Milk fat level

� Milk fat percentage declaration is not required.

Process

� If the dairy ingredients were homogenized, thenthe label may indicate “homogenized” (optional).

Sweetened

� If sweetened with a nutritive carbohydratesweetener without a characterizing flavor, then thelabel must indicate “sweetened.”

4 Regulations for Product Standards and Labeling 59

Characterizing organisms

� Name of the food may declare traditional orgeneric names of characterizing microbialorganisms (optional) or ingredients, e.g., “kefircultured milk,” “acidophilus cultured milk,” orwhen lactic acid producing organisms are used,“cultured buttermilk.”

Flavoring

� If characterizing flavors were added, then thename should indicate the common or usual nameof the flavoring.

Sour Cream (Cultured Sour Cream) 21 CFR§131.160


� Produced from souring pasteurized cream withlactic acid producing bacteria.

� May contain other optional ingredients listedbelow.

Composition

� Minimum of 18% milk fat� Minimum of 14.4% milk fat for bulky flavored

sour creams� Minimum of 0.5% titratable acidity

Other Ingredients

� Ingredients that improve texture, preventsyneresis, or extend shelf life of the sour cream.

� Flavor precursor—sodium citrate in a minimumquantity of 0.1% added prior to culturing.

� Rennet.� Salt.� Flavoring ingredients with or without coloring,

fruit or fruit juice (may be from concentrate), ornatural and artificial flavoring.

Nomenclature. The name of the food is “sourcream” or “cultured sour cream.”

Flavoring

� If characterizing flavors were added, then thename should indicate the common or usual nameof the flavoring.

Sweetened

� If the sour cream was sweetened with a nutritivesweetener without the addition of characterizingflavorings, then the label must indicate“sweetened.”

Yogurt (Includes Drinkable Yogurts) 21 CFR§131.200


� Produced by culturing with the lacticacid-producing bacteria Lactobacillus bulgaricusand Streptococcus thermophilus (may containother lactic acid-producing bacteria) one or moreof the following: cream, milk, partially skimmedmilk, skim milk, or reconstituted dairyingredients.

The standard of identity for yogurt does notinclude the addition of reconstituted dairyingredients as basic components in themanufacturing of yogurt. This exclusion has beenstayed, pending the outcome of a public hearing,and therefore, reconstituted dairy ingredientscould be used as a basic dairy component inyogurt.

� May be homogenized and must be pasteurized orultra-pasteurized prior to the addition of bacteriaculture.

� Flavoring ingredients may be added afterpasteurization or ultra-pasteurization.

� The product may be heat-treated to destroy viablemicroorganisms to extend shelf life.

� May contain other optional ingredients (listedlater below).

Composition

� The provision requiring the milk fat level to be aminimum of 3.25% before the addition of bulkyflavorings has been stayed, pending the outcomeof a public hearing.

� Minimum of 8.25% MSNF.� 2000 IU vitamin A/qt (optional).� 400 IU vitamin D/qt (optional).� The product does not have to meet the titratable

acidity requirement indicated in the standard(minimum of 0.9% titratable acidity). Thisprovision was stayed, pending the outcome of apublic hearing.

Other Ingredients

� Optional dairy ingredients include concentratedskim milk, nonfat dry milk, buttermilk, whey,lactose, lactalbumins, lactoglobulins, and whey(modified by partial or complete removal oflactose and/or minerals). The provision in thestandard of identity for yogurt limiting thesources of optional dairy ingredients has been


stayed, pending the outcome of a public hearing.Other milk-derived ingredients (e.g., caseinates)may be used to increase the nonfat solids contentin yogurt.

� Nutritive carbohydrate sweeteners such as beet orcane sugar (sucrose), inverted sugar (paste orsyrup), brown sugar, refiner’s sugar, molasses (notblackstrap), high fructose corn syrup, fructose,fructose syrup, maltose, maltose syrup, driedmaltose syrup, malt extract, dried malt extract,honey, maple sugar, dextrose anhydrous, dextrosemonohydrate, glucose syrup, dried glucose syrup,lactose, cane syrup, maple syrup, sorghum.

� Flavoring ingredients.� Color additives.� Stabilizers.� Preservatives as functional ingredients were not

provided for in the standard of identity for yogurt.This exclusion has been stayed, pending theoutcome of a public hearing, and therefore,preservatives could be added to yogurt as afunctional ingredient.

Nomenclature. The name of the food is “yogurt.”Alternate spelling of the food should not serve as thename of the food (e.g., “yogourt,” or “yoghurt”).

Process

� If the dairy ingredients were heat-treated afterculturing, then the name of the food must befollowed by the parenthetical phrase“(heat-treated after culturing).”

� If the dairy ingredients were homogenized, thenthe label may indicate “homogenized” (optional).

Vitamins

� If vitamins are added, then the following types ofphrases are stated as appropriate: “vitamin A” or“vitamin A added,” “vitamin D” or “vitamin Dadded,” or “vitamin A and D” or “vitamin A andD added.”

� The word “vitamin” may be abbreviated “vit.”

Flavorings

� If the yogurt contains characterizing flavorings,then the common or usual name of the flavoringsshall be indicated in the name.

Sweetened

� If the product is sweetened with a nutritivesweetener without any characterizing ingredientsadded, then the label must indicate “sweetened.”

Low-Fat Yogurt (Includes DrinkableLow-Fat Yogurts) 21 CFR §131.203

Same as yogurt except for the following:

Composition

� Either 1/2, 1, 11/2, or 2% milk fat (before theaddition of bulky flavorings).

Nomenclature. The name of the food is “low-fatyogurt.” Alternate spelling of the food should notserve as the name of the food (e.g., “low-fat yogourt,”“low-fat yoghurt”).

Milk fat level� The percentage of milk fat must be declared (not

in decimal notation) as “1/2% milk fat,” “1% milkfat,” “11/2% milk fat,” or “2% milk fat.”

Nonfat Yogurt (Includes Drinkable NonfatYogurts) 21 CFR §131.206

Same as yogurt except for the following:

Composition

� Less than 0.5% milk fat (before the addition ofbulky flavorings).

Nomenclature. The name of the food is “nonfatyogurt.” Alternate spelling of the food should notserve as the name of the food (e.g., “nonfat yogourt,”“nonfat yogurt”).

Stayed Provisions

It should be noted that as part of FDA’s administrativeprocedures for enacting and updating standards, anyperson who would be adversely affected by a changein a food standard may file objections specifying theprovisions being objected to, providing the groundsand requesting a public evidentiary hearing. The merefiling of the objection prevents the action from beingtaken (the action is stayed) and the FDA must hold apublic hearing.

Some requirements listed in the CFR have beenstayed following the outcome of a public hearing. Atthe time of printing, FDA had not acted to proceedwith such a public hearing. Therefore, the followingprovisions noted as being stayed are not in effect:

1. There is no restriction to those so named for thetype of milk-derived ingredients that may be used


to increase the nonfat solids content of culturedand acidified milks, eggnog, and yogurts.

2. Reconstituted dairy ingredients can be used as thebasic ingredient in the manufacture of yogurts.

3. Preservatives can be added to yogurts.4. There is no set minimum titratable acidity of 0.9%,

expressed as lactic acid.5. The requirement that the 3.25% minimum milk

fat level is eliminated after the addition of oneor more of the optional sources of MNSF foryogurt.

Proposed Changes to U.S. Standardsfor Yogurt and Fermented Milks

A citizen’s petition was filed in 2000 with FDA by theNational Yogurt Association (NYA) on behalf of itsmembers, requesting that FDA modernize the stan-dards of identity for yogurt to replace the existingyogurt standards and make conforming amendmentsto the existing cultured milk standard of identity. Asrequired under FDA’s procedural regulations, a citi-zen petition must include information regarding theaction requested, statement of grounds, environmen-tal impact, economic impact, and certification of allrelevant information, both favorable and unfavorable.The regulations also require FDA to rule on each pe-tition filed with the Agency.

NYA’s petition provides the basis for the FDA toconsider changes that would replace the currently ex-isting fragmented standards for yogurt, low-fat yo-gurt, and nonfat yogurt as these standards containnumerous stayed provisions. The proposed standardswould require that yogurt contain a minimum levelof certain live and active bacterial cultures and allowfor more flexibility to implement advances in foodtechnology.

The specific details of the proposed changes are asfollows:

� Single Standard of Identity: Incorporates full-fat,low-fat, nonfat standards in one standard ofidentity. It also suggests that a parallel“cultured/fermented milk” standard be created forsimilar products that do not meet the new yogurtstandard.

� Live and Active Characterizing Cultures: Requirethat yogurt be characterized by certain levels ofbacterial cultures of at least 107 CFU/g activecultures Lactobacillus delbrueckii subsp.bulgaricus and Streptococcus thermophilus at thetime of manufacture.

� Acidity: Originally the petition proposed aminimum acidity for yogurt of pH 4.6 or lowerrather than a titratable acidity. Later, this requestwas modified to maintain titratable acidity as themeasure of lactic acid production and recommenda standard of 0.6% titratable acidity, which moreclosely reflects industry practice and consumerpreference for less tart yogurt than the present0.9% lactic acid.

� Homogenization/Pasteurization: Clarifies that thestandard dairy ingredients must be pasteurized orultra-pasteurized before culturing and thatoptional ingredients may be added afterpasteurization and culturing.

� Standard Dairy Ingredients: Permits the use ofreconstituted dairy ingredients as the basic dairyingredients used to compose the minimum 8.25%nonfat milk solids. Restricts whey proteinconcentrate to be used as a dairy ingredient inlevels up to 25% of all nonfat milk solids.

� Optional Ingredients: Permits any “milk-derivedingredients used for technical or functionalpurpose.” Requires that dairy ingredientscomprise at least 51% of the product’s overallingredients by weight. Clarifies that otherbacterial cultures, in addition to the twocharacterizing cultures, are permitted. Also allowsany safe and suitable nutritive carbohydratesweeteners or nonnutritive sweeteners; flavoringingredients; color additives; stabilizers andemulsifiers; preservatives, vitamins, and minerals;and safe and suitable ingredients added fornutritional or functional purposes.

� Nomenclature: Characterizes products containingmore than 3.0 g of total fat per reference amountcommonly consumed (RACC) as “yogurt.”Products with at least 0.5 g, but not more than3.0 g of total fat per RACC will be named as“low-fat yogurt” and if the food is less than 0.5 gof total fat per RACC it will be “nonfat yogurt.”This change bases the identity of the product onthe total fat quantity in the entire product ratherthan just the milk fat of the yogurt prior toaddition of optional ingredients or flavorings.

At the time of writing, the FDA has not yet changedthe standards of identity to incorporate these sug-gested modifications. Under the rule-making process,the FDA must consider public comment for inter-ested stakeholders before promulgating new stan-dards of identity. The first step in this process oc-curred in early 2004 when the FDA published an


Advance Notice of Proposed Rule Making seekingcomments on the proposed NYA petition. The nextstep is for the FDA to consider the relevant commentsand publish either a Proposed Rule allowing for ad-ditional comments or a Final Rule Making. However,under FDA Procedures the law requires a very bur-densome process for issuance, amendment, or repealof standards of identity if anyone objects to the pro-posal being considered. Since some interested partieshave filed support of the yogurt modernization peti-tion and others have objected to specific provisions,it is not known when proposed changes might befinalized.

Food Additives and Packaging

Ingredients and food compounds that are added tomilk and fermented milk products must be safe andsuitable for their intended function. The FDA reviewsthe safety of food and color additives before manu-facturers and distributors can market them. To initiatethis review, food additive firms are required to submita petition or notification that includes appropriate testdata to demonstrate the safety of the intended use ofthe substance. The agency also has a notification pro-gram for substances that are “generally recognized assafe” (GRAS).

Food packaging is regulated as a food-contact sur-face. The FDA defines a food-contact substance as“any substance intended for use as a component ofmaterials used in manufacturing, packing, packag-ing, transporting, or holding food if such use is notintended to have a technical effect in such food.”Safety evaluations of food-contact surfaces are doneby an FDA notification process to authorize new usesof food additives that are food-contact substancesbased on a detailed analysis of the compounds chem-istry, toxicology, and environmental impact. An in-ventory of effective notifications for food-contactsubstances and additional information regarding thenotification program are listed on FDA’s Web pagehttp://www.cfsan.fda.gov/∼dms/opa-fcn.html.

An informational database on approved food ad-ditives is maintained by the FDA. It contains ad-ministrative, chemical, and toxicological informationon thousands of substances directly added to food,including substances regulated by the FDA as di-rect, “secondary” direct, color additives, GRAS, andprior-sanctioned substances. More than 3,000 totalsubstances together comprise an inventory often re-ferred to as “Everything” Added to Food in the United

States (EAFUS). This information can be found athttp://www.cfsan.fda.gov/∼dms/eafus.html.

LABELINGThe FDA sets forth general requirements for food la-beling in the FDA Federal Food Drug and CosmeticAct (FFD&C Act) and more detailed regulations inthe CFR Title 21 parts 100. The basic premise isthat food labels must be truthful and not mislead-ing to consumers. The NLEA established most fed-eral food labeling requirements as nationally uni-form standards through federal preemption of staterequirements. Under the preemptive authority of theNLEA, no state can directly or indirectly establishor continue to enforce any requirement that is notidentical to a federal requirement issued under thefollowing provisions of the FFD&C Act.

Any product introduced into interstate commerceis subject to FDA regulations. The U.S. Court hasinterpreted the scope of interstate commerce expan-sively for this purpose so as to apply federal regula-tion to virtually all products except those for whichthe product, including its ingredients and packagingmaterials, are produced, packaged, and sold withinthe given state. As a result, there are few “intrastate”products, but those that qualify are not subject to FDAregulation.

There are several types of state food labeling re-quirements that are not expressly preempted, andthus, may be enforced against food products in inter-state commerce. These include warning labels, opendate coding, unit price labeling, food grading, recy-clable container deposit labeling, religious dietary la-beling, and item price labeling.

While federal standards of identity preempt statestandards, states may continue to establish and en-force standards of identity for products for whichno federal standards of identity exist, for example,frozen yogurt or yogurt smoothies.

General Requirements

The food labeling regulations specify what informa-tion must appear on the package label, where infor-mation must be placed, the label format, and the sizefor mandatory labeling material such as nutrition in-formation. The part of the package that the consumeris most likely to see during normal retail display iscalled the “principal display panel.” Information re-lated to the product name including flavoring and


the net quantity expressed by weight or volume mustappear in a food product’s principal display panel.The “information panel” is typically located to theright of the principal display panel and must containthe full ingredient listing, name, and place of busi-ness of manufacturer, packer, or distributor, nutritionlabeling of food, and, if applicable, specific require-ments related to the use of nutrient content claims,food warnings, and statements of special dietary use.

In addition to the general labeling requirementsof the federal regulations, the vast majority of stateswill mandate the inclusion of additional labeling asrequired by the Grade “A” PMO discussed in Chap-ter 3. The Grade “A” PMO’s labeling requirementscall for all bottles, containers, and packages con-taining milk and milk products to be conspicuouslymarked with the term “Grade A,” identity of theplant where pasteurized, identification of processingif “ultra-pasteurized” or “aseptic,” “reconstituted” or“recombined” if the product is made by reconstitutionor recombination, and the terms “keep refrigeratedafter opening” in the case of aseptically processedmilk and milk products.

Nomenclature

The name of the food or “statement of identity” maybe established by regulation, or it may be dictated inthe nomenclature section of the product’s standard ofidentity. If the product does not fall under a federalstandard or, as applicable, state standard of identityor does not have a common or usual name, then anappropriate descriptive name must be used that willeasily be understood by consumers. The standards ofidentity for cultured milk and yogurt designate thename of the product. Descriptive names may onlybe used on a product that does not have a standardof identity, or a common or usual name. A descrip-tive name must be suggestive enough to reveal thebasic composition of the product and alleviate anyquestion regarding the product’s identity. For exam-ple, a beverage product made of a blend of yogurtand juice should not solely use the name “smoothie”but include that it is “a blend of yogurt and juice.”In addition, the form of the food must be stated ifit is not visible through the packaging. For example,drinkable yogurt would not require a disclosure thatthe product is a liquid rather than a semisolid if it ispackaged in a transparent container where the con-sumer can clearly see the viscosity or form of thefood.

Flavor Labeling

Milk and milk products including yogurt and otherfermented milks are labeled with the name of thefood and the flavoring if added. Flavorings are de-fined by the FDA as either natural or artificial. Arti-ficial flavors are compounds that impart flavor whichis NOT derived from a spice, fruit or fruit juice, veg-etable or vegetable juice, yeast, herb, bark, bud, root,leaf, or plant material, meat, seafood, poultry, eggs,dairy products, and fermented products. Natural fla-vor or natural flavoring is derived from the com-pounds listed above in the form of an essential oil,oleoresin or extract, protein, hydrolysate, distillatethat is used to impart flavor.

Flavor labeling is dictated by FDA food labelingregulation according to the general “6-Category” fla-vor labeling system. The 6-Category flavor labelingcategories will be referred to as Category A throughCategory F (IDFA, 2004).

The first three categories (A, B, and C) apply whena flavor, including artificial flavor, is added to a foodproduct in fluid form or “from the bottle” (e.g., vanillaextract, vanillin, coffee extract).

Category A

When the primary characterizing flavor ingredientis solely natural, not artificial, and is derived fromthe product whose flavor it simulates, resembles, orreinforces, the name of the food is accompanied bythe common or unusual name of the characterizingflavor (e.g., “Vanilla yogurt”).

Category B

When the food contains both natural flavor derivedfrom the characterizing flavor source and other natu-ral flavoring from a source that simulates, resembles,or reinforces the characterizing flavor, the name ofthe food is followed by the words “with other nat-ural flavor” (e.g., “Coffee yogurt with other naturalflavor”).

Category C

When natural flavor(s) used in the food is not derivedfrom the ingredient whose flavor has been determinedto be the characterizing flavor or if the food containsan artificial flavor that simulates, resembles, or re-inforces the declared characterizing flavor, the name


of the food must be accompanied by the words “ar-tificial” or “artificially flavored” (e.g., “Artificiallyflavored vanilla yogurt”).

The next two categories (D and E) apply to thoseproducts that consumers would commonly expect tocontain the characterizing food ingredient(s) (e.g.,strawberries, blueberries). In both of these categories,the characterizing food ingredient(s) is added toflavor the finished product at a level NOT suf-ficient to independently characterize the finishedproduct.

Category D

When the food contains an insufficient amount ofthe food ingredient to independently characterize theproduct, and it contains added natural flavor that isderived from the characterizing food ingredient, thefood is labeled as a naturally flavored food. The fla-vor may be immediately preceded by the word “nat-ural” and must be immediately followed by the word“flavored” (e.g., “Peach flavored yogurt” or “Naturalpeach flavored yogurt”).

Category E

When the food contains an insufficient amount ofthe food ingredient to independently characterize thefood and it contains other added natural flavors thatare not derived from the characterizing flavor de-clared on the label, but that simulate, resemble, orreinforce the characterizing flavor, the flavor maybe immediately preceded by the word “natural” andmust be immediately followed by the words “withother natural flavors” (e.g., “Peach yogurt with othernatural flavors” or “Natural peach yogurt with othernatural flavors”).

Category F applies to products that contain suffi-cient amounts of characterizing food ingredients toflavor the finished product (e.g., peaches, cherries).

Category F

If the food contains sufficient levels of the food in-gredient to independently characterize the food andcontains no added artificial flavors or natural flavors(“from the bottle”) that simulate, resemble, or rein-force the characterizing flavor, then the characteriz-ing ingredient is the flavor of the food (e.g., “Straw-berry yogurt”).

The name of the flavoring as described above mustaccompany the name of the food on the principal

display panel of the package or any panels wherethe product name occurs. A blend of three or moredistinctive artificial flavors can be described as a col-lective name, i.e., “Artificially Flavored Tutti Fruity.”The name of the flavoring must be in a type size notless than 1/2 the height of the letter used in the name ofthe food and the flavor-modifying terms must not beless than 1/2 the height of the name of the characteriz-ing flavor. Exemptions for category name declarationare made if the flavor name is part of a trademark suchas Lemon DropTM.

Ingredient Declaration

An ingredient statement is required on all food pack-ages intended for retail sale that contain more thanone ingredient. Except where exemptions are appli-cable, an individual ingredient must be declared in theingredient statement by its common or usual name. Inaddition, specific regulations exist for colors, sweet-eners, incidental additives, processing aids, and fatand/or oil ingredients. Special ingredient labeling sit-uations include the following:

All certified colors must be included by name in theingredient statement.

Any beverage product purporting to contain fruit orvegetable juice must declare the percent of juicepresent in the finished product.

Many standards of identity address ingredient la-beling, in that they allow for ingredient groupingsor provide a common or usual name for a particularingredient. Some examples are listed in Table 4.1.

The ingredient listing must appear prominentlyand conspicuously on either the principal displaypanel or the information panel. The entire list of in-gredients must appear in one place without other “in-tervening material” and, in general, must appear inletters not less than 1/16 of an inch in height.

Ingredients in multicomponent foods may be listedby either of the following two alternatives: groupingor dispersion. Although either method may be used,the grouping alternative may be more helpful to con-sumers in identifying the ingredients used in eachcomponent of the food.

The grouping alternative for ingredient declara-tions of multicomponent ingredients may be used bydeclaring the common or usual name of the ingredi-ent followed by a parenthetical listing of all ingredi-ents contained in each of the components in descend-ing order of predominance by weight. For example,an ingredient statement for raspberry yogurt with


Table 4.1. Common or Usual Names for Typical Ingredients Used in Dairy Products

Common or UsualIngredient Name

Skim milk, concentrated skim milk, reconstituted skim milk, and nonfatdry milk (21 CFR §101.4 Food; designation of ingredients)

Skim milk or nonfat milk

Milk, concentrated milk, reconstituted milk, and dry whole milk (21 CFR§133.129 Dry curd cottage cheese; 21 CFR §101.4 Food; designationof ingredients)

Milk

Bacteria cultures (21 CFR §131.160 Sour cream; 21 CFR §131.162Acidified sour cream; 21 CFR §101.4 Food; designation of ingredients)

Cultured (the blank isfilled in with the nameof the substrate)

Sweet cream buttermilk, concentrated sweet cream buttermilk,reconstituted sweet cream buttermilk, and dried sweet creambuttermilk (21 CFR §101.4 Food; designation of ingredients)

Buttermilk

Whey, concentrated whey, reconstituted whey, and dried whey (21 CFR§101.4 Food; designation of ingredients)

Whey

Cream, reconstituted cream, dried cream, and plastic cream (sometimesknown as concentrated milk fat) (21 CFR §101.4 Food; designation ofingredients)

Cream

Butter oil and anhydrous butterfat (21 CFR §101.4 Food; designation ofingredients)

Butterfat

Milk-clotting enzymes (21 CFR §133.128 Cottage cheese; 21 CFR§133.129 Dry curd cottage cheese)

Enzymes

Source: IDFA, 2004.

granola may state the following:

Ingredients: Yogurt (cultured milk, raspberries,sugar, gelatin, pectin, and natural flavors) and gra-nola topping (rolled oats, puffed rice, corn syrup,brown sugar, raisins, and almonds).

The dispersion alternative for ingredient declara-tions of multicomponent ingredients may be usedby incorporating into the ingredient statement (indescending order of predominance in the finishedfood) the common or usual name of every componentof the multicomponent ingredient without listing themulticomponent ingredient itself.

For example, an ingredient statement for raspberryyogurt with granola may state the following:

Ingredients: Cultured milk, sugar, rolled oats, cornsyrup, raspberries, puffed rice, brown sugar, raisins,almonds, gelatin, pectin, and natural flavors.

Nutrition Facts Panel

All food packages intended for retail sale must de-clare quantitative nutritional information expressedin terms of a “serving” of an individual food. A “serv-ing,” or as it appears on the label, “Serving Size,” isbased on the reference amount of food customarily

consumed per eating occasion by persons 4 years ofage or older as expressed by a common householdmeasure appropriate for the food.

FDA has established reference amounts for over100 food product categories. The established refer-ence amount is the benchmark for determining theserving size declared on the label and expressed as acommon household measure (e.g., cups, tablespoons,teaspoons). The serving size is required to be ex-pressed on the nutrition label in common householdmeasure followed in parentheses by an equivalentmetric quantity (fluid products in milliliters and allother foods in grams). For example, for acidophilusmilk, “Serving Size 1 cup (240 ml).” For the mostpart, the common household unit for similar productswill be the same, but because of the varying densitiesamong products, the metric equivalent may not beidentical.

Unless otherwise exempted, all nutrients and foodcomponent quantities must be declared on the ba-sis of the serving size derived from the referenceamount. FDA has established methods for convert-ing the reference amount to the “serving size” forlabeling purposes. The method employed is basedon the type of container in use (i.e., multiserv-ing vs. single-serving container) and the physical


characteristics of the product (discrete unit vs.nondiscrete fluid or bulk-type product).

For example, manufacturers producing frozen yo-gurt mix for retail sale must determine the amountof mix that will make (under normal conditions ofpreparation) 1/2 cup of the product. Since air (i.e.,overrun) is incorporated into the product, less than1/2 cup of mix will be required to produce 1/2 cupof finished product. The following reference amountcategories have been established for milk and milkproducts:

Product Category Reference Amount

Cheese used as an ingredient(e.g., dry cottage cheese)

55 g

Sour cream 30 gMilk and cultured or acidified

milk240 ml

Yogurt 225 gDairy-based dips 2 tbspDairy and nondairy whipped

topping2 tbsp

Juices, juice drinks, and juicemilk blend drinks

240 ml

Shakes or shake substitutes(e.g., dairy shake mixes)

240 ml

Nutrition information is presented to consumers“in the context of a total daily diet,” which is man-dated by regulations as a diet of 2,000 calories perday. From this theoretical 2,000 calorie per day diet,recommended intake levels or “daily values” (DV)of individual nutrients have been developed based oncurrent dietary guidelines. As a result, informationon individual nutrients is required to be expressedin most cases by a quantitative declaration (grams,milligrams, etc.) and a percentage of a DV for thenutrient.

Nutrient labeling information is referred to as theNutrition Facts box. The explicit amount (quantita-tive declaration) and, as applicable, the percentage ofthe DV must be included in the Nutrition Facts boxfor each of the following nutrients and food compo-nents:

Total caloriesCalories from fatTotal fatSaturated fatTrans fatCholesterol

SodiumTotal carbohydrateDietary fiberSugarsProteinVitamin AVitamin CCalciumIron

The following table gives a list of the Daily Refer-ence Values (DRV) based on a 2,000calorie diet.

Food Component Daily Reference Values

Total fat 65 gSaturated fat 20 gCholesterol 300 mgSodium 2,400 mgPotassium 3,500 mgTotal carbohydrate 300 gDietary fiber 25 gProtein 50 g

The percent DV is calculated by dividing the un-rounded (actual amount) or rounded amount of thenutrient present in the food per serving by the es-tablished DRV and multiplying by 100, except thatthe DRV for protein must be calculated from the un-rounded amount. The DV is expressed to the nearestwhole percentage. The percentage of DV is mandatedfor total fat, saturated fat, cholesterol, sodium, totalcarbohydrates, and dietary fiber, and is voluntary forpotassium and protein. There has been no DV set fortrans fat and so a percentage of DV declaration shouldnot be made.

Nutrient RDIa Value

Vitamin A 5,000 IUVitamin C (ascorbic acid) 60 mgCalcium 1,000 mgIron 18 mgVitamin D 400 IU

a Reference daily intake.

Depending on the size of the package, FDA allowsdifferent graphic formats for nutritional information.The most common is the Full Vertical format (seeFig. 4.1) used on all packages with greater than 40in.2 of available labeling space.


Nutrition FactsServing Size 1 cup (228g)Servings Per Container 2

Amount Per Serving

Calories 260 Calories from Fat 120

Total Fat 13g

Saturaled Fat 5g

Trans Fat 2g

% Daily Value*20 %

25%

10%28%

10%

0%

Cholesterol 30mg

Sodium 660mg

Total Carbohydrate 31g

Dielary Fiber 0g

Sugars 5g

Protein 5g

Vitamin A 4% Vitamin C 2%

Calcium 15% Iron 4%

*Percent Daily Values are based on a 2,000 caloriediet.Your Daily Values may be higher or lower dependingon your calorie needs.

Calories

Less thanLess thanLess thanLess than

Total FatSat Fat

CholesterolSodiumTotal Carbohydrate

Dielary Fiber

Calories per gram:

Fat 9 Carbohydrate 4 Protein 4

2,000 2,500

65g20g300mg 300mg2,400mg 2,400mg300g25g

25g80g

375g30g

Full Vertical Format

Figure 4.1. Full Vertical format for nutritionalinformation used for packages with greater than 40 in.2

of available labeling space.

Packages with less than 40 in.2 of labeling spacecan use a smaller tabular format (see Fig. 4.2).

Special Labeling Requirements

Food labeling often has additional nonmandatory in-formation used for marketing purposes. These arelisted below:

Real Seal

Dairy Management, Inc. has established a voluntaryprogram to promote dairy products and to distinguishbetween authentic and simulated dairy products.

They have chosen the “REAL r©” seal to indicate thisdistinction. Use of the “REAL r©” seal must be inconjunction with the “REAL r©” Seal Certified UserAgreement. Information about the seal may be ob-tained at http://www.dairyinfo.com.

Live and Active Cultures Seal

To help identify yogurt products that contain liveand active cultures, the National Yogurt Association(NYA) has established a special Live & Active Cul-tures seal. The NYA is a national nonprofit trade or-ganization whose purpose is to sponsor health andmedical research for yogurt with live and active cul-tures and serve as an information source to the tradeand the general public. The Live & Active Culturesseal, which appears on refrigerated and frozen yogurtcontainers, helps identify those products containingsignificant amounts of live and active cultures. Theseal is a voluntary identification available to all man-ufacturers whose refrigerated yogurt contain at least100 million cultures per gram at the time of man-ufacture, and whose frozen yogurt contains at least10 million cultures per gram at the time of manufac-ture. Since the seal program is voluntary but not allyogurt products carry the seal. More information canbe found at http://www.aboutyogurt.com.

Kosher Symbols

Observance of the biblical kosher laws can be facili-tated by kosher foods being certified by a rabbinicalorganization and labeled with an identifying symbol.The Jewish teachings written in the Jordon lists cer-tain basic categories of food items that are not kosher.These include certain animals, fowl, and fish (such aspork and rabbit, eagle and owl, catfish and sturgeon)and any shellfish, insect, or reptile. In addition, kosherspecies of meat and fowl must be slaughtered in aprescribed manner and meat and dairy products maynot be manufactured or consumed together. Kosherfood labeling regulations are not preempted by theimplementation of the NLEA and, therefore, stateregulatory officials can enforce their own state regu-lations. Although FDA does not discuss the criteriaby which these terms, “kosher” and “kosher style”may be used, they do indicate that these terms shouldbe used only on products that meet the religious di-etary requirements.

More information on kosher certification can beobtained by contacting the following organizations:the Union of Orthodox Jewish Congregations in NewYork at http://www.oukosher.org or the OK KosherCertification at http://www.okkosher.com.


Tabular Format

NutritionFactsServing Size 1/3 cup (56g)Servings about 3Calories 90Fat cal. 20

Amount/serving

Total Fat 2g

Sat. Fat 1g

Trans Fat 0.5g

Cholest. 10mg

Sodlum 200mg

Vitamin A 0% = Vitamin C 0% = Calcium 0% = Iron 6%

%DV* %DV*

3%

5%

3%

8%

Amount/serving

Total Card. 0g

Protein 17g

Fiber 0g

Sugars 0g

0%

0%

*Percent Daily Values (DV) arebased on a 2,000 calorie diet

Figure 4.2. Tabularformat fornutritionalinformation usedfor packages withless than 40 in.2 ofavailable labelingspace.

Universal Product Bar Codes

The Uniform Code Council was originally createdby the food industry in an effort to place a code andscanner-readable symbol on the package of contain-ers sold through retail outlets using automatic check-out equipment. The primary purpose of the Univer-sal Product Code (UPC) bar code system is to reduceretail store costs by providing an automatic comput-erized checkout system, to establish better inventorycontrol and ordering systems, and to provide morevaluable marketing information about products. AUPC manufacturer identification number for use inthe bar code may be obtained by contacting the Uni-form Code Council, Inc. in Dayton, OH, or Web sitehttp://www.uc-council.org.

Code Dating

Code dating, such as “sell by” or “best if used by”dating, is a requirement promulgated under the stateregulations and laws and enforced by state regulatoryofficials. There are no federal regulations addressingcode dating or “sell by” dating. Often a code dateprinted on the food label is used for tracking and iden-tifying the food by the date of production, plant loca-tion, filling line, or production vat. This informationmay be used for inventory purposes, product rotationin storage, display, and, if necessary, retrieval fromthe market. Therefore, it is important that the codedate or identifying information be legibly printed oneach container and shipper.

Food Warning Statements

FDA regulations require food warning statements toappear in the labeling of certain food products. Forexample, the regulations pertaining to the use of as-

partame in a food product require that the label stateon either the principal display panel or the informa-tion panel the following: “Phenylketonurics: Con-tains Phenylalanine.”

CODEX STANDARDS ANDDEFINITIONS FOR FERMENTEDMILK PRODUCTSThe Food and Agriculture Organization (FAO) andthe World Health Organization (WHO) developed theCodex Alimentarius Commission—the body chargedwith developing a worldwide food code. All im-portant aspects of food pertaining to the protectionof consumer health and fair practices in the foodtrade have come under the Commission’s scrutiny,including international food standards, also knownas Codex Standards. The Codex Web site lists moreinformation on the Codex Alimentarius and officialCodex Standards.

The Codex Standard for Fermented Milk (243-2003), recently updated in 2003, applies to all fer-mented milk including heat-treated fermented milks,concentrated fermented milks, and composite fer-mented milks (fermented milks with flavoring orother added nondairy ingredients) that are both di-rectly consumed or used for further processing (seeTable 4.2). The Codex fermented milk standardalso provides that certain fermented milk must becharacterized by specific starter cultures (Codex,2004).

Concentrated fermented milk such as strained yo-gurt, Labeneh, Ymer, and Ylette require that the pro-tein be increased to 5.6%. Flavored fermented milkmust contain not more than 50% (mass/mass) ofnondairy ingredients, such as sweeteners, fruits, veg-etables, juices, purees, cereals, nuts, spices, and othernatural flavorings.


Table 4.2. Culture Characterization for Codex Standard for Fermented Milk

Yogurt Symbiotic cultures of Streptococcus thermophilus and Lactobacillusdelbrueckii subsp. bulgaricus

Alternate culture yogurt Cultures of Streptococcus thermophilus and any Lactobacillus speciesAcidophilus milk Lactobacillus acidophilusKefir Starter culture prepared from kefir grains, Lactobacillus kefiri, species of

the genera Leuconostoc, Lactococcus, and Acetobacter growing in astrong specific relationship. Kefir grains constitute both lactosefermenting yeasts (Kluyveromyces marxianus) andnon-lactose-fermenting yeasts (Saccharomyces unisporus,Saccharomyces cerevisiae, and Saccharomyces exiguus)

Kumys Lactobacillus delbrueckii subsp.bulgaricus and Khuyveromyces marxianusNote: Microorganisms other than those constituting the specific starter culture(s) specified above may be added.Source: Codex Standard for Fermented Milk (243-2003).

Raw materials allowed in the Codex Standard forFermented Milks are limited to milk and/or milkproducts obtained from milk and potable water usedfor reconstitution. Additional permitted ingredientsinclude starter cultures and sodium chloride. Gelatinand starch are only allowed in heat-treated fermentedmilks, flavored fermented milks, and plain fermentedmilk if permitted by the regulations in the country ofsale to the final consumer.

Composition requirements for various Codex Fer-mented Milks are listed in Table 4.3.

The microbial criteria apply to the fermented milkportion only for flavored fermented milks. Compli-ance to the microbial criteria is verified though ana-lytical testing of the product through the end of the

shelf life on products that have been stored undernormal conditions and temperatures.

Allowable food additives are specified in Table 4.4.Labeling of the product is also specified by the

Codex Standard for Fermented Milks. It allows fornames to be replaced by designations such as Yo-gurt, Kefir, and Kuyums and provide for alternativespelling of the name to be appropriate in the coun-try of retail sale. Additionally, the qualifying labelingterms “milk” or “tangy” can be used. If the fermentedmilk product is subject to heat treatment after cultur-ing, it must be labeled as “Heat-Treated FermentedMilk”; unless the consumer would be misled by thisname, the product shall be named as permitted bythe regulations in the country of retail sale. Flavor

Table 4.3. Composition Requirements for Codex Standard for Fermented Milk

Yoghurt, AlternateFermented Culture Yoghurt, andMilk Acidophilus Milk Kefir Kumys

Milk proteina(% m/m) Min. 2.7% Min. 2.7% Min. 2.7%Milk fat (% m/m) Less than 10% Less than 15% Less than 10% Less than 10%Titrable acidity, expressed

as % lactic acid (% m/m)Min. 0.3% Min. 0.6% Min. 0.6% Min. 0.7%

Ethanol (% vol./w) Min. 0.5%Sum of microorganisms

constituting the starterculture defined in section2.1 (cfu/g, in total)

Min. 107 Min. 107 Min. 107 Min. 107

Labeled micororganismsb

(cfu/g, total)Min. 106 Min. 106

Yeast (cfu/g) Min. 104 Min. 104

a Protein content 6.38 multiplied by the total Kjeldahl nitrogen determined.b Applies where a content claim is made in the labeling that refers to the presence of a specific microorganism (other than

those specified in Table 4.2 for the product concerned) that has been added as a supplement to the specific starter culture.Source: Codex Standard for Fermented Milk (243-2003).


Table 4.4. Allowable Food Additives for Codex Standard for Fermented Milk

Fermented Milks Heat-TreatedFermented Milks After Fermentation

Additive Class Plain Flavored Plain Flavored

Colors – X – XSweeteners – X – XEmulsifiers – X – XFlavor enhancers – X – XAcids – X X XAcidity regulators – X X XStabilizers X1 X X XThickeners X1 X X XPreservatives – – – XPackaging gases – X X XNote: X = The use of additive belonging to the class is technologically justified. In the case of flavored products, the additiveis technologically justified in the dairy portion; – = the use of additives belonging to the class is not technologically justified;and 1 = use is restricted to reconstitution and recombination and if permitted by national legislation in the country of sale to thefinal consumer.Source: Codex Standard for Fermented Milk (243-2003).

designations and the term “sweetened,” if appropri-ate, shall also be included on the label. A declarationon milk fat content either in percentage or in gramsper serving should be provided if the consumer wouldbe misled by its omission.

GLOSSARYASEPTICALLY PROCESSED—When used to de-

scribe a milk product, the product has been subjectedto sufficient heat processing and packaged in a her-metically sealed container, to conform to the applica-ble requirements of the CFR and the Grade A PMOand to maintain the commercial sterility of the prod-uct under normal nonrefrigerated conditions.

CERTIFIED COLORS—Color additives manufac-tured from petroleum and coal sources listed in theCFR for use in foods, drugs, cosmetics, and medicaldevices.

CFU/G (COLONY FORMING UNITS PERGRAM)—An expression of measurement fordetermining the number of live microorganisms on avolume basis.

CODEX ALIMENTARIUS COMMISSION—An in-ternational body, created by FAO and WHO, to de-velop food standards, guidelines, and related textssuch as codes of practice. The main purposes areprotecting health of the consumers, ensuring fairtrade practices in the food industry, and promoting

coordination of all food standards work undertakenby international governmental and nongovernmentalorganizations.

COMMON OR USUAL NAME—The name of a foodthat is not set by law or regulation, but either throughcommon usage or through expert opinion (such asthat of the FDA).

DAILY REFERENCE VALUES (DRV)—An amountset by the CFR as the recommended level of in-take for certain nutrients (fat, saturated fat, choles-terol, total carbohydrate, fiber, sodium, potassium,and protein) based on a 2,000 calorie per daydiet.

FDA—U.S. Food and Drug Administration.FFD&CA (FEDERAL FOOD DRUG AND COS-

METIC ACT)—An act of the U.S. Congress thatspecified the basis for food safety standards.

GRADE “A” PMO (PASTEURIZED MILKORDINANCE)—Model milk regulations used forthe inspection of milk production and processingfacilities.

HOMOGENIZATION—The mechanical process ofshearing milk fat globules via pressure to reduce thesize of the fat globules and reduce the separation ofthe cream portion of the product.

IDFA (INTERNATIONAL DAIRY FOODASSOCIATION)—A trade association repre-senting dairy processors that provides informationand publications on dairy product regulations andstandards.


IU (INTERNATIONAL UNITS)—A unit of measure-ment for certain vitamins (Vitamins A, D, and K) forlabeling purposes.

MSNF—Milk solids nonfat portion of milk or milkproducts.

PASTEURIZATION—A process of heating fluid milkproducts to render them safe for human consump-tion by destroying the disease-producing organisms(pathogens). The process inactivates approximately95% of all microorganisms in milk.

RDI (REFERENCE DAILY INTAKE)—A value setby the CFR as the recommended level of intakefor vitamins and minerals essential for human nu-trition for adults and children 4 or more years ofage.

REFERENCE AMOUNT (REFERENCEAMOUNT CUSTOMARILY CONSUMED)—Values set by the CFR to reflect the amount of aparticular food usually consumed per eating occasionby people 4 years of age or older, based on the majorintended use of that food.

TITRATABLE ACIDITY—The measurement of theextent of growth of acid-producing bacteria by de-termining the lactic acid present in a food throughreacting the lactic acid with a standard solution ofalkali.

UHT (ULTRA-HIGH TEMPERATURE)—Heattreatment at a temperature of 135–150◦C for aholding time of 4–15 seconds that sterilizes theproduct for aseptic packaging to permit storage atambient temperatures.

REFERENCESCFSAN (Center for Food Safety and Applied

Nutrition). 2004. National Conference on InterstateMilk Shipments Model Documents—Milk SafetyReferences [Online]. Available at http://www.cfsan.fda.gov/∼ear/p-nci.html.

CFSAN (Center for Food Safety and AppliedNutrition). 2004. Food Additive Inventory ofEffective Notifications for Foods Contact Substances[Online]. Available at http://www.cfsan.fda.gov/∼dms/opa-fcn.html.

CFSAN (Center for Food Safety and AppliedNutrition). 2004. Everything Added to Food in theUnited States (EAFUS) [Online]. Available athttp://www.cfsan.fda.gov/∼dms/eafus.html.

Code of Federal Regulations. 2004. Title 21 Food andDrugs [Online]. Available athttp://www.access.gpo.gov/cgi-bin/cfrassemble.cgi?title=200321.

Codex Alimentarius. 2004. Codex Standard forFermented Milk (243-2003) [Online]. Available athttp://www.codexalimentarius.net/web/index en.jsp.

IDFA (International Dairy Foods Association). 2004.MIF Labeling Manual, 2004 Revision, MIF,Washington, DC.

USDHHS (U.S. Department of Health and HumanServices). 2003. Grade “A” Pasteurized MilkOrdinance, 2003 Revision, Department of PublicHealth, U.S. DHHS, Food and Drug Administration,Washington, DC.

5Basic Dairy Processing Principles

Arun Kilara

IntroductionOverview of Processing Equipment in a Dairy Plant

Fluid Transfer OperationsHeat Transfer OperationsMixing OperationsSeparationMicrobial Transformation

From farm to FactoryStorage of Raw MilkCentrifugal OperationsThermal Processing SystemsHomogenizationMembrane TechnologyBibliography

INTRODUCTIONMilk is a highly perishable biological fluid. The com-position of milk and the factors that contribute tovariability in the composition have been discussed inChapter 2. Milk from many farms are collected intankers two to three times a week and delivered toa processing facility. At this facility (also known asa dairy plant or factory) the milk is stored and pro-cessed further to make the appropriate products forwhich the dairy plant is designed for.

The safety of products is of major concern in dairyprocessing. Hence the regulations for the productionand storage of milk at the farm, for the transporta-tion from the farm to the factory, and for the holdingand processing required on the factory premises havebeen promulgated, and these have been discussedin Chapter 3. Regulations also apply for standard-ized food products that have to meet compositionalrequirements as well as the use of approved ingre-dients and processes. These aspects have been dis-cussed in Chapter 4. In addition, manufacturers of

products may have internal standards for insuring thequality of the products important to the consumer.Such attributes may include taste, texture, odor, fla-vor, mouthfeel, color, and keeping quality. These as-pects are covered in detail in Chapters 1, 9, 14, and 15.

The processing steps may involve one or more op-erations in combination, and the most common op-erations involve pumping or transfer of fluids, heattransfer (cooling and heating), mixing of ingredients,separation (fat standardization), and microbial trans-formation of milk (acid gel formation). These aspectsare discussed in the next section of this chapter.

OVERVIEW OF PROCESSINGEQUIPMENT IN A DAIRY PLANTFluid Transfer Operations

Fluid transfer processes involve transferring milkfrom the receiving tankers to storage silos and then forfurther transfer to appropriate unit operations. Thesetransfers are achieved by means of pumps. There aretwo main categories of these transfer agents used inthe dairy industry called centrifugal and positive dis-placement pumps. Within each category there are dif-ferent types of pumps.

The selection of the right type of pump for usein an operation is dependent upon a number of fac-tors including flow rate, product to be handled by thepump, viscosity, density, temperature, and pressurein the system. Pumps should be installed as closeto the tanks from which process liquids are beingtransferred with as few valves and bends in the lineas feasible. Any devices to restrict flow should beplaced at the exit or discharge side of the pump. Cav-itation is a problem in pumping caused by too low a

73




pressure at the inlet end of a pump relative to the vaporpressure of the fluid being transferred. As cavitationprogresses, pumping efficiencies decrease and even-tually the pump ceases to transfer the fluid. The ap-propriate size of the pump required for the transfer de-pends upon flow rate and head, required motor power,and the net positive suction head. Engineers usingcharts and formulas easily calculate these parameters.

Centrifugal Pumps

A motor drives an impeller that has vanes (Fig. 5.1).The motion is circular and the liquid being pumpedenters to the center of the impeller that imparts acircular motion to the liquid. The liquid exits thepump at a higher pressure than the pressure at theinlet. Centrifugal pumps are useful for transferringliquids that are not very viscous. Because of thelower costs (when compared with positive displace-ment pumps) of these pumps, they are widely usedin most applications in a dairy factory. These pumpsare not suitable for high-viscosity liquids or thoseitems requiring care in handling, for example fluidswhere structures should not be disturbed or ingre-dients whose identity is critical to product appeal.Flow control is achievable by three different means.The first is by throttling. This procedure is expensivebut offers the greatest flexibility. The second meansof achieving flow control is by changing the impellerdiameter. This method is the most economical butthe least flexible. A third means is to install an elec-tronic speed controller, which is both economical andflexible.

Positive Displacement Pumps

These pumps work on the principle of positive dis-placement in which in each rotation or reciprocat-ing movement a finite amount of fluid is pumped re-gardless of the manometric head. The main types ofpositive displacement pumps have been called rotaryand reciprocating pumps. These pumps are useful forhigher viscosity fluids and at lower viscosities mayexhibit some slip as the pressure increases. The netresult is a reduction in volumetric flow on each stroke.Throttling by flow control valves at the discharge endof the pump should be avoided and these pumps haveto be fitted with a pressure relief valve. Flow controlin positive displacement pumps is achieved by con-trolling the speed of the motor or by adjusting thevolume of reciprocating pumps. Positive displace-ment pumps must be placed as close to the feed tankas possible, and the diameters of the pipes should belarge relative to those of centrifugal pumps. If pipediameters are too small the pressure drop may be highenough to cause cavitation in the pump.

Positive lobe pumps generally have two rotors andon each rotor there are three lobes (Fig. 5.2). A vac-uum is created when the lobes move causing the pro-cess fluid to be inspired into the cavities of the lobes.The process fluid is then moved along the outer wallsof the pump toward the discharge end. The rotorsare driven independently by a reducing gear motor.And the lobes do not touch each other or the wallsof the pump casing. These pumps are used whenthe viscosity of the process fluid exceeds 300 cP,as is the choice for transferring cream and culturedproducts.

Figure 5.1. Centrifugal pump: (1) deliveryline, (2) shaft seal, (3) suction line, (4)impeller, (5) pump casing, (6) back plate, (7)motor shaft, (8) motor, (9) stainless steelshroud and sound insulation. Reproducedwith permission from Tetra Pak.

5 Basic Dairy Processing Principles 75

Figure 5.2. Lobe rotor principle. Reproduced withpermission from Tetra Pak.

Eccentric screw, piston, and diaphragm pumps arealso positive displacement pumps used for special-ized purposes in dairy plants.

Heat Transfer Operations

Heating and cooling are two common operations inany dairy plant. Collectively these operations involvethe transfer of heat from one medium to another.Transfer of heat can be routinely achieved through in-direct contact of a hot medium against a cool medium.In the case of heating of dairy fluids, the hot mediumis hot water. In the case of cooling, a cold medium re-moves heat from a dairy fluid. This cool mediummay be incoming cold raw milk (as is the case of re-generation section of a pasteurizer) or chilled water.Boilers produce steam that is directly injected intothe water and the result is hot water. Chilled wateris produced by contacting water with a refrigerant(commonly ammonia in the United States). The ap-paratus in which heating or cooling takes place isgenerically called a heat exchanger.

Calculating the heat transfer area required for aparticular operation is a complex process involvingproduct flow rate, physical properties of the fluid be-ing heated and the heating medium, temperature pro-gram necessary for the operation, allowed pressuredrops, design of the heat exchanger, sanitary require-ments, and necessary operational time. The productflow rate depends on the operating capacity of thedairy factory. Density, specific heat, and viscosity are

important parameters defining the physical propertiesof the fluids. Temperature program is dependent onthe legal requirements and temperature differentialsbetween the medium being heated and the heatingmedium. Temperature changes (often referred as �t)depend upon the inlet temperatures of the mediumbeing heated and the heating medium. Design of theheat exchanger refers to the flow of the fluid beingheated in relation to the flow of the heating medium.Such flows can be countercurrent (Fig. 5.3) or con-current (Fig. 5.4), meaning the fluid being heatedflows against the flow of the heating medium or inthe same direction as the heating medium, respec-tively. Design also refers to the physical nature of theheating apparatus and can be done by using plate heatexchangers or tubular heat exchangers and in somecases scraped surface heat exchangers. The ability toeffectively clean and sanitize food contact surfacesis vital in the food industry and therefore the designof a heat exchanger has to take this into considera-tion. The necessary operational time is the length oftime for which the equipment can be operated with-out cleaning and is dependent on a number of fac-tors. The operational time cannot be predicted andwill vary from factory to factory.

°Cti2to1

to1

to2

ti1

ti2

ti1

Time

to2

Figure 5.3. Temperature profile for a product in acountercurrent heat exchanger. Red Line/ fill is theheating medium and Blue line/fill is the product flow. t i

is inlet temperature and t o is outlet temperature.Subscripts 1 and 2 refer to product and heatingmedium, respectively. Reproduced with permissionfrom Tetra Pak.


°Cti2

Δtm

ti1

to1

to2

ti1

ti2

to1

Time

to2

Figure 5.4. Heat transfer in a concurrent heatexchanger. Red line/fill indicates heating medium andblue line/fill indicates product. t i is inlet temperatureand to is outlet temperature. Subscripts 1 and 2represent product and heating medium, respectively.Reproduced with permission from Tetra Pak.

Another aspect of cooling involves refrigeration.Refrigeration involves the removal of heat from aproduct and in this process the product cools downand the medium removing the heat warms up. In the

dairy industry, refrigeration is commonly achieved bychilled water or polyethylene glycol in some cases.The water is chilled by contacting it with a refrigerantsuch as ammonia or other fluorocarbon gases.

Mixing Operations

In the manufacture of many dairy products, certainingredients have to be mixed into milk. For exam-ple, in the manufacture of flavored milks, sweeten-ers, stabilizers, and flavorings are added to milk priorto processing. To fortify solids in certain types ofyogurts, milk solids are added to milk prior to pas-teurization. In other instances storage of raw milkin silos necessitates periodic agitation of the con-tents of the silo. In batch pasteurization, the milk isheated in a tank and the tank has an agitation systemto insure uniform heat transfer. In all these instancesmixing is required and is achieved by a number ofmeans.

For the incorporation of solid ingredients intomilk, batch and continuous processes are available.The simplest batch blending system is a funnelor hopper to feed the dry material to a closed-circuit circulation of the process fluid. A centrifugalpump is involved in circulation of the process fluid(Fig. 5.5).

The tank is filled with the process fluid and circula-tion is initiated. The centrifugal pump can be placed

Reconstitution with Tri-Blender8

5

63 3

4WaterSMP

Powder

Impeller Reconstituted mix

Belt drive

Water fromrecirculating line

Electricallycontrolled shut-offvalve

Figure 5.5. Mixing dry ingredients using a triblender.


Tangentialinlet

Recirculationpump

Recirculation line Reconstitutedmilk to the chiller

Duplexfilter

Powder

Screen

Hopper

Isolatingvalve

Water

Venturi unit (schematic) Rec

onst

itut

edm

ilk

Powder

Reconstitutiontank

Water meter

WaterAgitator

Venturiunit

Figure 5.6. Reconstitution in a system with a venturi, with the dry ingredients being added at the discharge side ofthe pump.

at either the suction or the discharge side of the hop-per. If the hopper is on the suction side of the pumprapid dispersal of powders are efficiently achieved asa result of the mixture of powder and fluid comingin contact with the impeller of the pump. The disad-vantage is that frequent blockages may occur in thehopper. If the hopper is placed on the discharge endof the pump the problem of blockage is avoided. Thisconfiguration requires the presence of a venturi to fa-cilitate the mixing of powder and the process fluid(Fig. 5.6).

Another type of batch mixing occurs in tanks andsilos. The tanks are equipped with agitators. The ag-itator systems can be paddle, propeller, and scrapedsurface. The agitators can be positioned at the top orbottom, perpendicular or centrally mounted. Besidesthese factors, the speed of agitation, tank geometry,vortex creation, air incorporation, and shearing ef-fects impact on the mixing efficiency.

In continuous mixing systems, also called in-line mixers, many types of devices are available. Inblenders such as Tri-Blender and Breddo Likwifier,a high-speed blender, the powder and process liquidare contacted and sheared in the mixer. Another in-line mixer is Silverson. This mixer operates at highspeeds and its action is somewhat similar to homog-enization.

Separation

It is necessary to separate the fat from the milk. Prin-ciples used to separate fat from milk are also appliedto remove fine extraneous material from milk and toreduce the bacterial content of milk. Separation offat from milk is called cream separation, the removalof fine extraneous particles is termed clarification,and the reduction in microbial numbers is obtainedthrough bactofugation. All of these processes rely oncentrifugal force to achieve their objective. The fac-tors that affect the efficiencies of these processes arediameter of the particle (d �m), density of the par-ticle (�p kg/m3), density of the continuous phase(� l kg/m3), viscosity of the continuous phase(�kg/ms), and the gravitational force (g = 9.81 ms2).For example a 3-�m diameter fat globule will riseat a velocity of 0.6 mm/h. To speed up this processcentrifugal force is applied and the sedimentation ve-locity is increased 6,500-fold. In order to achieve thisseparation under a centrifugal force field, a speciallydesigned equipment called a cream separator is used.

Another centrifugal operation in the dairy industryis a variant of cream separation and is used to removesolid impurities from milk. This piece of equipmentis called a clarifier. The principal difference betweenclarification and separation is in the design of the


disc stack in the centrifuge bowl and the number ofoutlets. In a clarifier the disc stack has no distributionholes and has only one outlet. In a separator the discstack has distribution holes and there are two outlets,one each for cream and skim milk.

A third application of centrifugal force in dairyprocessing is bactofugation. This is a process inwhich centrifugal force is used to reduce the bac-terial content of milk. Spore formers are effectivelyreduced by this process. It is more commonly usedin treating milk for milk powder and cheese manu-facture.

Microbial Transformation

Among the methods of preserving milk are drying,condensing, and fermentation. Fermentation is thecontrolled acidification of milk and cream. By con-trolled acidification, it is meant that the type of mi-croorganisms growing and the conditions for theirgrowth are carefully monitored and stopped. Thecharacteristics of the microorganisms used in fer-menting milk and cream are discussed in greater de-tail in Chapter 6. Here the main concepts of this trans-formation are outlined. Lactic acid bacteria are theprime agents of fermentation. Morphologically theseare rods and cocci. They stain Gram positive. The op-timal temperatures for their growths are either in themesophilic range (20–30◦C) or thermophilic range(35–45◦C). Lactic acid bacteria utilize lactose to pro-duce lactic acid. The transport of lactose into the cellsis facilitated by two enzyme systems; first the phos-phoenol pyruvate dependent phosphotransferase sys-tem while the second mode of lactose transport intothe cell is via an ATPase-dependent system. Lacticacid bacteria are also classified as homofermentativeor heterofermentative. Production of lactic acid onlyfrom lactose, as is the case with most mesophilic lac-tic acid bacteria, leads to such bacteria being labeledhomofermentative. One molecule of lactose resultsin four molecules of lactic acid. Heterofermentativelactic acid bacteria including Leuconostocs lack theenzymes called aldolases and cannot ferment lac-tose via the glycolytic pathway. This class of bacteriaferments one molecule of lactose to two moleculeseach of lactic acid, ethanol and carbon dioxide. Ho-mofermentative lactic acid bacteria do not produceethanol or carbon dioxide. Heterofermentative lac-tic acid bacteria do. Lactic acid production is not theonly change taking place in milk during fermentation.Caseins are also being modified by proteolytic en-zymes; others may produce polysaccharides, which

can alter the viscosity of the milk. Some lactic acidbacteria metabolize citric acid to produce aromavolatiles such as diacetyl.

Fermentation of milk is necessary for the manu-facture of yogurt, buttermilk, kefir, and cheese, whilethe fermentation of cream is essential for the manu-facture of sour cream, cream cheese and other typesof cheese, and for the manufacture of cultured creambutter. Some of these aspects are discussed in greaterdetail in other chapters (Chapters 11, 12, 16, 17, and18). With these basic operations understood, the nextsections will describe the milk processing steps com-monly employed.

FROM FARM TO FACTORYMilk production on the farm is done under strictguidelines that determine its grade (see Chapter 3).In 2002 the total milk production in the United Stateswas 75.47 billion kilograms (170 billion pounds).Farms with 200–500 milch animals accounted for ap-proximately 17.5% of the total milk produced. Farmswith 50–100 cows and >2000 cows accounted for17.4% and 15% of the total milk production, respec-tively. Also in 2002, 9.14 million cows were tendedby 91,900 production units, which means an averageof 99 cows per farm. The general trend in this area istoward less number of farms with larger herd sizes.

Farms use milking parlors of various designs andthe milking interval is unequal. Cows are milkedtwice a day, with a small minority milking threetimes a day. The milk from each animal is weighedand then mixed with milk from other animals in thebatch of cows being milked. Milk temperature im-mediately after milking is approximately at the bodytemperature of the cow (38◦C/101◦F). At this tem-perature many mesophilic microorganisms can growand therefore to minimize microbial growth the warmmilk is cooled rapidly. Cooling is commonly achievedby plate heat exchangers. Milk is thus collected ininsulated tanks called farm bulk milk tanks. Milkfrom several days of milking is collected in this tank(Fig. 5.7).

As the number of cows in the herd grows and thenumber of dairy farms shrinks, milk collection oc-curs more frequently on the farm. For example, inan Arizona dairy farm milking 7,000 cows two timesa day dispatches a tanker every 45 minutes to theirdairy. Smaller farms may use ice bank building tanks.For achieving the best grade of milk (Grade A), milkhas to be cooled to below 4◦C (40◦F) within time


Figure 5.7. Milk from the cow is measuredin-line and then sent to a bulk cooling tank.Reproduced with permission from Tetra Pak.

limits, e.g., 2 hours post-milking. For further detailsrefer to Chapter 3.

At the time of collecting the milk, the tanker driverobtains a sample for milk from each farm. This sam-ple is the basis for quality determination and for pay-ment based on milk composition.

The tanker itself is made of sanitary stainless steeland is fitted with baffles to prevent milk from be-ing vigorously shaken during transportation. Thus,churning of milk and the possibility of churning thecream into butter are avoided. At the back end of thetanker is a pump with a volumetric meter and an air-eliminating device. The tanker pulls up to the milkshed and the driver attaches a sanitary hose to thefarm milk storage tank and pumps the milk from thestorage tank to the milk transport tanker (Fig. 5.8).

When the farm bulk tank is empty the pump isturned off to prevent air from mixing with milk in

the tanker. Presence of air can cause foaming andchurning of milk. When the tanker has collected milkfrom several farms and is full it arrives at the dairyfactory.

STORAGE OF RAW MILKUpon arrival of the milk tanker at the dairy, it enters acovered special reception area. A technician from thequality assurance department checks the temperatureof the milk and draws a representative sample. Duringthis procedure, the technician also checks the odor ofthe milk and records if any off-odors are detected. Therepresentative sample collected from each tanker isanalyzed for sediments, antibiotic residues, somaticcell count, bacteria count, protein and fat content,and freezing point. Some dairies may also conducta direct microscopic count of the bacteria present in

Figure 5.8. Collection of milk on the farm. The tanker is pumping milk from the farm bulk milk tank for transport tothe dairy factory. Reproduced with permission from Tetra Pak.


milk. The normal bacteria count and Coliform counttake 24–48 hours. The results of the remaining testsare available within 15–20 minutes. If all tests meetstandards set by the dairy, the milk is then unloadedfrom the tanker.

The significance of the reception dock tests isas follows. Sediment tests point to the quality ofmilk production at the farm. Antibiotic tests indi-cate if milk from sick animals were commingled withmilk from healthy cows. If such commingling occursthe entire tanker load of milk is rejected. Presenceof antibiotics in milk poses a 2-fold danger. First,antibiotic-sensitive individuals can suffer from con-suming tainted milk. Second, in the manufacture ofcultured milk products, the presence of antibioticsmay pose a barrier for acidity development by inhibit-ing the starter culture growth. Somatic cell countsare indicative of general animal health. If they are<500,000 per milliliter of milk the animal herd healthis considered good. If however, the count exceeds1,000,000 per milliliter it suggests the presence ofmastitis in one or more animals in the herd. Mastiticcows are often treated with antibiotics and while re-ceiving the treatment and for a period after the treat-ment the milk from such animals is generally dis-carded on the farm. Protein and fat contents are usedto determine payments and to gain full accounting ofraw materials received. This is important for materialbalance calculations and for determination of lossesoccurring during processing and packaging. Freezingpoint of milk is another important test to determineadulteration with water, whether accidental or inten-tional. Adulteration of milk is a prosecutable offence.

The most common procedure is to record the vol-ume of milk delivered by a tanker. However, in somedairies the tanker may be weighed prior to emptyingand after discharging its load. Volumetric measure-ments involve a volumetric flow meter fitted with anair eliminator. Presence of air can distort readings ofthe volume of milk. The milk passes through the aireliminator and a filter into the metering device priorto going to storage silos.

The tanker after discharging its load of milk iscleaned in the reception bay or in a special cleaningbay. The inside of the tanker is washed by a cleaning-in-place system, which rinses the tanker, cleans itwith detergents, and rinses the detergent followed bysanitizing the tanker. While the inside of the tankeris being cleaned, the exterior is also often washed sothat the tankers always look clean on the road. Aftercleaning and sanitizing, the tanker goes to its nextround for milk collection.

Figure 5.9. Schematic of a milk silo with a propelleragitator. Reproduced with permission from Tetra Pak.

The raw milk is stored in large vertical tanks knownas silos (Fig. 5.9). These silos can have capacities of25,000–150,000 liters (6,000–37,000 U.S. gallons).The silos are placed outside the dairy with an insideoutlet bay. The silos have a double-wall constructionwith an outside welded sheet metal within which astainless steel tank is contained. The silos have meth-ods of agitating milk so as to prevent gravitational fatseparation.

The agitation must be very smooth to avoid rup-ture of the milk fat globule membranes, which cancause lipolysis of milk fat. Lipolysis generates off-flavors and odors. The most common agitation sys-tem is to use a propeller agitator. In the tanks there areinstruments that include a thermometer, level indica-tor, low level protector, overflow protector, and anempty tank indicator. Modern dairies have electroni-cally transmitted data on temperature, levels of milkin the silos, and the protection devices. Redundant vi-sual (nonelectronic) systems may also be employedin some dairies.


Milk storage silos are cleaned in place and visualinspections of the interior surfaces for any problemsare also conducted periodically. Since silos are con-sidered to be confined spaces, entry into a silo has tobe strictly according to the standards recommendedby the Occupational Safety and Health Administra-tion of the U.S. Government.

The temperature of the milk in the silo has to bemaintained at 4◦C or below (<40◦F). Even at thesetemperatures psychrotrophes can cause proteolysisand lipolysis if milk is stored for long periods of time.Therefore, it is recommended that the silos be emp-tied and cleaned and sanitized at regular intervals.The raw milk in the silo is further processed and themain elements in the processing are centrifugal oper-ations, thermal treatment, homogenization, cooling,and packaging.

CENTRIFUGAL OPERATIONSCentrifugal operations deal with removing some ormost of the fat, a step called standardization. Onemethod of standardization is to completely removeall the fat as cream leaving skim milk, then the creamand skim milk can be recombined in desired ratios toobtain low, light, and whole milk with 1%, 2%, and3.25% fat, respectively. More often this standardiza-tion is performed in a continuous manner.

The separation of cream from milk is achieved ina cream separator. Often the separator has the abil-ity to remove sediments from milk as well as sep-arate the cream from milk. Depending on the de-sign of the separator/clarifier, the sediment collectedcan be manually or automatically removed. Typi-cally milk can have 1 kg of sediment per 10,000liters (1 lb/1,100 U.S. gallons). Automatic discharg-ing separators/clarifiers are hermetically sealed andare cleanable in place. This is less cumbersome thanopening up the bowl assembly and cleaning manuallyboth the sediment and the disc stacks of a separator.

Control of fat content in the cream is possible by aparing disc in conjunction with a cream flow meter.A throttle valve at the cream discharge side controlsthe volume of cream leaving the separator. This iscounterbalanced by controlling the pressure of theskim milk outlet and is dependent on the make of theseparator and the throughput of the separator.

In paring disc separators the volume of cream dis-charged is controlled by a cream valve with a built-inflow meter (Fig. 5.10). The size of the valve apertureis controlled by a screw and the throttled flow passesthrough a graduated glass tube with an indicating

1

2

3

Figure 5.10. Paring disc separator with manualcontrols. (1) Skim milk outlet with regulator, (2) creamthrottling valve, (3) cream flow meter. Reproduced withpermission from Tetra Pak.

device. The art of balancing the cream flow and theskim milk pressure leads to obtaining the desired fatcontent in the cream.

In the more common hermetically sealed separa-tors, milk is supplied to the bowl through the bowlspindle. It is accelerated to the same speed as therotation of the bowl and continues through the dis-tribution holes in the disc stack. The bowl of a her-metic separator is completely filled with milk duringoperation. There is no air in the center, hence thename hermetic separator. It is a part of the closedpiping system of the dairy. The pressure generatedby the external product pump is sufficient to over-come the resistance to flow through the separatorto the discharge pump at the cream and skim milkoutlets.

An automatic constant pressure unit in a hermeticseparator is controlled by a diaphragm valve. Thepressure on the valve is controlled by compressed airabove the diaphragm (Fig. 5.11).

Direct in-line standardization of the fat content ofmilk is based on the principle of keeping the pressure


Figure 5.11. Hermetic separator bowl with anautomatic pressure unit on the skim milk outlet.Reproduced with permission from Tetra Pak.

of the skim milk constant. This pressure has to bemaintained regardless of flow fluctuations or pres-sure drop caused by the equipment after separation.This is done by a constant pressure valve at the skimmilk discharge side of the separator. Precision stan-dardization is also dependent upon fluctuations in fatcontent of the incoming milk, in throughput, and inpreheating temperatures. Centrifugal operations mayalso be used in some countries for the manufactureof cultured dairy products. In yogurt manufacture,skim milk (with 0.05–0.1% fat content) or milk hav-ing different fat contents (1%, 3.25%, etc.) is oftenused and in the more indulgent types of yogurt, milkhaving higher fat contents up to 8% may be used.All these different fat contents are arrived throughcentrifugal operations involving standardization

on-line. A schematic of an in-line standardization unitis shown in Figure 5.12.

Separation temperature is also an important vari-able. Cold separation of milk (<4◦C or 40◦F) de-creases the efficiency of fat recovery. Therefore, com-monly, warm separation is used where the efficiencyof fat removal is greater because the fat is in a fluidstate at temperatures of around 50◦C (122◦F). Warm-ing of the milk can take place during the regenerationphase of heat transfer (see below).

THERMAL PROCESSINGSYSTEMSThe standardized milk is thermally processed as re-quired by law. This treatment renders the milk freefrom pathogens. The term pasteurization describesthis process. Pasteurization can be a batch processor a continuous process. Batch processes are usedby small processors and is not common in moderndairies. The batch process is called Long Time LowTemperature (LTLT) pasteurization. In this process,standardized milk is heated to 62.5◦C (145◦F) andheld at that temperature for 30 minutes. The process-ing tanks used for such purposes should have certaincharacteristics defined in the Pasteurized Milk Or-dinance (PMO). Homogenization takes place post-pasteurization, followed by cooling. Homogeniza-tion may also take place after the regeneration sectionand prior to entering the heating section. If the tem-perature of the milk is around 40◦C (104◦F), lipoly-sis can be enhanced by homogenization. Therefore,homogenization temperature has to be above 45◦C(113◦F). At this temperature milk lipase and manymicrobial lipases are rendered ineffective.

Figure 5.12. The complete process forin-line standardization of milk and cream.(1) Density transmitter, (2) flow transmitter,(3) control valve, (4) control panel, (5)constant pressure valve, (6) shut-off valve,and (7) check valve. Reproduced withpermission from Tetra Pak.


Figure 5.13. A complete pasteurizer plant. (1) Balance tank, (2) feed pump, (3) flow controller, (4) regenerativepreheating sections, (5) centrifugal clarifier, (6) heating section, (7) booster pump, (8) holding tube, (9) hot waterheating, (10) regenerative cooling sections, (11) cooling sections, (12) flow diversion valve, (13) control panel, A.temperature transmitter, B. pressure gauge. Reproduced with permission from Tetra Pak.

The continuous pasteurization process is termedHigh Temperature Short Time Pasteurization (HTST)and entails heating milk to 71.5◦C (161◦F) and hold-ing the milk for a minimum time of 15 seconds priorto cooling and storage. Yogurt manufacture necessi-tates the holding of milk for longer periods of time inorder to denature the whey proteins and thus improvethe gel strength of yogurt. Therefore, in yogurt man-ufacture milk may be held at 71◦C for 30 minutesor it may be heated to 90◦C (194◦F) and held for10 minutes (see Chapters 11 and 12 for furtherdetails). The HTST process involves plate heatexchangers and the PMO has prescribed variouscontrols and requirements for the equipment.

The effect of heat treatment on milk is to reducethe rate of deterioration due to microbial and enzy-matic action. In addition, the milk may look whiterand appear more viscous, with appreciable flavorchanges and a decrease in nutritive value. The effec-tiveness of pasteurization is estimated by assayingfor an enzyme called phosphatase. In fresh properlypasteurized milk, no phosphatase activity is detected.Upon storage sometimes microbial phosphatases orthe milk phosphatase itself can regain some of its ac-tivity. If the presence of phosphatase is detected in

stored pasteurized milk, further tests are often con-ducted to determine the cause of this positive test.

In the HTST pasteurization process (Fig. 5.13),cold milk enters a balance tank with a float valve.The purpose of the balance tank (also known as aconstant level tank) is to maintain a constant level ofmilk in the plate heat exchanger as the pasteurizershould be filled at all times during operation to pre-vent the product from burning onto the plates. Thebalance tank may be fitted with an electronic sensorthat transmits a signal to the flow diversion valve.If the level in the balance tank goes below a certainlevel and fresh milk is not coming in to raise the level,this electrode transmits a signal for the flow diversionvalve to open and to return the milk in the system tothe balance tank. The milk is replaced by water ifcirculation has continued for a certain predeterminedtime.

Milk is pumped from the balance tank to the plateheat exchanger. The pump is fitted with a flow con-troller to ensure that a constant flow is maintained at apredetermined value. This value is dependent on thecharacteristics of the pump and the heat exchangercapacity. The flow control device also guarantees astable temperature and constant length of holding.


The flow control device may also be located after thefirst regeneration section.

Regenerative preheating is an energy-saving stepin pasteurization. Cold untreated milk is heated bythe outgoing pasteurized milk. Thus, cold milk ispreheated and the hot milk is cooled simultaneously.The regeneration section is divided into two sections.After the cold milk is preheated in the first regener-ation section, it is separated and homogenized andthen the standardized, homogenized milk enters thesecond regeneration section where it is further heatedby the hot pasteurized milk. Heating is accomplishedby using hot water as the medium. The hot water, inturn, is produced by injecting culinary steam into thewater. The steam is generated in boilers of the dairyfactory.

After this regeneration section the milk enters thepasteurization section where it is heated to the re-quired temperature. The heated milk exits the heat-ing section and enters an external holding tube. Theflow rate of hot milk determines the residence time inthis holding tube. The flow rate in turn is controlledby the flow controller referred to earlier. After thetransit through the holding tube the exiting milk tem-perature is measured and transmitted to a temperaturecontroller and a recording chart.

A sensor at the exit of the holding tube transmitsa signal to the temperature monitor. As soon as thetemperature falls below a preset minimum value themonitor switches the flow diversion valve to “divertedflow.” In diverted flow, the hot milk returns to thebalance tank as it is not considered pasteurized. Thereason for the fluctuation is determined and correctedand if the correct temperature is maintained at theexit point of milk from the holding tube, further flowis continued past the flow diversion valve. Often abooster pump may be added after the milk exits theholding tube. The hot pasteurized milk enters the re-generation section of the pasteurizer to heat the in-coming raw milk.

In the regeneration section unpasteurized milkflows on one side of the plate and hot pasteurizedmilk flows on the other; if there are pinholes in theplates of the heat exchanger, unpasteurized milk cancommingle with pasteurized milk. This violates theintegrity of the pasteurized milk and the fluid is notconsidered pasteurized. To avoid such a problem, thepasteurized milk is always at a higher pressure thanthe raw milk. To measure the pressures a pressure dif-ferential meter is often installed on the control panel.If the pressure differential between raw and pasteur-ized milk drops below a preset value, a signal is sent

to the flow diversion valve to open. Therefore, twodifferent causes for flow diversion are temperaturefalling below preset values and the pressure differen-tial between raw and cold milk falling below a certainpreset limit. The milk is not considered pasteurizedif either of these events occurs. For milk to be des-ignated as pasteurized, every drop of milk has to beheated to and held at the specified minimum temper-ature for a specified amount of time.

Pasteurized milk in the regeneration section iscooled giving off its heat to the cold incoming rawmilk. This cools down the milk but not to the desired4◦C (40◦F) or below. The final step in pasteurizationis to cool the milk to below 4◦C in the cooling section.Cooling is achieved by chilled water or cold glycolas the refrigerant. The water is chilled by a refrig-eration system that commonly uses ammonia as therefrigerant. Other hydrocarbons may also act as re-frigerants. Since the pasteurized milk transmits con-siderable heat to the cold raw milk, less refrigerationcapacity is required to cool the milk to below 4◦C.

In yogurt manufacture the cooling system may notbe used. Once the pasteurized milk has been cooledto around 43–45◦C it may be pumped to the fer-mentation tanks for further processing. It is obviousthat reheating cold pasteurized milk to the incubat-ing temperatures of 43–45◦C will require a greaterconsumption of energy than avoiding this step in thefirst place.

HOMOGENIZATIONHomogenization is a process of reducing the sizeof fat globules. Homogenization prevents creaming(separation of a fat enriched layer from the aque-ous phase). Reduction in the globule size is achievedthrough a combination of turbulence and cavitation.The apparatus in which such particle size reductionoccurs is called a homogenizer.

Cold milk cannot be homogenized efficiently be-cause the milk fat still is solid. Therefore, homog-enization occurs best at temperatures greater than37◦C (99◦F). Another necessity for efficient homoge-nization is the presence of protein. A suggested min-imum value of 0.2 g of casein per gram of fat isrecommended.

Homogenizers are manufactured as single-stageand dual-stage machines. In single-stage homoge-nization the whole pressure drop is used over onedevice. It is used for products with low fat contentand in products requiring a high viscosity (e.g., sourcream, coffee cream, whipping cream). Dual-stage


Figure 5.14. The homogenizer is a largehigh-pressure pump with a homogenizingdevice. (1) Main drive motor, (2) V-belttransmission, (3) gear box, (4) damper,(5) hydraulic pressure setting system,(6) homogenizing device, second stage,(7) homogenizing device, first stage, (8) solidstainless steel pump block, (9) pistons,(10) crank case. Reproduced withpermission from Tetra Pak.

homogenizers are used in breaking down the fat glob-ule in two stages. This is effective for products withhigh fat content, high solids content, or for productswhere low viscosity is desired (Fig. 5.14).

The effects of homogenization are smaller fat glob-ule size (prevention of creaming), whiter and moreappetizing color, reduced sensitivity to fat oxidation,and a fuller bodied flavor and mouthfeel. In culturedmilk products a better stability is also achieved. Ho-mogenizers are high-pressure machines in which re-ciprocating pistons create the pressure. Pressurizedmilk is passed through a narrow aperture. When thepressurized milk exits into atmospheric pressure cav-itation is created, which results in large fat globulesbeing reduced to smaller ones. The narrow aperture

is called the homogenizer valve. There are manydesigns for the homogenizer valve all of which havea similar effect on the fat globule (Fig. 5.15).

When a large fat globule is disintegrated to a num-ber of small droplets, a tremendous increase in sur-face area of the fat occurs. Onto the surfaces of thesenewly created droplets casein adsorbs and stabilizesthe droplet. If this step does not occur, the fat dropletscould recombine to form a larger globule. The adsorp-tion time has been estimated to be around 0.25 �s,the encounter time between the protein and fat is es-timated to be 015 �s, and the deformation time isaround 0.3 �s for 4% fat milk being homogenizedat 20 MPa. In this process, the average fat glob-ule diameter of 9 �m for 4% fat milk is reduced to

Figure 5.15. The milk is forced through a narrowgap, which results in the fat globules splitting intosmaller sized droplets. Reproduced withpermission from Tetra Pak.


1.6 �m. The protein that is adsorbed onto the newlyformed surfaces is casein. Approximately 75% of thesurface area is covered with casein. Larger micellesare preferentially adsorbed over smaller ones. Pro-tein adsorption is greatest on smaller globules. Thesurface concentration of protein has been measuredat 10 mg/m2.

Single-stage homogenization uses only one stageto reduce the fat globule size. In dual-stage homog-enization two stages for pressure reduction are used.First a low-pressure treatment is followed by a secondhigher pressure treatment. A two-stage homogenizeris useful with low-viscosity fluids.

MEMBRANE TECHNOLOGYMembrane technology is useful in selectively en-riching certain components. Membrane technology

consists of four distinct processes. Reverse osmosis(RO) is useful in concentrating solids by removal ofwater. Nanofiltration (NF) can concentrate organiccomponents by removal of monovalent ions likesodium and chloride thereby resulting in deminer-alization. Ultrafiltration (UF) is the process in whichmacromolecules are concentrated. The major macro-molecules in milk are fat and proteins. The fourthmembrane process is microfiltration (MF). This pro-cess removes bacteria and it can also separate macro-molecules.

These techniques utilize cross flow membrane inwhich the feed solution is forced through the mem-brane under pressure (Fig. 5.16). The solution flowsover the membrane and solids are retained (retentate)while the removed materials are present in the perme-ate. The membranes are classified according to theirmolecular weight cutoff, supposedly the molecular

Figure 5.16. Different membrane processes and their characteristics. Reproduced with permission from Tetra Pak.


weight of the smallest molecule that cannot passthrough the pores of the membranes.

The filter modules themselves are available in var-ious geometries. Spiral wound is the most commonbut others available are plate and frame, tubular, andhollow fiber. Tubular filters can be made out of ce-ramics or polymers.

Membrane separation capacity depends on a num-ber of factors. Foremost among them is membraneresistance, which is determined by membrane thick-ness, surface area, and the pore diameter. Next istransport resistance (also known as fouling effect).This effect occurs on the membrane surface as filtra-tion proceeds. The formation of a layer of depositleading eventually to membrane fouling is due tothe flow of macromolecules at right angles to thedirection of flow. A concentration gradient leads todiffusion in the opposite direction. Parallel to themembrane the macromolecules present in the layerclose to the membrane move at varying velocitiesdependent on the axial flow rate. The concentra-tion polarization is not uniformly distributed, espe-cially when the pressure drop gives different trans-membrane pressures along the membrane surface.The upstream end of the membrane clogs first andgradually spreads across the whole surface of the

membrane reducing capacity and making cleaningnecessary.

Membrane operations can be batch or continuous.In dairy plants continuous processes are more desir-able. Process temperatures are maintained at around50◦C to minimize microbial growth and to improvemembrane flux.

The use of membrane processing in the cultureddairy products area is restricted to concentration ofskim milk for fat-free yogurt manufacture. Some ofthe lactose and minerals are removed from skim milkthereby increasing the protein content. This processcan concentrate skim milk with 9% solids to 12%solids. There is still enough lactose in the retentateto facilitate fermentation. A higher protein content inthe concentrated milk results in a firmer acid gel inyogurt.

BIBLIOGRAPHYTetra Pak. 1995. Dairy Processing Handbook. Tetra

Pak Processing Systems, Lund, Sweden.Walstra P, Geurts TJ, Noomen A, Jellema A, van

Boekel MAJS. 1999. Dairy Technology—Principlesof Milk, Properties and Processes. Marcel Dekker,New York.

6Starter Cultures for Yogurt

and Fermented MilksEbenezer R. Vedamuthu

IntroductionStarter FunctionsFactors Affecting Starter Performance

Intrinsic FactorsExtrinsic FactorsMiscellaneous Factors

Microorganisms Used in Starters for Cultured Dairy ProductsGenus LactococcusGenus LeuconostocGenus StreptococcusGenus LactobacillusGenus Bifidobacterium

Starter Culture ProductionBulk Starter ProductionCommercial Starter Culture Production

BibliographyBooksChapters in BooksReview Articles and Research Papers

INTRODUCTIONStarter culture is at the heart of cultured dairy productmanufacture. With the exception of certain probioticmilks, the centerpiece of cultured dairy product man-ufacture is fermentation. Fermentation is a biologicalprocess. In the context of cultured dairy products, theagents of fermentation are microorganisms. Fermen-tation in the physiological sense is anaerobic respira-tion. In microbial metabolism, the oxidation of sub-strates involves a series of transfers of hydrogen viacarriers (coenzymes) to a final acceptor. In aerobicrespiration the final hydrogen acceptor is molecu-lar oxygen. Depending on the electron (hydrogen)transfer system, the final transfer of the hydrogen tooxygen would result in the formation of water andmolecular oxygen or hydrogen peroxide. Hydrogen

peroxide, a powerful oxidizing agent unless detoxi-fied, would be detrimental to cell viability. In aerobicmicroorganisms, hydrogen peroxide is transformedinto nontoxic components, water, and oxygen by theenzyme catalase. In fermentation, the final hydrogenacceptor is a truncated molecule of the substrate. Toa large measure respiration involves the oxidation ofcarbohydrates, which yields energy in the form ofhigh-energy chemical bonds, as well as short-chaincarbon compounds needed for cellular synthesis. Inthe fermentation of sugars, the truncated intermedi-ate, pyruvate, is the final hydrogen acceptor resultingin the formation of lactic acid. In certain other fer-mentations, acetaldehyde derived from pyruvate isthe final hydrogen acceptor yielding ethyl alcohol asthe final product. In mixed fermentations, both lacticacid and ethyl alcohol are formed. In terms of energyyield, fermentation yields only substrate-level phos-phorylation, which is much less than complete aero-bic respiration. Fermentative microorganisms gener-ally do not possess catalase, and hence cannot tolerateaerobic conditions.

Cultured dairy product manufacture largely in-volves lactic acid fermentation. And, the microor-ganisms fomenting the change are lactic acid bacteria(LAB). In mixed lactic acid – alcohol fermentations,as in Kefir and Koumiss, in addition to LAB, yeastsare also associated. Yeasts are the agents of alcoholformation in these products. Certain LAB in cultureddairy products impart flavor attributes through thefermentation of citric acid or citrates.

Starter culture, or starter for short, consists of se-lected microorganism(s) deliberately added to milkor a dairy mix to bring about desired changes thatresult in the production of a specific cultured dairyproduct with the desired attributes. The term “starter”

89




in this context is entirely appropriate, because thestarter initiates and carries through the necessarychanges in the starting material to yield the cultureddairy product. The entire cultured dairy product man-ufacture is dependent upon the activity of the starter.It is very similar to the ignition switch (which acti-vates the starter) in an automobile. Unless the starteris activated or operating in an automobile, the carwill have no mobility and will be useless in gettingone from point A to point B. That somewhat portraysthe role of the starter culture in cultured dairy prod-uct manufacture. The parallel between the functionof the starter in a car and that in the production ofcultured dairy products relates only to the initiationof the process and does not adequately represent thefull gamut of the roles the starter culture plays in cul-tured dairy product manufacture and quality. Startercultures not only initiate, but also carry through everychange to attain the desired body, texture, and flavorin the cultured dairy product. Furthermore, startersplay a preservative function in suppressing spoilageflora, thus increasing shelf life. Another vital functionrelates to their protective role in retarding or inhibit-ing pathogenic flora, and the formation of entero-toxins in the finished culture dairy product. In short,starter culture determines the shelf life and the safetyof cultured dairy products. In probiotic products, theadded cultures impart health-promoting properties tothe consumer.

Because of the aforementioned vital functions ofstarter cultures in fermented and nonfermented dairyproducts, the selection, propagation, and handlingof starter cultures are of paramount importance insuccessful cultured dairy product manufacture andmerchandizing. That holds true in the industrial pro-duction of starter cultures, which would entail anadditional burden in using the most optimum har-vesting and preservative techniques that would en-sure optimum functionality of the starter duringapplication.

As mentioned earlier, starter cultures are com-posed of living entities. Living organisms requireproper environmental conditions to thrive and per-form their functions. Environmental conditions com-prise optimum temperature ranges, proper nutrition,and optimum pH range, absence of toxic substancesor by-products, and careful handling procedures.Some of the manufacturing processes for cultureddairy products require sequential operations, whichwould involve manipulations that favor or retardthe growth and biochemical activities of starter cul-tures. Some fermentations require the use of starters

composed of different microorganisms with differentgrowth requirements. In such operations, associativeaction by components in the starter mixtures may bedesired, and in other cases, the conditions need tobe manipulated to curtail the growth and activity ofone component, but favor the other or promote a bal-anced growth and activity of both components. Allthose events have to be carefully controlled to obtainconsistently superior end products. Yogurt manufac-ture exemplifies a process where synergism betweentwo different starter components is desired. In cul-tured buttermilk, conditions are manipulated to pre-vent dominance by acid-producing bacteria, so thatthe flavor-producing component(s) in the starter mix-ture can function, assuring a balanced growth andactivity of both components.

Because of the complex interactions between mi-croorganisms, and complex substrates in which thestarter flora have to function, even a slight devia-tion from standard operating procedures could causeproblems in the fermentation industry. The qualityof materials being transformed through fermenta-tion in some cases could be detrimental to starterfunctions. The physical and chemical properties (forexample, the concentration of solids contributing toosmolarity, presence of toxic substances like antibi-otics, residual sanitizers, or mastitic milk, etc.) orvariability in the quality of the milk or dairy mixwould result in malfunction of starter flora and poorerquality end products. Another complicating factorin cultured dairy product manufacture is the infec-tion of starter bacteria by bacterial viruses or bac-teriophages, or phages for short. Starters infectedwith phages are either killed or functionally crip-pled. Economic consequences of phage-related fail-ures of dairy fermentations are manyfold. Firstly,there could be complete failure of the desired fermen-tation(s). Secondly, slowing down of the process maydisrupt daily schedules and result in erratic turnoverof equipment, overtime wages, overall loss in the fi-nal quality of the products, undergrade products, andloss in value. Most importantly, there is likelihoodof unchecked development of chance contaminantssuch as spoilage flora and pathogenic or toxigenicflora in the product.

Fermentation failures may be caused either bytechnological or microbiological factors or by a com-bination of the two. Troubleshooting in the fermen-tation industry thus requires good knowledge of bothtechnological and microbiological facets involved inany specific fermentation. Using yogurt as an exam-ple, some of these aspects can be illustrated. Yogurt

6 Starter Cultures for Yogurt and Fermented Milks 91

today is a multifaceted product. In the United Statesyogurt is available as “plain yogurt,” which is theproduct obtained after fermentation without any ad-ditions. Within the “plain yogurt” category, in addi-tion to the solid product, there is also liquid, drinkableplain yogurt. Another variation within this group isthe solid or drinkable yogurt with probiotic culturescomprising one or more species or different strains ofthe same species. Subgroups in the plain yogurt vari-ety are made up of products with different fat contents(fat-free, low fat, and full fat). Plain yogurt is, how-ever, not very popular because of its acid taste, andshunned by most consumers. Most customers pre-fer the flavored and sweetened products. Within theflavored category, there are varieties with added fla-vor essences only, such as vanilla, chocolate, coffee,lemon, lime, orange, banana, etc; others with fruitpieces and fruit flavors/syrups exemplified by straw-berry, raspberry, blueberry, apple, etc; and special-ized flavors and combinations like nuts and cereals,pina colada, apple-cinnamon, etc. Then there are vari-ations based upon how the fruit is distributed—fruitat the bottom/sundae style and the blended style inwhich the fruit is uniformly distributed. Within theflavored yogurts, there are the solid and drinkabletypes, as well as classes distinguished by different fatlevels. Flavored yogurts are also available with addedprobiotic cultures. There are yogurt varieties targetedfor youth and children, special dietary yogurts con-taining artificial sweeteners, and yogurts packaged insqueezable containers for people “on-the-go.”

All the foregoing yogurt products need to meetcertain basic criteria in body, texture, color, flavor,fruit distribution, and resilience to handling throughmarketing channels. Various operations in the man-ufacture of the wide variety of yogurt products exertstresses on the starter organisms. For example, theaddition of fairly high concentrations of sugar (su-crose or high fructose corn syrup or corn syrup) be-fore culturing increases the osmotic pressure of themix; the addition of fruit preparations preserved insugar syrups after culturing also has the same effect.There are trade requirements that specify that yo-gurt should have a certain level of live starter organ-isms present throughout the prescribed shelf life ofthe product. Agitation of coagulated curd, pumpingthrough pipelines, and other related processes intro-duce air into the product, which also cause stress con-ditions. Such stress conditions cause cell destructionor injury. These stresses affect the viability of yo-gurt starter bacteria as well as other probiotic strainsadded to the yogurt.

In terms of flavor, “mildness” both in terms of acid-ity and “greenness or acetaldehyde flavor” is highlydesired by manufacturers. Mildness allows the manu-facturers to use a wide assortment of single and com-plex flavors, for example, chocolate and coffee fla-vors. The selection of starter strains becomes criticalin obtaining mildness. To obtain a smooth texturewithout whey separation, starters containing strainsthat produce exopolysaccharides (EPS) are neces-sary, but there is a fine line between the smoothnessdesired and the stringiness or “ropiness.” Here, too,starter selection and cultural conditions are critical.Use of EPS-producing strains also helps to give yo-gurt a heavy body that would hold in suspension fruitpieces within the yogurt matrix. Bleaching or fadingof the natural hues of fruits and fruit juices is often en-countered in fruit yogurts. The bleaching or fading offruit pigments (anthocyanins) is caused by pH and ox-idation/reduction changes introduced by starter bac-teria. Starter selection, proper cultural conditions andchoice of stabilizers, and fruit preparations are impor-tant in controlling the quality of the finished product.The need for viable starter bacteria in the product tillthe “open date” and the complexity introduced by theinclusion of probiotic strains add another dimensionto the difficulties in yogurt fermentation and yogurtsystems. The foregoing illustration using yogurt ina nutshell shows the importance of starter cultureand the need for “holistic” analyses of both tech-nological and microbiological aspects in successfulfermentations.

STARTER FUNCTIONSThe primary starter function is to generate lactic acidby the fermentation of the major sugar in milk ordairy mixes, lactose. The rate at which the acid de-velopment is desired depends upon the cultured dairyproduct, the turnover desired in the manufacturingplant, the starter flora used, the temperature of fer-mentation, the flavor generation needed in the cul-tured product (need for balanced growth of the mixedstarter flora), and the body characteristics (in termsof EPS generation) desired in the cultured product.As acid accumulates during fermentation of sugar,the pH progressively decreases. When the pH dropsto the isoelectric point of casein, the colloidal disper-sion of casein micelles collapses, and the acid caseinprecipitates forming the curd. Thus, the acid gener-ated from the fermentation of lactose not only im-parts a pleasantly acid flavor to the cultured product,but also transforms the starting liquid milk or dairy


mix into a semisolid-to-solid curd. Within the solidcasein matrix, the whey and other soluble compo-nents of milk and milk fat are entrapped. Unless thecurd is unduly disrupted by rough handling or ex-cessive pumping, the entrapped components are heldfairly intact with the casein network. Excessive acidgeneration by starter organisms because of uncon-trolled fermentation (failure to arrest fermentation byprompt and proper cooling at the desired acid level orimproper temperature control during fermentation)will result in the shrinkage of the curd and the ex-pulsion of whey and soluble components. Excessiveacid concentration also imparts a harsh, acrid flavorand masks the delicate dairy flavor notes like diacetyldesired in cultured buttermilk, sour cream, and a fewother cultured dairy products.

The acid generated and the gradual lowering ofthe pH facilitate the transport of citrate present inmilk or dairy mixes into the cells of “flavor bacteria”efficiently, resulting in the formation of the primaryflavor compound, diacetyl. Transport of citrate intothe cells of flavor bacteria is facilitated by an enzyme,citrate permease, which functions optimally belowpH 6.0 (the initial pH of milk is around 6.6, and indairy mixes, the pH may range from 6.3 to 6.4).

Another important function of lactic acid is itspreservative effect. Undissociated lactic acid is in-hibitory to many spoilage and pathogenic bacteria,and the lowered pH is an additional stabilizing factor.In most cultured dairy products, the maximum acidityattained ranges between 1.3% and 1.5%, expressed aslactic acid. To yield 1 lb of lactic acid, 1 lb of lactoseis consumed. Milk contains around 4.8% lactose, andto yield 1.5% lactic acid, only about 30% of the totallactose content is consumed, leaving a large portionof the lactose intact at the end of fermentation.

The secondary functions of the starter culture incultured dairy products include flavor generation,special body and texture production, and the elab-oration of miscellaneous inhibitory metabolites thatimpart preservative effects. In cultured buttermilk,dahi (an Indian cultured milk), sour cream, and re-lated products, the nutmeat-like “buttery” flavor isdesirable. Diacetyl is the key compound that impartsthe buttery flavor. Diacetyl is a diketone, derived bythe fermentation of citrate present in milk and dairymixes. Flavor bacteria included in starters for suchproducts possess the enzymatic pathways to convertcitrate to diacetyl and other closely related reducedderivatives of the diketone. The reduced forms of di-acetyl do not possess the desired buttery notes prizedin the aforelisted cultured dairy products. Flavor

bacteria consist of selected, compatible strains ofLeuconostoc spp. and citrate-fermenting Lactococ-cus lactis subsp. lactis. Among the two, Leuconostocspp. are preferred over citrate-fermenting L. lactissubsp. lactis organisms in cultured buttermilk andsour cream starters. The citrate-fermenting lactococciaccumulate fairly high concentrations of acetalde-hyde, which introduces unwanted harsh, “green,yogurt-like” flavors in cultured buttermilk and sourcream. Dairy Leuconostoc spp. on the other handscavenge undesirable acetaldehyde, converting thealdehyde to ethanol, which provides a complemen-tary flavor to the overall characteristic flavor bou-quet of cultured buttermilk and sour cream. The rel-atively high alcohol dehrydrogenase activity of dairyleuconostocs plays a vital part in the scavenging ofacetaldehyde. To obtain a characteristic cultured but-termilk flavor, a balanced ratio of diacetyl to acetalde-hyde is necessary. The desirable ratio of diacetyl toacetaldehyde falls between 3.2:1 and 4.4:1. In dahi,the presence of slightly higher concentrations of ac-etaldehyde is not considered a defect. The flavor bac-teria are heterofermentative, and from lactose pro-duce fairly high amounts (about 30%) of metabolicend products other than lactic acid. The non lacticacid metabolites include acetic acid, ethanol, and car-bon dioxide. The fermentation of citrate in additionto diacetyl and its reduction products also yields car-bon dioxide. Carbon dioxide plays a role in the flavorperception of cultured buttermilk, very similar to theeffervescence or the “lift” imparted by carbonationin “soft drinks.”

In yogurt, on the other hand, acetaldehyde is a keycomponent in furnishing the desirable “green apple”flavor. Although for typical plain yogurt a fairly highconcentration of acetaldehyde is needed, the presenttrend as mentioned earlier is to select starter strainsthat produce low amounts of the aldehyde to give amild-flavored yogurt, compatible for the addition ofa wide variety of flavors.

In Kefir and Koumiss, ethyl alcohol and carbondioxide provide essential flavor notes. The yeasts as-sociated with the Kefir grains and the starters usedfor Koumiss generate the needed alcohol and carbondioxide. In dahi, in certain areas, a slight “yeastiness”is preferred. Yeasts acquired through chance contam-ination and carried over by “back slopping” practiceare attributable to the yeastiness in dahi. The startersused in Viili contain a mold, Geotrichum candidum,that forms a layer or mat on the surface of the prod-uct (aerobic growth). The mold metabolizes lacticacid, and induces a “layered mildness” to the product


and also imparts a “musty” aroma. The exact role ofmolds associated with certain Koumiss starters is stillundefined.

Starters additionally impart special body and tex-ture characteristics to certain cultured dairy prod-ucts. In Viili and closely related Scandinavian cul-tured milks, a viscous and a ropy or stringy body andtexture is caused by EPS-producing strains includedin the starters. As described earlier, EPS-producingstarter strains in yogurt starters provide the heavybody to hold fruit pieces in suspension. Lately, theuse of EPS-producing starter strains is widespread incultured buttermilk and sour cream production. Withthe ever-increasing price of milk solids, these strainsprovide cost-effective means to impart a heavy bodyto these products. The cost savings are realized ei-ther by reducing the amount of milk powder forti-fication or by complete elimination of fortification.During filling operations for cultured buttermilk, theEPS-induced texture in the finished product preventsfoaming, and allows easy filling of bottles to the re-quired level.

LAB used as starters produce other metabolitesthat are inhibitory to spoilage flora. These metabo-lites contribute to shelf-life extension of cultureddairy products. The secondary metabolites that aresignificant include hydrogen peroxide, which is in-hibitory to spoilage bacteria such as Pseudomonasspp. Hydrogen peroxide in combination with thelactoperoxide system of milk exerts suppressive ef-fect on spoilage flora. Certain starter bacteria pro-duce benzoic acid as a metabolite. Benzoic acid hasa bacteriostatic and fungistatic effect. Starter LABproduce bacteriocins such as nisin, acidophilin, bul-garicin, and other uncharacterized inhibitory pep-tides. Nisin is active against spore-forming bacteria.Citrate-fermenting L. lactis subsp. lactis strains exertan inhibitory action against Gram-negative spoilagebacteria as well as pathogens. Some of the inhibitorypeptides elaborated by that Lactococcus subspecieshave recently been described.

FACTORS AFFECTING STARTERPERFORMANCEThe factors influencing starter performance may beclassified under two headings, namely intrinsic andextrinsic.

Intrinsic Factors

Among the intrinsic factors, the genetic makeup ofthe starter cells is vital in starter functions. Cellular

functions are a reflection of the genetic infor-mation encoded in the nuclear materials (DNA—chromosomal and extrachromosal) contained withinthe cells. Metabolic functions of the cell are carriedout via various catabolic and synthetic enzymaticpathways. Enzymes are biological catalysts that drivethe catabolic and synthetic reactions. Enzymes areproteins made up of amino acids strung together inspecific sequences, which are encoded in the DNA ofthe cells. The specific folding of the amino acid se-quences, and the specific reactive sites thus formed,facilitates the reactivity of enzymes. The structureand the reactive site(s) of enzymes determine theirspecificity for substrates.

The genetic materials in the cell could be alteredby mutations. Mutations (spontaneous or induced) inenzymatic pathways would profoundly affect cellularmetabolism. Such mutations in carbohydrate utiliza-tion would affect acid production, a primary functionof starters. Similarly, other functions could also beaffected.

As mentioned earlier, the genetic material of thecell could be organized in the chromosome or inextrachromosomal elements. Plasmids, transposons,and introns represent some of the extrachromoso-mal elements found in starter bacteria. Nuclear mate-rial of bacteriophages (or phages) specific for starterbacteria sometimes exist as extrachromosomal en-tities within starter cells. Many of the vital starterfunctions are encoded on plasmid DNA. During celldivision, extrachromosomal DNA replicate in syn-chrony with the chromosomal DNA. But, errors dur-ing replication occur more frequently in plasmids.And, failures in the transfer of plasmids to daugh-ter cells are also more frequent. This phenomenonis often referred to as “plasmid loss.” Loss of plas-mids in starter cells results in loss of specific starterfunctions. Loss of plasmids among Lactococcus spp.is quite prevalent. Repeated transfer of starter cul-tures, sudden thermal shocking during propagation,or exposure to overacidic environment increases thefrequency of plasmid loss in lactococcal starters.

Lactose utilization (Lac+) is one of the plasmid-encoded traits in dairy lactococci. The loss of Lac-plasmid results in the inability of the strain toefficiently ferment lactose. Such a phenotype is des-ignated as Lac−. Another important plasmid-encodedtrait is the ability to break down protein(s). This traitis designated as Prt+. Proteolytic ability is closelylinked with efficient lactose utilization. Milk con-tains only traces of free amino acids. To synthesizeenzymes involved in lactose utilization, free amino


acids are needed. Breakdown of milk proteins wouldyield the necessary amino acids for synthesizing theneeded enzymes for lactose fermentation. So thePrt+ phenotype is critical for lactose fermentation.In short, for efficient acid production in milk or dairymixes, Lac+/Prt+ phenotype is mandatory.

Another important functional trait that is plasmid-encoded is the transport of citrate into the cell. Cit-rate present in milk and dairy mixes is converted bycitrate-utilizing lactococci to diacetyl, which is thekey flavor component in cultured dairy products suchas cultured buttermilk and sour cream. The citrate inthe environment first has to be transported into thecells before it can be converted into diacetyl. Cit-rate transport is mediated by the enzyme citrate per-mease. Cells possessing active citrate permease, andhence capable of citrate conversion to flavor com-pounds, are designated Cit+. The loss of Cit-plasmidrenders the cell Cit–, which is incapable of diacetylproduction.

Some of the genes connected with EPS synthesis indairy lactococci are plasmid-encoded. So EPS pro-duction is an unstable trait in those bacteria. Also,efficient EPS synthesis in LAB is favored at tem-peratures lower than optimum for growth. Loss ofplasmids encoding some of the genetic informationfor EPS synthesis results in the inability to producethe viscosity and “ropiness” desired in specific cul-tured dairy products, where lactococcal starters areused. The entire genetic material that codes for EPSproduction in lactococci has been unraveled. And,genetic probes to identify EPS-producing lactococcihave been described.

Among the dairy lactococci, the production ofwide-spectrum bacteriocins known as lactacins isplasmid-encoded. The genes for another broad-spectrum bacteriocin, nisin, are encoded on a transpo-son, a highly mobile genetic element. The loss of suchextrachromosomal elements throws up cells inca-pable of producing bacteriocins that inhibit spoilage(spore-forming bacteria) and pathogenic bacteria(clostridia and Listeria monocytogenes).

In certain LAB strains used in dairy starters (Lac-tococcus subsp. and Streptococcus thermophilus),mechanisms that provide resistance to destruction byphages are encoded on plasmids and on a transposon.The loss of those transient genetic elements makesthose cells vulnerable to phages.

Other intrinsic factors that affect starter perfor-mance may be categorized under the heading physio-logical condition or state of the starter bacteria. Thephysiological state or condition of starter bacteria

depends upon how the culture was propagated, han-dled, and preserved. Many of the enzyme systemsvital in acid and flavor production are inducible.

Enzyme induction is a control mechanism that op-erates at the genetic level. An inducible enzyme isexpressed only when the specific substrate is present.Enzymes that cleave lactose among starter LAB(�-galactosidase and phospho-�-galactose galacto-hydrolase) are inducible. Starter bacteria that havebeen propagated in the absence of lactose (using sug-ars like glucose) when added to milk have to un-dergo an adaptive lag for induction. In other words,the cells are not “primed up” to use lactose. Citratepermease involved in flavor production is induciblein both citrate-fermenting Lactococcus lactis subsp.lactis and Leuconostoc cremoris. The enzyme thatcleaves citrate leading to diacetyl production is in-ducible in Leuconostoc cremoris. Thus, for efficientflavor generation, starter cultures need to be prop-agated with the inducer (citrate) in the propagationmedium.

Lack of essential factors in propagation mediumsignificantly affects cellular integrity of certainstarter LAB. A good example is Lactobacillus del-brueckii subsp. bulgaricus (hereto referred to as Lac-tobacillus bulgaricus for convenience). Availabilityof Ca++ in the propagation medium affects the in-tegrity of the cell walls of those bacteria; Lb. bulgar-icus cultures propagated in media lacking free Ca++

display distorted cell morphology, and fragility to cellharvesting and preservative processes.

In commercial production of starter cultures, thestarter strains are grown in a relatively clear mediumor one that contains low, undissolved suspendedsolids. Dairy starter cultures that need to function inmilk should preferably be grown in milk containingmedium with lactose as the carbon source. Exces-sive use of protein hydrolysates should be avoided.Inclusion of milk as the nitrogen source and lactoseas the carbon and energy source in the propagationmedium exerts a “selective pressure” to obtain an ac-tive cell crop. The choice of the neutralizing agentduring starter propagation is another factor in obtain-ing the best cell crop. The optimum neutralizer varieswith different strains. Because of the convenience andamenability to electronically controlled addition, am-monia gas is generally preferred as the neutralizer ofchoice by commercial culture manufacturers.

At the end of propagation, the cells are harvested.Harvesting could be achieved either by centrifu-gal separation or by filtration using ultrafiltrationequipment (ceramic filters that could be efficiently


sterilized are preferred). Harvested cell concentratesmay then be frozen in cups or in bead-like, pel-letilized form. Suitable cryoprotectants are addedbefore freezing. An alternative to freezing is freeze-drying or lyophilization. Proper selection of cryopro-tectants is important to prevent cell injury, damage,or loss of viability. The method of freezing also af-fects cell viability and damage. Rapid rate of freez-ing is preferable. Use of liquid nitrogen or dry ice ordry ice-alcohol bath as cryogenic agents gives bettercell integrity than freezing at –20◦C (in a mechanicalfreezer). Proper freeze-drying conditions have to beworked out for different starter organisms, and “pro-grammed” into commercial freeze dryers. Generally,the rod-shaped LAB (Lactobacillus spp.) are moresensitive to the production processes than the spheri-cal LAB (Lactococcus and Streptococcus spp.) usedas starters. All the factors discussed in the forego-ing paragraphs have significant influence on starterperformance.

Extrinsic Factors

Extrinsic factors come into play during applicationof starter cultures or in the preparation of starter cul-tures in the dairy plant. The same principles govern-ing the “physiological condition” of the starter cellsdiscussed for commercial production apply for thepreparation of the starter in the dairy plant. Further,commercial cultures could be damaged by improperhandling in the dairy plant. At receipt, frozen culturesshould be carefully examined whether during transitany thawing had taken place. If partial or completethawing had occurred, the cultures should be dis-carded. Till use frozen cultures need to be stored at–40◦C. An ice cream hardening room would also suf-fice. If the frozen cultures go through freeze-thaw cy-cles, the starter bacteria will be severely damaged. Itis beneficial to store freeze-dried cultures in a freezerto keep the cells active.

Fast thawing of frozen cultures just before usein lightly chlorinated warm water at 35◦C is advis-able. Thawing frozen cultures in a refrigerator causescell damage. Proper conditions for rehydration oflyophilized (temperature and rehydration menstrum)cultures assure maximum cell viability, and recov-ery of injured cells. The rehydration processes fordifferent strains vary, and should be determined foreach culture combination in consultation with the cul-ture supplier. For optimal performance of starters, thesooner the culture is used after thawing or rehydrationthe better the results.

When bulk starters are made in the plant, propertemperature control, close monitoring of acidity, andprompt and efficient cooling of the starter at the end-point are critical in avoiding cell injury and assuringhigh performance in the product vat. All the abovefactors that are encountered in the dairy plant, theactual site of application, relate to the physiologicalcondition of the starter bacteria (the innate proper-ties of starter cells) at the time they are added to theproduct vat. In the strict sense of the term, they arenot true extrinsic factors.

The extrinsic factors in the real sense of the term re-late to external influences, as opposed to innate prop-erties of starter cells. The external factors includepresence of antibiotics in milk or dairy mix, pres-ence of fairly high sanitizer residues, presence of highproportions of agglutinins (colostrum or early lacta-tion milk), and infection with phage. Antibiotics areused in treating udder infections like mastitis. Some-times because of improper adherence to regulatorymandates, antibiotic-tainted milk finds its way intopooled milk. S. thermophilus is extremely sensitiveto antibiotics. Although not as sensitive as S. ther-mophilus, the dairy lactococci and starter lactobacilliare functionally impaired in the presence of antibi-otics used for mastitis therapy. Excessive or improperuse of sanitizers affects starter performance. Certainsanitizers like quaternary ammonium compounds arenot dissipated easily, and could remain in active formin the vat milk. These residues would inhibit starters.

Agglutinins are antibodies produced by the de-fense mechanisms of cells in response to infections.Mastitic milk contains high titer of agglutinins. Toprotect young suckling calves against infection, theearly mammary secretion called colostrum containshigh titers of antibodies including agglutinins. Manystarter lactococcal strains are susceptible to clumping(reduction of surface area) by agglutinins, and theiracid-generating function is severely affected by thepresence of these antibodies in the vat milk.

Phages constitute the most insidious agent affect-ing starter function. The consequences of phage in-fection of starter bacteria in dairy fermentations werediscussed earlier. Phages in terms of host relation-ships are of two types, namely, virulent or lytic, whichdestroy host cells, and temperate or prophage or lyso-genic, which normally exist in benign relationshipwithin the host cell. Sometimes, the prophage couldbe “induced” (either spontaneously or by externalagents like ultraviolet radiation or chemical agents)into the virulent form. Prophages may exist as an in-dependent DNA element in the cytoplasm of the host


cell or attached to the host chromosome. Lysogenicphages could sometimes act as vectors for genetic ex-change between closely related bacteria by a mech-anism called “transduction.” Such lysogenic phagesare called “transducing phages.” All these types ofphages are found in starter LAB.

Phages are tadpole-shaped particles. They have adefinite head, which in some cases are symmetrical(isometric) and in others elongated (prolate) isoco-hederal structures, attached to a tail. The DNA of thephage is enclosed within the head. The tail differsin length and is a hollow structure. The tail may bestriated, and may be rigid or contractile. The tail maypossess a tail plate, and spikes at its extremity. Lacto-coccal phages have rigid tails. The nuclear materialof the phages infecting starter LAB is composed ofDNA. The head and the tail of phages are made up ofprotein. Generally, phages have host specificity, butphages crossing species boundaries are known.

During the infective cycle, the phages attach tospecific receptor sites of the host cells, and in thepresence of Ca++ form an irreversible bond with thehost cell creating a channel to the interior of the cell.The phage DNA is expelled by the contraction ofthe head, and the DNA travels through the channelin the tail and is delivered to the interior of the hostcell. The host receptor sites in most cases are com-posed of carbohydrate entities, rhamnose being themost prevalent, and in one case the attachment (alsocalled adsorption) is dependent upon a chromoso-mally encoded protein embedded in the cell mem-brane. Soon after the entry of the phage DNA, thehost cell chromosome is degraded, and the host syn-thetic mechanisms are used in phage DNA replica-tion followed by components making up the phageprotein-coat. The assembly of the phage occurs instages till the entire (mature) phage particle is com-pleted. When a genetically determined number ofphage particles are assembled, through the concertedaction of two enzymes, holin and lysin, the host cellwall is breached, and the phage particles spill outto the surrounding environment. The genetically de-termined number of particles released from the hostcell is called the burst size. The time lag between theentry of the phage DNA into the host cell and therelease of mature phage particles from the host cellsis called the eclipse period. Among dairy lactococci,the burst size is around 200 particles. As the cyclecontinues unabated, the phage numbers (or titer) in-crease exponentially with concomitant destruction ofhost cells. When the phage titer reaches to high levels,the level of lysin also increases considerably in the

environment. Lysin is a nonspecific enzyme thatcleaves cell walls of closely related bacteria. Highlevels of lysin could destroy phage-unrelated com-ponent strains in starter mixtures by cell lysis. Thisphenomenon is often referred to as “lysis fromwithout.”

In dairy fermentations, a phage titer of 1.0 ×105 per milliliter is considered detrimental to theprocess. Considerable research has been devoted tophages infecting dairy lactococci. The informationon phages infecting yogurt starter bacteria has alsobeen accumulating rapidly over the past decade. Withthe advent of modern molecular techniques, phagesare classified on the basis of DNA homology. Cur-rently, phages are divided into 10 species under fam-ilies Siphoviridae and Podoviridae. Phages affectinglactococci used in cultured buttermilk and sour creamplants in the United States have been extensively sur-veyed. A large majority of phages isolated from prod-uct samples were grouped into 936 species. Othergroups found in these samples belonged to c2 andP355 species. The prevalence of P355 species wassparse. Phage species P355 is a relatively new phagethat has emerged in cultured dairy product plants,and is considered as a serious threat to dairy fer-mentations, because of its ability to rapidly evolveinto new, resistant types by genetic exchange. Phageslacking lytic ability but possessing mechanisms to de-polymerize EPS produced by lactococci have beenisolated from cultured buttermilk and sour creamsamples in the United States. A phage with similar ac-tivity, KSY 1, has been isolated from Viili in Finland.Phage KSY 1 falls under the family Podoviridae.

Phages affecting S. thermophilus possess isometricheads and long noncontractile tails. All those phagesare grouped under the family Siphoviridae. The vir-ulent phages fall into one DNA homology group.Lysogenic relationships among S. thermophilus arequite complex. Phages affecting Lb. bulgaricus anddairy leuconostocs have been isolated. The leuconos-toc phages have isometric heads and noncontractiletails with distinct tail plates.

Phage control in dairy plants involves separationof the starter room from other manufacturing areas,having a separate crew for starter room duties, pro-vision of air locks between the starter room and therest of the plant, provision for separate locker roomsand uniforms for starter room workers, provision offootbaths containing sanitizers at the entrance to thestarter room, restricting the movement of plant per-sonnel from and to the starter room, maintenance ofpositive air pressure in the starter room, the use of


laminated air flow through microfilters (HEPA filters)in the starter room, preventing the dispersal of phageparticles via air-circulating systems, and other meansof physical containment necessary. Fogging the plantenvirons with 100 ppm chlorine at the end of opera-tions is also recommended.

Another practical means of controlling phages isusing phage inhibitory media (PIM) for propagatingstarter bacteria. PIM are carefully formulated nutri-ent media containing phosphates or other chelatingagents like citrates. Phosphates and citrates chelatefree Ca++ in the system, and thus prevent irreversiblephage adsorption to sensitive cells. The yogurt starterbacteria and Leuconostoc spp. do not grow well inPIM containing high levels of phosphates. For thesebacteria special formulations of PIM containing lowlevels of phosphates and other chelators like citrateand stimulants for cell growth are used. The lacto-cocci are relatively more tolerant of levels of phos-phate necessary to inhibit phage proliferation.

Culture rotation is another strategy used for phagecontrol in dairy plants. In this plan, starter strains withunrelated phage specificities are used in rotation dur-ing production week, so that the chances of buildupof phage titer for any one set of strains in the dairyplant are avoided. This strategy works well when usedin combination with other measures described ear-lier. Some workers have suggested rotating strainsselected on the basis of sensitivity to differing phagespecies and elimination of starter strains that are af-fected by the rapidly evolving P335 phage species inthe rotation scheme.

Over the past two decades, a new strategy has beenintroduced to confront phage-related problems. Thescheme comprises several steps. First, the phages ap-pearing in a dairy plant are monitored over a period oftime against a bank of active starter strains, and a bat-tery of strains resistant to the phages appearing in theplant is selected. Three to six of the resistant strainsare supplied as single units to be combined to makeup a mixed culture. A set of three such potential mix-tures are kept in reserve. One mixture is introduced inthe plant, and the cultured products made in the plantare monitored daily for the appearance of phages af-fecting any of the strains being used. If a phage isdetected for any strain in the mixture, that strain isremoved and a reserve strain is substituted. The strainthat was pulled out is challenged against the infectingphage isolated from the cultured product, and spon-taneous insensitive mutants that emerge are isolatedfrom a special plating medium (fast–slow differentialagar) and purified of any residual phage particles. The

insensitive mutant is introduced to make up the orig-inal mixture. The cycle is repeated as required. Thesuccess of the scheme depends on using only lim-ited number of carefully selected strains in produc-tion, and daily monitoring for phages. The schemehas been successfully used in cultured dairy productplants in the United States and in Ireland. The insen-sitive strains thus selected are generally composedof cells with phage adsorption site mutations. Thescheme has been successfully used with lactococciand S. thermophilus.

There are several innate phage-resistance mecha-nisms encoded in the genetic material of starter LAB.These mechanisms in dairy lactococci have beenstudied extensively. As mentioned earlier, manyof these resistance mechanisms are encoded onplasmids. Developments in molecular biology havefacilitated plasmid isolation, analysis, base sequencedeterminations, transfer of functional sequences be-tween lactococcal strains, and functional expressionof resistant traits in sensitive recipients. The knownresistance mechanisms include modification ofadsorption sites, restriction-modification, blockingof phage DNA penetration, and abortive infectionmechanisms. In adsorption modification, the phagereceptor sites are modified (by masking) such thatphage is unable to attach to the cell. In restriction-modification system (R/M) the incoming phageDNA is degraded by “restriction enzymes,” and madenonfunctional. To protect the host cell DNA frombeing chopped up by the restriction enzymes, “mod-ifying enzymes” are produced, which render the hostDNA invulnerable by methylation of the DNA sites.Modified methylated sites in the DNA are not recog-nized by the restriction enzymes. The restriction andmodification components in the R/M system work inconcert to confer phage resistance to the host. In theblockage of phage DNA penetration, a modificationof or a defect in a cell membrane embedded proteincalled phage infection protein (PIP) that facilitatesphage DNA penetration (PIP is encoded on a plasmidin some organisms and on the chromosome in someothers) confers resistance to the host. In abortiveinfection mechanism, the phage DNA replication orphage assembly is disrupted and hence no release ofmature particles occurs. In effect, the infecting phageis entrapped by the host cell. Plasmids conferringsome of the phage-resistance mechanisms havebeen transferred to sensitive strains, making themresistant through conjugation and electrotransforma-tion. Conjugation involves cell-to-cell contact andmobilization of DNA from a donor to a recipient.


Electrotransformation involves the introduction ofplasmid DNA into recipient cells by facilitating thepenetration of DNA via pores created in the recipientcells by short high-voltage electric pulse. Commer-cially viable and successful phage-resistant starterstrains have been produced by using such techniques.

Similar phage-resistant systems have been foundamong other starter LAB. Plasmid conferring R/M-related phage resistance from a Lactococcus strainwhen introduced into a S. thermophilus strain wasfunctional in conferring resistance to the heterolo-gous recipient against phage lytic for that S. ther-mophilus strain. Recently S. thermophilus plasmidshave revealed DNA sequences closely homologous toR/M sequences found in lactococci. This observationsuggests that during the evolution of these closely re-lated bacteria, there has been horizontal transfer ofgenetic material between these bacteria.

Miscellaneous Factors

There are a couple of other factors that affect cultureperformance, which could be considered under thisheading. These factors in reality are intrinsic to starterorganisms, but come into play only when the strainsare combined for use in fermentations. One such fac-tor is compatibility. The component strains in a mixedculture should be compatible with one another tofunction in concert. Some lactococcal strains pro-duce bacteriocins called lactococcins that kill otherlactococci, and are thus incompatible for use in mix-tures. Similar antagonistic activity occurs amongother LAB too. When such strains are used in mixturesconsisting of phage-unrelated strains with the intentto ensure unmitigated progress of dairy fermentation(so that if phages for one or two strains are presentin the dairy environment, the other phage-unrelatedstrains could function unimpaired), the strategy fails,because if a phage infecting the dominant or onlysurviving antagonistic strain is present in the sys-tem, there are no other surviving strains to carry outthe function to completion. Another bacteriocin pro-duced by certain strains of Lactococcus lactis subsp.cremoris called diplococcin specifically kills L. lac-tis subsp. lactis strains. Dominance among starterLAB because of other inherent factors (for example,metabolic efficiency, faster growth rate, etc.) is alsoknown. So, careful selection and pairing or mixingof strains is important.

Another factor that affects culture performance re-lates directly to yogurt starters. Yogurt starters con-sist of symbiotic mixture(s) of S. thermophilus and

Lb. bulgaricus. Symbiosis is a cooperative relation-ship, where one organism stimulates or promotes thegrowth and activity of another. The functional ef-ficiency is much greater when the symbiotic com-ponents operate together than when acting singly.There are strain differences in symbiotic compati-bility. Strain selection and pairing for yogurt startersis thus directly related to culture performance.

MICROORGANISMS USED INSTARTERS FOR CULTUREDDAIRY PRODUCTSMicroorganisms used in starters for cultured dairyproducts are divided into two types based on thetemperature ranges at which they operate well. LABused in products that are incubated in the tempera-ture range of 20–30◦C are referred to as mesophilicstarter bacteria, and those that are used in productsthat are fermented above 35◦C are referred to as ther-mophilic starter bacteria. The latter term is scientifi-cally erroneous, because thermophilic bacteria growoptimally above 50◦C, and the organisms comprisingthermophilic starters do not fit that definition. Theseorganisms should be more appropriately labeled asthermotolerant starters.

In addition to the two types of starters discussedabove, there are other groupings for starter cultures,which are used in Europe. Cultures composed ex-clusively of L. lactis subspp. lactis and cremoris areknown as “O” type cultures; those that contain in ad-dition to the acid-producing lactis and cremoris sub-species strain(s) of Cit+ L. lactis subsp. lactis (flavorproducer) are called “D” type cultures; cultures con-taining a combination of acid-producing lactis andcremoris subspecies and dairy Leuconostoc spp. arereferred to as type “L” or “B” type cultures (referringto Betococcus, a former nomenclature for Leuconos-toc bacteria); and, cultures containing lactis and cre-moris subspecies plus Cit+ L. lactis subsp. lactis andLeuconostoc spp. are known as “LD” or “BD” types.In Holland, a different appellation is used for mixedstrain starters.

Those that are propagated under aseptic conditionsin the laboratory or the dairy plant are labeled “L”type (letter L standing for “laboratory”). And, thosein contrast propagated under nonaseptic conditions(i.e., without any precautions) to exclude phages inthe environment in the dairy plant are called “P” type(letter P standing for “practice”). The P-type startersare used with good success under factory conditions,without phage-related failures. These cultures being


constantly exposed to phages prevalent in the fac-tory environment serve to exert selective pressure tonaturally develop phage-resistant derivatives of thestrains present in the culture. There is a complex dy-namic operating in that system between the starterstrains and the “disturbing phages” and the evolutionof resistant starter strains, which keeps the starterperforming satisfactorily. The L-type cultures, onthe other hand, are readily labile to phage-relatedfailures.

Another category that has come into recognitionrecently is artisanal or natural starters. These startersare composed of a mixture of undefined starter bac-teria, which have been carried according to the tradi-tional practice of using a small portion of the previ-ous batch of fermented products to seed a new batch.This is often referred to as “back slopping.” Arti-sanal starters are still used in small-scale, cottage, orfarm operations in Europe. A similar system is foundin small-scale production of dahi in South Asiancountries.

Other arbitrary groupings of cultures are basedupon the composition of starters. Starters that are car-ried in mixtures made of strains that have not beenfully characterized with respect to acid-producingabilities, phage susceptibility, etc. are lumped un-der the grouping “undefined mixed-strain starters.”Starters made up of well-characterized strains (whichcould be maintained as either separate entities oras a mixture) are called “defined-strain mixed cul-tures.” The latter came into prominence with the de-velopment of phage-insensitive replacement strategyto overcome phage-related problems in dairy plants.Defined-strain mixed cultures have been used verysuccessfully in New Zealand in large dairy plants.

Mesophilic starter bacteria consist of dairy L. lac-tis subspecies and dairy Leuconostoc spp. Citrate-fermenting L. lactis subsp. lactis is often referred toas L. lactis subsp. lactis biovar. diacetylactis in theliterature. The other subspecies are L. lactis subspp.cremoris and lactis. The Leuconostoc bacteria gen-erally used in dairy fermentations in association withlactococci are Leuconostoc lactis and Leuconostocmesenteroides subsp. cremoris.

Thermotolerant starters used for dairy fermenta-tions consist of S. thermophilus and Lactobacillusspp. Among the lactobacilli two subspecies of Lac-tobacillus delbrueckii, namely, bulgaricus and lac-tis, are most widely used for cultured milk products.Lactobacillus acidophilus, Lactobacillus helveticus,and Lactobacillus casei subsp. casei are other lacto-bacilli used in fermented dairy milks in association

with other specific microflora. Yogurt by definitionis the fermented dairy product produced by culturingwith a starter made up of S. thermophilus and Lb.bulgaricus, and should contain viable cells of bothbacteria till the end of the shelf life of the product.

In Table 6.1, the microorganisms used as startersfor some of the major cultured dairy products con-sumed in the West, Eastern Europe, and the Far Eastare listed under the column “Primary Microorgan-isms.”

In the production of dahi, the mesophilic lacto-cocci, and in some instances leuconostocs, are usedas starter flora. For detailed information on starterflora for many of the fermented products discussedin this book, the individual chapters should be con-sulted. Some of the physiological and biochemicalcharacteristics of starter bacteria are summarized inTables 6.2 and 6.3.

Genus LACTOCOCCUS

Genus Lactococcus is a relatively new taxonomicgrouping. Five species were hived off the larger genusStreptococcus to make up genus Lactococcus. Onlyone species of genus Lactococcus (L. lactis) is usedin dairy fermentations. Current taxonomic groupingsrely on phenotypical, biochemical, and molecularcharacteristics of the organisms. The two subspeciesof L. lactis, namely lactis and cremoris, with a biova-riety of subspecies lactis, Cit+ or diacetylactis, for-merly were included in the lactic group of Sherman.The distinguishing characteristics of the organismsplaced in various groups by Sherman are shown inTable 6.4.

Lancefield grouped the organisms included in theformer large genus Streptococcus on the basis ofserology of their cell-wall carbohydrates. The or-ganisms within Sherman’s lactic group fell underLancefield’s group N. When the dairy lactococci wereclassified within the genus Streptococcus, they wentthrough several changes. At one time, Lactococcussubspecies, lactis and cremoris, had full species sta-tus within genus Streptococcus (Streptococcus lactisand Streptococcus cremoris). And so did the currentCit+ biovariety (Streptococcus diacetylactis). Vari-ations in the spelling for the Cit+ biovariety alsofeatured in taxonomic changes (diactilactis versusdiacetylactis). Later in further changes within genusStreptococcus, the full species status for lactis andcremoris was modified to the subspecies level. Thedifferentiating characteristics of the dairy lactococciare summarized in Table 6.5.

Table 6.1. Microorganisms Used in Starter Cultures for Cultured Dairy Products and TheirFunctions.

IncubationPrimary Secondary/Optional Temperature Major Function

Product Microorganism(s) Microorganism(s) and Time of Culture

Yogurt Lactobacillus delbrueckii subsp.bulgaricus

Streptococcus sulvarius subsp.thermophilus

Lactobacillusacidophilus

Bifidobacterim longum/bifdus/infantis

43–45◦C/2.5 hours

Acidity, texture,aroma, flavor,probiotic

Lactobacillus casei/lactis/jugurti/helveticus

Culturedbuttermilkand sourcream

Lactococcus lactis subsp. lactisLactococcus lactis subsp.

cremorisLactococcus lactis subsp. lactis

var. diacetylactis

Leuconostoc lactisLeuconostoc

mesenteroidessubsp. cremoris

22◦C/12–14 hours

Acidity, flavor,aroma

Fermentedmilk

Streptococcus sulvarius subsp.thermophilus

Leuconostoc lactissubsp. lactis/cremoris

23–37◦C/8–14 hours

Acidity, flavor,probiotic

Lactobacillus acidophilusBifidobacterim longum/bifdus

Acidophilusmilk

Lactobacillus acidophilus 37–40◦C/16–18 hours

Acidity,probiotic

Bulgarianbuttermilk

Lactobacillus delbrueckii subsp.bulgaricus

37–40◦C/8–12 hours

Acidity,probiotic

Kefir Lactococcus lactis subsp.lactis/cremoris

Lactobacillus delbrueckii subsp.bulgaricus

Lactobacillus delbrueckii subsp.lactis

15–22◦C/24–36 hours

Acidity, aroma,flavor, gas(CO2),alcohol,probiotic

Lactobacillus casei/helveticus/brevis/kefir

Leuconostoc mesenteroides/dextranicum

Yeasts:Kluyveromyces marxianus

subsp. marxianusTorulaspoa delbrueckiiSaccharomyces cerevisiaeCandida kefir

Acetic acid bacteria:Acetobacter aceti

Koumiss Lactobacillus delbrueckii subsp.bulgaricus

Lactobacillus kefir/lactis

Yeasts:Saccharomyces lactisSaccharomyces cartilaginosusMycoderma spp.

20–25◦C/12–24 hours

Acidity, alcohol,flavor, gas(CO2)

Acetic acid bacteria:Acetobacter aceti

Yakult Lactobacillus casei 30–37◦C/16–18 hours

Acidity,probiotic

Source: Reproduced with permission from Chandan RC, Shahani KM. 1995. Other fermented dairy products. In: H-J Rhem, GReed (Eds), Biotechnology, Vol. 9. Wiley-VCH, Hoboken, NJ, pp. 390–391.

100

Tab

le6.

2.C

hara

cter

istic

sof

Mes

ophi

licS

tart

erB

acte

riaU

sed

for

Cul

ture

dD

airy

Pro

duct

s

Lac

toco

ccus

lact

isL

euco

nost

ocL

euco

nost

ocL

acto

cocc

usL

acto

cocc

ussu

bsp.

lact

isbi

ovar

.m

esen

tero

ides

mes

ente

roid

esC

hara

cter

istic

lact

issu

bsp.

lact

isla

ctis

subs

p.cr

emor

isdi

acet

ylac

tis

subs

p.cr

emor

issu

bsp.

dext

rani

cum

Cel

lsha

pean

dco

nfigu

ratio

nC

occi

,pai

rs,

shor

tcha

ins

Coc

ci,p

airs

,sh

ort/l

ong

chai

nsC

occi

,pai

rs,s

hort

chai

nsC

occi

,pai

rs,

shor

t/lon

gch

ains

Coc

ci,p

airs

,cha

ins

Cat

alas

ere

actio

n−

−−

−−

Gro

wth

tem

pera

ture

(◦ C)

Opt

imum

28–3

122

2820

–25

20–2

5M

inim

um8–

108–

108–

104–

104–

10M

axim

um40

37–3

940

3737

Incu

batio

nte

mpe

ratu

re(◦ C

)21

–30

22–3

022

–28

2222

Hea

ttol

eran

ce(6

0◦ C/3

0m

inut

es)

∀∀

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actic

acid

isom

ers

L(+

)L

(+)

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)D

(−)

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)L

actic

acid

prod

uced

inm

ilk(%

)0.

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00.

8–1.

00.

8–1.

00.

1–0.

30.

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3A

cetic

acid

prod

uctio

n(%

)−

−−

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0.4

0.2–

0.4

Gas

(CO

2)

prod

uctio

n−

−+

∀∀

Prot

eoly

ticac

tivity

++

+∀

∀L

ipol

ytic

activ

ity∀

∀∀

∀∀

Citr

ate

ferm

enta

tion

−−

++

+Fl

avor

/aro

ma

com

poun

d+

++

++

++

++

++

Muc

opol

ysac

char

ide

prod

uctio

n∀

∀∀

No

dext

ran

from

sucr

ose

Dex

tran

from

sucr

ose

Hyd

roge

npe

roxi

depr

oduc

tion

++

+∀

∀A

lcoh

olpr

oduc

tion

∀∀

∀∀

∀Sa

ltto

lera

nce

(%m

ax)

4–6.

54.

04–

6.5

6.5

6.5

Not

e:+

=Po

sitiv

efo

rth

etr

ait(

num

ber

ofsy

mbo

lsre

pres

entd

egre

eof

expr

essi

on);

−=

Neg

ativ

efo

rth

etr

ait;

∀=V

aria

ble

for

the

trai

t.So

urce

:R

epro

duce

dw

ithpe

rmis

sion

from

Cha

ndan

RC

,Sh

ahan

iK

M.

1995

.O

ther

ferm

ente

dda

iry

prod

ucts

.In

:H

-JR

hem

,G

Ree

d(E

ds),

Bio

tech

nolo

gy,

Vol

.9,

Wile

y-V

CH

,H

obok

en,N

J,p.

396.

101

Tab

le6.

3.C

hara

cter

istic

sof

The

rmot

oler

antS

tart

erB

acte

riaU

sed

for

Cul

ture

dD

airy

Pro

duct

s

Lac

toba

cill

usL

acto

baci

llus

Stre

ptoc

occu

sde

lbru

ecki

isub

sp.

delb

ruec

kii

Lac

toba

cill

usL

acto

baci

llus

Cha

ract

eris

ticth

erm

ophi

lus

bulg

aric

ussu

bsp.

lact

isac

idop

hilu

sca

seis

ubsp

.cas

ei

Cel

lsha

pean

dco

nfigu

ratio

nSp

heri

calt

oov

oid,

pair

sto

long

chai

ns

Rod

sw

ithro

und

ends

,si

ngle

,sho

rtch

ains

,m

etac

hrom

atic

gran

ules

Rod

sw

ithro

und

ends

,m

etac

hrom

atic

gran

ules

Rod

sw

ithro

und

ends

,pa

irs,

shor

tcha

ins,

nom

etac

hrom

atic

gran

ules

Rod

sw

ithsq

uare

ends

,sho

rt/lo

ngch

ains

Cat

alas

ere

actio

n−

−−

−−

Gro

wth

tem

pera

ture

(◦ C)

Opt

imum

40–4

540

–45

40–4

537

37M

inim

um20

2222

20–2

215

–20

Max

imum

5052

5245

–48

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5In

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tion

tem

pera

ture

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40–4

542

40–4

537

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oler

ance

(60◦ C

/30

min

utes

)++

++

−−

Lac

ticac

idis

omer

sL

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)D

(−)

DL

L(+

)L

actic

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prod

uced

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01.

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01.

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cetic

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race

Tra

ceT

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++

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(CO

2)

prod

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n−

−−

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Prot

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ticac

tivity

∀+

+∀

∀L

ipol

ytic

activ

ity∀

∀∀

∀∀

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ate

ferm

enta

tion

−−

−−

−Fl

avor

/aro

ma

com

poun

d++

+++

+∀

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opol

ysac

char

ide

prod

uctio

n∀

++−

−∀

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roge

npe

roxi

depr

oduc

tion

∀+

++

+A

lcoh

olpr

oduc

tion

−T

race

Tra

ceT

race

Tra

ceSa

ltto

lera

nce

(%m

ax)

2.0

2.0

2.0

6.5

2.0

Not

e:+

=Po

sitiv

efo

rth

etr

ait(

num

ber

ofsy

mbo

lsre

pres

entd

egre

eof

expr

essi

on);

−=

Neg

ativ

efo

rth

etr

ait;

∀=V

aria

ble

for

the

trai

t.So

urce

:R

epro

duce

dw

ithpe

rmis

sion

from

Cha

ndan

RC

,Sh

ahan

iK

M.

1995

.O

ther

ferm

ente

dda

iry

prod

ucts

.In

:H

-JR

hem

,G

Ree

d(E

ds),

Bio

tech

nolo

gy,

Vol

.9.

Wile

y-V

CH

,H

obok

en,N

J,p.

397.

102


Table 6.4. Sherman’s Grouping of Bacteria Comprising the Former Genus Streptococcus

Growth At

Groups 10◦C 45◦C Hemolysis Bacteria

Pyogenic − − Beta Pathogenic StreptococciVaridans − + Alpha S. bovis, S. equi, S. thermophilusLactic + − Gamma Dairy StreptococciEnterococcus + + Alpha, Beta Enteric StreptococciNote: + = Positive for the trait (number of symbols represent degree of expression); − = Negative for the trait.

Recently, a new differentiating physiological char-acteristic between lactis and cremoris subspecies hasbeen reported. Organisms belonging to lactis sub-species are capable of decarboxylating glutamate,while cremoris subspecies lack that property.

Lactococci are morphologically spherical cells.The cells, however, are not round but oblong. Thecells occur in short chains, but most commonly aspairs. Single cells also could be found. Some strains,especially those susceptible to agglutinins found inmilk, exhibit long chains. Lactococci are Gram-positive. They are microaerophilic, lack catalase, andare fermentative. L. lactis subspp. lactis and cremorisare homofermentative.

Lactose Fermentation in Lactococci

The lactococci possess a unique, multicomponenttransport system to ferry lactose into the cells,called the phosphoenolpyruvate–phosphotransferasesystem (PEP-PTS). In this system, phosphoenolpyruvate plays a crucial role in phosphorylating lac-tose at the sixth carbon of galactose moiety of thedisaccharide. The lactose phosphate is cleaved intoglucose and galactose-6-phosphate by the enzymephosphogalactoside galactohydrolase (P-�-gal). Thephosphorylated galactose is suitably modified viathe tagatose pathway to feed into the major path-way(s) of carbohydrate metabolism. There are a fewunique lactococcal strains that transport lactose via

Table 6.5. Differentiating Characteristics for the Dairy Lactococci

Growth At

Subspecies 41◦C 4% salt Arginine Hydrolysis Citrate Utilization

lactis + + + −lactis biovar. diacetylactis + + +/− +cremoris − − − −Note: + = Positive for the trait (number of symbols represent degree of expression); − = Negative for the trait.

the �-galactoside permease. The lactose that is con-veyed into the cell is split into glucose and galactoseby the enzyme �-galactosidase (�-gal). Galactoseis modified through the Leloir pathway for feedinginto major pathway(s) of carbohydrate metabolism.Homofermentative lactococci metabolize carbohy-drates through the hexose monophosphate pathway(HMP or EMP). Figure 6.1 depicts the homofer-mentative pathway for lactose metabolism amonglactococci.

Under normal fermentative conditions, homolacticfermentation is dominant in lactococci. Low levels ofenzymes operative in heterolactic fermentation, how-ever, have been detected in lactococci. Under certainconditions, for example aeration, the eclipsed het-erolactic pathway enzymes in lactococci are also ex-pressed, giving rise to mixed end products.

Citrate Metabolism in Lactococci

Citrate metabolism by Cit+ lactococci plays a sig-nificant part in flavor generation in cultured dairyproducts. Some of the features of citrate utiliza-tion by starter bacteria were discussed earlier. Cit-rate is translocated into the cells by citrate permease,which is optimally active at slightly acidic conditions(<pH 6.0). Citrate metabolic pathway in mesophilicstarter bacteria is shown in Figure 6.2.

Pyruvate plays a central role in carbon metabolism.As seen in Figures 6.1 and 6.2, metabolism of lactose

Lactose Lactose

1

3

5

4

2

67 8

910

11

12

13

NAD+

NADH

NAD+

NADH

14

Pi

16

17

1819

20

15

Lactose-P

GlucoseGalactose

LeloirPathway

TagatosePathway

Galactose-1-P

Glucose-1-PGlucose-6-P

Fructose-6-P

Fructose-1,6-diP

ATPHPr-P

HPr

HPr-P

HPr

ADP

ATP

ADP

ATP

ADP

ATP

ADP

ATP

ADP

ATP

ADP

Galactose-6-P

Tagatose-6-P

Tagatose-1,6-diP

Dihydroxyacetone-P Glyceraldehyde-3-P

1,3-Diphosphoglycerate

3-Phosphoglycerate

2-Phosphoglycerate

Phosphoenolpyruvate

Pyruvate

L-Lactate

Figure 6.1. Embden-Meyerhoff -parnas pathway for lactose metabolism among homofermentative lactic acidbacteria. 1 = �-galactosidase, 2 = P-�-galactosidase, 3 = galactose 6-phosphate isomerase,4 = tagatose-6-phosphate kinase, 5 = tagatose-1,6-diphosphate aldolase, 6 = glucokinase, 7 = enzyme II,8 = galactokinase, 9 = glucose:galactose-1-phosphate uridyl transferase uridine diphosphate-glucose epimerase,10 = phosphoglucomutase, 11 = phosphogucose isomerase, 12 = phosphofructokinase,13 = fructose-1,6-diphosphate aldolase, 14 = triose phosphate dehydrogenase, 15 = phosphoglycerokinase,16 = phosphoglyceromutase, 17 = enolase, 18 = pyruvate kinase, 19 = enzyme I, 20 = lactate dehydrogenase.Adapted from Zourari et al., 1992; Cogan and Accolas, 1996; Hutkins, 2001; and Ray, 2004.

104


Citrate

Citrate lyaseAcetate

Oxaloacetate

Oxaloacetate decarboxylase

AcetylCoA

CoA

Acetaldehyde TPP

TPP

Diacetylsynthase

TPP

DiacetylDiacetyl reductase

Pyruvate

Acetolactate

Acetolactatesynthase

Acetolactatedecarboxylase

Acetoin

Acetoinreductase NAD(P)H NAD(P)H

NAD(P)

NAD(P)

2,3-Butane diol

CO2

CO2

CO2

Figure 6.2. Pathway for citrate metabolism amongstarter lactic acid bacteria. Adapted from Hutkins,2001, and Ray, 2004.

and citrate leads to the formation of pyruvate. Pyru-vate derived from lactose is converted into lacticacid to keep the cycle sustained by regeneration ofnicotinamide adenine diphosphate (NAD+). Whenthe intracellular level of pyruvate increases with ad-ditional accretion from citrate, the cell has to finda way to detoxify excess pyruvate. Detoxification isachieved by converting pyruvate to neutral C-4 com-pounds such as diacetyl and its reduced forms. Citratemetabolism does not yield bond energy, but servesin keeping the cellular oxidative–reductive power inbalance.

Diacetyl derived from citrate does not accumulateindefinitely. When the concentration of citrate fallsbelow a critical threshold, diacetyl is rapidly reducedto acetoin and further to 2,3-butanediol. The reduc-tion of diacetyl results in the loss of the characteristicnutmeat flavor of cultured dairy products. It is cru-cial that the desirable nutmeat flavor is conserved inthe cultured product. The reduction of diacetyl playsa physiological role in the regeneration of NAD+ tokeep the cycle operative. There are a few practicalsteps that could be taken to conserve diacetyl. Undernormal incubation temperatures used for productionof cultured buttermilk and sour cream (21–24◦C),the product should be cooled rapidly soon after the

titratable acidity of the product reaches 0.75–0.8%.At that level of acidity, the diacetyl concentration isat its peak. Rapid cooling will retard the reduction ofdiacetyl by the enzyme diacetyl reductase and con-serve the flavor. If a greater acidity (>0.8%) is desiredin the product, the rapid reduction of diacetyl couldbe arrested by initial fortification of the milk or dairymix with citrate (regulations allow addition of 0.15%citrate in cultured buttermilk and sour cream). Suffi-cient availability of citrate not only provides higherconcentration of precursor for diacetyl, but also actsas a damper against diacetyl reductase activity. An-other way to prevent the loss of diacetyl is to in-corporate air into the product, accompanied by rapidcooling once the acidity reaches 0.8%. This couldbe done by agitation. Cit+ lactococci possess a classof NAD—oxidases that facilitate the transfer of hy-drogens from NADH + H+ (reduced nicotinamideadenine dinucleotide) directly to oxygen (or air) withthe formation of nontoxic water and molecular oxy-gen as by-products. The reaction thus provides analternate route for the regeneration NAD+. The al-ternate regeneration mechanism thus spares diacetylfrom functioning as the hydrogen acceptor. The en-tire operation could be accomplished by simultane-ous cooling of the product with gentle agitation to


incorporate air. Agitation also helps in rapid heattransfer.

With the rapid strides in biochemical analyses, en-zyme assays, and molecular biology, strategies havebeen worked out for metabolic engineering of highdiacetyl-producing lactococci. A few successful ge-netic constructs with high potential have already beenmade. For information on these subjects, the readeris encouraged to consult references listed at the endof this chapter.

More is now known about the nature of EPS pro-duced by lactococci, the pathways involved in thesynthesis of EPS, and the genetic sequences that codefor EPS production. Some of these aspects are cov-ered under specific cultured products discussed else-where in this book. References provided at the end ofthis chapter should be consulted for greater details.

Comments on Cit + L. lactis subsp. lactis

Generally, citrate-metabolizing lactococci are slowacid producers. Most strains take longer than20–24 hours to form a firm coagulum in milk. Moststrains produce a lot of gas (CO2) in milk. They pro-duce a fairly high concentration of diacetyl in milk,but they also rapidly reduce diacetyl (have an activediacetyl reductase). They are capable of competingwell in the presence of rapid acid-generating(non-citrate-fermenting) lactococci. They, however,produce relatively high concentrations of acetalde-hyde, which skews the ratio of diacetyl and acetalde-hyde in favor of the aldehyde. This imparts an un-desirable “green apple flavor” to cultured buttermilkand sour cream. For this reason, they are not gener-ally preferred in starters for cultured buttermilk andsour cream.

Genus LEUCONOSTOC

Dairy leuconostocs constitute the secondary or as-sociated bacteria in mesophilic lactic acid starters.The function of leuconostocs in these starters is fla-vor generation. Leuconostocs in pure cultures in milkdo not bring about much change, and are generallyconsidered inert. In association with lactococci, how-ever, leuconostoc metabolize citrate present in milkto produce diacetyl. Dairy leuconostocs ferment lac-tose, but very slowly. Lactococci and leuconostocsact synergistically in generating diacetyl from citratefound in milk. For optimal activity of citrate perme-ase, acid environment is necessary. The lactococci,which rapidly ferment lactose in milk, facilitatethe uptake of citrate by leuconostocs. Leuconostocs

possess the enzymes necessary to ferment citrate todiacetyl, but the associated acid-producing lactococci(subspecies cremoris and Cit− lactis) lack these en-zymes. Thus, diacetyl generation by mesophilic lacticstarters represents coordinate or cooperative activityof lactococci and leuconostocs.

In selecting Leuconostoc strains for inclusion inmixed starters, functional compatibility with lac-tococci should be first determined. Otherwise, thecultures will fail to generate flavor in the culturedproduct. Leuconostocs lack the metabolic vigor oflactococci in milk, and to get good flavor generation,lower incubation temperature is necessary so that abalanced growth of both leuconostocs and lactococciis obtained.

The natural habitat of leuconostocs, like the lac-tococci, is vegetable matter containing fermentablesugars. They are introduced in dairy environs fromthe green pasture and via fodder fed to the cows.Morphologically, leuconostocs are spherical cells oc-curring in long chains. They are Gram-positive bac-teria, and display unusual resistance to fairly highconcentration (about 500 �g/ml) vancomycin, anantibiotic. Leuconostocs are heterofermentative andproduce D-lactic acid. They are like other LAB,catalase-negative. The citrate metabolic pathway inleuconostocs is the same as that for Cit+ lactococci(Fig. 6.2). The heterofermentative dissimilation ofsugar by leuconostocs through the phosphoketolasepathway (PK) is shown in Figure 6.3. Lactose is trans-ported in leuconostocs by �-galactoside permease,and the disaccharide is cleaved into its hexose unitsby �-galactosidase.

Genus STREPTOCOCCUS

Streptococcus thermophilus is the only species in thegenus that is used in dairy starter cultures. The or-ganism is thermotolerant, and is used in dairy fer-mentations that require a little higher temperature forincubation and processing (incubation at 35–43◦C;processing or cooking of certain cheese in the tem-perature range of 48–53◦C). Young cells of S. ther-mophilus are spherical in shape and occur in chains.Older cultures or colonial growth on solid media of-ten display altered morphology, almost resemblingshort rod-shaped bacteria. S. thermophilus is includedin Sherman’s varidans group, but does not fall underany of Lansfield’s serological groupings. Transporta-tion of lactose into S. thermophilus cells is medi-ated by �-galactoside permease, and �-galactosidasecleaves the disaccharide. The organism metabolizes

Lactose

GlucoseGalactose

1

2

3 5

6

7

8

9

10

17

18

19

4LeloirPathway

Glucose-6-PGlucose-1-P

ATP

ADP

ATP

ADP

ATP

ADPGalactose-1-P

NAD+

NADH

6-Phosphogluconate

Ribulose-5-P

Xylulose-5-P

Acetyl-P

Acetyl-CoA

Acetaldehyde

Ethanol

Acetate

CoASH

CoASH

Pi

CO2

NAD+

NAD+

NADH

NADH

Pi

Glyceraldehyde-3-P

11

12

13

14

15

16

NAD+

NADH

NAD+

NADH

Pi

ATP

ADP

ATP

ADP

1,3-Diphosphoglycerate

3-Phosphoglycerate

2-Phosphoglycerate

Phosphoenolpyruvate

Pyruvate

D-Lactate

Figure 6.3. Heterofermentative pathway for lactose metabolism among starter lactic acid bacteria.1 = �-galactosidase, 2 = galactokinase, 3 = glucose:galactose-1-phosphate uridyl transferase uridinediphosphate-glucose epimerase, 4 = glucokinase, 5 = phosphoglucomutase, 6 = glucose-6-phosphatedehydrogenase, 7 = 6-phosphogluconate dehydrogenase, 8 = epimerase, 9 = phosphoketolase, 10 = acetatekinase, 11 = triose phosphate dehydrogenase, 12 = phosphoglycerokinase, 13 = phosphoglyceromutase,14 = enolase, 15 = pyruvate kinase, 16 = lactate dehydrogenase, 17 = phosphoacetyl transferase,18 = acetaldehyde dehydrogenase, 19 = ethanol dehydrogenase. Adapted from Hutkins, 2001, and Ray, 2004.

107


only the glucose portion of lactose via HMP, andgalactose is expelled from the cell into the environ-ment. In the dairy industry, the organism is often re-ferred to as “coccus.”

S. thermophilus cultures generally produce a weakcoagulum in milk because of low acid production.Some strains, however, are rapid acid producers andgenerate acidity comparable to lactococci. The acid-producing ability of S. thermophilus strains was re-cently shown to be inversely related to its urease ac-tivity. Urea normally occurs in milk, and the enzymeurease splits urea into ammonia and carbon dioxide.S. thermophilus strains are normally used in asso-ciation with Lb. delbrueckii subsp. bulgaricus. TheLactobacillus subspecies is commonly referred to as“rod” in the dairy industry, and the combination of thetwo bacteria is called “rod-coccus.” The rod-coccuscombinations display synergistic growth response inmilk. To maximize the synergistic effect, strains ofthe bacteria need to be paired with care after exper-imenting with various combinations.

The synergism between the coccus and the rod isrooted in their individual physiological characteris-tics. S. thermophilus is more aerotolerant than Lb.bulgaricus. The coccus lacks good proteolytic abil-ity relative to the rod, but possesses greater peptidaseactivity than the rod. When growing together in milk,S. thermophilus grows vigorously at first, because ofgreater aerotolerance. The rod at this stage growsslowly but because of its greater proteolytic activityprovides sufficient peptides to stimulate the growthof the coccus. Fermentation by S. thermophilus de-presses the oxidation–reduction O/R potential of thesystem, and releases formate as a metabolic by-product. Lowered oxygen tension and formate inturn stimulate Lb. bulgaricus growth, which is fur-ther aided by the amino acids released by the activepeptidases secreted by the coccus. The coordinatedtandem activities of the coccus and the rod acceleratethe entire fermentation, which neither the coccus northe rod would be able to achieve individually. Thedominance of S. thermophilus in the milk fermenta-tion wanes when the pH approaches 5.0. Beyond that,Lb. bulgaricus gradually supplants the coccus in theoverall fermentation.

The cell morphology of S. thermophilus as it ap-pears under a light microscope is shown in Figure6.4. In Figure 6.5, the cell morphology of Lb. bul-garicus is shown. Cells of yogurt starter bacteria in amicroscopic smear are shown in Figure 6.6.

S. thermophilus strains also produce EPS. Suchstrains are used in yogurt fermentations to obtain

Figure 6.4. Stained cells of Streptococcusthermophilus under light microscope.

viscous body and smooth texture. The genetics andphysiology of EPS production by coccus are nowwell understood. More information on the geneticsof S. thermophilus is now available in the literature.

Genus LACTOBACILLUS

Lactobacilli are rod-shaped, Gram-positive bacteria.Morphologically, they are variable. Some occur aslong slender straight rods; others are curved. Someothers are short, almost coccoid rods. A few exhibitpleomorphic cells. On the basis of sugar metabolism,lactobacilli are divided into three groups. The lacto-bacilli generally used as starters for cultured milksare Lb. delbrueckii subsp. bulgaricus and Lb. aci-dophilus. Occasionally, Lb. delbrueckii subsp. lactismay be used. All the aforementioned lactobacilli be-long to group 1. Group 1 lactobacilli ferment hexosesvia HMP to lactic acid, and do not ferment pentoses.The morphological and physiological characteristics


Figure 6.5. Stained cells of Lactobacillusdelbrueckii ssp. bulgaricus under lightmicroscope.

of lactobacilli used in dairy starter cultures are givenin Tables 6.2–6.4.

Lb. bulgaricus is used in combination with S. ther-mophilus for the production of yogurt and the in-dustrial production of dahi. Lb. bulgaricus is an ex-tremely fastidious organism. Lack of certain essen-tial nutrients and minerals in propagation mediumaffects the cellular integrity of these bacteria, andthe cells exhibit abnormal morphology under nutri-tional stress. Additionally, commercial preparationof “rod” cultures is an extremely challenging task,because of their nutritional and environmental (tem-perature and pH control, exclusion of air) fastidious-ness, compounded by the need for close control ofharvesting and preservation operations.

Lactobacillus subsp. lactis, on the other hand, iscomparatively a rugged organism and is easier togrow and concentrate. Because regulations call forthe use of subspecies bulgaricus in yogurt, the use ofsubspecies lactis in yogurt starters is no more prac-ticed.

Lb. acidophilus is a unique organism that is foundin the gut of humans, animals, and birds. The organ-ism possesses the characteristics necessary to sur-vive the harsh environmental conditions in the gut,namely, high acid tolerance and tolerance of surface-reducing effect of bile salts. Lb. acidophilus growsslowly in milk, but produces high amounts of lacticacid. It is used for the production of acidophilus milk,which is a highly acidic, acrid product. Acidophilus

Figure 6.6. Stained microscopic smear ofyogurt bacteria.


Figure 6.7. Stained cells of Lactobacillusacidophilus under light microscope.

milk, however, has long been known to be therapeu-tic, and helpful in maintaining intestinal health. It isthe forerunner of the present-day sweet acidophilusmilk and probiotic milks. For a more extensive dis-cussion of the use of Lb. acidophilus in cultured dairyproducts, the chapters in this book dealing with yo-gurt and probiotic milk(s) should be consulted. Cellsof Lb. acidophilus are shown in Figure 6.7.

Lactobacilli are also used as probiotic cultures.Probiotics are microbial cell preparations that havea beneficial effect on health and well-being of thehost. Probiotic cultures may be incorporated into fer-mented and nonfermented milk products to providebeneficial health effects to the consumer. Probioticcultures, however, cannot be classified as starter cul-tures, because probiotic cultures do not play a partin the fermentation or the preparation of the dairyproduct. The cultured or the noncultured milk servesas the carrier or the vehicle for the delivery of thehealth-promoting probiotic cells. Table 6.6 lists var-ious probiotic microorganisms in commercial prod-ucts. Several Lactobacillus spp. are included in thelist.

Genus BIFIDOBACTERIUM

Genus Bifidobacterium consists of cleft, rod-shapedbacteria in the shape of the letter “Y.” Not all cellsin a culture exhibit the split, Y-shaped morphology;most of the cells occur as short straight rods. Bifi-dobacteria are obligate anaerobes and are catalase-negative. Some strains may tolerate limited amountof air slightly better than others. They are classifiedunder Actinomyces, a subdivision under eubacteria.

Table 6.6. Microorganisms Used asProbiotics

Lactobacillus spp. Bifidobacterium spp.

L. acidophilusL. caseiL. reuteriL. gasseri ADHL. johnsoni LAI B. bifidumL. plantarum B. longumL. casei subsp. rhamnosus B. infantisL. brevis B. breveL. delbrueckii subsp.

bulgaricusB. adolescentis

L. fermentum B. animalisL. helveticus

Other organismsStreptococcust thermophilusEnterococcus faeciumPediococcus acidilacticiSaccharomyces boulardiiSource: Reproduced with permission from Chandan RC.1999. Enhancing market value of milk. J. Dairy Sci. 62:2248,American Dairy Science Association.

Nutritionally bifidobacteria are fastidious. They arefrom a portion of the normal intestinal flora of hu-mans. Bifidobacteria could be isolated from the fe-ces of newborn infants. The bifidobacterial speciesfound in newborn infants differ from that found inadults. Bifidobacteria are considered to play a rolein regulating the ecology and microbial flora of thegut. This role is considered to have a beneficial,


Lactose

GlucoseGalactose

1

2

3

5

6

7

8

9

10

4

LeloirPathway

Glucose-6-P

Glucose-6-P

Fructose-6-P

Fructose-6-P

Erythrose-4-P

Sedoheptulose-7-P

ATP

ADP

ATPADP

ATPADP

Galactose-1-P

Ribulose-5-P

Xylulose-5-P

Xylulose-5-P

2-Glyceraldehyde-3-P

Acetyl-P

Acetate

Embden-Meyerhoff Pathway Enzymes

Formate

Acetate

Acetyl-P

Acetate

Ribose-5-P

Pi

2 NAD+

2NAD+

2 NADH

2NADH

Pi

Glyceraldehyde-3-P

11

12

13

1415

16

Pi

ATP

ADP

4 ATP

4 ADP

2-Pyruvate

2-L-Lactate

Figure 6.8. Pathway used by Bifidobacteriafor lactose metabolism.1 = �-galactosidase, 2 = glucokinase,3 = phosphoglucose mutase,4 = phosphoglucose isomerase,5 = transaldolase, 6 = phosphoglucoseisomerase, 7 = fructose-6-phosphatephosphoketolase, 8 = acetate kinase,9 = transketolase, 10 = xylulose-5-phosphate phosphoketolase,11 = ribose-5-phosphate isomerase,12 = ribulose-5-phosphate-3 epimerase,13 = xylulose-5-phosphatephosphoketolase, 14 = acetate kinase,15 = Embden-Meyerhoff pathway enzymes,16 = lactate dehydrogenase. Adapted fromCogan and Accolas, 1996, and Ray, 2004.

probiotic effect on intestinal health. Bifidobacteriause a unique pathway for carbohydrate metabolism.The by-products consist of a mixture of acetic andlactic acids. The pathway includes a unique enzyme,fructose-6-phosphate phosphoketolase, and is used asa key diagnostic test to identify bifidobacteria. Thepathway for lactose metabolism by bifidobacteria isdepicted in Figure 6.8.

Because of the anaerobic nature of bifidobacteria,they are somewhat difficult to grow, harvest, and pre-serve. Their viability is of critical importance in theiruse as probiotics. Their interaction with yogurt starterbacteria and other probiotic lactobacilli greatly influ-ences their viability in these systems. Hydrogen per-oxide generated by the associated flora also affectsbifidobacterial viability in mixed culture systems.


Further details are given in the chapter dealing withprobiotic milks in this book.

STARTER CULTUREPRODUCTIONThis section may be discussed under two subhead-ings, namely, bulk starter production in the dairy plantand commercial starter culture production. With theexception of yogurt production, where bulk startersare still widely used, for most other cultured dairyproducts, commercial, concentrated direct-to-vat-set(DVS) cultures are used to inoculate product vats. Forprobiotic supplementation of cultured dairy productsand nonfermented milk, DVS cultures of probioticsare used. Currently DVS cultures to inoculate up to4,000 liters are commercially available.

Bulk Starter Production

Unlike starters for cheese production, starter culturesfor cultured milks are made with milk. Reconstitutedskim milk powder (nonfat dry milk powder) is pre-ferred for making up starter cultures, because consis-tency in composition, microbial quality, and absenceof inhibitors and antibiotics are necessary. Pretestednonfat milk powder (tested for absence of inhibitors,good solubility, and for supporting good growth and“activity” of cultures) procured in bulk from specificlots are reserved for starter production. The powderis reconstituted to give 10–11% solids.

Stainless steel double-jacketed vats equipped withsuitable agitators, connected to appropriate plumbingfor circulating hot and cold water (for heating andcooling cycles), and provided with thermostat equip-ment for temperature control are used. The vats alsoneed sufficient number of sanitary ports for venting,sampling, and temperature and pH probes. The ventsneed filter setup to exclude microflora and phage dur-ing cooling, when pressure equilibration takes place.Additional ports for adding the inoculum or other ma-terials are also provided. Another requirement is tohave a manhole for inspecting and manual cleaning ofthe vat periodically. Additionally, provisions shouldbe made for cleaning-in-place (spray-ball) connec-tion to the vats.

The preparation of starter consists of the followingsteps:

1. Reconstitution of skim milk powder to the re-quired solids level by metering in the required vol-ume of water, followed by the addition of weighed

amount of powder and mixing to get the solidscompletely dissolved. Care should be exercised towash down any milk solids adhering to the sidesof the vat above the liquid level.

2. Heating the milk to 85–90◦C, and holding at thattemperature for 30–45 minutes to destroy contam-inants in the milk including spore-forming bacte-ria and phages if any.

3. Cooling to the required incubation temperature byturning on the chill water with the agitator turnedon.

4. Inoculation with the culture using aseptic precau-tions with agitation to uniformly mix in the inocu-lum.

5. Incubating at thermostatically preset temperaturequiescently. If the temperature and pH recordingequipment are connected to the vat, they need tobe turned on.

6. When the desired pH is reached, cooling withagitation should be promptly initiated. Agitationshould be slow and gentle. The starter is readyfor use once the cooling to the desired tempera-ture (preferably 5–7◦C if needed to be held longerbefore use) is reached.

The incubation temperature would vary with thestarter flora. For cultured buttermilk and sour creamproduction, the starter is incubated at 20–22◦C. Foryogurt, the starter is incubated at 35–37◦C if it con-tains EPS producers; for regular yogurt starters, mostdairy plants incubate them at around 40–43◦C. Care-ful calibration of temperature and pH probes at leasttwice a week is recommended. It is advisable to usethe starter as soon as it is ready. Other precautionswere discussed earlier in this chapter.

Very few dairy plants nowadays carry their ownstrains or maintain a frozen or lyophilized stock.From the stock culture a mother culture is prepared.The mother culture is made up in volumes no greaterthan 1 liter. The milk used in mother culture is heat-treated in a steam chamber for 45 minutes. Themother culture is used to inoculate an intermediateculture, which is used to inoculate the starter vat. In-oculation rate for cultured buttermilk and sour creamproduction is normally 1.0%. Current yogurt produc-tion demanding 4-hour turnovers require inoculationrates ranging from 2.5% to 5.0%. To attain shorterincubation time in product vats, higher incubationtemperature (40–42◦C) is necessary. For more de-tailed information on starter preparation for the var-ious products discussed in this book, the relevantchapters should be consulted.


Commercial Starter CultureProduction

Commercial starter culture production is a highlydemanding operation. It requires specialized knowl-edge of microbiology, microbial physiology, processengineering, and cryobiology. In addition to produc-tion knowledge, a full-fledged quality control pro-gram is necessary to test incoming raw materials,design and maintain plant sanitation, test sterility ofproduction contact surfaces, monitor plant environ-ment quality, and test every product lot for the pre-scribed quality standards. The quality control sectionis also required to train and update plant personnelon the importance of sanitation and strict adherenceto process control protocols. The maintenance of thestarter culture strain bank, and the entire stepwiseprocess of preparing the final inoculum for the large-scale fermentor (from the stock or “seed” culturestage), falls under the purview of the quality controlsection.

Commercial starter cultures currently available fordirect addition to production vats contain billions ofviable bacteria per gram, preserved in a form thatcould be readily and rapidly activated in the productmix to perform the functions necessary to transformthe product mix to the desired cultured product. Toattain that, the selected starter bacteria need to begrown in a suitable menstruum to high numbers andto concentrate the cells. The composition of the me-dia used to grow various bacteria differs. Usually, thematerials used in the growth media consist of food-grade, agricultural by-products and their derivatives.The trade has special requirements for the raw mate-rials that go into media formulations and for the waythey are mixed and processed. Examples of such re-quirements include Kosher standards, absence of in-gredients derived from genetically modified crops,absence of allergenic materials, etc.

The generally used ingredients in media formu-lations include nonfat milk, whey, hydrolysates ofmilk and whey proteins, soy isolates, soy protein hy-drolysates, meat hydrolysates and extracts, egg pro-teins, corn steep liquor, malt extracts, potato infu-sions, yeast extracts/yeast autolysates, sugars suchas lactose, glucose, high-fructose corn syrup, cornsugar, sucrose, and minerals such as magnesium,manganese, calcium, iron, phosphates, salt, etc. Forsome fastidious bacteria, amino acids and vitaminsmay be included. The phosphates are added to pro-vide mineral requirements as well as for buffering.For some bacteria, which need unsaturated fatty acids

to protect cell membranes, trace quantities of polysor-bates (Tweens) are added. To control foaming, food-grade antifoam ingredients may be incorporated.

The medium is then either sterilized by heating at121◦C for a minimum of 15 minutes or heat-treatedat 85–95◦C for 45 minutes or subjected to ultra-high temperature treatment (UHT) for a few seconds.After heat treatment, the medium is cooled to the in-cubation temperature. After the addition of the in-oculum, the medium is incubated until the predeter-mined endpoint is reached. During incubation, the pHis maintained at a predetermined level (constant neu-tralization to maintain pH). Generally, the endpointcoincides with the exhaustion of sugar reflected bythe trace of the neutralization curve. The frequencyof neutralization reflects the activity of the culturein the fermentor, and when the frequency decreases,it indicates the near depletion of the sugar. Samplesare usually taken to microscopically examine the fer-mentate for cell morphology, for any gross contam-ination, for a rough estimation of cell numbers, andfor quantitative measurement of sugar content. Afterascertaining these, the fermentor is cooled.

The cells are harvested either by centrifugation orby ultrafiltration. The cell concentrate is obtainedin the form of a thick liquid of the consistencyof cream and is weighed and rapidly cooled. Ster-ile preparations of cryoprotectants (glycerol, nonfatmilk, monosodium glutamate, sugars, etc.) are added,and uniformly mixed with the cell concentrate. Theconcentrate may be filled as such into cans and frozenor frozen in droplet form in liquid nitrogen (pellets),retrieved, and packaged. The concentrate as such orin pellet form may also be lyophilized in industrial-scale freeze dryers.

Quality control tests for commercial cultures in-clude the following:

� Viable cell numbers.� Absence of contaminants, pathogens, and

extraneous matter.� Acid-producing and other functional activities.� Package integrity, accuracy of label information

on the package.� Shelf life of the product according to

specification.

Miscellaneous Starters

In traditional production of Kefir, the starter consistsof Kefir grains. Kefir grains are made up of polysac-charide matrix with a convoluted structure. Within


the folds of the grain yeasts, an assortment of LABis found. This flora is responsible for Kefir fermenta-tion. The grains could be reused. After the completionof one batch, the grains are strained out, washed inwater, dried, and reused. More details on the Kefirgrains and other starters used in Koumiss produc-tion are discussed in the chapter dealing with thoseproducts.

BIBLIOGRAPHYLiterature on starter cultures is extensive and volu-minous. It is difficult to cover the vast amount ofinformation on starter culture bacteria in a chapter.Literature citations were deliberately avoided in thischapter to provide continuity, and to avoid an exten-sive bibliography. Instead references for the follow-ing books, book chapters, monographs, reviews andresearch articles are provided for the reader to gaina greater understanding of starter flora, their phys-iology, their genetics, their functions in fermenteddairy products, and their various applications in dairyfoods.

For a comprehensive treatment of starter cultures,the reader should consult Dairy Starter Cultures(1996), Bacterial Starter Cultures for Foods (1985),and Lactic Acid Bacteria—Microbiology and Func-tional Aspects (1998). For the technology and prac-tical aspects of dairy starter cultures, the monographLactic Starter Culture Technology is recommended.

Other practical information on starter cultures maybe gleaned from Cheese and Fermented Milk Foods,Volumes I and II (1997), and the trade publica-tion Cultures for the Manufacture of Dairy Products(1985). For historical and basic information on lacticstarter cultures, the book Dairy Microbiology (1957)is excellent.

There are chapters from several books that dealwith starter cultures. They contain valuable infor-mation. In Dairy Microbiology Handbook (2002),Tamime has covered several aspects of the organismsused in dairy starter cultures, and their production.In Food Biotechnology (1995), dairy lactococci arediscussed by Sanders, dairy lactobacilli by Ariharaand Luchansky, and dairy leuconostocs by Dessartand Steenson. The book Applied Dairy Microbiol-ogy (1998) contains a chapter on starter cultures byFrank and Hassan, and the genetics and metabolismof starter cultures are covered by Steele. Vedamuthuhas discussed the role of starter cultures in flavor gen-eration in fermented foods in a chapter in Handbookon Anaerobic Fermentations (1988).

The recommended reviews listed below cover spe-cific starter bacteria, bacteriophages affecting starterbacteria, genetics and physiology of EPS productionby starter bacteria, and other relevant topics on starterbacteria.

Books

Cogan TM, Accolas J-P (Eds). 1996. Dairy StarterCultures. VCH Publishers, New York, p. 277.

Foster EM, Nelson FE, Speck ML, Doetsch RN, OlsonJC Jr. 1957. Dairy Microbiology. Prentice-Hall,Englewood Cliffs, NJ, p. 492.

Gilliland SE (Ed). 1985. Bacterial Starter Cultures forFoods. CRC Press, Boca Raton, FL, p. 205.

Kosikowski FV, Mistry VV. 1997. Cheese andFermented Milk Foods, Vols. I and II, 3rd ed. F.V.Kosikowski, L.L.C., Westport, CT.

Ray B. 2004. Fundamental Food Microbiology. CRCPress, Boca Raton, FL, pp. 142–146.

Salminen S, von Wright A (Eds). 1998. Lactic AcidBacteria—Microbiology and Functional Aspects.Marcel Dekker, New York, p. 617.

Sandine WE. 1979. Lactic Starter Culture Technology,Pfizer Cheese Monographs. Pfizer Inc., New York,p. 55.

Sellars RL, Babel FJ. 1985. Cultures for theManufacture of Dairy Products, 2nd ed. Chr.Hansen’s Laboratory Inc., Milwaukee, WI, p. 62.

Chapters in Books

Arihara K, Luchansky JB. 1995. Dairy Lactobacilli. In:YH Hui, GG Khachataurians (Eds), FoodBiotechnology: Microorganisms. VCH Publishers,New York, pp. 609–643.

Chandan RC, Shahani KM. 1995. Other fermenteddairy products. In: H-J Rehm, G Reed (Eds),Biotechnology, Vol. 9: Enzymes, Biomass, Food andFeed. VCH Publishers, New York, pp. 386–418.

Dessart SR, Steenson LR. 1995. Biotechnology ofdairy Leuconostoc. In: YH Hui, GG Khachataurians(Eds), Food Biotechnology: Microorganisms. VCHPublishers, New York, pp. 665–702.

Frank JF, Hassan AN. 2001. Starter cultures and theiruse. In: EH Marth, JL Steele (Eds), Applied DairyMicrobiology, 2nd ed. Marcel Dekker, New York,pp. 151–206.

Hutkins RW. 2001. Metabolism of starter cultures. In:EH Marth, JL Steele (Eds), Applied DairyMicrobiology, 2nd ed. Marcel Dekker, New York,pp. 207–241.


Porubcan RS, Sellars RL. 1979. Lactic starter cultureconcentrates. In: HJ Peppler, D Perlman (Eds),Microbial Technology, Vol. 1, 2nd ed. AcademicPress, New York, pp. 59–92.

Sanders ME. 1995. Lactococci. In: YH Hui, GGKhachataurians (Eds), Food Biotechnology:Microorganisms. VCH Publishers, New York, pp.645–664.

Steele JL. 1998. Genetics and metabolism of startercultures. In: EH Marth, JL Steele (Eds), AppliedDairy Microbiology, 1st ed. Marcel Dekker, NewYork, pp. 173–194.

Tamime AY. 2002. Microbiology of starter cultures. In:RK Robinson (Ed), Dairy Microbiology Handbook:Microbiology of Milk and Milk Products, 3rd ed.John Wiley & Sons, New York, pp. 261–366.

Vedamuthu ER. 1998. Engineering flavor intofermented foods. In: LE Erickson, DCY Fung (Eds),Handbook on Anaerobic Fermentations. MarcelDekker, New York, pp. 641–694.

Review Articles andResearch Papers

Allison GE, Klaenhammer TR. 1998. Phage resistancemechanisms in lactic acid bacteria. Int. Dairy J.8:207–226.

Boucher I, Moineau S. 2001. Phages of Lactococcuslactis: An ecological and economical equilibrium.Recent Res. Dev. Virol. 3:243–256.

Broadbent JR, McMahon DJ, Walker DL, Oberg CJ,Moineau S. 2003. Biochemistry, genetics andapplications of exopolysaccharide production inStreptococcus thermophilus: A review. J. Dairy Sci.86:407–423.


Cogan TM, Peitersen N, Sellars RL. 1991. Startersystem. Bull. Int. Dairy Fed. 263.

Deveau H, Moineau S. 2003. Use of RFLP tocharacterize Lactococcus lactis strains producingexoploysaccharides. J. Dairy Sci. 86:1472–1475.

Everson TC. 1991. Control of phage in the dairy plant.Bull. Int. Dairy Fed. 263.

Hemme D, Foucaud-Scheunmann C. 2004.Leuconostoc, characteristics, use in dairytechnology and prospects in functional foods. Int.Dairy J. 14:467–494.

Hugenholtz JM. 1993. Citrate metabolism in lacticacid bacteria. FEMS Microbiol. Rev. 12:165–178.

Hugenholtz JM, Starrenburg JC, Veerkamp AH. 1994.Diacetyl production by Lactococcus lactis:Optimisation and metabolic engineering. In:Proceedings of the 6th European Congress onBiotechnology, pp. 225–228.

Mercenier A. 1990. Molecular genetics ofStreptococcus thermophilus. FEMS Microbiol. Rev.87:61–74.

Moineau S, Tremblay D, Labrie S. 2002. Phages oflactic acid bacteria: From genomics to industrialapplications. ASM News 68:388–393.

Neve H, Teuber M. 1991. Basic microbiology andmolecular biology of bacteriophages of lactic acidbacteria in dairies. Bull. Int. Dairy Fed. 263.

Nomura M, Kobayashi M, Ohmomo S, Okamoto T.2000. Inactivation of the glutamate dehydrogenasegene in Lactococcus lactis subsp. cremoris. Appl.Environ. Microbiol. 66:2235–2237.

Oberg CJ, Broadbent JR. 1993. Thermophilic startercultures: Another set of problems. J. Dairy Sci.76:2392–2406.

Orban JL, Patterson JA. 2000. Modification of thephosphoketolase assay for rapid identification ofbifidobacteria. J. Microbiol. Methods 40:221–224.

Van Kranenberg R. 1999. Exopolysaccharidebiosynthesis in Lactococcus lactis: A molecularcharacterization. Doctoral Dissertation, WageningenUniversity, Holland, Ponsen Looijen BV,Wageningen, Holland.

Vedamuthu ER. 1994. The dairy Leuconostoc: Use indairy products. J. Dairy Sci. 77:2725–2737.

Zourari A, Accolas JP, Desmazeaud MJ. 1992.Metabolism and biochemical characteristics ofyogurt bacteria. A review. Lait 72:1–34.

7Laboratory Analysis of

Fermented MilksRobert T. Marshall

Compositional TestsTests for Fat ContentTests for Moisture and Total SolidsTests for Nonfat Milk SolidsTests for ProteinTests for LactoseTitratable AcidityMeasurement of pH

Chemical TestsTests for Flavorful SubstancesTests for Free Fatty Acids

Physical Properties TestsDensity and Specific GravityRheological TestsWater-Holding Capacity

Microbiological PropertiesTests for Coliform BacteriaTests for EnterobacteriaceaeYeast and Mold CountsTests for Culture Bacteria

Antimicrobial SubstancesSensory Tests

Preference TestingAcceptance TestingDescriptive AnalysisSensory Tests for Quality Control

References

Routine analyses of fermented milk products are lim-ited normally to those that are pertaining to the grosscomposition of the product and to its quality andsafety. The progress of fermentation is monitoredwith tests of the acidity or pH value. Compositionis controlled primarily by tests done on the ingredi-ents at the time of preparation of the basic mix. Thesetests are usually limited to the analyses of the con-tent of fat and total solids of the dairy ingredients.

Tests of the fermented product, done prior to the ad-dition of fruits, flavorings, and other additives, revealwhether the formulated and processed product meetsthe specifications. Together these pre- and postpro-cessing tests reveal whether the product contains thecorrect amount of valuable characterizing ingredientsand has been fermented correctly. When flavoringsor other additives are added, further testing may beneeded to determine whether specifications for color,viscosity, flavor, distribution of particulates, and fill-ing of containers have been satisfied. The finishedproduct then needs to be tested for microorganismsthat are indicators of postprocessing contamination.Usually this is done with a test for coliform bacteriaor for enterobacteria. Some manufacturers test foryeasts and molds. Microbiological tests of ingredi-ents are needed when significant risks to safety and/orquality are encountered.

This chapter has been designed to present a com-prehensive discussion of tests that may be used withfermented dairy products and their ingredients. Thecategories are compositional, chemical, physical, mi-crobiological, antimicrobial substance, and sensorytests. The approach used is to discuss the generalprinciples and applications of the tests, to providereferences of sources of most of them, and to com-ment on the utility of the tests.

COMPOSITIONAL TESTSThe main purpose of compositional testing is to deter-mine whether the amounts of valuable characterizingingredients are within formulated tolerances. Mostimportant among these are the milk fat and nonfatmilk solids components. When concentrated or dried

117




sources of ingredients are used, moisture content ortotal solids must be known. Knowing these parame-ters, the process of standardization can proceed. Forexample, in preparing sour cream, nonfat milk maybe combined with heavy cream to adjust the fat con-tent to 18%. The formula then depends on how muchfat is present in each ingredient and on how much thefat will be diluted with other additives such as nonfatdry milk and stabilizer.

Tests for Fat Content

The volumetric Babcock and Gerber methods, thegravimetric ether extraction method, and instrumen-tal tests are available. These methods are describedin Standard Methods for the Examination of DairyProducts (Hooi et al., 2004). The International DairyFederation has set tolerances for testing the percent-age of fat in dairy foods as follows: milk, 0.02%; skimmilk, 0.01%; and 20% cream, 0.1%. Application ofa satisfactory method should result in no more than5% of the tests falling outside these limits. Althoughthe varying viscosities of cream make it necessaryto weigh the sample in performing the Babcock andGerber tests, the amount of fat extracted is deter-mined by measurement of the height of fat column inthe graduated cylinder of the test bottle. Applicationsof these “volumetric-type” tests are limited to liquidproducts, and added sugars may produce charred par-ticles that occlude the fat column.

Babcock Test

The method calls for measuring a specific volumeof milk, nonfat milk, or cream into a bottle that hasa calibrated neck, digesting the nonfat organic sub-stances of the sample with concentrated sulfuric acid,centrifuging to separate the light-weight fat from theheavier serum. Then water is added to the sample tocause the fat to rise into a calibrated neck of the testbottle, and the sample is centrifuged again to cleanlyseparate the fat into the neck where its volume is mea-sured. Close control of the temperature of the test isrequired, especially at the time of reading the volumeof fat in the neck of the bottle. Heat produced by thechemical degradation of the milk’s protein and car-bohydrate components, as well as the high densityof the sulfuric acid provides a large difference in thedensities of the serum and fat. In addition, the acidbreaks the emulsion of the fat by digesting the fatglobule membrane. Because of the large differencein the amount of fat contained in skim (nonfat) milk,

milk, and cream, diameters of the necks of test bottlesvary directly with the expected fat content.

Gerber Test

Similar to the Babcock test, a volume of sample ismeasured into a test bottle containing concentratedsulfuric acid. After the milk or cream is mixed withthe acid, isoamyl alcohol is added and further mixingis done to fully digest the nonfat components. Cen-trifugation separates the fat from the aqueous phase,and tempering in a water bath permits reading of thevolume of extracted fat in the calibrated neck of thespecially designed Gerber test bottle.

Ether Extraction Test

Precise determination of fat content is provided bythe ether extraction method, which is also known asthe Roese–Gottlieb test or the Mojonnier modifica-tion of that test. This is the official reference methodfor milk fat. Weighing of the sample and of the ex-tracted fat reduces the probability of error that may beintroduced by the volumetric measurements used inthe Babcock and Gerber tests. Furthermore, this testis easily adapted to testing all types of fermented milkproducts regardless of their viscosity and composi-tion. Ammonium hydroxide and ethanol are added tocondition the sample prior to the extraction of fat withethyl ether and petroleum ether. The lighter weightsolvent layer that contains the fat is separated fromthe aqueous layer by centrifugation before it is pouredinto a clean, dried, and preweighed dish. Traces of fatare removed from the residue in the extraction flaskby twice-repeated extractions with ether. The etheris then evaporated from the dish leaving the fat inthe dish. After cooling in a desiccator, the dish plusfat is weighed and the net weight of the fat is de-termined. The percentage of fat is then calculated asweight of fat divided by weight of sample × 100.Sample weight varies inversely with the percentageof fat expected in the sample. In transferring the sam-ple to the extraction flask it is important to assure thatthe sample is homogenous. Warming of raw milk de-creases the tendency for fat to stick to the surfaces ofpipets.

Instrumental Tests

The absorption of infrared energy at different wave-lengths by certain bonds of fats, proteins, and

7 Laboratory Analysis of Fermented Milks 119

carbohydrates coupled with the abilities to measurethat absorption has made possible the developmentof instruments that can quantify the amount of thesecomponents in milk and certain milk products. Op-timal absorption is observed for carbonyl groups inester linkages of fat molecules at 5.723 nm, for car-bon to hydrogen bonds in fatty acids at 3.47 nm, forpeptide linkages of proteins at 6.465 nm, and for hy-droxyl groups in lactose molecules at 9.610 nm. Al-though absorption is not solely by these bonds, cor-rections can be made for absorption by other speciesof bonds. Although the instruments are expensive therate of testing can be quite high. Samples of milkmust be homogenized uniformly to minimize the er-ror caused by light scattering. The instrument mustbe calibrated with samples of the same type of milkthat are being tested by the reference method.

Another instrumental method of determining fatcontent of samples employs nuclear magnetic res-onance (NMR) technology developed by the CEMCorporation. The sample must first be dried to re-move hydrogen bound in water of the sample. Theinstrument then sends a pulse of radio-frequency en-ergy through the sample causing the remaining hy-drogen to generate a signal known as free inductiondecay (FID). The intensity of the FID is then ana-lyzed to determine the amount of protons of the fatpresent in the sample. In the application by the CEMfirm the sample is dried in their moisture/solids an-alyzer, rolled into a film, and inserted into the NMRchamber for analysis. The test is reported to have aprecision of ±0.01%, is applicable to a wide varietyof samples, and requires a few minutes for comple-tion (www.cem.com).

Tests for Moisture and Total Solids

Hot Air Oven Tests

The rather simple test for moisture and total solidsin most milk products involves evaporation of wa-ter from a weighed sample followed by weigh-backof the cooled dish containing the dry sample. Ei-ther a vacuum oven or a forced-draft oven may beused in the official method for fermented dairy foods(see AOAC Official Methods of Analysis or Stan-dard Methods for the Examination of Dairy Prod-ucts) (Horowitz, 2003; Wehr and Frank, 2004). Theprocedure calls for accurate and quick weighing of3 ± 0.5 g of sample into a dry “moisture dish” on ananalytical balance. Conditions of drying vary with thetype of sample and oven. The sand pan method for

concentrated dairy products, including yogurt, callsfor adding about 25 g of clean sand and a small stir-ring rod to the weighing dish then drying this in avacuum oven at 102◦C for at least 1 hour. After thesample is weighed into the center of the cooled pan,the sample is mixed into the sand with the stirringrod and is covered with a dried fiberglass cover. Theentire unit is then placed in the vacuum oven to dryfor 2 hours at 102◦C and at a minimum vacuum of−86 kPa. After cooling the dish in a desiccator atroom temperature for 45 minutes, the dish is weighedon an analytical balance. The percent moisture is cal-culated by dividing the loss in weight by the weightof the sample and then multiplying the result by 100.The percent solids is 100 minus the percent mois-ture. A small amount of dried air is permitted to passthrough the oven during drying. The reference meth-ods of the International Dairy Federation for milk,cream, and evaporated milk (Anonymous, 1987) andfor yogurt (Anonymous, 1991) call for drying thesamples at 102◦C.

The forced-draft oven may be used for most of themilk products and their ingredients. After weighinginto the dried dish, liquid samples are evaporated toa semidry state on a steam bath. Oven temperaturefor milk products is 100◦C and the time of heatingis 3 hours. Following drying the procedure continuesas with the vacuum oven method.

Microwave Oven Test

Moisture of solid and semisolid samples can be de-termined by a microwave oven method. Since mi-crowave units vary in power and uniformity of dis-tribution of that power, power setting, position in theunit, and time of drying must be determined for eachunit and the expected moisture content of the sam-ple. These results should be compared to the resultsobtained by a reference method. The sample, locatedbetween the dried fiberglass pads, is placed on the an-alytical balance inside the oven where it is weighed,dried, and weighed back. Some instruments providedirect reading of the moisture or solids.

Infrared Instrument Test

Total solids in milk can be estimated using infraredmilk analysis instruments that are capable of deter-mining the content of fat, protein, and lactose. An ex-perimentally determined factor is added to the sum ofthe content of these major fractions of milk to providethe amount of total solids.


Tests for Nonfat Milk Solids

When the sample is composed only of the con-stituents of milk, the percentage of nonfat milk solidsis the product of subtraction of the percent fat fromthe percent total solids. Direct determination of non-fat solids content of products containing constituentsother than milk requires detailed analyses and is notpractical under industrial conditions. Knowledge ofthe amount of each ingredient used plus the composi-tion of the ingredients containing milk solids permitsaccurate calculation of the nonfat solids content of theproduct. For example, when 20% flavoring is addedto plain nonfat yogurt that contains 14% total nonfatmilk solids, the nonfat solids content of the finishedproduct is [(100–20)/100] 14 = 11.2%.

Tests for Protein

Although the content of protein is not determined rou-tinely for most dairy products, protein in raw milk ismeasured in markets in which producers receive pay-ment on a component basis. Furthermore, the aver-age protein content must be known for the purpose ofcreating nutrition facts labels. Therefore, processorsmay need to know the protein content of ingredientsor products.

Kjeldahl Test

This is the reference method for protein. The majorsteps in the procedure follow. A known quantity ofsample is digested by boiling in concentrated sulfuricacid plus a catalyst. The nitrogen that is freed fromthe protein and the nonprotein nitrogen of the sam-ple are converted to ammonia, and then distilled intoan acid that is partially neutralized by the ammonia.The excess acid in the receiving flask is then deter-mined by titration, and the concentration of protein iscalculated by multiplying the percent nitrogen in thedistillate by the accepted factor of 6.38 that applies tomilk proteins. Although this method provides accu-rate results, it is time-consuming and fails to providea precise value. However, it is the method on whichthe instrumental tests are calibrated.

Dye-Binding Test

Certain dyes in acidic conditions are bound to aminogroups of lysine, arginine and histidine, amino acidsof milk proteins, in a constant manner such that when

an excess of dye is added to a specified quantity ofacidified sample, the dye-protein complex that formscan be removed and the amount of unbound dyecan be quantified colorimetrically. This value is thencompared to values in a calibration curve to ascer-tain the protein content. Acid orange 12 is the dyethat has been selected for the official dye-binding testpublished in Standard Methods for the Examinationof Dairy Products ( Hooi et al., 2004). Since the dye-binding constant between normal milk protein andacid orange 12 is known, the amount of dye boundin a test can be used to calculate the amount of milkprotein in a tested sample. Treatments that change thenature of the protein affect the dye-binding constantand, therefore, produce error in the test. Since con-centrations of the various protein fractions of milkvary among animals, the test is more variable amongcows than among lots of mixed herd milk.

Infrared Analyzer Test

As presented in the preceding discussion of instru-mental methods of determining fat content, the ap-plication of infrared light to compositional analysisincludes quantification of protein. Because of theirunique absorption of infrared energy, the number ofpeptide bonds of proteins can be quantified and thedata used in comparison to a standard curve. Thiscurve is constructed using samples that have beentested by the Kjeldahl reference method. These “cal-ibration samples” are tested on the infrared analyzer,and the standard curve is developed by the softwareof the instrument.

Tests for Lactose

The concentration of lactose in fermented milk prod-ucts decreases as fermentation progresses, lactic acidbeing the end product of a series of enzymatic reac-tions produced by culture bacteria under anaerobicconditions. The concentration of lactose in a productcan be important to persons who are lactose malab-sorbers and need to limit their intake of this naturalsugar of milk. Whereas milk normally contains 4.6–5.0% lactose, development of 1% titratable acidityin that milk reduces the lactose content to about 4%.However, the addition of nonfat milk solids to milkor nonfat milk, as is often done in making culturedbuttermilk and yogurt, raises the lactose content byabout one-half of the amount of nonfat milk solidsadded. For these reasons it is necessary to quantify


the amount of lactose in products to provide infor-mation for writing the nutrition facts label.

Polarimetric Method

This is the reference method for lactose measure-ment in liquid milks. The procedure calls for precip-itating the protein from milk with mercuric iodideand phosphotungstic acid and removing the coagu-lum, including the fat, by filtration. The rotation ofplane-polarized light in a polarimeter is then read andconverted to concentration of lactose.

HPLC Method

This method provides for weighing 10 ± 0.003 gof sample into a 100 ml volumetric flask, and thenadding 1 ml of 0.9N sulfuric acid to precipitate theprotein. The sample is diluted to volume before be-ing vigorously shaken. After the curds have settled,filtrate is collected for injection through a membranefilter (0.45-�m pore size) and into the high-pressureliquid chromatograph. Samples are carried throughthe chromatographic column with a mixture of ace-tonitrile and water. Standards, made with �-lactoseand �-lactose, are used as quantitative references. Ar-eas under the peaks of the samples are compared withareas under the peaks of the standards to determineconcentrations of lactose in the samples.

In a similar manner concentrations of glucose andgalactose, the products of lactose hydrolysis, can bequantified in fermented milk products.

Titratable Acidity

The most important characterizing component com-mon to fermented dairy foods is lactic acid. The mostcommon method of estimating the content of lacticacid in dairy products is the test for titratable acidity.Although lactic acid is not the only acidic substancein these fermented products, it is the dominant oneso that the result of this test is expressed in percent-age lactic acid. The titratable acidity of fresh milkin which no fermentation has occurred ranges from0.12% to 0.16% and varies directly with the amountof phosphates, citrates, protein, and carbon dioxide inthe sample. This “titer” is called the apparent acidity,and the additional titer that results from fermentationof the sugars of milk is called the “developed acidity.”Together they constitute the total or titratable acid-ity. Addition of nonfat milk solids to products such

as yogurt increases the apparent acidity, and, conse-quently, the titratable acidity. Milk tastes sour to mostpeople when the developed acidity is between 0.05%and 0.10%. When the titratable acidity of yogurt con-taining 14% nonfat milk solids is 1%, the apparentacidity would be expected to be about 0.20% and thedeveloped acidity about 0.80%.

The test involves measurement of 9 or 18 g of sam-ple into a beaker, addition of two volumes of waterplus 0.5 ml of the pH indicator phenolphthalein, andtitration to the first permanent shade of pink producedby the indicator. This color appears at a pH of approx-imately 8.3, a pH at which the buffering capacity ofmilk is quite low. The titrant, 0.1000N sodium hy-droxide, is added from a calibrated buret. When thesample weight is 9 g and normality of the alkali is0.1000, the titer is easily read as the ml of NaOH usedin the titration divided by 10. This is true because 1 mlof 0.1N NaOH neutralizes 0.009 g of lactic acid thathas a molecular weight of 90.

Error in the test occurs with variations in the appar-ent acidity, speed of titration, amount of indicator, andtemperature of the sample. When the rate of titrationis slow, the calcium phosphate of milk precipitatesfreeing hydrogen ions thus neutralizing some alkali.Therefore, consistent speed of titration is important.Addition of water to the sample lowers the rate of pre-cipitation of these phosphates and limits the effect ofthem on the titer.

When the color of the sample can interfere with thecolor of phenolphthalein, it is necessary to detect theend point of the titration at pH 8.3 with a pH meter.

Measurement of pH

The quick and dependable method of measuring theacid produced during fermentation is with a pH me-ter. The instrument is standardized with solutions ofbuffers that have pH values above and below the ex-pected pH of the samples to be tested. For fermenteddairy foods this normally means that buffers of pH4 and 7 are used to calibrate the instrument. Whenmeasuring or standardizing, the electrode must beimmersed sufficiently to cover both the pH-sensitivebulb and the wick of the reference electrode. Often a“combination electrode” is used so that a single bulbis visible. To assure that potassium chloride movesthrough the wick, the vent hole on the side of theelectrode must be open. The electrode must be keptclean. Coatings of fat on the surface can be removedby swabbing the bulb with hexane, isopropanol, or


dilute detergent. The most accurate results are ob-tained when the buffers and samples are at the sameambient temperature.

CHEMICAL TESTSTests for Flavorful Substances

Certain components of fermented milk productscharacterize typical flavors. The most important ofthese flavors are diacetyl of cultured buttermilk, sourcream, and cottage cheese; acetaldehyde of yogurt;and ethanol of the yeast-fermented products that in-clude kefir and koumiss. Because of the high volatil-ity of these flavorful substances, their concentrationscan be determined by gas chromatography (GC).Richelieu et al. (1997) developed a method that es-sentially prevents the oxidative decarboxylation of�-acetolactic acid to diacetyl and its subsequent re-duction to acetoin during analysis. This is a potentialproblem in the quantification of diacetyl because ofthe chemical instability of �-acetolactic acid. Themethod involves adjustment of pH to 7 followed byheadspace analysis by GC. The procedure (Riche-lieu et al., 1997) permits the quantification of othervolatiles in samples including acetone, ethylacetate,2-butanone, ethanol, and acetoin.

Tests for Free Fatty Acids

Chemical substances that are detrimental to flavorsof fermented milk products include free fatty acidsthat can be enzymatically released from the acylglyc-erides of milk lipids. Milk that contains an excessamount of free fatty acids is said to be rancid orlipolyzed. Concentrations of free fatty acids are mostoften determined by the acid degree value test. Theprocedure calls for combining 18 g of liquid milkproduct with surface-active BDI reagent (Bureau ofDairy Industry reagent) that consists of Triton X-100and sodium tetraphosphate. This mixture, in aBabcock test bottle, is agitated and placed in a boil-ing water bath. After agitating the hot mixture andexposing it to heat for 15–20 minutes, the bottles arecentrifuged and then filled with aqueous methanol sothe separated fat rises into the slim neck of the bottle.After centrifuging again, the sample is tempered to57◦C in a water bath before 1 ml of fat is removed,dissolved in a 4:1 mixture of petroleum ether andn-propanol, and titrated to the phenolphthalein endpoint with 0.02N potassium hydroxide. Acid degree

value is defined as the milliliters of 1N base requiredto neutralize the acids in 100 g of fat. Raw milk nor-mally tests between 0.25 and 0.40. Values exceeding1.0 are suspect, and most people can detect the rancidflavor when values reach 1.5.

Abnormal fermentations can produce significantquantities of acetic and propionic acids. Quantifica-tion of these acids can be done by gas chromatogra-phy.

PHYSICAL PROPERTIES TESTSProducers of fermented milk products generally tar-get their product’s physical characteristics towarda selected market. These characteristics are primar-ily color, texture, body, and, in products containingfruits or other inclusions, the size, color, and dis-tribution of particulates. Several of the physical at-tributes can be measured instrumentally while sen-sory tests are required to match the results with thelikes and needs of consumers. In general the desir-able attributes of fermented milk products includecolor typical of the flavor, body that has significantviscosity or is a soft gel, texture that is smooth, andan abundance of particulates that are typical in colorand are distributed uniformly throughout the prod-uct. The weight per unit volume is of importance informulation and preparation of the mix as well as insome aspects of packaging. Determination of the ef-fects on viscosity of using “ropy cultures” may be ofparticular interest for yogurt producers who seek toenhance the body of yogurts with capsule-producinglactic cultures. Furthermore, tests of the effects ofvariations in solids content and of added stabilizersand emulsifiers include measurements of the physicalproperties.

Density and Specific Gravity

Weight per unit volume is rather easily determined,but density varies inversely with temperature, espe-cially with water and fat. Therefore, change in densitywith change in temperature may demand considera-tion especially when the ingredients are not at thesame temperature as is the final product. The densityof the final product can be predicted when densitiesand quantities of the ingredients are known. For ex-ample, assume that sour cream contains 18% fat (F),8% nonfat milk solids (NMS), and 74% water (W)for which the densities (at 15◦C) are 0.93, 1.58, and1, respectively. The following formula is used in the


calculation:

Density = 100

(%F/0.93) + (%NMS/1.58) + (%W/1)

= 100

(18/0.93) + (8/1.58) + (74/1)

= 1.016g/ml

Specific gravity of a substance is the density of thesubstance divided by the density of water at the sametemperature. Although the density of milk decreasesconsiderably with increases in temperature, for ex-ample from about 1.032 at 10◦C to about 1.027 at40◦C, specific gravity of milk changes little over thesame temperature range. This is true because wateris the major component of milk.

Rheological Tests

The structure of yogurts is basically a protein networkthat forms during successful lactic fermentation whenthe pH is lowered to the isoelectric point of casein,about pH 4.7. The strength of this network is affectedby several factors. Most processes for yogurt produc-tion involve high heat treatment of the milk that re-sults in denaturation of the �-lactoglobulin and the�-lactalbumin causing them to form complexes withthe casein micelles. These complexes increase theviscosity of the system. As fat globules are brokendown during homogenization, proteins are adsorbedto the newly formed surfaces and the surface areaincreases markedly. For example, a globule 5 �m indiameter will produce 125 globules 1�m in diameter(d3) and these will have five times the surface area ofthe original globule. Associations among the restruc-tured fat globules, resulting from depositions of de-natured whey proteins and caseins on their surfaces,add strength to the structure. Formulation is an im-portant determinant of consistency of fermented milkproducts. As solids are added, with the consequentreduction in water content, viscosity and firmnessincrease. This is especially true when proteins areadded, because they bind water and their increasedconcentration enhances the protein structure. Pren-tice (1992) reported that increasing the dry matter ofyogurt from 12% to 15% resulted in an increase inthe firmness of a set yogurt by a factor of nearly 2and of stirred yogurt by slightly more.

Although it is possible to measure an apparentviscosity of broken down yogurt gel, a more use-ful measure of the firmness of the set-type yogurt isits resistance to rupture, i.e., the yield point of the

structure as determined by a compression-type test.As the gel is compressed, an instrument, such as anInstron texture-measuring device, records the stress(force divided by area of application) in kPa. Thepoint at which there is a break in the stress/straincurve is the yield point, and this point coincideswith the rearrangement of the internal structure. At asomewhat higher stress, called the rupture stress, thestructure collapses completely and the product hasproperties of a viscous fluid, i.e., it will flow. Stirredyogurts may be induced to flow so that the apparentviscosity can be measured as with a thin paste. Thisviscosity is shear-sensitive and the yogurt may bedescribed as partially thixotropic. (With thixotrophicfluids, as shear rate increases apparent viscosity de-creases.) Apparent viscosity tends to decrease withtime during application of continuous shearing in thesame way as with cream.

The low stresses that must be applied in measuringthe rheological properties of yogurt require the use ofdelicate instruments. The structure of the yogurt mustbe undisturbed as measurement commences. There-fore, preparing of set-type yogurt in the test appara-tus is preferred. With stirred yogurts, recovery of thestructure may take place within a few minutes afterit is disturbed. In comparisons among treatments itis necessary to avoid differences in time and tem-perature among samples within the experiment. Thepresence of particulates within yogurt leads to vari-ance in measurements of rheological parameters.

The fluid nature of cultured buttermilk and othersuch fermented milks permits their viscosities to bemeasured with instruments such as the cone andplate viscometer or the double cylinder Couette-typeviscometer. However, the capillary-type viscometerdoes not work well for such viscous materials. It isimportant to observe that with most fermented milkproducts the measured viscosity decreases progres-sively as shear rate is increased. Since the viscositythat is measured over the span of stresses is not aconstant value, as would be true of Newtonian fluids,this response is said to be non-Newtonian, and thevalue derived at a single designated stress is referredto as the apparent viscosity.

Water-Holding Capacity

One of the defects in appearance of fermented dairyfoods is free whey. Although free whey is not in it-self detrimental to the food, presence of it may sug-gest there were problems in production or distribu-tion of the product. Factors that favor the release of


whey from the product include insufficient proteins orstabilizing ingredients, improper processing, excessacidity, high storage temperature, and/or vibrationsof the containers sufficient to destroy a gel network.Although visual inspection of the finished product isthe usual method of determining the presence and ex-tent of the defect, it is possible to quantify the water-holding capacity of these products by centrifugingthem at the normal storage temperature in a trans-parent graduated centrifuge tube. Set-type yogurtsshould be set in the tube. Stirred-type yogurts andcultured cream products should be permitted to restand be refrigerated after filling the tubes to allow de-velopment of the normal structure. This type of testis useful when comparisons are being made amongformulas, especially in tests of stabilizers, proteintypes or concentrations, and among heat treatments.Laboratories should develop their own standards ofacceptability based on their unique formulas and op-erations. The objective is to minimize the occurrenceand magnitude of the defect under acceptable condi-tions of operation.

MICROBIOLOGICALPROPERTIESFermented products of milk were first naturally pro-duced and became accepted by humans who cameto realize that natural souring not only prolonged theuseful life of milk but also decreased the incidence oftransmission of disease through it. The production oflactic acid in milk decreases the pH to a point belowwhich many spoilage bacteria and some pathogensgrow. Furthermore, fermentation reduces the amountof lactose in the product making it more suitable forconsumption to lactose malabsorbing persons thanthe unfermented form of the product. Still there issome risk that pathogenic microorganisms may sur-vive in fermented dairy foods. Therefore, tests havebeen developed to detect and/or enumerate undesir-able bacteria in fermented milk products.

Tests for Coliform Bacteria

This method selects for aerobic or facultativelyanaerobic, Gram-negative, nonspore-forming, rod-shaped bacteria that are able to ferment lactose withthe production of acid and gas within 48 hourswhen incubated at 32◦C or 35◦C. These bacteriaare destroyed by pasteurization; therefore, their pres-ence in finished dairy products is an evidence of

postpasteurization contamination. The test has somelimitations in application to fermented dairy prod-ucts because viability of coliforms is decreased inthe acid environment of these products. It is recom-mended that tests be completed on freshly processedsamples. Furthermore, the presence of fermentablesweeteners in flavored yogurts or other products maylead to false positive results.

Several methods are described in Standard Meth-ods for the Examination of Dairy Products (Davidsonet al., 2004). The most applicable to fermented prod-ucts are the plate method with violet red bile (VRB)agar or the dry rehydratable film (Petrifilm) method.The plate method can be modified to improve thechances of recovering cells that may have been in-jured. The modification calls for plating the samplein a layer of tryptic soy agar, allowing it to solidify,then overlaying that layer with an equal amount ofdouble-strength VRB agar. Pectin may be substitutedfor agar as the gelling agent in the plate test whenthe probability exists that injured cells will be killedby the heat of the VRB agar. Incubation is at 32◦Cfor 24 ± hours. Typical colonies are dark red and atleast 0.5 mm in diameter on uncrowded plates. Con-firmation of the identities of representative coloniesshould be done when products contain sugars otherthan lactose.

The Petrifilm method requires that 1 ml of sam-ple be deposited onto a 20 cm2 area of an absorbentpad that contains nutrients, inhibitor, lactose, gellingagent, and an indicator dye. A transparent film is low-ered onto the surface of the prepared plate. After in-cubation under the conditions cited above, counts aremade of red colonies that are associated with a gasbubble.

Tests for ENTEROBACTERIACEAE

This group of Gram-negative bacteria containing thecoliform group plus similar microorganisms can fer-ment glucose when plated in MacConkey glucoseagar and incubated at 35◦C for 24 ± 2 hours. The testis otherwise completed as is the plate-type coliformtest, and it is a more sensitive indicator of postpas-teurization contamination than is the coliform test.

Yeast and Mold Counts

Yeast and molds grow well in acidic environments.However, their rates of growth at cold temperaturesare slow. They can be selected from among bac-teria in samples by using media acidified to pH


3.5 or media containing broad-spectrum antibiotics,i.e., equal portions of chlortetracycline hydrochlo-ride and chloramphenicol (Frank and Yousef, 2004).The latter favors recovery of acid-sensitive fungalcells. Greater recovery of these aerobic fungi is ex-pected when samples are surface-plated rather thanpour-plated. Because these organisms typically growslowly at the incubation temperature of 25◦C, in-cubation time is 5 days. To limit the spreading ofcertain fungi on the plate surfaces, it is recom-mended that rose bengal and dicloran be added to themedium.

Tests for Culture Bacteria

Developments in microbiology have made it possibleto select, reproduce, and store bacteria that consis-tently produce the desired flavor, aroma, texture, andappearance in several types of fermented dairy foods.It is sometimes necessary to selectively quantify theirnumbers in these foods.

Counts of lactic acid bacteria are done usingElliker’s lactic agar in plates that are either over-laid with a layer of the medium or are incubated inan oxygen-reduced environment. Incubation is for48 hours at 32◦C for mesophilic or 37◦C for ther-moduric bacteria. Because the method has a low de-gree of selectivity, confirmation of the identities ofrepresentative colonies should reveal Gram-positive,catalase-negative rods, or cocci as expected in thesample. Acid production by well-separated coloniescan be detected when bromcresol purple indicator isadded to the medium.

Counts of yogurt bacteria are facilitated by theuse of yogurt lactic agar that differentiates rods fromcocci (Frank and Yousef, 2004). The medium is com-posed of Elliker’s lactic agar supplemented with non-fat milk solids. Yogurt is diluted 1:100 in 0.1% pep-tone water and blended at high speed for 2 minutes tobreak up the chains and clumps of cells. Then 0.1 mlportions of serial dilutions are surface-plated on driedsurfaces of the plates. Incubation in an atmospherelow in oxygen and high in CO2 is at 37◦C for 48 hours.Colonies of Streptococcus thermophilus are small,white, and without a cloudy zone; whereas, those ofLactobacillus bulgaricus are large, white, and sur-rounded by a cloudy zone.

Diacetyl is produced primarily from citrate byLeuconostoc cremoris and Lactococcus lactis var.diacetylactis. These citrate-fermenting bacteria canbe enumerated according to the International DairyFederation Standard 180:1997 (Anonymous, 1997).

ANTIMICROBIAL SUBSTANCESAlthough the two major reasons for excluding an-tibiotics from human foods are to protect the con-sumer from untoward reactions to the antibiotic andto avoid development of resistance by microorgan-isms to antibiotics, the manufacturer of fermenteddairy foods has the additional and vital concern thatthere be no inhibition of growth of the culture bac-teria by antimicrobial substances. Therefore, antimi-crobial tests should be done routinely on the milk tobe fermented. In the United States it is required thatall bulk truckloads of milk be screened for antibiotics.This affords a minimal level of protection to the man-ufacturer of fermented products. However, screeningtests do not detect all antibiotics nor are they suffi-ciently sensitive to assure that there will be no inhi-bition of any specific culture. Standard Methods forthe Examination of Dairy Products (Bulthaus, 2004)provides 18 methods for antimicrobial testing. Themajor indicator bacterium used in the tests is Bacillusstearothermophilus var. calidolactis. In the referencemethod, spores suspended in an agar medium germi-nate and grow rapidly making the medium cloudy ifthe antibiotic is not present at an inhibitory concen-tration. The milk to be tested is placed on a paper discresting on the medium, and the diameter of the zoneof inhibition around the paper disc indicates the con-centration of the inhibitor present. The test bacteriumis sensitive to varying concentrations of several an-tibiotics. The same bacterium is used in the Delvotest.In this method a pH indicator dye, nutrients, and milkare added to a small glass vial containing the bacte-rial spores and agar. After incubation for 2.5 hours,the analyst checks the color of the medium to seewhether the bacterium has grown and produced acidsufficient to change the color of the medium frompurple to yellow. The Brilliant Black Reduction Test(BR Test AS) is similar to the Delvotest, the maindifference being the indicator. In the BR Test AS,growth of the B. stearothermophilus var. calidolactisstrain C953 cells is indicated when the black dye isreduced to the colorless state.

Immunoassays have been developed for specificantibiotics. In general these assays can be describedas follows. A sample of milk is introduced to a solidphase, such as polystyrene, to which are adsorbedantibodies for specific antibiotics. Any such antibi-otics are adsorbed from the milk onto the specificantibodies. This solid phase is then washed to re-move the unadsorbed material, and a tracer with anattached enzyme is then added. The tracer is adsorbed


to sites on the antibody that contain no antibiotic. Achromagenic substrate for the specific enzyme is thenadded. The amount of color that develops during anincubation period indicates the amount of the spe-cific inhibitor present. The more antibiotic presentthe less color develops, because the adsorbed antibi-otic limits the adsorption of the tracer and, thus, theconcentration of the enzyme.

SENSORY TESTSManufacturers must have the likes and dislikes ofconsumers in mind as they formulate and produce fer-mented milk products. Regardless of how positivelythe consumer thinks about the nutritional and healthbenefits of consumption of these foods, repeated pur-chases depend heavily on flavor, body, texture, andappearance. Therefore, it is vital that the producershave in place an effective process of evaluating thesecharacteristics using members of the target popula-tion. Obtaining representative respondents is essen-tial. Frequency of use or purchase of the product is agood criterion for making selections.

Preference Testing

Consumers are often asked to indicate a preferencefor one product versus another or to rank a groupof products in order of preference. Results of suchtests are useful in product development. Of course,the analyst wants results of preference testing to bevalid. When the question is “Which product do youlike better?” consumers respond to the characteris-tics of the product as a whole. To ask them whythey like it better is likely to lead to confusion ontheir part and to difficulty in the analysis on thepart of the analyst. Numbers of respondents must belarge, and samples must be presented in random orderand coded. The results may be tested with the two-tailed z value. Tables showing minimum numbersof agreeing judgments for numbers of participantsup to 100 are published in most statistics or sensoryanalysis books. Analysts must realize that showingno significant preference of one sample over anotherdoes not mean the samples do not differ. For exam-ple, there may be no difference in preference betweenpeppermint and spearmint, but the two flavors aredifferent.

In preference ranking there must be a forced-choice for each participant so that no ties in rank arepermitted. Although rankings provide preferences

among a group of samples, they do not reveal themagnitude of differences within the ranking. How-ever, if one sample is consistently ranked at the topor bottom of the group, while others are inconsis-tently ranked, that sample can be considered to differmarkedly from the others. Analysis of the results ofranking tests can be analyzed by reference to Basker’stables (Basker, 1988).

It is also possible to do a preference test in whichthe panelists scale their degree of preference. For ex-ample, they may indicate whether the difference islarge or moderate in the like or dislike direction orwhether there is no preference.

Acceptance Testing

The common method of acceptance testing involvesthe use of a hedonic scale that may have 9 or 11 points.A 9-point scale contains the following points: like ex-tremely, like very much, like moderately, like slightly,neither like nor dislike, dislike slightly, dislike mod-erately, dislike very much, and dislike extremely.Consumer preferences are considered to exist on acontinuum. Samples are served in randomized suc-cession and panelists respond by marking on the he-donic scale. Truncating the scale to 5 or 7 points isnot advised since there is a tendency for panelists toavoid extremes in ranking. Such a practice will tendto force the results toward the center—neither likenor dislike.

“Just right” scaling is useful in testing whether aselected characteristic is at the desirable level of in-tensity. For example, a “just right” scale of sournesswould be anchored on the left with “highly lackingsourness” and at the other end with “much too sour.”It would have “just right” in the center. The distribu-tion of a desirable set of responses should be peakedin the center and symmetrical. The center of the plot-ted distribution may not, of course, occur over the“just right” segment of the scale. Furthermore, themean may not reflect the true result if, for example,the panel contains two groups of consumers, one thatprefers a high and another low level of the charac-teristic being tested. The latter may yield a bimodaldistribution.

Descriptive Analysis

Sometimes a detailed description of the sensory at-tributes of a product is needed to enable comparisonof one product to another or to characterize a single


product. Such a test is called descriptive analysis.The method requires that a specific defined languagebe used in the description of product attributes—alanguage that is fully understood by the sensory pan-elists. Therefore, sensory judges must be trained touse exact product descriptors, ones that will reflecttrue differences among the tested products. Further-more, terms should not be redundant of or correlatedto other descriptors. For example, it is not advisable touse both the terms smooth and coarse in describingtexture. Panelists should be able to readily agree onthe meaning of a specific term. Reference standardsfor each descriptor are highly recommended.

Descriptive analysis is often used in developing aflavor profile of a product. Four to six highly trainedjudges are required. Panelists precisely define the fla-vors of the product category over a period of severaldays before they are employed in describing the fla-vorful components of the target product. Both theintensity of the flavor and the order of occurrenceamong all of the flavor notes are recorded. The panelleader, through discussion and consensus, derives aconsensus profile from the responses of the panelists.

The method described above has been expandedto provide quantitative results, i.e., quantitative de-scriptive analysis (QDA). Data are generated on anunstructured line scale by a panel of 10 to 12 judgeswho individually generate a set of terms to describethe product. The panel then develops a standard vo-cabulary by consensus. They choose reference sam-ples and define the descriptors. Evaluations of coded,randomly served samples are performed individuallyby the panelists. Panelists mark on 6-inch graphiclines anchored with single chosen descriptors (exam-ple: sourness—from weak on the left end to strong onthe right end of the scale). Numerical values are thenfound for each descriptor by measurement from theleft end of the line. The resulting data can be analyzedstatistically.

Another method of describing the sensory at-tributes of a food product is called “free-choice pro-filing.” Each individual panelist describes the sensoryattributes and develops a personal rating scale. Thisset of attributes and rating scale are then used by thepanelist to describe the product in question. Resultsare then subjected to an elaborate statistical proce-dure called the generalized Procrustes analysis. Thismethod allows for minimal training of panelists, butinterpretation of the meaning of the chosen descrip-tors is difficult. Furthermore, the number of descrip-tors may vary widely among panelists.

Sensory Tests for Quality Control

In the dairy industry it is a common practice to usehighly trained analysts to evaluate finished productsusing as a reference the scoring guide generated bythe Committee on the Sensory Evaluation of DairyProducts of the American Dairy Science Association.In this practice the judge must have a mental standardof the high quality desired in the product. Defects thatare observed in a product are then given a numericalvalue that determines the acceptability of a product.Often multiple trained judges meet around a set ofrepresentative samples and, using the scoring guide,come to an agreement as to the acceptability of theseproducts. By describing the defects of the productthey can develop recommendations for improvingproducts produced in the future.

It is vital that sensory analysts be screened for re-liability and consistency in judgment. A procedureshould be in place to ensure that multiple judges agreeboth on types and intensities of defects, as well astheir relative importance to the acceptability of thefermented dairy food. Use of reference and controlsamples is highly recommended. Reference samplesare those that have been described by experts as rep-resenting the ideal product profile of the firm. Controlsamples are unidentified samples taken from one ormore of those being evaluated and placed within theseries of samples being evaluated. Consistency canbe determined by randomly presenting to the analystsa set of coded samples in which there are multiplesamples of the same product. Abilities to reproducethe equivalent quality ratings on replicated productsshould be required.

Since analysts vary in the flavor thresholds forsignificant off-flavors, especially bitter and rancid(lipolyzed), it is important that these deficiencies berecognized and controlled.

Implementation of a sensory QC program has fourrequirements. First, representative products must beused to establish quality specifications. Second, qual-ified sensory analysts must be employed. Third, pro-tocols that will minimize error must be developedfor testing. These include instructions for collecting,storing, and handling samples; methods of serving,blind coding, and provision of reference samples.Fourth, procedures must be developed for reportingand using the data generated, including criteria foraction.

Readers are directed to the textbook by Lawlessand Heymann (1999) for further descriptions of thesemethods of sensory analysis.


REFERENCESAnonymous. 1987. Determination of Total Solids in

Milk, Cream and Evaporated Milk. Standard21B:1987. Brussels: IDF/ISO/AOAC.

Anonymous. 1991. Determination of Total SolidsContent in Yogurt. Standard 151:1991. Brussels:IDF/ISO/AOAC.

Anonymous. 1997. Enumeration of CitrateFermenting Lactic Acid Bacteria in MesophilicStarter Cultures. Standard 180:1997. Brussels: IDF/ISO/AOAC.

Basker KD. 1988. Critical values of differences amongrank sums for multiple comparisons. Food Technol.42(2):79–84, 42(7):88–89.

Bulthaus M. 2004. Detection of antibiotic/drugresidues in milk and dairy products. In: H Wehr, JFFrank (Eds), Standard Methods for the Examinationof Dairy Products, 17th ed. American Public HealthAssociation, Washington, pp. 293–323.

Davidson PM, Roth LA, Gambrel-Lenarz SA. 2004.Coliform and other indicator bacteria. In: H Wehr, JFFrank (Eds), Standard Methods for the Examinationof Dairy Products, 17th ed. American Public HealthAssociation, Washington, pp. 187–226.

Frank JF, Yousef AE. 2004. Tests for groups ofmicroorganisms. In: H Wehr, JF Frank (Eds),Standard Methods for the Examination of DairyProducts, 17th ed. American Public HealthAssociation, Washington, pp. 227–247.

Hooi R, Barbano DM, Bradley Jr RL, Budde D,Bulthaus M, Chettiar M, Lynch J, Reddy R. 2004.Chemical and physical methods. In: H Wehr, JFFrank (Eds), Standard Methods for the Examinationof Dairy Products, 17th ed. American Public HealthAssociation, Washington, pp. 363–536.

Horowitz W. 2003. Official Methods of Analysis, 17thed., 2nd rev. AOAC International, Gaithersberg.

Lawless HT, Heymann H. 1999. Sensory Evaluation ofFood: Principles and Practices. Kluwer AcademicPublishers, Hingham.

Prentice JH. 1992. Dairy Rheology: A Concise Guide.VCH Publishers, New York.

Richelieu M, Houlberg U, Nielsen JC. 1997.Determination of a-acetolactic acid and volatilecompounds by headspace gas chromatography.J. Dairy Sci. 80:1918–1925.

Wehr H, Frank JF. 2004. Standard Methods for theExamination of Dairy Products. 17th ed. AmericanPublic Health Association, Washington.

8Fermented Dairy Packaging

MaterialsAaron L. Brody

IntroductionFundamentals of Packaging

DefinitionPackaging TechnologyGraphicsStructural Design

Packaging MaterialsPaper and PaperboardMetalGlassPlasticPackaging Levels

Interactions of Product and PackagingThe Package in Product DistributionGraphic Design and AssessmentEconomics of PackagingRegulationPackaging and the Environment

Source ReductionRecyclingIncinerationBiodegradability

Packaging for Yogurt and Fermented Dairy ProductsPasteurized Fluid MilkShelf Stable Fluid Dairy ProductsSolid Dairy Product Packaging

Future trendsBibliography

INTRODUCTIONPerhaps as much as any component of the dairy prod-uct processing and distribution system, packagingcontributes to the safe delivery of the contained prod-ucts to end consumers. Without packaging the con-tained dairy products would not be protected against

the environment whose elements are always workingto revert contents back to their original molecularcomponents.

This chapter addresses the totality of containmentand protection of yogurt and fermented dairy prod-ucts from process through consumer use but, ofcourse, represents only a brief overview. Readers whorequire greater depth are referred to various textbooksand articles on the subject cited in the bibliography.Much of the secondary literature on this topic is notin the peer-review journals, but will be found in tradejournals and analogous publications. The informa-tion to be derived from such a probe is generallycontemporary and relevant, and should be valuableto readers.

This chapter begins with fundamentals, includ-ing the requirements, the major package materialsemployed, and their principal applications in dairyfoods. Dairy packaging operations, including thosefor fermented dairy products such as yogurt and cot-tage cheese are also described. Since suppliers playa major role in providing packaging integers, theyare classified and in some instances, identified, withno implication of endorsement as a result of inclu-sion or criticism as a result of omission. The moretraditional (from a dairy technologist’s standpoint)“packaging” or product/packaging interactions arereviewed. The more traditional (from a packagingtechnologist’s standpoint) distribution packaging isalso discussed briefly. Graphic design, regulationsaffecting packaging, and the role of packaging solidwaste in the environment are discussed. This chap-ter concludes with an enumeration of fermented dairyproduct packaging, both current and projected for thefuture.

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FUNDAMENTALS OFPACKAGINGPackaging is the most effective means to protectcontained fresh, stable, and fermented dairy prod-ucts from their point of manufacture through to theirconsumption. It is also arguably the most effectivemeans of communication between the dairy prod-ucts marketer and the end user of the fermenteddairy products, since the form and graphics of pack-ages are visible at the instant of purchase decisionand subsequently in the home and/or point of actualconsumption.

Definition

Packaging is the totality of all elements required tocontain the product within an envelope that functionsas a barrier between the product and the environ-ment that is invariably hostile to the product unlessthe protection afforded by packaging is present. En-vironmental insults include temperature, moisture,oxygen, microorganisms, animals, insects, vibration,impact shock, and human intrusion. By totality ismeant the package material and its visual and tactileappearance, the machinery for linking the product tothe package materials, the external distribution pack-aging and its associated equipment, the distributionitself, opening and removing the contents when andwhere desired, disposal of the spent package, etc.

The package is the material in its structural formsuch as a bottle, jar, can, pouch, bag, carton, case, etc.

The most important definitional element is thatpackaging is a means of protection for the productwhile it is in distribution.

Primary Packaging

Primary packaging is that which is in intimate and di-rect contact with the contents. As such it representsthe principal barrier between the product and the en-vironment. Most if not all of the protection againstoxygen, microorganisms, light, moisture gain, orloss, etc., is built into the primary packaging. Amongthe more common primary packages are metal cansand bottles; glass jars and bottles; flexible pouches,paperboard folding cartons; and plastic cups, bowls,tubs, and trays.

Secondary Packaging

Secondary packaging is external to the primary pack-aging and often an outer carton or a multipacker. It

enables the consumer to carry more than one primarypackage of a product at a time, i.e., the multipacker.It is also the external label, carton, tag, etc., that com-plements the primary package.

Distribution Packaging

Distribution packaging is a means of unitizing manyprimary and/or secondary packages to facilitate themovement of a large multiple of packages as a sin-gle entity. In this manner the packages are protectedand may be economically moved rather than havingto move one package at a time. Typical distributionpackages include corrugated fiberboard cases, shrinkfilm bundles, and pallets.

Packaging Technology

Packaging technology is the application of scien-tific and technical principles to employ packaging forfunctional purposes, including protection and com-munication.

Graphics

Graphics represent the external appearance of thepackage and usually includes copy, form, shape,color, typography, pictorials, etc., to communicatesome essential or desired information to the con-sumer or intermediary.

Structural Design

Structural design is the three-dimensional shapeof the package, cylinder, rectangular solid, taperedcylinder, flat, etc. Structure is also the word used toconnote the components and order of a multilayerpackage material such as a flexible lamination.

PACKAGING MATERIALSIn an ideal world a single package material and struc-ture would suffice to protect all yogurts and fer-mented dairy products. In this case, a steel can couldfunction in this role, but the size, heavy weight, andadverse economics of a steel can in many contextsdictate that it may not necessarily be employed whena less expensive and lighter weight material is avail-able. Because of the nature of package materials it isusually necessary to combine different materials toachieve a desired objective, but even the combinationof materials is usually less expensive than employ-ing all metal or glass plus a metal closure for many

8 Fermented Dairy Packaging Materials 131

applications. Even metal requires coating for protec-tion to be useful in most food applications, and soeven the “single-ply” package materials are reallymultiples.

Paper and Paperboard

Paper and paperboard represent by far the mostwidely used package material both in the UnitedStates and around the world. Because of its derivationfrom cellulose fibers, paper per se is not a barrier tomoisture or oxygen and so it is generally combinedwith other materials such as plastic or even aluminumfoil to render it effective in packaging applications.Most of this category is comprised of paperboardrather than paper, with the dividing boundary being0.010 inch caliber or gauge, paper being below theline and paperboard being above 0.010 inch.

The two basic types of paperboard are virgin orthat originating directly and primarily from trees andtheir wood, and recycled, or that whose raw materialis used paper and paperboard. Generally virgin pa-perboard, i.e., from tree wood, is cleaner and moreuniform, and has the greatest strength per caliper (unitgauge). Furthermore, it accepts the barrier materialfor coating more easily than does recycled paper-board. On the other hand recycled paperboard may,if desired, have a superior surface for printing. Recy-cled paperboard has been used as a secondary (non-food contact) package material for many decades,with the origins of the material being largely trim-mings and scrap from paper, paperboard, and corru-gated fiberboard converting plants.

Because paperboard is moisture sensitive, for dairyproducts packaging it is generally necessary to pro-tect the paperboard, which then functions primarilyas a structural material. Among the coatings used arelow-density polyethylene applied by hot melt extru-sion over the entire surface. Polyethylene is an ex-cellent moisture and water barrier to protect the basepaperboard.

Paperboard is used in dairy product packagingas the substrate for both gable top and asepticbrick/block-shaped cartons to contain fluids. In thelatter application it is extrusion laminated with plas-tic and aluminum foil to foster a long time shelf life.Coated paperboard is also used to fabricate cups andtrays to contain semisolid dairy products such as yo-gurt and cottage cheese.

Probably the major dairy products packaging ap-plication for paperboard, however, is in three-layerform in corrugated fiberboard cases used for distribu-

tion. The corrugated structure consists of three layersof two outer flat sheets called liners of paperboard,usually virgin, plus an inner fluted sheet or mediumthat can be either virgin or recycled. The corrugatedstructure offers vertical and horizontal compressionand impact strength to protect the contents, usuallyprimary packages.

Increasingly, the printing on corrugated fiberboardliners is being improved to permit the cases to be usedas retail displays or even as consumer packages andmultipacks.

Metal

Metal is most often used for cylindrical cans, whichare either thermally processed for microbiologicalstability, e.g., evaporated milk, or internally pressur-ized with carbon dioxide as for beer, and carbonatedbeverages. Aluminum is by far the most importantmetal used for can fabrication, being the primarymetal for beer and carbonated beverage cans, andincreasingly used for still beverage cans such as forjuices and aseptically canned milk, but only sparselyfor food cans except for shallow pet food and fishcans. In the past aluminum cans with easy open topswere used to contain milk-based puddings and yo-gurts that were filled aseptically. This applicationhas been replaced by barrier plastic cups with pee-lable flexible lidding materials. Almost all aluminumcans are two-piece. More recently, impact/extrusion-formed aluminum bottles are being applied for dairyproducts. Bottles are narrow neck structures, usuallyclosed with metal screw closures, but sometimes withpolypropylene closures.

Steel represents the major metal used for food cans,usually being coated with chromium oxide and latercoated with a thermoset plastic to protect the metalfrom corrosion.

Aluminum is also used in very thin or foil gauges−ca 0.00035 inch or below, as a flexible or semirigidpackaging laminant to impart oxygen and water vaporbarrier to the lamination. In this form, because it isfragile, the aluminum must be protected from damageby plastic or paper.

Glass

Glass is historically the oldest packaging materialstill in use. Glass is the best barrier known and by farthe most inert to product contents. Furthermore, inappropriate structures, glass has the greatest verticalcompressive strength. On the other hand, glass is very


heavy per unit of contents contained, is energy inten-sive to manufacture, and, as is well known, is prone tobreakage with impact. Glass may be fabricated intobottles and jars, almost all of which require plasticor metal devices to close. Although glass was themost widely used material for packaging fluid milkand its fermented analogues during the first half ofthe twentieth century, its dairy products applicationsduring the past two decades have dwindled to virtu-ally zero. Occasionally, a few dairies offer yogurt inglass to convey a high quality image, but most dairiesshun glass as a hazardous material in production andpackaging operations.

Plastic

Plastic is the newest package material having beendeveloped during the last century and having comeinto prominence only since the 1950s. In actuality,the term “plastic” describes a family of materials re-lated by their common derivation from petrochemicalsources. Each is quite different in properties relativeto packaging requirements, and so no single plasticmaterial is capable of being universally employed.All plastic package materials are characterized bytheir lightweight, relative ease of fabrication, lowcost, and ability to be tailored for specific end ap-plications. Together, by weight, all plastics compriseabout 20% of package materials, but because of theirlow densities, protect far larger volumes of contentsthan any other package materials, perhaps 60–70%of all foods and dairy products.

Polyethylene

The most commonly used packaging plastic ispolyethylene, which may be obtained in high,medium, and low densities with variations now avail-able on each of these. Low-density polyethylene(LDPE) is tough, flexible, easily formed after heat-ing, lightweight, and forgiving as a heat sealant. Itis an excellent water and water vapor barrier, but apoor oxygen and flavor barrier. LDPE’s most com-mon uses are as flexible pouches and bags, and asthe heat sealable extrusion coatings on paper, paper-board, and aluminum foil. Thus LDPE is the coatingon gable top fluid cartons, the laminant on asepticbricks and blocks, and the heat seal coating on manyflexible lidding materials.

High-density polyethylene (HDPE) is a semirigid,somewhat stiff translucent easily thermoformableplastic. With fairly good heat resistance, HDPE has

excellent moisture and water resistance but is a verypoor gas barrier. HDPE is used to form bottles formilk and many other liquids, as well as a wide varietyof other products with modest barrier requirements.HDPE may also be formed into cups, tubs, or traysto contain yogurt and cottage cheese.

Polyester

Polyethylene terephthalate polyester (PET) has beenavailable as a specialty film packaging material formany years, but only since the late 1970s did it enteras a significant package material. A modest oxygenand water vapor barrier, in package form after ori-entation, PET is tough and transparent. PET’s ma-jor packaging applications today are for carbonatedbeverage bottles, with other bottles and jars as fordrinkable yogurt, salad dressing, peanut butter, etc.,thermoformed cups and tubs, etc., in the semirigidcategory are secondary applications at present. PETmay also be formed into films that are tough and di-mensionally stable and, therefore, are quite good aslaminants to protect aluminum foil or for lidding-typeflexible closures. In partially crystallized form PETmay be fabricated into trays for dual oven (microwaveand conventional conduction–convection) reheating.

Polypropylene

In oriented film form, polypropylene is an excellent,economic, tough, transparent, high-moisture barrier,low-gas barrier package material, which has capturedalmost the entire quality flexible packaging mar-ket. Among the packages being made with orientedpolypropylene (OPP) are potato chip pouches, bak-ery goods overwraps, and candy bar wraps. Becauseof its relatively high temperature resistance (up to250◦F), polypropylene resin is combined with otherhigher barrier packaging materials to produce multi-layer plastic bottles and cans such as for ketchup orfor “bucket-type” cans for microwave reheating. Foreconomic reasons (i.e., when the commodity price isfavorable), polypropylene may be injection moldedinto tubs and cups to contain fermented dairy prod-ucts such as yogurt and cottage cheese.

Polystyrene

Polystyrene is a plastic with a relatively poor oxygenand water vapor barrier but good structural proper-ties. Being inexpensive and easy to form by sheetextrusion and thermoforming or injection molding


methods, polystyrene has been one plastic of choicefor cup/tub containment of yogurt, cottage cheese,etc., since the demise of wax-coated paperboard dur-ing the late twentieth century.

Oxygen-Barrier Materials

Most of the above plastics are not good oxygen bar-riers. To obtain the oxygen barrier, two plastic resins,polyvinylidene chloride (PVDC), and ethylene vinylalcohol (EVOH) are employed commercially. PVDCis the older of the two and has excellent water vaporand fat resistance but is relatively difficult to fab-ricate, as well as being questioned on environmen-tal grounds for its hydrogen chloride content. MuchPVDC is used in emulsion-coating form on films toachieve oxygen barrier in films used for processedmeats and cured cheese.

EVOH is a better oxygen-barrier material and iseasier to fabricate but is very sensitive to moisture.The economics of both high-oxygen barrier mate-rials dictate that they be combined with other lessexpensive structural plastic resins. Thus EVOH isusually coextruded (i.e., forced with another plasticthrough a common die) with polypropylene to pro-duce films, sheets, or coatings. The EVOH is pro-tected from environmental or product moisture inthese applications. In addition to its involvement in“bucket-style” cans, EVOH is also an increasinglyimportant material to protect food and beverage con-tents from flavor interaction with packaging mate-rials. With many food and beverage contents nowbeing held for prolonged periods up to a year at am-bient temperature, the probability of adverse prod-uct plastic interactions, largely flavor changes, isrelatively high. Consequently, an intermediate high-barrier material such as EVOH serves to minimizesuch interactions in packages such as those for chilledjuices.

Packaging Levels

No such entity as comprehensive packaging exists ina single supplier or user organization, even thoughcomprehensiveness should be indispensable to ef-fective and functional packaging. All packaging isdivided into a large number of individual entities se-lected from a broad array of offerings to permit thedairy products packager to select according to theproduct, protection, distribution, marketing, need, ordesire. These operations may be defined in tier orhorizontal form. Examples of the levels include the

suppliers of raw materials, those who convert theseraw materials into useful packages, suppliers of ma-chinery, designers, publishers, schools, etc.

Raw Material Suppliers

Raw material suppliers include organizations, whichobtain basic materials from the planetary resourcessuch as the ground, air, or oceans and transform themin very large quantities into bulk materials that maythen be converted into packaging. Among such orga-nizations that generally do not supply dairies are alu-minum miners and refiners, steel mills, paper and pa-perboard mills, and petrochemical companies. Suchcompanies deliver materials such as coils of metalsheet, rolls of paperboard, carloads of plastic resin,etc., to converters. The principal exception to this isthe glass industry whose nature fosters the direct in-tegration of raw material and converting into bottlesand jars without intermediate companies.

Among the packaging material, suppliers of inter-est to dairy product packagers currently are in thearea of paperboard: International Paper; Blue Ridge;Smurfit Stone; and Weyerhaueser, which are exam-ples of companies that manufacture virgin paper-board used downstream in gable top cartons and/orcorrugated fiberboard cases. Basic aluminum suppli-ers include Alcan and Alcoa. Steel suppliers includeUSX and Weirton. Plastic resin suppliers includeDuPont, Dow, and Exxon Mobil for polyethylene;Voridian for polyester; Dow for polystyrene; and BPChemical for polypropylenes.

Converters

Converters are organizations, which supply usefulpackaging to dairies and other food packagers. Suchorganizations acquire commodity-type raw materialsfrom their own suppliers and process and combinethem to produce flexible films, sheets, cups, cans,tubs, trays, bottles, jars, cartons, cases, etc. Amongthe operations provided by converters are printing,extruding, cutting, molding, lamination, adhesion,cup formation, nesting, slitting, and coating. Quanti-ties involved are generally much smaller than thoseoffered by their new material suppliers, and sufficientfor their dairy and food users.

Converters tending to focus on the dairy industryinclude International Paper, Blue Ridge, and TetraPak for gable top paperboard cartons; and Sweetheartand Sealright for paperboard rounds. Corrugatedfiberboard case manufacturers include International


Paper, Smurfit-Stone, and several hundred othersmaller companies. Ice cream and frozen yogurt car-ton manufacturers are headed by Graphic Packag-ing, with Sealright (Huhtamaki) as the major sup-plier for bulk ice cream containers. Steel metalcan makers include Rexam and Crown Cork andSeal. Aluminum can makers include Ball and CrownCork and Seal. Glass bottle manufacturers includeOwens Illinois, St. Gobain, and Consumers. Flex-ible packaging converters include Curwood, Print-pack, Alcan, Winpak, and Cryovac, as well as severalhundred smaller firms. Plastic bottle blow moldersand injection blow molders include Owens–Illinois,Consolidated, Amcor and Alcan, as well as manysmaller companies and self-manufacturers. Cup andtub molders include Fabri-Kal, Berry, Sweetheart,and Solo (particularly for polyester cups). These areintended only to indicate a few of the wide arrayof suppliers which are available to fermented dairyproduct packagers to provide their package materialneeds. In almost every instance there are many sup-pliers. In no instance can a single supplier providea complete range of all package materials that a fer-mented dairy packager might require.

Packagers

Packagers are the yogurt and fermented dairy prod-uct processors which marry the package materials tothe food and dairy products. Packagers employ ma-chinery designed, engineered, and built by specialistfirms.

Distributors

Distributors include the means to deliver the pack-aged dairy and food products to the consumers.Distribution channels include warehouses, trans-portation, wholesalers, brokers, jobbers, retailers,etc. Retailers include grocery and food service out-lets.

In addition to these tiers a range of suppliersprovide goods and services to comprehend the re-quirements of comprehensive packaging. Graphicdesigners, for example, offer the services, which areconverted by printing plate makers into the hardwarerequired to deliver ready-to-display packages. Theoutput of graphic designers is intended to complywith regulatory requirements, as well as to meet thedesires of marketing managers for retail communi-cation.

Packaging Equipment

Not the least important of providers are the packagingequipment manufacturers, agents, and importers. Ofsome importance to dairy packagers are Evergreenand Nimco for gable top paperboard cartoning. TetraPak now supplies not only its traditional aseptic pack-aging equipment but also gable top cartoning ma-chinery. Among the aseptic plastic cup equipmentsuppliers are Bosch, Hassia, Hamba, Autoprod, andHolmatic. Plastic bottle-filling equipment is suppliedby U. S. Bottlers, Krones, etc. Cup fillers may beobtained from Autoprod, Holmatic, and Sealright.Suppliers for flexible packaging equipment for prod-ucts such as cheese include Hayssen, Multivac, andTiromat. Secondary packaging equipment suppli-ers include MeadWestvaco and Graphic Packaging.Suppliers of machinery for distribution packaging in-clude ABC, Salwasser, Douglas, and Pearson.

Packaging Development

The development of packaging is a sequence that in-volves a broad range of disciplines and professionalswho interact in overlapping to finally deliver pack-ages to the consumer. The most indispensable con-sideration in developing packaging is the product,and hence, consumer safety, with the interaction ofpackaging and contained food or dairy product beingone element, and the interaction of processing andpackage another. Interactions are not permitted thatmight in distribution extract contaminants from thecontained food or dairy contents.

No processing operation such as heating can com-promise the safety as, for example, hot filling orretort processing, which could conceivably disruptheat seals and permit recontamination by microor-ganisms.

The above are axiomatic in the selection of packagematerials and structures.

The next requirement in the development of pack-aging is the technical function. If the package cancontain and protect the product in normal distribu-tion, it has fulfilled its basic objective. Thus, an ini-tial step in packaging development is the engineeringto ensure technical functionality. Variables such asmoisture protection, seal integrity, protection againstthe entry of oxygen or microorganisms, resistance toheat or cold or both in sequence, product/packageflavor interaction, etc., are specified and measuredversus the ability of the package to meet the other


necessary and desired criteria. Subsequently, the abil-ity of the package to withstand the distribution en-vironment using such measures as impact, vibra-tion, and compression resistance are predicted andmeasured.

In some instances, the variables may be predictedby mathematical models knowing the end objectivein terms, first, of desired shelf life under specific tem-peratures; and second, the effect of that variable onthe shelf life. A typical example might be a cottagecheese product in refrigerated distribution that wouldhave a target shelf life of 40 days. The model wouldbegin with microbiological growth as probably inde-pendent of packaging. From a packaging perspectivea variable such as no more than 1% moisture lossthrough the package structure in those 40 days at40◦F would be inputted to predict the gauge of thepackage material options required in the particularstructure being considered. Of course the mathemat-ical models in shelf-life prediction are only screeningthe guidelines today, and so actual laboratory testingwill be required to verify the tests.

Similarly distribution resistance may be mathe-matically predicted with fairly good accuracy, butactual laboratory testing is needed in almost every in-stance. In many instances, the use of real distributionis employed although, of course, the test variables ofa single truck ride are such that the results can bemisleading. Nevertheless, many packaging develop-ers use actual truck shipments as a testing protocolin lieu of vibration and drop testers.

Most of the time the sequence is to extrapolatefrom known packages of similar products such as,for example, if the product is a flavor variation of anexisting commercial product, relatively little shelf-life testing is necessary. Some testing should be per-formed to ascertain the effects of the differences suchas flavor interactions.

Although laboratory samples are satisfactory forinitial evaluations, it is necessary to conduct testson actual production samples, since these invari-ably differ significantly from the pristine prototypes.When actual production line sample packages arenot immediately available, the closer the samples areto machine-made, the better for real-life prediction.While functionality testing and its associated reengi-neering of the package structure are underway, themarketing inputs are incorporated into the package.These include the graphic requirements, both legaland those desired for marketing and communication,structural features such as pour spouts, reclosure tabs,

tamper-evident/tamper-resistant devices, etc. When-ever a structural change is made, the resulting pack-age should be reevaluated, but this step is not alwaysperformed in the haste of meeting the marketing, pro-duction, distribution, financial, etc. schedules.

Today graphic design is usually performed withcomputer assistance and so rapid action is quite fea-sible. In a large project, it is highly recommended thatthe package design including all its structural featuresundergo both consumer and retail display testing.Too much investment has been made in the packageto avoid this key step, although many dairy productcompanies may overlook it. A host of consumer andmarketing research firms conduct such tests rangingfrom focus groups to actual in-store displays or in-home testing. None is perfect and comprehensive,although each purveyor of a test procedure believesthat it is the ideal measuring tool. The most importantdesign test must be the simulation of in-store display,i.e., perception of the package by consumers in thenormal shopping environment as in a mass displayamong other similar and competitive products. Yetanother necessary test is how consumers actually usethe package to deliver the product to themselves toascertain any consumer perceived flaws or areas, inwhich the package design may be improved.

During the development of the package, it is nec-essary to select the equipment on which the pack-age is to be made to ensure that the product, pack-age material, and machine are compatible. Machineretrofitting and reengineering is not only feasible, itis to be encouraged prior to completion of develop-ment. Package and equipment development shouldbe a totally integrated effort and should be continu-ous from the inception of any packaging developmentproject. As much as possible, off-the-shelf equipmentshould be used since custom equipment developmentrequires high investment. Standard equipment can bemodified to accommodate special requirements of theproduct and package.

Not the final step in the initial development is sec-ondary and tertiary or distribution packaging. Hereboth the package and the equipment must be devel-oped and selected or modified for the unitization andcontainment of primary packages.

Throughout the process, it is desirable to developthe economics of the package including the cost ofthe package materials, equipment, labor, utilities, etc.Each should be developed in a total systems contextto ensure that the economics are not dictated solelyby the purchase price of the package materials—a


variable that can be highly misleading in the contextof the total distribution and marketing objectives.

All packaging development must include contin-uous monitoring, feedback, and refining to ensurethat some environmental variable has not changed,or that there has not been a change in the product,or that some improvement in package materials hasnot introduced the possibility of effecting a changeto better the performance or the economics, or both.

Resources Available for PackagingDevelopment and Implementation

In addition to the suppliers indicated above for pro-viding the hardware and software, there are manyother resources that are not always immediately vis-ible. As indicated above, graphic designers are val-ued suppliers since, unlike mainstream advertisingagency or free lance artists, they are experienced inpackaging design including the peculiar nature ofshelf display and the vagaries of package materialconverter printing.

Consulting firms (such as, for example, Packag-ing/Brody, Inc.) deliver a variety of accurate insightsinto the technologies of packaging, and also can, ifdesired, actually engineer and test the package struc-tures and broker the supply. Most consulting organi-zations, if they are indeed organizations and not sin-gle persons, offer advice based on information notgleaned from experience but rather education. Pack-agers seeking insights from consultants are urged tostudy their dossiers carefully to determine that theircounsel is really that and not merely superficial bitsof little or no real value. It is also important to ascer-tain that the counsel is coming from the professionalwith whom the communication is made. Many largerconsultancies often delegate the actual consulting topersons who are either juniors or who are not busy sothe inputs contain little relevant substance. The as-signed person(s) have been learning about the topicduring the consultancy assignment.

Many packaging journals are published in both theUnited States and the other parts of the world. Eachis distinctive in its coverage of packaging subjectmaterial, but all share one characteristic: They areassembled and edited by journalists for maximumreader interest. Despite the reporting and investiga-tive research behind the published pieces, they oftenlack the critical insights that a packaging professionalwould impact. Furthermore, there is little follow-up to ascertain the progress on developments. Thuspackaging journals provide a highlighting service

that can represent an education for novices, and astimulus for those who function in packaging on anevery day basis. For in-depth information there is nooutstanding periodical today. Nevertheless, the rolesof Packaging Digest with its large sprawling person-alized articles and Food and Drug Packaging withits not infrequent features and editorials, PackagingWorld, and BrandPackaging, targeted at marketers,cannot in any way be minimized: All offer good andtimely information and are a must-reading for dairyproducts packaging professionals.

Nonpackaging trade periodicals such as DairyField cover packaging with rewritten press releases,reporting or, occasionally, professionally preparedpieces. Unfortunately, such journals do not provideregular information on packaging and cannot be de-pended upon as a source. On the other hand, whenthere is coverage, the information on the specific ap-plication is usually quite good. Food Technology of-fers in-depth pieces, contemporary, and future pack-aging technologies.

A number of books on packaging have been pub-lished, including some by this author, for example,Encyclopedia of Packaging Technology, second edi-tion, 1997, John Wiley and Sons, NY. The books areusually general texts and contain only brief or passingreferences to dairy packaging per se. To date, to ourknowledge no definitive text on dairy products pack-aging has been written and published. Dairy productstexts often contain single chapters on packaging likethis one, which is necessarily sketchy since such abroad field must be covered in such a short space.

Professional and trade associations both publishinformation on packaging and sponsor meetings andconferences on the subject. Those by the US profes-sional packaging society, Institute of Packaging Pro-fessionals (IOPP), generally emphasize more generalpackaging topics rather than focusing on specifics of aparticular group such as dairy. Recently, however, in-creased emphasis has been placed on food and bever-age, including dairy products packaging. The reverseis true for dairy associations, which tend to focus onthe mainstream of dairy products rather than on pack-aging for dairy products. On the other hand when aprofessional group covers a dairy packaging subject,the treatment tends to be quite good.

Both professional and trade associations, as wellas for-profit companies organize and produce exhi-bitions and conferences on packaging and on dairyproducts. There has not yet been an American dairyproducts packaging exhibition, although in Europe,excellent dairy packaging expositions have been


presented from time to time. The major world pack-aging exposition is Interpack held every three years inGermany, but generally absent of much direct dairypackaging. In the United States, the major packag-ing exhibition is Pack Expo held every other year,but also suffering, in this context, from a paucity ofdairy products packaging. Regardless packaging pro-fessionals involved in dairy packaging have much togain from alert attendance at major packaging exhibi-tions, which usually present much that is innovativeand applicable to dairy product packaging interests.

Thirteen American universities offer degree pro-grams in packaging with one, Clemson University,offering a program in food packaging. The largestpackaging program is the Michigan State UniversitySchool of Packaging. Behind them is Rochester Insti-tute of Technology. Among the other universities of-fering packaging are: University of Missouri (Rolla);Rutgers, the State University of New Jersey; Univer-sity of Wisconsin (Stout); Indiana State University;and San Jose State University. Generally universi-ties offering curricula in food science and technologyhave a single course in food packaging. Dairy curric-ula may sometimes offer a course in packaging froma nonpackaging faculty member. A few universitieshave research programs dealing with dairy packag-ing, the most prominent of which is North CarolinaState University with an aseptic packaging center.

A very limited number of federal and state govern-ment agencies conduct research in packaging withthe FDA being the most prominent among these, fo-cusing, as might be expected, on safety aspects. Off-shore, however, government and quasi-governmentagencies perform both basic and applied researchon packaging. Among these are Campden Chorley-wood Food & Drink Research Association and SIK inSweden.

All of these groups represent resources that shouldbe employed in comprehending the totality of pack-aging as it applies to dairy products packaging issues.

INTERACTIONS OF PRODUCTAND PACKAGINGAs has been previously mentioned, it is axiomaticthat no significant interaction takes place betweenthe contained product and the package material. Thisis particularly important in considering the possibil-ity of any potentially toxic materials being extractedfrom the package materials into the contained prod-uct, an event specifically prohibited by law and reg-ulation. From a business perspective any interaction

that perceptibly alters the quality of the containedproduct is highly undesirable.

Although the notion of extraction is relatively easyto understand, it is also necessary to grasp the ideathat extraction can occur not only in what might beregarded as normal contact but also under unusualconditions. For example migration of package ma-terial constituents can occur in distribution, whichmay take place at ambient, chilled, or frozen con-ditions. Migration rates vary considerably under thethree different temperature conditions with the ambi-ent generally more rapid in accordance with Arrhe-nius laws that dictate exponentially increasing ratesas a function of temperature. But if the product isplaced in contact with the interior package materialat an elevated temperature during some processing orconsumer preparation time, migration can be greatlyaccelerated, thus leading to brief but nevertheless sig-nificant component migration. This situation becameevident in the case of microwave susceptors whosenormal component migration patterns in original pro-cessing, packaging, and distribution demonstratedbenign activity. When the susceptors perform theirnormal function of surface heating, however brief,very high temperature periods occur during whichnew chemical entities are formed, which may mi-grate during the interval from the package materialinto the food. Although this specific situation provedto not present any public health problems, it alertedboth officials and food packagers to the possibilityand the potential consequences when actual use con-ditions are not considered.

The microwave susceptor case also highlighted an-other effect that was initially demonstrated with re-tort pouches many years ago: indirect migration. Theterm “indirect” is used in regulatory contexts to indi-cate a component that is not intentionally introducedinto a food or dairy product, but enters from a sec-ondary source such as from the surrounding packagematerial. In this context, however, indirect means thatthe component comes not from the package mate-rial in direct and intimate contact with the product,but rather from a layer that is remote from contact,e.g., an adhesive or an outer ply. In this situationthe migrant not only leaves its own substrate, it alsomigrates across other packaging components to thesurface of the inner layer and potential contact withthe contained dairy product.

Contact is not necessary since the migrant mightevaporate or sublime into the interior package en-vironment and then be borne to the food surfacefor interaction. As indicated above, these actions are


accelerated at elevated temperatures, even brief ex-posures.

One variable that was not always considered wasthat for most of the history of packaged dairy prod-ucts, contact between plastic and contents was usu-ally brief and at relatively low temperatures, thusminimizing or even hiding any adverse interaction.With the development of aseptic packaging systems,hot filling and extended shelf life using plastic pack-aging, product-package material contact time at am-bient temperatures extended to weeks, months, andeven, occasionally, years. Under these circumstances,measurable interactions can take place, with somecaution required to ensure against harmful migra-tion. Some of the interior package materials such aspolyethylene are not inert to organics, and so long-term exposure can and does result in undesirable in-teractions. Since no known package material containsor transmutes to components that might be harm-ful in final product consumption, and this effect isvery carefully monitored by plastic resin suppliers,the probability of a public health problem is almostabsent. On the other hand interactions that can al-ter product quality can occur, and even if they arenot harmful to consumers, they can be detrimental tosales. Thus all packaging should be tested to ensurethat under the total conditions of processing, pack-aging, and distribution, no measurable interaction ofproduct and package occurs.

The reverse of entry of undesirable materials is theremoval of desirable constituents, another of the is-sues of employing plastics in proximity with the dairyproduct contents. Scalping or loss of product com-ponents to the contact package materials has beena known phenomenon for many years, but largelyoverlooked, since only infrequently was there anyprolonged contact time of plastic and liquid or fluidproduct at ambient temperature. Since the advent ofaseptic and extended shelf-life packaging, however,long-time intimate contact was initiated and con-ditions were established for the plastic material toremove desirable product compounds. These havebeen largely oil-based compounds that dissolve inpolyethylene, but also include volatiles, which nor-mally contribute to the desirable flavor attributes.Many juices are subject to scalping, an event that hasled to the replacement or modification of the interiorplastic heat sealants with more inert plastics.

Of some interest to fermented dairy product pack-agers is that measurable losses may be measured inlong-term refrigerated distribution. For example dur-ing the 50+ day chilled extended shelf life of juices

in gable top polyethylene-coated paperboard cartons,the desirable flavor constituents are scalped suffi-ciently to be detectable by consumers. To overcomethis serious problem, chilled juice packers often nowspecify flavor barrier plastics on the interiors of theircartons. Scalping of desirable flavor constituents ofdairy products by polyolefin has been noted. Lipid-soluble volatiles might be expected to be found inthe interior heat-sealant layers of dairy product pack-aging and to be responsible for some of the flavordeteriorations because of product over time. Dairyproduct packagers should be alert for this possibil-ity in developing packaging for their products, eventhose being distributed under refrigerated conditionsfor short periods.

Yet another interaction that should be of some con-cern is the change in package material properties overtime or the change in either product contents or theenvironment. For example, paperboard loses most ofits physical strength when exposed to water or evenwater vapor. Consequently, the protection of paper-board is essential to the protection of the product. Wetstrength paperboard has been a standard for years, butthis is only a relatively minor temporary expedient.Hiding all raw paperboard edges and seals is anothermore expensive, but significant step, and is almostalways employed for long-term distribution such asfor aseptic packages. Perhaps this should also be stan-dard practice for all paperboard packaging for liquidand fluid dairy products.

The nylon gas barriers of cured cheese packagingare altered by the inevitable presence of moisture andmust be accounted for in developing packaging forany dairy products. The situation with the newer oxy-gen barrier, ethylene vinyl alcohol (EVOH), is evenmore severe, with as much as 75% of the gas bar-rier properties being lost at relative humidities above70%. Even under these circumstances these two sen-sitive plastics are commercially employed for dairyproduct packaging because even after the propertydecreases, they represent superior barrier to the al-ternatives.

These recitations on problems with plastic packag-ing materials hint that perhaps avoidance of plasticmight be a desirable alternative. Given that plasticmaterials are imperfect, in total, they generally rep-resent a better alternative than attempting, for ex-ample, to package in uncoated paperboard, whichwould have no liquid barrier, or in glass that would beboth expensive and hazardous to consumers in theselitigious times. Furthermore, the cleaning of glass,particularly in reusable situations, is not devoid of


problems with respect to energy, breakage, and resid-ual cleaning compounds. Metal cans would be an al-ternative, but metal must be plastic coated in the inte-rior to protect the metal with almost all the problemsassociated with plastic in contact with product.

It is better to employ the packaging with the bestcombination of properties knowing in advance theproblems that might be encountered, and to accountfor these issues, than to use a suboptimum material orstructure. If plastics appear to present serious prob-lems in this context, consider the alternatives that,in reality, could present even more serious majorproblems.

THE PACKAGE IN PRODUCTDISTRIBUTIONAmong the many functions of packaging are to pro-tect the contents from distributional physical abusesuch as vibration, impact, compression, etc. The no-tion of delivering dairy products one at a time is, ofcourse, preposterous. Therefore, primary packagesshould be unitized into groups that are more easilymoved en masse. All packaging including the pri-mary packages must be protected throughout the en-tire distribution cycle, including warehousing, trans-portation, docking, inventorying, retailer handling,etc. The primary package itself must be able to with-stand retail display, handling by the consumer, andin-home or food service handling when applicable.

Since the primary package is the principal barrier,it is necessary to engineer it to remain intact through-out the entire distribution cycle. It must withstandphysical stresses such as would be encountered onthe production and packaging lines, including im-pact, abrading, turning corners, compression, and, indairy product plants, heat and water. Subsequent tothe packaging lines, primary packages are unitized,sometimes under compression, sometimes by drop-ping, but in any case, to be further contained and pro-tected by some outer unitizer. The next outer packageis most often a corrugated fiberboard case, which isengineered to resist modest vibration impacts, com-pression, and drops. Unfortunately, corrugated fiber-board cases are susceptible to moisture and water andlose their protective properties rapidly as a result ofexposure. This vulnerability must be accounted forwhen employing corrugated fiberboard as a distribu-tion package.

Alternatives to the corrugated fiberboard case in-clude corrugated fiberboard trays or pads combinedwith plastic (usually low-density polyethylene film

or a variation) shrink film capable of tightly bindingprimary packages into a single unit that is strongerthan the individual primary packages because of the“cellular” construction. Shrink film is also a goodmoisture barrier and so protects interior paperboardfrom the inevitable moisture of dairy product distri-bution environments. The small amount of heat re-quired to shrink the film around the unitized primarypackages is so inconsequential that even ice creampackages are readily unitized and held together byheat shrunk plastic film.

Many dairy products are distributed in returnablerigid plastic crates, totes, or cases. These units, usu-ally injection molded high-density polyethylene butsometimes polypropylene or other structures, are en-gineered to cradle and contain numbers of primarypackages to protect them from virtually any physi-cal abuse. Often the individual primary packages arein cells within the crate or tote to prevent the pri-mary packages from any contact with each other andthus eliminate surface abrasion that can damage glassbottles, paperboard cartons, and even plastic bottles.When the dairy’s distribution system permits, i.e.,direct delivery by a person who can take back the rel-atively bulky and expensive returnable plastic case, itmakes physical and economic sense to employ suchdistribution packaging. The initial capital investmentis high but the total system cost over time and re-peated reuse, when the infrastructure is available andin place, is well below that of purchasing individualdisposable distribution packages.

Distribution stresses and the protection affordedby various alternative distribution packaging systemsmay be computed by reliable tested methods with ex-cellent predictability. These methods are more oftenemployed by packaging engineers associated withhigh-price hardware items, but the test bed and com-puter techniques may be readily applied to distribu-tion packaging for dairy products. In the system, testpackages are subjected to known stress inputs such asvibration or impact, and the point of failure is quan-tified. Knowing the properties of alternative distri-bution packaging such as corrugated fiberboard of aspecific edge crush test and dimension, or an internalegg crate-type structure, computer modeling can pre-dict the distribution performance. In this manner theminimum distribution packaging required to protectthe primary packaging may be derived by computa-tion rather than by empirical methods. Nevertheless,it is advisable to conduct actual test shipments to ver-ify the theoretical results. Computer methods avoidthe long and tedious and often very inaccurate trial


and error methods that have been the hallmark ofdistribution packaging selection.

GRAPHIC DESIGN ANDASSESSMENTGraphic design is the development of the externalappearance of the packaging to comply with regu-lations and to meet marketing desires that are hope-fully dictated by consumer and retailer needs andperceived needs. Good graphic designers also incor-porate structural features that are not incompatiblewith the protection requirements of the product butare compatible with retail display or consumer use,e.g., dispensing spouts. Good graphic design is per-formed to ensure that the package appearance in retaildisplay has visual impact in mass among an array ofother competitive packages. Designs may appear ex-cellent in isolation, but in mass display at retail level,they might be lost. When media advertising is used, itis necessary to ensure that the package appearance isattractive in photography or on television as the casemay be.

Graphic design is usually best managed from amarketing department since this is the group that ismost influenced by the shelf appearance of the pack-age. It is important, however, that the packaging de-velopment professional be actively involved in theprocess to ensure that the technical aspects are notviolated in the name of appearance. Shelf appear-ance and other marketing oriented features are alsoimportant.

Graphic design today should be performed bypackaging design professionals. The use of free-lanceor advertising agency artists with little or no experi-ence in packaging design is not to be encouraged. It iseven better to employ professionals with experiencein yogurt and fermented dairy products packaging.

In the past, all graphic design was performed withpaper, pencil, colored pens, ink, etc. Such artist’s ren-ditions required time and relative difficulty of chang-ing and evaluating changes. Today most graphicdesigners are able to design on graphic comput-ers, permitting marketing managers to experiencedesign variations immediately. Three-dimensionalviews may be depicted on the two-dimensional videodisplay screen, and hard copy versions. Mass displayscan be represented in virtual reality on video displayscreens. Almost instant color copies may be wrappedaround physical structures to enable marketing man-agers to actually see and touch three-dimensionalsamples immediately. While permitting instant

packaging design, computer graphics also generatemultiple variations for evaluation. Computer-graphiccapabilities are so sophisticated that the camera-ready art for printing plate manufacture are generatedby the computer and can even drive the plate-makingprocess.

With design being so critical for market accep-tance, personal opinion by marketing managers orgraphic design managers is a poor means of selectingthe optimum design. Objective evaluation of designis nearly as important for evaluation as is consumertesting of the product. If the consumer does not try theproduct or cannot find the product, it is of little valueto the dairy. Many different techniques for packag-ing (graphic) evaluation are offered, not one of whichis universally accepted. Each, however, has its ownadvocates. The most common evaluation techniqueprobably is a focus group in which a small group ofrepresentative consumers examines and discusses thetotality under the guidance of a moderator.

Among the more intriguing evaluation methods aremeasurement of eye movement, time required to rec-ognize the package on a darkened screen, and mea-surement of brain waves responding to exposure tothe design. Perhaps the best method is placement ofthe package in a mass display in a test store environ-ment followed by measurement of sales and follow-up with a selected sample of purchasers to ascertaintheir reasons for their decision.

ECONOMICS OF PACKAGINGContrary to general belief, with infrequent excep-tions, packaging does not cost more than the productcontained. Generally packaging costs represent con-siderably less than 10% of the retail price of the foodor dairy product on the retail shelf.

Not too long ago packaging costs were generallycomputed solely by the primary package materialspurchase price. With education, however, packag-ing purchasing and marketing managers now usu-ally measure packaging costs by adding all relevantvariables and allocating all fixed, including capital,expenditures for equipment. Thus, the economics ofpackaging include such costs as those for the acqui-sition of the primary packaging materials; plus thesecondary and distribution packaging materials; plusthe labels, adhesives, coding inks, etc., i.e., the ad-juncts, plus the labor, plus the utilities, etc. In addi-tion, allocation of fixed plant costs such as supervi-sion and maintenance, floor space, etc. is included.Just as important in determination of economics of


packaging is the machinery which invariably has ahigh initial cost and must be evaluated for output,output speed, efficiency, scrap losses, both for pack-aging materials and product, down time, and ability tolink efficiently with both downstream and upstreampackaging equipment. Only after examining all facetsof packaging costs can the true economics of packag-ing be accurately evaluated. Soon the days of judgingpackaging costs on the basis of the number of colorson the label, such as was, and perhaps still is, beingdone for the no frills levels of packaged food anddairy products, will be ended. There is much more topackaging economics than number of colors printed,which is usually a trivial contributor to the total eco-nomics.

REGULATIONBeyond the regulatory issues relating to the safety ofpackage materials and the contained products are theregulations governing on-package information, i.e.,the so-called labeling declarations. As should be wellknown to every dairy technologist, a host of federal,state, and local agencies have some manner of labeljurisdiction over dairy product packaging.

The most important of these, of course, is Food andDrug Administration (FDA) whose authority usuallytakes precedence. Were the products meat, the UnitedStates Department of Agriculture (USDA) wouldhave jurisdiction, taking their lead from FDA, butexercising a difference in that prior approval is oftenrequired. Alcoholic beverages fall under the Bureauof Alcohol, Tobacco, and Firearms of the TreasuryDepartment, taking their lead from the FDA. A con-siderable amount of authority, usually unexercised,rests with the Federal Trade Commission, which hasthe power to regulate relationship of on-package in-formation to advertising promotion and other com-munications.

In addition to those with legal authority are thequasi-legal groups and trade regulations, which stip-ulate packaging information requirements. For ex-ample the Railroad Board stipulates the mandatorylabeling relating to board strength on the corrugatedshipping cases. Supermarkets dictate the presence ofa machine-readable universal product code (UPC) onprimary packages. FDA regulations prescribe fivemajor information items on food and dairy pack-ages including the generic identity of the contents,net weight, source of the product, a list of ingredi-ents in descending order or weight or volume im-portance, and nutritional attributes. Since 1994, all

foods offered at retail outside of food service out-lets have been required to carry a complete statementof nutritional attributes in a prescribed format. Theregulations also established rules for making limitedhealth claims based on nutritional value or any otheraspect of the product.

During the 1970s, FDA established a set of rulesfor Good Manufacturing Practices, many of whichare aimed at ensuring that the packaging is safe, notonly from a content standpoint but also from a pro-cessing and containment perspective. Specific rulesfor handling low-acid foods, and many dairy productscertainly falling into this category, are in effect. Theserules might be regarded as the common sense rules ofoperating a fermented dairy processing or packagingline, formalized as a regulation. For example anyoneoperating a retort must be trained in retort operation.Complete records must be kept for all low-acid retortoperations. Closures for cans and glass jars, as wellas other retort packages for retorted low acid foodsare specified. Regulations for aseptic packaging espe-cially with regard to thermal processing of contents,sterilization of package materials, and seal integrityare stipulated with provision made for application toFDA, if the system has not been used previously incommercial practice. FDA also requires that any or-ganization packaging and processing low acid foodsfor ambient temperature distribution submit its pro-cess to FDA prior to initiating operations so that FDAcan ascertain that the persons and equipment and op-erations are qualified to function.

The several highly publicized incidents of tamper-ing with over-the-counter drugs and a few foods thatoccurred in the 1980s triggered a number of lawsand regulations stipulating tamper evidence/tamperresistance for these drug products. Simultaneouslymany food and dairy processors and packagers imple-mented tamper evident/tamper resistant package fea-tures both to deter criminal intent and to deter inno-cent in-store taste-testing and content contamination.The rules apply only to the proprietary drugs, and sofood and dairy processor/packagers are not requiredto follow the specific guidelines of the FDA regula-tions. Nevertheless, almost all food and dairy pack-agers that have incorporated tamper evident/tamperresistant features use the regulatory guidelines. Theseguidelines specify a number of devices, which are re-garded as being generally effective, and the presenceof a printed instruction to signal to the consumer theabsence of the device or a tampered package.

In general, government regulations regarding pro-cessing and packaging of food and dairy products


are quite good and make very good sense to food anddairy packaging technologists. There is little onerousabout any of the regulations since they are reiterationsof good technical and commercial practices designedfor delivery of safe products in packages that com-municate accurate information.

PACKAGING AND THEENVIRONMENTProbably the most widely discussed and debated as-pect of packaging today since 1970 has been theenvironmental impact of the solid waste generatedfrom packaging. Regardless of the merits of the pub-lic and private declarations, the issue has generatedmore laws, regulations, proposals, consumer actions,and media discussion than the combined total of allother issues related to food and dairy product pack-aging during that period.

According to the environmentalists fostering thisissue, packaging is the major component of the mu-nicipal solid waste stream and should be eliminatedor made of nothing but materials that have been re-cycled from the solid waste from consumers’ homes.If not, goes their story, the rapidly diminishing num-ber of landfills will overflow with this solid wasteand contaminate the soil and ground water. As a re-sult of these claims, hundreds of laws and regulationshave been passed restricting food and dairy packag-ing, or at the very least, dictating household sepa-ration of packaging solid waste and curbside place-ment for recycling pick-up. Thousands of laws andregulations have been proposed to limit packaging,including stipulating minimum contents of postcon-sumer solid waste to be incorporated into the pack-aging materials. In extreme instances, packages havebeen banned, as in the State of Maine where the paper-board/plastic/aluminum foil aseptic brick/block packwas largely banned on the grounds that it was “notrecyclable.”

The actual facts refute almost all the claims regard-ing the role of packaging in the solid waste stream,and the chronology of the environmentalists move-ment in this regard reflects abrupt turns to reflect thereactions to initial misinformation that precipitatedmost of the laws and actions. For example, at the out-set, most environmentalist groups cited “biodegrad-able” packaging as the best answer to the problemof solid waste, but after it was clearly and loudlydemonstrated that biodegradation does not occur inreasonable time within properly constituted sanitarylandfills, biodegradability was virtually erased as a

viable alternative. When recycling was demanded onthe basis that no packaging was being recycled, thefood and packaging industries responded with validdata demonstrating that large fractions of spent pack-aging materials were already being recycled.

In actual fact only 27–28% of the municipal solidwaste stream is package material, a proportion thathas been declining even as the rate of growth of thestream has been declining.

The argument presented is that paper is recyclableand so newspapers and telephone books may be re-moved from the waste stream and recycled. Althoughtrue in the technical sense, paper loses properties ineach recycle and indefinite recycling can lead to nouseful raw material. Properties of recycled paper-board are quite different from those of virgin andthe two cannot be used interchangeably in all appli-cations.

Without imposed laws, the paper and paperboardindustry functioned well using economic laws of sup-ply and demand. The cost of returning used glasspackaging to the rapidly decreasing number of glassfurnaces in the United States is too high for economicjustification, but nevertheless, many municipalitiesare doing just that. In our lifetime there will be noeconomic driving force for spent glass return withone probable result being that the decline of glass asa packaging material will be accelerated.

Because the price of aluminum is so high and alsobecause aluminum may be safely and economicallyrecycled, aluminum can recycling has been a com-mercial practice for more than two decades now, orever since the aluminum can took a commanding leadin the beer and carbonated beverage packaging mar-ket. An infrastructure has been in position, function-ing well, even as the supply grows and the demandremains static.

Plastics have been the particular target of envi-ronmental agitation and regulation on the rationalethat plastic does not degrade in sanitary landfills andthat it is an unnecessary expenditure of our limitedplanetary energy resources. Consumer (and politi-cian, often dairy technologist, marketer, journalist,etc.) perception is that plastics constitute over half ofthe total packaging solid waste stream. The reality isthat plastics constitute about 20% of the weight ofpackaging.

Both the Environmental Protection Agency and re-sponsible professional and trade organizations havedeveloped a hierarchy of means of “coping” withpackaging solid waste, with EPA also indicating thattheir recommendations deal with all of solid waste


and not just the minority that is packaging. Their or-der is source reduction, recycling, incineration, san-itary landfill, and degradability.

Source Reduction

The reduction in the quantity of packaging materi-als used to contain food, dairy, and other products.Source reduction is and has always been one of theprimary activities of food and dairy packagers. Sincethese business entities produce volume and profit bylowering the delivering of the best products at thelowest cost, reducing the cost of packaging by render-ing it more efficient is a normal operating procedure.

Recycling

This category may be divided into reuse of packagesdirectly for the same purposes such as returnableglass or plastic bottles, a procedure that involvesconsiderable caution relative to product safety;closed-loop recycling, which means reuse of thepackaging material for the same application; andrecycling of the spent materials into some useful butnot necessarily similar application (which is often notpackaging). Much of the commercial activity centerson recycling into some packaging application that isnot the same as the original or into a nonpackagingapplication. Among the more advanced package ma-terial recycling efforts are aluminum cans returned toproduce aluminum cans, high-density polyethylenemilk and detergent bottles into motor oil and liquiddetergent bottles, polyester carbonated beveragebottles into polyester carpet fiber and insulatedjacket filling, glass bottles into new glass bottles,and paperboard into recycled paperboard cartonsor corrugated fiberboard fluting medium. The high-density polyethylene bottle recycling businesses arerelatively new to the package-recycling scene and soare still relatively small.

Incineration

When paper and plastic are burned in appropriatefacilities, the energy generated can be used to heator to produce electricity, a useful and cost effectiveoutlet. Well-engineered incinerators can burn wasteefficiently with no air contamination and with littleresidual ash. Although the initial capital cost is high,financial returns can be very good from the sale ofsteam or electric power. Obstacles to waste to energyplants include consumer perception, particularly of

the property values, dirt, and air pollution; the highamount of truck traffic necessary to feed the inputscrap; and the disposal of the ash, which is perceivedto be high in undesirable heavy metal elements. The“not in my backyard,” “not in my term of office” syn-dromes dominate the development of effective wasteto energy incinerators.

Biodegradability

Self-degradation was viewed by many in the envi-ronmentalist movement as the ideal answer to pack-aging solid waste. The so-called “biodegradability”would remove all packaging, particularly plastic,solid waste just as soon as the packaging had per-formed its protection function. Archaeological stud-ies of landfills indicate, however, that both plastic andpaper in landfills did not degrade in finite times. Fur-thermore, if the landfills were intended for an even-tual use for building foundation or any other use-ful application, a base that would degrade after timewould be highly undesirable. Self-degradation alsointerferes with recycling efforts. Yet another issue ofdegradable plastics is the unknown end products ofself-degradation, which could be toxic or even moredestructive to the environment than the perceived ad-verse effects of packaging solid waste.

Nevertheless, efforts and investments are under-way to develop and produce degradable packagingmaterials with the term “degradable” meaning eitherbiodegradable or photodegradable.

Dairy interests are working diligently to minimizeboth the real and perceived effects of packaging onthe solid waste stream. Professionals experienced infood and dairy packaging are sensitive to the roleof packaging in protecting the contents on behalf ofthe consuming public, and of the resultant relativelyminimum contribution of packaging to solid waste.Regardless of the facts, the packaging industry isworking toward the resolution of the real problem,but attempting to employ only rational technical andeconomic means.

PACKAGING FOR YOGURT ANDFERMENTED DAIRY PRODUCTSTo this point, this chapter has addressed dairy pack-aging principles and not focused on fermented dairyproducts packaging. This section deals with the spe-cific applications and descriptions of some of themajor systems in use or proposed for dairy productspackaging.


Pasteurized Fluid Milk

Almost by definition pasteurized fluid milk andderivatives such as buttermilk, kefir, and drinkableyogurt are distributed under refrigeration and so arenot expected to deliver long shelf lives. Microbiolog-ical control protocols today are prolonging chilledshelf lives for such products.

Glass Bottles

The classical package for pasteurized fluid milk andanalogs is the returnable glass bottle that is cleanedafter each use, refilled with the milk, and resealedwith a reclosable but disposable closure. Returnable,reusable glass bottles are used occasionally in theUnited States but are generally regarded as archaiceven as they are advocated by environmentalists’ in-terests. From time to time glass jars are employed foryogurt. Such product packaging is usually applied toconvey premium quality. Closure is often with alu-minum foil sealed to the glass finish.

Returnable Plastic Bottles

Largely in response to the environmentalist move-ment, returnable plastic bottles were introduced intothe fluid milk and analog distribution system. Any re-turnable/reusable distribution system requires an in-frastructure that can recover the used containers andreturn them efficiently. To ensure the continued useof such a system, it must be economic to all involved.The thrust of the returnable plastic bottle movementin the United States was for public school-size bottlesinvolving few, if any, fermented dairy products. Thepreferred plastic, polycarbonate is a tough, low bar-rier/high temperature-resistant plastic, which is usedin packaging mainly for returnable carboys for drink-ing water. No commercial applications are known forreturnable polycarbonate bottle or jar packaging forfermented dairy products.

Plastic Pouches

For decades flexible polyethylene pouches have beenused to contain fluid milk and analogues in bag-in-box configurations. The box is corrugated fiberboardfor structural rigidity. Both filling and dispensing isthrough a plastic fitment, i.e., device, heat-weldedinto the plastic film at the bottom.

In Europe and Canada, consumer-size pouchesfabricated from medium-density or linear low-density polyethylene films are commonly used for

fluid milk. The particular grade of polyethylene isrequired to achieve an effective heat seal to ensureagainst leakage either during filling or distribution.The resulting pouch resists impact from drops andfrom internal hydraulic action by the contents. Thepouch is filled on a vertical form–fill–seal machineespecially engineered for liquid filling. The pouch isintended to be inserted into a rigid plastic pitcher,manually cut open by the consumer, and dispensedfrom the opened pouch in the pitcher.

Tetrahedrons

Developed as the original structure by Tetra Pakin Sweden more than 50 years ago, the tetrahedralshape has been used for fluid milk and dairy prod-ucts packaging because it employed less packagematerial per unit volume contents than any othercommercial package. The shape continues to beused in Europe and occasionally in North Americafor liquids, despite its awkward shape for inclu-sion in distribution packaging, and difficulty of shelfdisplay, in-home storage, opening, and dispensing.Tetrahedrons for pasteurized fluid milk, puddings,etc., containment are fabricated from polyethylene-coated virgin paperboard, or if for ambient tempera-ture, shelf stable contents of a lamination of paper-board/polyethylene/aluminum foil. The package isfilled and sealed on vertical form/fill/seal equipmenton which the two transverse seals are at 90◦ angles toeach other. The internal polyethylene coating servesas the heat sealant.

Plastic Bottles

Extrusion blow-molded high-density polyethylenebottles are among the most popular package formsfor fluid milk and its fermented and flavored ana-logues. The weight per unit volume of fluid contentsis the lowest of any packaging structure that can beopened, reclosed, and comfortably dispensed. High-density polyethylene is an excellent water and watervapor barrier, and therefore is well suited to con-tain fluid dairy and analogue products. It is a lowcost and easy to fabricate plastic package material,which produces a bottle that is tough and impact re-sistant. Bottles are filled on standard in-line or ro-tary turret liquid gravity filling equipment and closedwith friction fit injection molded polypropylene clo-sures usually with tamper resistant features. In re-cent years both unit-portion and liter-size plastic bot-tles have been labeled with printed full body shrinkfilm that are highly decorated. Coupled with extended


shelf-life processing and packaging, these advanceshave sparked major exponential increases in sales offluid milk products.

Injection blow-molded polyester bottles are alsobeing applied for fluid dairy product containment.Polyester bottles are usually more expensive thanhigh-density polyethylene but may be useful becauseof their clarity.

Gable Top Paperboard Cartons

Below gallon size and especially in quart andhalf-pint sizes popular in the United States for fluidmilk products packaging are gable top paperboardcartons. These cartons are made from liquid resistant,virgin paperboard extrusion-coated with low-densitypolyethylene to impart liquid and water vaporresistance, as well as broad range heat sealability.The cartons are delivered to dairies in knocked-downsleeve form that permits rapid erection into open topcartons on appropriate packaging equipment. On thisequipment the sleeves are opened and forced over amandrel on which a flat bottom heat seal is made byafter overlapping the bottom flaps of the carton. Theerected open top carton is stripped from the mandrel,set upright and filled using gravity-type filler. Thetop is heat-sealed by folding in a portion of the edgesand face-to-face sealing the gable top using pressureand conduction heat. The cartons are sufficientlyrobust to contain fluid milk and analogues forthe distribution times required with longer termshelf-life impractical because of the edge wickingof the paperboard (for longer distribution times,the internal construction is changed). Among theadvantages of paperboard cartons are that they maybe preprinted almost always with basic flexographicdecoration, and now, increasingly with rotogravureor web-offset high-resolution graphics for consumerdisplay impact. Gable top cartons are not easy toopen, but are reasonable to dispense from, and areimpossible to reclose improperly. They are relativelyinexpensive in almost all small sizes.

Shelf Stable Fluid Dairy Products

Shelf stability implies heat treatment, either beforeor after filling to sterilize the contents, i.e., rendersthem free of all microorganisms of public health sig-nificance and of microorganisms that could causespoilage under normal conditions of distribution,i.e., ambient temperature. (Obviously, altering thewater activity of solids could also permit ambient

temperature shelf stability.) The term “shelf stable”means that the contents will not spoil microbiologi-cally but does not necessarily mean that the productwill not deteriorate biochemically and thus retain itsinitial quality.

Post-Fill Retorting

Traditional shelf stability is achieved by sealing thepackage and applying heat sufficient for sterilization,taking account of the rate of thermal death of themicroorganisms and the rate of heat penetration. Forfluid dairy products, which are low acid or at a pHabove 4.6, temperatures required are usually above250◦F, which implies retorting and control of externaland internal pressures of the packages. Canning is thetraditional postfilling heat process to achieve ambienttemperature shelf stability.

Canning is largely in cylindrical steel or now alu-minum cans, which are hermetically sealed mechan-ically by double-seaming a metal end to the bodyflange after filling. After closure, the cans are cookedunder pressure and cooled to generate a partial vac-uum within the container and reduce the rate of bio-chemical oxidative deterioration. Glass bottles andjars may also be considered as a segment of the can-ning spectrum.

After filling glass containers are hermeticallyclosed with rubber compound-lined steel or linedpolypropylene closures. The glass packages are care-fully aligned and placed in retorts for pressure-cooking during which the pressure is carefully con-trolled with an external overpressure to ensure againstinternal steam pressure blowing off the closures. Fur-thermore, because of the usual sensitivity of glassto thermal stresses, careful increase and decrease oftemperature is practiced. Very little fluid dairy prod-uct today is packaged in glass in the United States,although the practice was not uncommon two gener-ations ago or now in Europe.

In Europe also, retorting in plastic bottles isnot uncommon with high-density polyethylene andpolypropylene being the packaging materials ofchoice. Both are resistant to retort temperatures, butare poor oxygen barriers, and so the contents aresubject to significant biochemical deterioration atambient temperatures. The system is used for rela-tively short-term ambient temperature distribution.Recently in the United States, liquid dairy meal sub-stitutes have been packaged in multiplayer barrierplastic bottles that are retorted after hermetic sealingwith semirigid closures.


Aseptic Packaging

Aseptic packaging is the independent sterilization ofproduct and package and assembly of the componentsunder sterile conditions to achieve ambient tempera-ture shelf stability. Because of the several operations,aseptic packaging is statistically riskier than canning,which has a final heat process to compensate for anyerrors prior to closure. One reason for using asepticprocedures is to significantly reduce the thermal in-put to the product since it can be heat sterilized inthin film in heat exchangers prior to filling. A secondreason is that almost any package material, structure,or size may be used. Lightweight flexible or compos-ite materials may be sterilized by various technolo-gies that render the material sterile without damagingit. Sterilization of the container may be by thermalmethods such as dry heat, steam, or chemicals suchas hydrogen peroxide.

The most widely used aseptic packaging is paper-board composite bricks or blocks. In the Tetra Paksystem, on a presterilized machine, a prescored webof packaging material is unwound into a bath of hothydrogen peroxide and dried in a sterile environment.The web is formed into a tube in which previouslysterilized, cooled fluid is pumped. Induction energyheat seals both a back longitudinal and transverseseam. The latter takes place through the product con-tents thus eliminating any headspace. The sealed tubeis cut from the web and the pouch is formed into abrick shape on a mandrel.

On Hassia equipment, flexible tubes of barrier flex-ible laminations are sterilized by exposure to hydro-gen peroxide followed by heat drying. The tubes arefilled with presterilized yogurt or pudding and sealedat both ends to produce either sterile, or in some cases,extended refrigerated shelf life, puddings, or yogurtsthat have gained great popularity since the late 1990s.

In the Combibloc system, used more in Europe,paperboard composite materials are preformed inthe converting plant into prescored knocked-downsleeves. At the presterilized aseptic packaging ma-chine, the blanks are erected and set upright. Hydro-gen peroxide is sprayed into the open top containersand then heated to both raise the operating tempera-ture of the chemical and evaporate away the residual.Filling takes place in a horizontal mode with face-to-face heat sealing of the material using ultrasonicmethods. Because the machine is horizontal, multi-lane operation is possible and speed can be as highas 400 packages per minute.

The Pure Pak gable top paperboard carton sys-tem that continues to be used occasionally in aseptic

mode is quite similar in principle of operation to thatof Combibloc. Products include liquid egg, long-lifecream and flavored milk.

Aseptic packaging of plastic cups may be accom-plished on thermoform-fill-seal or preformed cupdeposit-fill-seal systems. In thermoform-fill-seal sys-tems, sterilization may be previous to the dairy in theconverting plant or may be on the aseptic packagingmachine. The most widely used aseptic thermoform-fill-seal system is from France’s ERCA. On oneERCA system, the heat of extrusion of plastic maysterilize the webs to be used. On the machine a pro-tective web of film is stripped away from the inte-rior surface and the remaining thermoformable webis heated sufficiently to soften it. Sterile air pressureis applied to form the plastic into a cup shape in amold. The open top cup is filled in-line and a flexi-ble closure material is stripped of its protective filmand heat sealed to the flange of the base cups. Witha rate of about 20 cycles per minute 10 or more cupsare formed, filled, and sealed simultaneously. Outputcan be as high as 300+ per minute for 4 to 8 ouncecapacity cups.

Other thermoform-fill-seal machines such as an-other by ERCA or Bosch immerse the two webs inhydrogen peroxide and evaporate the sterilant withinthe machine to achieve sterility.

On the Hassia thermoform-fill-seal machine,steam is used both to sterilize the materials and tothermoform the base plastic web into cup shape.Hassia equipment has not been accepted for asepti-cally packaging low-acid dairy products in the UnitedStates. Thermoform-fill-seal systems generally usecoextrusions of polystyrene as the thermoformablestructural component and polyvinylidene chloride asthe barrier component.

Deposit-fill-seal systems use inputs of preformedcups, which may or may not be sterilized on the ma-chine. All are closed by heat sealing with flexiblematerials, which are either predie cut or cut froma web on the machine. The most widely used arethose for liquid coffee lighteners in which the nestedcups are presterilized by ionizing radiation and thenaseptically transferred to the machine for denesting,filling with sterile product, and heat sealed. PortionPackaging and Purity Packaging systems are simi-lar in operation. Both use thermoformed polystyrenecups and aluminum foil/heat seal coating closures.Generally the output is maintained under refrigeratedconditions despite their sterility, thus accounting fortheir use of nonbarrier packaging materials.

Hamba machines are applied for aseptic packag-ing of milk-based puddings using prethermoformed


polypropylene cups. To date, Hamba machines havenot been accepted by regulatory authorities for asep-tic operation in the United States, thus accountingfor the refrigerated or extended shelf-life distribu-tion. The product’s quality, however, benefits fromthe chilled distribution.

In Europe several aseptic bottle fillers are com-mercial with hydrogen peroxide as the sterilant ofchoice. The systems may employ either glass or plas-tic with polypropylene or high-density polyethyleneas the preferred materials for short-term ambient tem-perature distribution, and coextrusions with ethylenevinyl alcohol for longer term distribution. Bosch sys-tems have been used for infant formula; Serac, Stork,and Krones systems have been used for fluid milkproducts. All are more widely used today in an ul-traclean mode to produce extended (chilled) shelf-life fluid dairy products including flavored milks anddrinkable yogurts. Shelf lives of more than 2 monthsare commonly commercial.

For larger size bag-in-box, preformed pouches fab-ricated from metallized polyester film and fitted withfilling and dispensing fitments are presterilized us-ing ionizing gamma radiation. On Scholle, DuPontCanada, or similar type aseptic filling equipment,sterile product is introduced through the fitment,which is subsequently sealed. Some web verticalform/fill/seal machines are also operated in asepticmode.

Solid Dairy Product Packaging

Often in dairy product packaging, there is little dif-ference in filling and closing between solid and fluidproducts. The difference comes later in distributionafter the product has set. Thus, from an initial pack-aging standpoint, packaging is the same, but froma package selection standpoint, it is important tochoose structures that will contain the final productand be useful to the consumer. Products such as yo-gurt and pudding whose packaging was referred topreviously are handled from a packaging operationstandpoint as if they were fluids, but from a con-sumer standpoint, their packages must take accountof spoonability. Numerous soft cheeses, spreads, etc.,fall into this category.

Soft cheeses are generally pumped into ei-ther thermoformed polystyrene or injection-moldedpolypropylene cups or tubs, which are then closedby a combination of aluminum foil heat-sealed tothe flange; friction fit thermoform, with or with-out tamper resistant ring around the rim. Some softcheeses are pumped into molds and then cut to be

overwrapped, or the cheese may be pumped hot intoaluminum foil lamination overwraps with the heatused to reduce the microbiological count. In Europeconsiderable quantities of soft cheeses are packagedon thermoform-fill-seal machines using polystyreneas the base cup material and aluminum foil lamina-tion as the heat seal closure.

Frozen yogurt may be packaged in bulk for foodservice scooping and dispensing. Bulk packaging isgenerally, but increasingly less so, cylindrical spi-ral wound virgin paperboard coated with polyethy-lene with heat-sealed similar paperboard base andfriction fit top, also paperboard. Cylindrical shapesare almost traditional from Sealright (Huhtamaki),with filling by fluid methods on their equipment. Thecylinders may be received in knocked down form tosave on package material inventory space in whichcase Sealright equipment is employed to erect thecontainers.

Most frozen yogurt is packaged in coated, bleachedvirgin paperboard half-gallon cartons received inthe form of knocked down sleeves. Cartons are au-tomatically erected and filled through one end af-ter which they are mechanically closed by lock-ing the tabs on the cartons. Increasing quantities ofconsumer size ice cream, particularly the premiumtypes, are packaged in rectangular corner convolutewound paperboard containers which are closed byfriction fit overcaps, again either paperboard or in-sert injection-molded paperboard/plastic. Noveltiesare first overwrapped on continuous motion horizon-tal form/fill/seal equipment with polyethylene coatedpaper or cavitated core oriented polypropylene as thematerial. Wrapped novelties are then unitized andplaced in the ends of opened paperboard folding car-tons, which are closed by hot melt adhesive.

Numerous other packaging technologies and ma-terials are used commercially and are proposed fordairy product packaging. This dissertation cannotencompass every packaging means available to thedairy packager. A sampling has been offered to re-flect the principal technologies and basic informationhas been presented to suggest to dairy packagers al-ternatives should the suppliers current offerings beless than desired.

FUTURE TRENDSThere will be continued application of aseptic tech-niques to deliver products for refrigerated distribu-tion. The quality of thermally processed dairy prod-ucts will be better retained by chilled distribution pro-cedures. The quality retention durations for chilled


dairy products will be extended by introduction ofclean room extended shelf-life technologies.

No longer will there be specific technologies. Thenew dairy packager will integrate more than onepackaging technology into systems that will deliver asynergy of the benefits from each of the contributingtechnologies. In the more distant future, packagingsystems will become so sensitive and responsive thatthey, and not the process, will be the dominant factorsin the delivery of quality dairy products. In an era ofactive packaging, the package will be called upon tosense the contents and to adjust to its technical needsfor lower temperature, or aroma enhancement, or mi-crobiological suppression; and to the marketers de-sire for impact communications with light and soundtaking over for mere passive graphics.

The environmental issue is emotional and repletewith misinformation and misperceptions. Regardlessof the facts, numerous problems are already present.The issue will continue to mushroom with few pre-dictable paths. Dairy packagers must be cognizantof the volatile situation and be prepared to respondto those having either the force of law or consumerperceptions, however erroneous they might be. Dairypackager suppliers are reactive to environmentalists’pressures and will usually be active in assisting theircustomers. The decision must be made by the dairyon response: Do they accommodate every single sug-gestion from the field, regardless of how it disturbsor how much it costs, or do they assume a proac-tive position and attempt to bring a reasoned ap-proach to the total picture of packaging in the solidwaste environment? No matter what stance they take,environmentalism will be the top priority for manyyears.

As dairy packaging is being advanced, its progresstoward a new dimension is already visible on thetechnological horizon that will be recognized by aperceptive consumer.

BIBLIOGRAPHYBrody A, Marsh KS. 1997. Encyclopedia of Packaging

Technology,. 2nd ed. John Wiley & Sons, New York.Brody AL, Lord J. 2000. Developing New Food

Products for a Changing Marketplace, CRC Press,Boca Raton, FL.

Brody AL, Strupinsky E, Kline L. 2001. ActivePackaging for Food Applications, CRC Press BocaRaton, FL.

David J, Graves R, Carlson VR. 1996. AsepticProcessing and Packaging of Food, CRC Press,Boca Raton, FL.

Doyle M. 1996. Packaging Strategy, CRC Press, BocaRaton, FL .

Gray I, Harte B, Miltz J. 1987. Food Product—PackageCompatability, Technomic, CRC Press, Boca Raton,FL.

Hanlon JF, Kelsey RJ, Forcino H. 1998. Handbook ofPackage Engineering, 3rd ed. CRC Press, BocaRaton, FL.

Harkham, A. 1989. Packaging Strategy, CRC Press(Technomic) Boca Raton, FL.

Holdsworth SD. 1992. Aseptic Processing andPackaging of Food Products, Elsevier, New York.

Hotchkiss J. 1988. Food and packaging interactions.American Chemical Society, Washington, DC.

Institute of Food Science and Technology. 1985. In:Proceedings of Symposium on Aseptic Processingand Packaging of Foods, Lund University, Sweden,SIK.

Institute of Packaging Professionals. 1991. IOPPPackaging Reduction Recycling and DisposalGuidelines, Institute of Packaging Professionals,Naperville, IL.

Jenkins W, Harrington J. 1991. Packaging Foods withPlastics, CRC Press (Technomic), Boca Raton, FL.

Man D, Jones A. 2000. Shelf-Life Evaluation ofFoods. Apsen Publications, Gaitherburg, MD.

Osborn KR, Jenkins W. 1992. Plastic Films,Technology and Packaging Applications, CRC Press(Technomic), Boca Raton, FL.

Package Machinery Manufacturers Institute. 2004.Packaging Machinery Directory. Alexandria, VA.

Packaging Strategies. 1990. Aseptic Packaging, USA.Packaging Strategies, West Chester, PA.

Paine F, Paine H. 1983. A Handbook of FoodPackaging, United Kingdom, Leonard Hill, London,UK.

Reuter H. 1989. Aseptic Packaging of Food, CRCPress (Technomic), Boca Raton, FL. Robertson G.1993. Food Packaging, Marcel Dekker, New York.

Selke S. 1990. Packaging and the Environment, CRCPress (Technomic), Boca Raton, FL.

Selke S. 1997. Understanding Plastics PackagingTechnology, Gardner Publications,Cincinnati/Hanser.

Soroka W. 2002. Fundamentals of PackagingTechnology, Institute of Packaging Professionals, St.Charles, IL.

Stern W. 1981. Handbook of Package DesignResearch, John Wiley & Sons, New York.

Part IIManufacture of Yogurt



9Yogurt: Fruit Preparations

and Flavoring MaterialsKevin R. O’Rell and Ramesh C. Chandan

IntroductionFruit as Raw Material for Yogurt Preparations

Processing of Fruit for Use in Yogurt FruitPreparations

Formulation of Fruit PreparationsSpecialty Fruit Preparations

Processing Yogurt Fruit PreparationsPackaging of Fruit Preparations

ReferencesAcknowledgement

INTRODUCTIONPlain yogurt, which makes up 5% of the total re-frigerated yogurt category, is used by consumersas low/nonfat dressing for salads, as a topping forpotatoes and vegetables, as well as for cookingmeals. Nevertheless, the popularity of yogurt hasbeen propelled by the availability of sweetened fruit-flavored product (Chandan, 1982, 2004; Chandanand Shahani, 1993; Tamime and Robinson, 1999).The addition of fruit preparations, fruit flavors, fruitpurees, and flavor extracts enhances versatility oftaste, color, and texture for the consumer. Fruitsare generally perceived as healthy by the consumer.The soluble and insoluble fiber located in the fruitextends protection against cardiovascular diseasesand colon cancer, respectively. Also, some fruits,especially blueberries, contain high levels of an-thocyanins, which are flavonoids that have poten-tial health benefits functioning as antioxidants. Ac-cordingly, fruit association with yogurt endorses thehealthy image of yogurt even further.

The top 10 selling flavors that account for nearly70% of the total volume of yogurt sold based ondollar sales in descending order are: strawberry,

vanilla, peach, raspberry, strawberry-banana, plain,blueberry, lemon-lime, cherry, and mixed berry.

The fruit preparations for addition to yogurt arespecially designed to meet the marketing require-ments for different types of yogurt. The stirredvariety that now makes up 74% of the total refrig-erated yogurt category involves mechanical blend-ing of the fermented mass with fruit preparation.Therefore, the fruit preparation is formulated to fur-nish adequate viscosity for thorough blending intoyogurt mass without significant dilution of the fin-ished product. At the same time, the fruit piecesare designed to be interdispersed throughout thebody of yogurt without settling on the bottom ofthe cup. The sensory attributes (aroma, flavor, andcolor) and pH (acid–sweetness balance) of the fin-ished product depend on the contribution from fruitpreparation.

In the case of fruit-on-the bottom (FOB) style thatmakes up 8% of refrigerated yogurt sales, the fruitpreparation is designed to stay at the bottom, whileeither white unfermented yogurt mass (low in viscos-ity) or finished yogurt previously incubated in bulk isbeing deposited on the top of the cup. For FOB, ide-ally, the fruit preparation is thickened (but not gelled)to suppress fruit floatation, or mixing with the milkphase during filling or transportation. In addition, thestabilization, the calcium content, the pH, and the os-motic pressure generated by the fruit preparation atthe interface of fruit and yogurt base is taken intoconsideration to assure compatibility of the two lay-ers during incubation of the cup. The casein fromthe yogurt can precipitate out due to exposure to lowpH and the osmotic pressure difference between theyogurt and the fruit preparation resulting in a lumpyor gritty texture after stirring.

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152 Part II: Manufacture of Yogurt

The yogurt fruit preparations for consumption bytoddlers and children are designed to integrate spe-cial requirements for the consumer. For instance, intoddler yogurts, to avoid choking, the fruit prepara-tions are made from fruit purees, fruit juices, and/orflavors. This is also true for yogurt targeting children,where market research has shown a preference forno fruit particulates. Similarly, in the manufacture ofwhipped yogurt, the fruit preparation generally usesfruit puree that contains fruit fragments small enoughso as to avoid interference with the foaming process.In case of drinks, fruit preparations are designed tocontain juices, purees, and small fragments to avoidsettling of fruit during shelf life of the product andenhance the drinking experience.

Fruit preparation for use in yogurt manufacturemay be defined as a stabilized suspension of fruitparticles or puree in a sweetened, acidified matrix,with or without added flavors/coloring material. Thepreparation is heat processed to effect enhancementin shelf life by destroying microorganisms and con-stituent enzymes. The fruit preparations are generallyadded to yogurt products within a range of 10–20%level in the final product. In addition, most fruited yo-gurts contain natural or artificial flavorings to boostthe fruit flavor profile of the product. For enhancingthe eye appeal, appropriate color preparations maybe incorporated in the fruit-for-yogurt preparations.

The most popular fruit flavored yogurts are straw-berry, raspberry, cherry, blueberry, mixed berry, boy-senberry, peach, banana, lemon, tropical blends, apri-cot, apple, and their combinations. Also, addition offruit and other flavors popular in the bakery and icecream industries are incorporated to bring an inno-vative assortment of creative flavor profiles to theconsumer.

FRUIT AS RAW MATERIAL FORYOGURT PREPARATIONSThe diversity of fruits available for fruit-for-yogurtpreparations necessitates selection of cultivars thatwould be relevant to fruit integrity and flavor require-ments in the finished yogurt product. Accordingly,the fruit should be compatible with the rigors of theprocessing techniques.

The quality of fruit is determined by the variety,the stock of tree/ bush, growing practices, and soiland weather conditions. The fruit grower picks thefruit according to its ripeness and maturity. Matu-rity of fruit pertains to the condition of fruit ready toeat right away or after a predetermined time period ofripening. Ripeness of fruit refers to peak condition of

color, flavor, and texture. For instance, fruit picking isappropriate depending on the softness of the ripenedfruit. Soft fruit varieties are picked at mature stage toavoid overripeness, which other would near to unde-sirable transportation and processing problems.

The time to pick fruit depends on the type, va-riety, location, weather, and end-product use. Cit-rus fruits do not ripen after harvesting, while someother fruits continue to ripen under favorable con-ditions. The quality of fruit is generally measuredby objective physical–chemical procedures. Textureis measured by compression or by force required topenetrate the fruit. The concentration of juice solids(mostly sugars) as a measure of maturity of fruit canbe assessed by a refractometer or a hydrometer. Therefractometer determines the ability of a solution torefract or bend a beam of light. The degree of refrac-tion is directly proportional to the strength of the so-lution. The hand-held refractometers are very conve-nient in field conditions. A hydrometer also measuresthe concentration of juice. It consists of a weightedspindle with graduated stem. The hydrometer floatsin a juice and the reading at the meniscus of juice andair is a measure of the density/concentration of thejuice. The acid concentration changes with fruit ma-turity. It is measured by simple titration with standardalkali.

The flavor profile of many fruits is a function ofsugar and acid ratio. Sweetness and tartness of theflavor of fruit product is assessed by this ratio. Per-centage of soluble solids in a fruit is stated as degreesBrix, which relates specific gravity of a solution orjuice to equivalent concentration of sucrose. In thefruit industry, the term Brix (sugar) to acid ratio iscommonly used. When the Brix-acid ratio is high, thefruit contains high sugar and less acid, which in turnimplies that the fruit is sweet and less tart. Seasonalvariations in Brix and Brix-acid ratio are noticeablein most fruits.

After the fruit reaches certain Brix and Brix-acidratio, it is ready for harvesting. Harvesting by handis labor-intensive but is unavoidable in certain fruits.Use of a mechanical harvester is increasing, but pre-cautions must be taken to avoid damage to the fruit.The harvested fruit is washed thoroughly to get rid ofcontaminants like soil, microorganisms, pesticides,leaves, and stems. It may be sorted according to thesize and grades. Unless the fruit is grown strictly forprocessing, it is likely that the best quality will beshipped to the fresh market where it can commandpremium prices. Declining quality generally corre-sponds with smaller piece size. After the fresh mar-ket, the best quality is typically used for individually

9 Yogurt: Fruit Preparations and Flavoring Materials 153

quick frozen (IQF) and bulk frozen as a straightpack or a sweetened pack. The IQF processingprovides fruit that will most closely approach fresh.This is because in IQF no sugar is added and freez-ing takes place relatively quickly, minimizing dam-age to the tissue by the ice crystal formation. Freezingin any form will extend the fruit shelf life for morethan a year. Generally, the poorer qualities go to thepurees and juice/juice concentrates. These selectedfruit lots are processed further for use in the manu-facture of juice, jam, fruit toppings, bakery fillings,and fruit preparations for ice cream, yogurt, and cot-tage cheese.

Processing of Fruit for Use inYogurt Fruit Preparations

Yogurt manufacturers use specially processed fruitpreparations because of convenience of use and toimpart added value to yogurt. Since fruit suppliersspecialize in general fruit processing, the economiesof scale in purchasing fruit offer economical advan-tage to the yogurt processor. Also, the expertise ofthe fruit processor extends food safety and shelf-lifeoptimization in yogurt.

Major fruit processing techniques in order of im-portance are canning, freezing, drying, preserva-tion with sugar syrups, concentrating by moistureremoval, preservation with chemicals, fermentationwith yeasts and bacteria, pickling with vinegar, sugarand spices, reduction of oxidation with antioxidants,reducing agents and vacuum treatment, and screen-ing of fruit from light exposure (Woodroof, 1990).The industry utilizes a combination of two or moreof these techniques. Some processing methods aremore suitable for certain fruits.

Strawberries

In the United States 75% of strawberry production isfrom California, followed by the Northwestern re-gion. Of the total frozen strawberries used in theUnited States, about 25–30% are imported, mostlyfrom Mexico and Poland. Strawberries are hand har-vested in the winter and spring in the southern States,and spring and summer in the northern areas. Straw-berries for processing are washed, inspected for greenand defective fruit, and then sorted for quality. Typi-cal packs include IQF and bulk frozen, with and with-out sugar. Sugar levels most commonly available are4 + 1 and 3 + 1 (fruit to sugar) and the berries may bewhole, sliced or crushed. The berries that do not meetgrade standards are used for production of puree or

juice concentrate. Puree is produced with and withoutsugar and can be concentrated. For juice concentrate,berries are pressed, filtered and concentrated undervacuum to produce product from 42 to 70◦Brix.

Blueberries

In North America, two distinct types of blueberriesare grown. Wild blueberries that are small berries (1/4to 3/8 inches) known for their sweet intense flavor,and cultivated blueberries that are larger berries (1/2to 5/8 inches or larger). The wild crop is harvestedby hand and the season begins in late July and ex-tends for up to 6 weeks. Most cultivated blueberriesare mechanically harvested and the season runs fromApril to September. Before processing, the berriesare cleaned by blowing away the twigs, leaves andother debris. They are then graded for size, washed,and hand inspected for green and defective fruit. Ap-proximately three-quarters of the processed berriesare frozen, either IQF or bulk pack, straight or sugarpack (usually 4 + 1). Some blueberries are directlycanned with a starch and sugar solution added. Pureeand juice products are made from crushed berries,thermally treated to inactivate enzymes. Puree is typ-ically 10–12◦Brix, but can be concentrated. For mak-ing juice, berries are pressed, filtered and concen-trated to 45–65% soluble solids.

Raspberries and Other Berries

Raspberries come in many varieties, mostly basedon color: red, black, purple, or golden. They growon canes and, depending on the variety, produce onecrop midsummer or a second, smaller crop in thefall. The fruit is soft and easily damaged; therefore,it must be harvested by hand. The berries are washedwith gentle water sprays, then drained and inspectedfor leaves and other foreign debris. Frozen berriesare processed as IQF, unsweetened bulk or 3 + 1sweetened pack. Raspberries are pulped to producepuree with or without seeds. For seedless puree, thepulped puree is put through a sieve to remove theseeds. Raspberry juice is typically concentrated to the68–70◦ Brix.

Blackberries, boysenberries and loganberries aregrown and processed in a manner similar to raspber-ries.

Peaches

There are many varieties grown in the United States,but they fall into two classifications: clingstone or


freestone. The name indicates whether or not the fleshadheres tightly to the pit. Freestones are usually soldin the fresh market, but some are processed. Cling-stones are typically used for processing and these arecanned or frozen. When the fruit is ripe but firm,it is harvested by hand. Peaches for either canningor frozen processing are inspected, graded for size,and put through a pitting machine that automaticallyhalves the fruit. The pitted halves are processed in alye solution to loosen the skins, which are then re-moved by shaker-washers. The halves may be slicedor diced in the desired size. Canned peaches are madefrom fruit and juice or syrups with 20–55% sugar.Frozen peaches may be packed as IQF or as syruppack, in halves, slices or dices. The fruit-to-sugar ra-tios vary from 3–1 to 9–1. They may receive an ascor-bic acid or citric acid treatment to preserve color.Puree is obtained from the machine pitting processor from whole fruit that is pulped, mixed with citricacid and ascorbic acid, and then pumped through twofinishers, 0.25 and 0.02 inches.

Cherries

There are many varieties of cherries but there are twomain categories: tart or sweet. Tart cherries providethe majority of the fruit for the US processing. Har-vesting, typically in late June through August, is byhand for the fresh market, or by mechanical shak-ers for processing cherries. Tart cherries for process-ing are first placed in a cool water bath, destemmed,washed, inspected, sorted, and then mechanically pit-ted. The pitting process is not 100% effective and onepit typically appears in 100 to 1,000 ounces of pro-cessed fruit. Many processors of yogurt fruit prepa-ration further hand sort cherries before processing tohighly reduce the risk of a pit in their products. Mostcherries are packed as IQF or as a frozen 5 + 1 packor puree. Some cherries are canned in juice or syrup.Juice and concentrate (typically 68◦Brix) are pressedfrom whole frozen or fresh cherries.

Bananas

Bananas are grown in tropical areas of Mexico, Cen-tral and South America, the Caribbean and Asia.Bananas are harvested when mature but green. Toripen quickly, they are held at 60◦F with ethylene gasadded. Bananas can be processed into many forms—frozen whole fruit and slices and puree, canned slices,and puree, all with or without syrup, and asepticallyprocessed and concentrated purees.

Organic fruits

Almost all variety of fruits can be found in organicform. Depending on the fruit, the cost premium fororganic fruits is as much as 30–50% higher comparedto conventional. Much of this cost is associated withthe strict requirements that must be followed in pro-duction. Organic fruits must be grown and handledunder the requirements of FDA 7 CFR Part 205 Na-tional Organic Program; Final Rule (FDA 2004). Forthe land to qualify for organic certification, it mustbe free of prohibited substances, as listed in 205.105for a minimum of 3 years. For the crops, there arespecific requirements for soil and crop nutrient man-agement practice standards 205.203, seeds and plant-ing stock practice standards 205.204, crop pest, weedand disease management practice standards 205.206,and wild-crop harvesting practice standards 205.207.The synthetic substances that are allowed for use inorganic production are listed in 205.601. The pro-ducer must develop an organic system handling planto outline how they plan to manage the land, crops,and harvesting within the organic regulations. Theproducer then files an application for organic cer-tification with an Accredited Certification Agency(ACA), a third party that has been accredited by theUSDA to conduct certification activities as a certifiedagent under the rule. The organic system plan, facil-ities, and appropriate records are then inspected bythe ACA and considered for approval. After organiccertification is granted, there are detailed yearly in-spections to assure compliance with the regulations.All relevant records must be maintained for a mini-mum of 5 years.

Formulation of Fruit Preparations

Typical fruit base formulation for use in yogurt us-ing modified starch (MFS) or Pectin is shown inTable 9.1.

In the formulation of fruit preparation, the ingredi-ents of choice are: fruit, fruit puree and juice, sweet-ener, stabilizer(s), acidifying/buffering agent, color,flavor, and sometimes a preservative. In addition, thefruit preparation can be used as a vehicle to incorpo-rate vitamins, minerals, intensive sweeteners or func-tional ingredients (i.e., fiber, nutraceuticals).

The various forms of fruit, fruit purees, and juicesused in fruit preparations have been mentioned ear-lier. The manufacturer of yogurt fruit preparationwill set raw material specifications based on theircustomers need in the finished yogurt. In general,


Table 9.1. Formulation of Fruit Base UsingModified Food Starch or Pectin

Percentages

Ingredients Starch Pectin

Fruit 35–40 35–40Sugar 35–45 35–45Water 12–18 12–18Modified starch 3–4% 0LM pectin 0 0.5–0.7Flavors <1 <1Color (optional) <1 <1Citric acid (to desired pH) <0.5 <0.5Sodium citrate (as needed for

pH control)<0.5 <0.5

Preservatives (optional) <0.1 <0.1

for fruit particulates, the manufacturer requires fruit“practically” free from defects and extraneous mate-rial, of good character and color, and normal flavorand odor. In addition, they also specify fruit variety,size, form, and microbiological limits. The followingis an example of a typical raw material specificationfor blueberries (Table 9.2).

There would be similar raw material specifica-tions for puree that would include form (i.e., canned,frozen, concentration, added sugar), flavor, color, andmicrobiological parameters. For fruit juices, the raw

material specification would include concentration,◦Brix, flavor, color, and microbiological parameters.

Sweeteners

The next major component of fruit preparations aresweeteners. The standard of identity for yogurt, lowfat yogurt and nonfat yogurt (FDA CFR Parts 131.200to 206) (FDA 2004) specifies the allowable nutri-tive sweeteners that can be used. Generally mostfruit preparations for FOB or Swiss/blended style yo-gurt applications, which are sweetened using nutri-tive sweeteners, use blends of sugar and high fructosecorn syrup (HFCS). The sugar can be in granulatedor liquid form. For liquid sugar (67.5◦Brix of a su-crose solution) the facility must be equipped with anappropriate storage tank to maintain a 70–100◦F tem-perature. Usually a 42% HFCS is used and it mustalso be stored in an appropriate tank to maintain a90–100◦F temperature. From these storage tanks thesyrup is pumped to the batch/mixing kettles.

The most common blends of sugar and HFCS aremade up in a 50 : 50 mix based on solids. This blendprovides a good balance between clean flavor releaseand cost. Increasing the portion of HFCS will providea lower cost, but can mask some of the flavor release.Some private label or economy brands could utilize100% HFCS as the sweetener. On the other hand,

Table 9.2. Typical Specification of Blueberries for Manufacture of Fruit Preparation Designedfor Use in Yogurt

Company Information Date :Raw Material SpecificationMaterial item number :Material : Wild blueberries.1. Fruit variety: Wild blueberries (no specific variety) sourced from the Northwest or Canada.2. Form: IQF or frozen straight bulk pack3. Character: The berries should have reasonably uniform dark blue-purple color with no more than 8%

red-purple color. Berries should be firm, reasonably fleshy, practically all whole with no morethan 5% by weight that are crushed, mushy or broken.

4. Size: 1/4 to 3/8 inch preferred. 1000 berries per pound with a range of 900 to 1200.5. Extraneous material: Per 30 pound box. No more than 3 whole leaves or 8 stems (larger than 1/2 inch) and

no more than 3 stem clusters. No more than 25 green, undeveloped edible berries.6. Foreign material: No insects, nonberry related wood, debris or dirt of any kind.7. Microbiological:

Standard plate count—10,000 CFU/g maxYeast and mold—2,000 CFU/g maxColiform—50 CFU/g maxSalmonella—NegativeListeria—NegativeHepatitis—Negative


for those looking to get a cleaner ingredient labelfor their consumer and to provide a sharp, cleanerflavor release, 100% sugar can be used in the fruitpreparation.

Other nutritive sweeteners that might be used infruit preparations include crystalline fructose, fruitjuice concentrate, tapioca or rice syrup, agave, honeyor maple syrup. The choice of these sweeteners isusually determined by marketing considerations forthe label declaration. In addition to providing a “cleanlabel,” crystalline fructose provides more sweetnessat the same solids level as sucrose and a cleaner flavorrelease, but at a higher cost.

The total sweetness of the fruit preparation mustbe balanced with the usage rate and sweetness, ifany, of the yogurt base. Most fruit preparations forSwiss or blended yogurts are used at 12–18% andare formulated for a 36–55◦Brix. For FOB fruits, themost common usage is from 15% to 20% with fruitpreparation formulated for a 45–50◦Brix.

High Intensity Sweeteners. There are several highintensity and noncaloric or nonnutritive sweeten-ers used as sweeteners in fruit preparations usedin yogurt. Some of the FDA approved high inten-sity or nonnutritive sweetener options are: aspartame(APM), sucralose, and acesulfame-K (Ace-K). Thesecan be used alone or in combination with nutritive orother nonnutritive sweeteners.

Aspartame was one of the first high intensitysweeteners used in yogurt fruit preparations. APM ismade from two amino acids (L-phenylalanine and L-aspartic acid) and, therefore contributes four caloriesper gram. But since it is 180 to 200 times sweeter thansugar, the usage levels are so low that it contributesessentially no calories. Limitations of APM includelack of stability and loss of sweetness when exposedto high temperatures over extended periods. For bestresults, it is recommended not to process APM con-taining fruit preparations above 96.1◦C (205◦F) formore than 5 minutes. In addition, the fruit should becooled down to 32.2◦C (90◦F) or lower, immediatelyafter heat treatment. Therefore its use is limited toaseptic fruit processing systems, and the packagedfruit is recommended to be stored refrigerated dur-ing its code life. Because of these limitations, todaymost yogurt products add the APM as a sweetenerduring the time of yogurt manufacturing. In yogurtproducts, the stability of APM is increased due to re-frigeration and the pH range of yogurt. Today, APMis used in combination with Ace-K, HFCS or crys-talline fructose in yogurt.

Ace-K is a white, odorless, crystalline sweetenerthat is not metabolized by the body and is thereforeclassified as nonnutritive. It is 200 times sweeter thansucrose and remains stable under high temperatures.Studies have shown that after several months of stor-age at room temperature, virtually no change in Ace-K concentration was found in the pH range commonin fruit preparations. Ace-K has a slight aftertaste;however blending with other sweeteners can improvethe taste profiles, in addition to offering economic andstability advantages. Ace-K is commonly blendedwith APM or sucralose in fruit preparations for yo-gurt.

Sucralose is made from sugar through a patentedprocess involving the selective chlorination of su-crose replacing three hydroxyl groups of the sugarmolecule with chlorine atoms. It is 600 times sweeterthan sucrose and does not break down in the body(nonnutritive). Sucralose has excellent stability un-der a broad range of processing, pH, and tempera-ture conditions and does not lose sweetness over ex-tended periods of time. Because of these attributes,it is an excellent sweetener for fruit preparations thatare designed for use in low sugar yogurt products. Itcan be used alone or sometimes it is combined withother nonnutritive sweeteners like Ace-K. There isa synergistic effect using the sucralose-ace-k com-bination that improves the taste profile and limitsthe lingering aftertaste sometimes associated withsucralose.

Stabilizers

The most common stabilizer used for both blendedand FOB yogurts is modified food starch (MFS) usu-ally derived from corn. The starch undergoes a twostep chemical modification that provides resistance toshear, and stability against retrogradation and synere-sis during long term storage in fruit preparation. Inaddition to its excellent functionality, MFS is easy tohandle in processing and is cost effective. One disad-vantage of some modified food starches, particularlycook-up starches, is their tendency to mask flavorrelease. MFS that is derived from tapioca is some-times desired for labeling purposes and it can exhibitless flavor masking. There are also organic and natu-ral starches that have not been chemically modified.These have been evaluated in fruit preparations, butto date, because of their lack of stability, they havehad limited success in commercial production.

Another popular stabilizer used in fruit prepara-tions is pectin derived from either citrus peel or apple


pomace. Pectin is more expensive but is preferred inapplications that require a natural label perception.Many FOB fruit preparations use pectin or a blend ofpectin and locust bean gum as the stabilizer of choice.(Hoefler, 2004). Various pectins are primarily poly-mers of polygalacturonic acid, which are esterified todifferent degrees. Pectin functions as a gelling agent,thickener, and suspending agent in fruit preparations.They are processed to yield two general types of com-mercial pectin products—high and low methoxyl.

High methoxyl (HM) pectins are characterized byan esterification degree of greater than 50% and arecapable of forming gel networks at high acid pH’s(around pH 3) in the presence of high soluble solids(greater that 55%). HM pectins are used as the stabi-lizer for traditional fruit preserves.

Most modern fruit preparations use low methoxyl(LM) pectins either alone or in combination with lo-cust bean gum or a small amount of HM pectin. LMpectins require only a controlled amount of calciumions to form gels. Gelation can take place across a

wide pH range (from pH 2.9 to 5.6) and soluble solidscontent from 10% to 80%. LM pectins offer the fol-lowing advantages in fruit preparations:

� Setting temperature is independent of cooling rate� The final product is thermo-reversible� The fruit preparation has an excellent resistance

to shearing during mixing or pumping andexhibits no syneresis

When using LM pectin in FOB yogurt fruit prepa-rations, it is essential to obtain the right level ofcalcium saturation to avoid problems with the fruittexture and degradation of yogurt white mass at theinterface. If the LM pectin is too short in calcium sat-uration, the fruit preparation will form a firm “hockeypuck” at the bottom of the cup and the resultingstir-out will contain small colored gelled lumps. Ifthe LM pectin is fully saturated, free ionic calciumfrom the yogurt, along with citric acid and other con-stituents from the fruit will result in white mass degra-dation or a “leathery–gritty” interface. The ideal fruit

Figure 9.1. Effect of low methoxy pectin on the properties of fruit. The Control FOB yogurt fruit contains highmethoxy fruit. Following inversion of yogurt cup, notice the fruit flows freely around the yogurt gel. When lowmethoxy pectin is used in the Experimental samples, the fruit forms a cohesive mass on the top of yogurt layer.


preparation will not cause white mass degradationand will stand upon the inverted white mass withonly minimal run off (Fig. 9.1). It will appear to bea soft hockey puck and can be easily stirred into theyogurt, resulting in a smooth appearance.

Locust bean gum (LBG), at range of 0.2–0.3%,is sometimes used in combination with 0.5–0.6%LM pectin. Locust or carob bean gum is a hydro-colloid produced from the seeds of the evergreen lo-cust bean tree, which grows in the coastal regions ofthe Mediterranean. Chemically, LBG is classed as agalactomannan. It is primarily used for its ability toincrease viscosity and it is helpful in preventing fruitflotation especially in large size containers. Whenused in combination with pectin, it results in a differ-ent gel set, usually softer, and provides a slight costsavings.

Flavor Preparations

Flavor preparations used in yogurt manufacturingconsist of vanilla or fruit flavors.

Vanilla. This flavor is the second best selling fla-vor of commercial yogurt accounting for more than$200 million in total sales. Most of the vanilla beans(65–70%) come from Bourbon islands (Madagascar,Comro, Reunion, and the Seychelles). Indonesia andIndia supply 25–30% of the world’s bean produc-tion. However, Bourbon beans are considered as thesource of finest vanilla. Vanilla beans are derivedfrom the fruit of Vanilla fragrance. This plant belongsto orchid family. The beans are harvested, and cured.During this process, fermentation and “sweating” ofbeans gives rise to methyl vanillin, the predominantflavor principal of natural vanilla extract. To preparethe extract, beans are extracted with a mixture of wa-ter and alcohol. Optional ingredients of extractingsolvent are glycerin and sugar. One gallon of standardstrength vanilla extract is equivalent to 13.34 oz. ofvanilla beans. Alcohol content of the extract rangesfrom 30% to 50%. By evaporating solvent, con-centrated extracts (2 to 5 fold) are also available(Marshall and Arbuckle, 1996).

It is most common to use vanilla extract addedin yogurt production after fermentation for blendedyogurts or added prior to fermentation for cup set yo-gurt. Some manufacturers prefer to obtain vanilla inprocessed syrup from a typical fruit preparation sup-plier. To prepare these vanilla syrups, vanilla extractis processed with sugar and/or HFCS to a finishedBrix of 50–60◦, usually at a similar Brix level to the

fruit preparation that they are purchasing. With thissyrup, it is possible to produce both vanilla and fruitedyogurts using one plain yogurt base.

Some yogurt producers prefer powdered vanillabecause it does not cause dilution of yogurt withvanilla solvent, alcohol. To prepare the powder,vanilla beans are ground with sugar. Specks of vanillabeans are visible in this type of powder. If no specksare required, the powder is obtained by drying un-der vacuum a blended paste of single strength vanillaextract and sugar. The proportion of vanilla extractand sugar is designed to yield single strength vanillapowder.

Artificial vanilla flavor is prepared from syntheticmethyl vanillin. This flavoring offers cost savings be-cause of its flavor potency but the label of the productmust indicate artificial flavor. Furthermore, its flavorbalance and aroma are considered less desirable thannatural vanilla. In relation to flavor strength, 0.7%solution of vanillin is equivalent to one pound of dryvanilla beans. Pure vanilla flavoring has a standard ofidentity (FDA 21 CFR 169.175) (FDA 2004). Mix-tures of pure vanilla and vanillin are covered in FDA21 CFR 169.177 (FDA 2004). Imitation vanilla isidentified in FDA 21 (FDA 2004) CFR .169.181.

Fruit Flavors. The flavor options commonly usedin fruit preparations or flavored syrups are natural,natural/WONF (with other natural flavors), N&A(natural and artificial) or artificial. The majority offruit preparations today use natural/WONF. Mostmanufacturers will custom-formulate the flavor sys-tem to meet the customer’s need. Usually the purposeof using N&A or artificial flavors is to reduce the fla-vor cost. Drinkable yogurts might use flavored syrupsthat consist of sugar or HFCS, a small amount of sta-bilizer for viscosity and flavoring.

Colors

The color of the fruit preparation is usually used tocolor the finished yogurt. The options include, nocolor added therefore relying on the natural color ofthe fruit, or color added, natural colors, or artificialcolors. Artificial colors (red #40, blue #1, and yellow#5 & #6) are very stable during processing, fruit shelflife and during code life of the yogurt. These are themost economical choice, but have fallen out of favorfor labeling reasons.

The use of natural colors in fruit preparations ismore common. Natural colors used in the finishedyogurt, added either through the fruit preparation


or to the yogurt directly, are considered “color ad-ditives” and must be declared as “color added” orby the ingredient name in the ingredient declaration.Color additives not subject to certification may be de-clared as “Artificial Color,” “Artificial Color Added,”or “Color Added.” Alternatively, such color additivesmay be declared as “Colored with ” or “color,”the blank to be filled with the name of the color ad-ditive listed in the applicable regulation in part 73 ofthis chapter FDA 21 CFR 101.30(k)(2) (FDA 2004).Some of the natural colors that are preferred becauseof their heat stability during processing are blackcarrot, grape extract (Kosher or non-Kosher), chokeberries, elderberry, red cabbage, radish, black cur-rent, carmine, annatto, and turmeric. Some of thesecolors that are used will simply appear as “vegetablecolor” in the ingredient declaration. Beet juice issometimes used in fruit preparations, but because ofits instability to heat processing, many times it willbe added at the yogurt manufacturing step.

Acidulants

Fruit preparations are generally acidified to pH 3.4–4.1. The most commonly used acidulant is citric acid.If a more natural label is desired, lemon juice con-centrate, a more costly alternative, can be used. Forsome fruits, such as strawberry, blueberry, or rasp-berry, malic acid can be used to help enhance certain

flavor notes. The high acidity level helps bring out thefruit flavor and is more compatible with the acidityof the yogurt. When using acids in fruit preparations,it is common to also add buffering agents such assodium citrate.

Preservatives

Some fruit preparations contain added preservatives.This is especially the case for fruit preparations thatare processed using the “hot pack” method. The mostcommon preservative used is potassium sorbate, ei-ther alone or in combination with sodium benzoate.The total usage rate will range from 0.075% to 0.20%in the fruit preparation. Fruit processed using an asep-tic system does not require added preservatives, butsome product manufacturers will add them for addedprotection. Most fruit preparations have a 4-monthshelf life, but some formulations that use artificialcolors and/or flavors can have as much as a 6-monthshelf life.

A sample specification sheet for a raspberry fruitpreparation for blended or Swiss style yogurt isshown in Table 9.3.

Specialty Fruit Preparations

There are also other specialty fruit preparations thatare produced for a specific application, or market,

Table 9.3. Typical Specification Sheet for Fruit Preparation Designed for Use inBlended/Swiss-Style Yogurt

Company Information Date:Product: Raspberry swiss-style fruit for yogurtProduct code #:Recommended usage: 15% in a yogurt with 3% added sugarIngredient statement: Sugar, water, raspberries, pectin, locust bean gum, natural flavorsPhysical Specifications:

◦Brix: 50 ± 2.0pH: 3.6 ± 0.02%Fruit: 30%

Appearance: Red, opaque viscous liquid without seeds.Microbiological Specifications:

Total plate count: <10 CFU per gramYeast & mold: <10 CFU per gramColiform: <10 CFU per gram

E. coli: NegativeSalmonella: NegativeStaphylococcus: NegativeShelf life & Storage: 150 days refrigerated; 90 days between 60−90◦FPackaging: 2000 lb stainless steel tote


Table 9.4. Organic Ingredients as Defined by FDA 7 CFR 205 (FDA 2004)

Organic fruits, fruit puree, and fruit juice/concentrateOrganic sugar or organic evaporated cane juiceOrganic Compliant Ingredients (as defined by 7 CFR 205)Citric acid––allowed 205.605 (a) (1) (ii)––produced by microbial fermentation of carbohydrate substances

Calcium chloride––allowed 205.605 (a) (4)Vegetable colors––allowed 205.605 (a) (5)––nonsynthetic sources onlyFlavors––allowed 205.605 (a) (9)––nonsynthetic sources only and must not be produced using synthetic

solvents and carrier systems or any artificial preservatives.Ascorbic acid––allowed 205.605 (b) (4)LM pectin––allowed 205.605 (b) (21)Sodium citrate––allowed 205.605 (b) (31)Locust bean gum––allowed 205.606 (b)—gums water extracted onlyHM pectin––allowed 205.606 (e)

such as organic or unsweetened/concentrated fruitpreparations. Unsweetened fruit preparations arevery low Brix (12–30◦), have a high concentra-tion of fruit (40– 60%), and are processed asep-tically. They are added at lower usage rates (10–12%) in a yogurt sweetened with nutritive or highintensity/nonnutritive sweeteners. They can pro-vide in-plant flexibility to be used in an array ofproduct formulations, and offer freight and storagesavings.

The organic yogurt market is growing at 22% peryear in dollar sales, and is gaining interest from yo-gurt producers. Because fruit preparations are formu-lated using some ingredients that are nonagricultural,they can not be made to meet the 100% organic la-bel. However, it is very possible to produce organicfruit preparations that meet the 95% minimum of or-ganic agricultural products by weight, excluding wa-ter and salt. This is possible because the remaining5% or less of the necessary ingredients needed areallowed in 7 CFR 205.605—nonagricultural (nonor-ganic) substances allowed as ingredients in or on pro-cessed products labeled as “organic”. . . . . (a) nonsyn-thetics allowed and (b) synthetics allowed and 7 CFR205.606—nonorganically produced agricultural al-lowed as ingredients in or on processed products la-beled as “organic” . . . . . .

Table 9.4 lists organic and organic compliantingredients typically used in the preparation of anorganic fruit preparation.

It should be noted that if any agricultural ingre-dient, including those listed in 205.606, becomesavailable commercially it must be used in an organicproduct. Commercially available is defined in 7 CFR205.2 as the ability to obtain a production input in anappropriate form, quality, or quantity, to fulfill an

essential function in a system of organic productionor handling, as determined by the certifying agent inthe course of reviewing the organic plan. Today an or-ganic LBG is being produced, and will be tested inorganic formulations to assess its function and qual-ity as a replacement for conventional LBG currentlybeing used.

Table 9.5 shows more popular fruits and fla-vors/colors used in yogurt. This list contains an arrayof fruits and flavor combinations to offer a wide va-riety of innovative selections for various segments ofyogurt consumers.

PROCESSING YOGURT FRUITPREPARATIONSThere are two basic processes used in the manufac-ture and packaging of yogurt fruit preparations. Theconventional “hot pack” processes using open cook-ing kettles, and the closed aseptic process and pack-aging system.

In the conventional hot pack process (Figure 9.2)using modified food starch as the stabilizer, the basicprocessing steps are:

1. Add fruit, 75% of the sugar, 50% of the water,and preservatives to a steam jacketed kettle withagitation.

2. In a second kettle, add the starch to the remainingwater. Mix well and then add the starch slurry tothe first kettle.

3. Heat to 85– 87.8◦C (185–190◦F) with continuousagitation.

4. Add the remaining sugar to cool the batch.5. Add flavor and color and mix well. At this point,

the quality control check is applied. Pull sample


Table 9.5. Various Fruit Flavors Used in Commercial Yogurt

Style of Yogurt Flavors Available

Fruit-on-the bottom Apple cinnamon, blueberry, boysenberry, cherry, mixed berry, peach,raspberry, strawberry, strawberry banana, tropical blends

Stirred/blended Strawberry, strawberry banana, blueberry, cherry, raspberry, peach, raspberrybanana creme, berry banana, blackberry harvest, blueberry crumble,boysenberry, cherry orchard, coconut cream pie, french vanilla, harvestpeach, key lime pie, lemon burst, mandarin orange, mixed berry, mountainblueberry, orange creme, peach cobbler, pina colada, pineapple, redraspberry, strawberry, strawberry banana, strawberry cheesecake, strawberrykiwi, strawberry mango, tropical peach, white chocolate raspberry

Whipped Strawberry, strawberry mist, raspberry mousse, cherry chiffon, french vanilla,key lime pie, orange creme, peaches n’ cream, blueberry mist, strawberrybanana bliss

Drinks/smoothies Strawberry, strawberry banana, tropical, raspberry, peach, mixed berry, peachpassion fruit

Extra-thick Banana, blackberry harvest, blueberries ’n cream. creme caramel, key lime pie,lemon supreme, orange creme, peaches n’ cream, royal raspberry,strawberry, strawberry banana, vanilla

Light Apple turnover, apricot mango, banana creme pie, berries n’ cream, blackberry,blackberry pie, blueberry, blueberry patch, boston cream pie, cherry vanilla,harvest peach, key lime pie, lemon cream pie, lemon chiffon, orange creme,orange mango, peach, raspberry, red raspberry, strawberry, strawberry kiwi,strawberries n’ banana, strawberry orange sunrise, very cherry, very vanilla,white chocolate raspberry, white chocolate strawberry

Children’s dual color Cotton candy/strawberry kiwi, raspberry rainbow/strawberry bash, rockin’rainbow sherbet/outrageous bubble gum, triple cherry/wild berry blue,watermelon burst/strawberry punch

Toddler’s Strawberry-banana, strawberry-strawberry vanilla, strawberry banana-peachesn’ cream, peach, pear

Lo carb Strawberry creme, peach creme, blueberry creme, raspberry creme, peaches ’ncream, raspberry ’n cream, strawberries n’ cream, vanilla cream

Probiotic/bio-yogurt Strawberry, vanilla, orangeYogurt in a tube/portable Strawberry milkshake/banana split, red raspberry/paradise punch, strawberry

banana burst/watermelon meltdown, strawberry kiwi kick/chill out cherry,strawberry splash/berry blue blast, cool cotton candy/burstin’ melon berry,crazy berry bolt/extreme red rush

from fully batched and mixed kettle and check◦Brix, pH and color, as per specification.

6. Pack the product at 71.1–73.9◦C (160–165◦ F) intothe appropriate container.

7. Cool the product in the container with blast cool-ing.

Generally preservatives, such as potassium sor-bate, are added to the fruit preparation that is pro-duced using the conventional hot pack process.

In the aseptic process (Figure 9.3) and packagingsystem, using modified food starch as the stabilizer,the basic processing steps are:

1. Add fruit, sugar and 50% water to a steam jacketedkettle with agitation.

2. In a second kettle, add starch to the remainingwater and mix well. Add starch slurry to the firstkettle.

3. Preheat ingredients to 37.8◦C(100◦F).4. Add flavor and color and mix well.

Quality Control check: Pull sample from fullybatched and mixed kettle and check ◦Brix, pH, andcolor as per specification.

5. Pump mixture through an aseptic system capableof rendering the finished product commercially


Figure 9.2. Process flow sheet for fruit preparation using the Hot Pack kettle procedure.

sterile. Most systems use scraped-surface heatexchangers to achieve temperatures of at least87.8◦C (190◦F) (usually 90.6–93.3◦C (195–200◦F) with continual agitation to insure thoroughheating and mixing. After heating, the product isheld for 3 minutes to allow heat penetration of thelargest particulates.

6. The product is then cooled by scraped-surface heatexchangers to 26.7–32.2◦C (80–90◦F).

7. Pack the product using filling equipment designedto maintain commercial sterility into a hermeti-cally sealed container of choice.

When pectin is used as the stabilizer for the fruitpreparation, it is prepared as a solution in hot wa-ter using a high speed mixer and a separate kettle orslurry tank. The high speed mixer is necessary be-cause pectins swell very fast and lumps may occur.The pectin solution is then added to the hot mix be-fore addition of the bulk of the sugar. If low methoxylpectin is used, any additional acid should be addedwith the fruit at the beginning of the boil (cooking),

while with high methoxyl pectin it must be addednear the end of the boil. The same high speed mixer-kettle/tank set-up can be used for addition of otherhydrocolloids such as locust bean gum or guar gum.

Hermetically sealed container means a containerthat is designed and intended to be secure against theentry of microorganisms and thereby to maintain thecommercial sterility of its contents after processing.[FDA 21 CFR 113.3(j) (FDA 2004)]

Aseptic processing and packaging means the fill-ing of a commercially sterilized cooled product intopresterilized containers, followed by aseptic hermet-ical sealing, with a presterilized closure, in an at-mosphere free of microorganisms. [FDA 21 CFR113.3 (a) (FDA 2004)]

“Commercial Sterility” of thermally processedfood means the condition achieved by the applica-tion of heat, which renders the food free of:

� Microorganisms capable of reproducing in thefood under normal nonrefrigerated conditions ofstorage and distribution; and


Figure 9.3. Flow diagram for Aseptic process of manufacturing fruit preparation for yogurt.

� Viable microorganisms (including spores) ofpublic health significance.

� Commercial Sterility of equipment and containersused for aseptic processing and packaging of foodmeans:

� The condition achieved by application of heat,chemical sterilant(s), or other appropriatetreatment that renders the equipment andcontainers free of viable microorganisms havingpublic health significance, as well asmicroorganisms of nonhealth significance,capable of reproducing in the food under normal

nonrefrigerated conditions of storage anddistribution. [FDA 21 CFR 113.3 (e) (FDA 2004)]

In aseptic processing systems the heating and cool-ing is usually performed in either vertical or horizon-tal scraped-surface heat exchangers constructed of ahollow stainless steel or nickel. The heat exchangecylinder is most often six inches in diameter. Aroundthe heat exchange tube, another cylinder is weldedor attached creating space for a heat exchange me-dia such as steam for heating, or water, glycol, orammonia, for cooling. Product is pumped through


the inner tube while heat exchange media is circu-lated in the annular space between the tubes.

To prevent the product from burning or freezing onthe heat exchange wall, a mutator with blades is con-centrically positioned inside the inner cylinder. Asthe mutator turns within the tube, the scraper bladeslightly and continuously scrape the wall. This actionassures less damage to the particulate identity of thefruit in suspension during heating and cooling.

The filler used in aseptic packaging is indepen-dently sterilized by circulating 121.1◦C (250◦F)steam for approximately 30 minutes. Sterile, heatedair is then introduced into the filling chamber of themachine. When filling bags (from 5 to 200 gal), thebags come to the processor presterilized by gammaradiation. During filling, the bag is put inside the ster-ile filling chamber, the bag cap is removed, the fillinghead is inserted into the spout area of the bag, andthe product flow begins. When the proper amount ofproduct is in the bag as determined by a scale or flowmeter, the product flow stops, the filling head is re-moved form the bag, and the cap is replaced. The bagis then ejected from the filling chamber.

Using fruit preparation that is aseptically pro-cessed, not only assures the microbiological steril-ity of the fruit, but improves the overall quality andgreatly helps improve convenience, transportation,and in-plant handling. There are advantages usingaseptic processing and packaging as compared toopen-kettle or hot-pack processing for the manufac-ture of yogurt fruit preparation. These include:

� Greater retention of natural fruit color. Openkettle/hot pack processing requires a 30–40minute heating period to reach the 87.8–93.3◦C(190–200◦F) cook temperature with a packagingtemperature of 60.0–71.1◦C (140–160◦F),depending on the total solids, preservatives, andpH. After hot filling, the bulk container (5–55gallons) takes from 4 to 36 hours to bring theequilibrium temperature of the product in thepackage to 37.8◦C (100◦F) or below. In an asepticprocess system, continuous heating and coolingwithin required sterilization time exposes theproduct to considerably less heat, resulting in aretained natural color.

� Improved flavor—Since heating takes place in acompletely closed heat exchanger, the volatileflavor components or essences of the fruit cannotescape into the atmosphere.

Better retention of nutrients also results from anenclosed heat exchanger. As much as 90–95% of thenutrients can be retained.

The need for preservatives is eliminated becausethe product has been heated for sterilization, cooledand filled in a sterile atmosphere, and packaged asep-tically. This also means that the product does notrequire refrigeration in transportation and storage of-fering refrigeration savings.

A more consistent product can be produced byaseptic fruit processing. Fruit flotation in the packageis virtually eliminated by the rapid cool down andaccompanying viscosity build-up possible throughroom temperature packing.

The aseptic process is energy efficient. Approxi-mately 50% of the thermal energy of open kettle heatprocessing is lost to the atmosphere. In addition lessthermal energy usage is required to get the asepticproduct back to room temperature.

Packaging of Fruit Preparations

Fruit preparations for yogurt can be packaged into avariety of sizes and container styles (Fig. 9.4).

Sizes generally range from 50 lb bag-in-box to2000 lb aseptically filled containers. The 50 lbbag-in-box filled either aseptically or “hot packed”is still a popular container choice for yogurt manu-facturers. It provides flexibility in the plant for pro-duction of small flavor runs. However, it is labor in-tensive, creates a potential source of contaminationwhen unloading, despite the best efforts to sanitizeboth bag and hands and it can introduce unwantedcorrugated packaging material into the filler room.The next size to consider is the 400–500 lb bag-in-drum. This container is usually aseptically pro-cessed where it can be filled at 80–90◦F. There aresome “hot packed” bag-in-drum products manufac-tured, but cooling is a challenge and it may not workfor all formulations. The 400–500 lb bag-in-drumcan be the traditional type bag that is opened at thetop and evacuated using a Graco-type fruit pump, orit can be equipped with a bottom unloading valvethat can be attached and unloaded with a positivepump.

Large volume yogurt manufacturers prefer to re-ceive and handle fruit preparation in 1800–2000 lbtote containers. Because this size container would notbe able to be cooled efficiently and quickly, it is filledusing an aseptic processing system. There are gener-ally three types of these containers used, the one-waytote, the collapsible tote, and the returnable stainlesssteel tote. The one-way tote uses a large multilayeredlaminate bag equipped with both a filling cap and anevacuation fitting that has been sterilized prior to de-livery to the fruit processor. This bag is then filled


Figure 9.4. Packaging containers of fruit-for-yogurt. Courtesy of Eric Ducey, Fruit Crown.

aseptically and placed into a large heavy corrugatedcontainer and delivered on a pallet. The yogurt man-ufacturer will recycle the corrugated and dispose ofthe plastic liner. The collapsible tote uses a similarinner bag but uses a custom crate to hold the bag inplace during shipping and use at the yogurt manufac-turing plant. After use, the inner bag is disposed atthe plant and the crate “breaks down” or collapses foreasier and more economical shipping back to the fruitpreparation supplier. The stainless steel tote is steamsterilized at the fruit preparation manufacturing plantand then filled on the aseptic process system. The toteis equipped with an outlet that is used for unloadingat the yogurt plant. Because the outlet is stainlesssteel, it is possible to attach a steam barrier prior tounloading to establish a sterile connection. Becausethe empty stainless steel totes must be returned tothe fruit processor, it is generally not economical touse them when the yogurt manufacturer is locatedmore than 500 miles from the fruit processor.

Twenty four hours after packaging, first prepara-tion samples are evaluated to assure compliance tothe product specification prior to release of the prod-uct. The following are usually the criteria used forevaluation:

� ◦Brix (by refractometer)� pH—Must use a consistent temperature for

product testing.

� Viscosity/Consistency—The best method forproducts containing fruit particulates is aBostwick consistometer measuring device, wherethe sample is measured at a specific temperatureand time, i.e., 21.1◦C (70◦F) for 30 seconds. TheBostwick consistometer provides accuratedetermination of sample consistency bymeasuring the distance, which a material flowsunder its own weight during a given time intervaland temperature. It consists of a level,stainless-steel trough with two compartments.The first compartment, which holds the sample ata predetermined temperature, is separated fromthe second compartment by a spring loaded gate.The second compartment is 24 cm long and hasgraduated parallel lines at 0.5 cm intervals. Themeasurement is taken by fully filling the firstcompartment with the sample to be tested,releasing the gate, and letting the fruit preparationflow freely down the slope. The distance thatthe fruit preparation flows from the gate after30 seconds is measured in centimeters as theBostwick reading. A Brookfield viscometer canbe used for products without particulates orflavored syrups. Brookfield instruments utilize aprinciple of rotation viscosity measurement incentipoises. The device consists of a spindleimmersed in the fluid sample to sense torqueresistance when running at a constant speed.


Color. It is usually done visually comparing fruitcolor in relation to a control sample. Sometimes thefruit is mixed in the finished product to augment thecolor. Some companies use pantone charts for thisevaluation, while other companies might use instru-ments like colorimeters or spectrophotometers thatquantify color by assigning a numerical descriptionas opposed to a qualitative description.

Organoleptic. Sensory evaluation is conducted toinsure that the product complies with sensory stan-dards.

Microbiological testing. Standard Plate count,Yeast & Mold count and Coliform count.

REFERENCESChandan RC. 1982. Fermented Dairy Products in

Prescott and Dunn’s Industrial Microbiology, 4th ed.AVI Publ, Westport, CT, pp. 113–184.

Chandan RC. 2004. Dairy: yogurt. In: P Smith, YHHui (Eds), Food Processing, Blackwell, PublishingCo., Ames, IA.

Chandan RC, Shahani KM. 1993. Yogurt. In:YH Hui (Ed), Dairy Science and TechnologyHandbook, Vol. 2. VCH Publications, New York,pp. 1–56.

Food and Drug Administration (FDA), 2004. U.S.Department of Health and Human Services. Code ofFederal Regulations. Washington DC.

Hoefler AC. 2004. Hydrocolloids. Eagen Press, St.Paul, MN, pp. 78–82.

Marshall RT, Arbuckle WS. 1996. Ice Cream. 5th ed.Chapman and Hall, New York, pp. 91–103.

Tamime AY, Robinson RK. 1999. Yogurt Scienceand Technology, 2nd ed. Woodhead Publ,Cambridge, England, and CRC Press, Boca Raton,FL.

Woodroof JG. 1990. 50 years of fruit and vegetableprocessing. Food Technology, pp. 92–95.

ACKNOWLEDGEMENTWe are grateful to Andrew Hoefler for sharing hisexpertise on the use of LM pectin for sundae styleyogurt. We also appreciate the contribution of BrentCannell for preparing flow sheet diagrams.

10Milk and Milk-Based Dairy

IngredientsIsabelle Sodini and Phillip S. Tong

IntroductionComposition and SpecificationsPerformance in Yogurt Formulation

Fresh MilkCreamMilk PowdersCondensed MilkButtermilk PowderMilk Protein ConcentratesWhey ProductsCaseinates

ConclusionReferences

INTRODUCTIONMilk is the primary ingredient in fermented milkmanufacturing. Historically, fresh milk was concen-trated by evaporation (reduction of 1/3) to increasethe dry matter before fermentation and coagulation.Now, this practice is limited to rural communities andthe standardization of the fat content, protein content,and dry matter in industrial yogurt manufacture is re-alized by the addition of dairy ingredients (powdersor concentrates). Furthermore, high quality, readilyavailable, convenient dairy-based concentrates, andpowdered ingredients can be used to replace (par-tially or totally) fresh milk when it is not available(e.g., recombined milk yogurts). The choice of thedairy ingredients used in yogurt formulation has animpact on yogurt characteristics (acidification, flavor,texture).

COMPOSITION ANDSPECIFICATIONSTable 10.1a gives the composition of a wide range ofdairy ingredients, which have been and are availableand evaluated in yogurt formulations. The impact ofthese ingredients on the observed properties of yogurtis presented in Performance in Yogurt Formulationsection . Broadly speaking, the major differences inthe effect of such products on yogurt can be attributedto differences in composition (proximate, ratios ofprotein to lactose, mineral content, and ratio of caseinto whey proteins). However, the physical state of theconstituents of these ingredients is also important totheir observed behavior in yogurt. This can be relatedto the ingredients thermal history, morphology, andparticle size distribution—particularly in the case ofdry dairy ingredients.

Therefore, specifications usually detail the prox-imate composition, microbiological quality, and as-pects of the physical properties of the ingredient. Inmany cases industry standards (e.g., American DryProducts Institute) are used to facilitate a commonlanguage of communication regarding specification.In addition, customer specific standards can be devel-oped to provide additional specifications not coveredby various industry standards.

Nonetheless, one key standard that has been com-monly used is the whey protein nitrogen index(WPNI). This is a test, which measures the amountof soluble nitrogen in a fixed weight of an ingredient(ADPI, 1990). Although the test is not without its

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Table 10.1a. Proximate Composition of Select Dry Dairy Ingredients

Ingredient Fat Protein Lactose Ash Moisture

Sweet whey 1–1.5% 11–14.5% 63–75% 8.2–8.6% 3–4.5%Reduced lactose whey 1–4% 18–24% 52–58% 11–22% 3–4%Demineralized whey 0.5–1.8% 11–15% 70–80% 1–7% 3–4.5%Whey protein concentrate 34 5–6% 34–36% 48–52% 6.5–8% 3.5–4.5%Whey protein concentrate 80 4–8% 80–82% 4–8% 3–4% 3.5–4.5%Whey protein isolate 0.5–1% 90–92% 0.5–1% 2–3% 4–5%Nonfat dry milk 0.7–1.5% 34–37% 48–52% 8.2% 3.5–55Milk-protein concentrate 3.0% 65% 22% 6% 4.0%Source: ADPI Bulletin 916, 1990; Chandan, 1997.

limitations, it continues to be widely utilized to pro-vide a basic “heat classification” of milk powders.Table 10.1b gives the basic classification of thesepowders based on WPNI.

PERFORMANCES IN YOGURTFORMULATIONFresh Milk

Fresh milk is the major ingredient in yogurt manufac-ture. Its chemical composition fluctuates dependingon various factors as species, breed, and season ofthe year. This can affect the fermentation, as well asthe properties of the yogurts.

Effect of the Species of Mammals onYogurt Properties

The gross composition of the milk of different speciesof mammals used for manufacture of fermented milksis given in Table 10. 2. The dry matter is very differ-ent according to the species, from 18.8% for sheepmilk to 10.8% for mare’s milk. Carbohydrate con-tent ranges from 4.6% to 6%. They are in excess forfermentation, so their variation does not affect theacidification of the milk. However, naturally presentinhibitory substances in milk can affect the rate ofacidification. It has been reported that camel milk

exhibits a slower acidification rate than in cow, sheep,or goat milk (Fig.10.1). This could be due to a higherconcentration of lysozyme in camel milk as com-pared to the other milks (El-Agamy, 2000).

The texture and the flavor of the fermented milksare dependent on the protein and fat content, whichshows strong differences according to the species.Sheep and buffalo milk exhibit very high fat con-tent, more than 7%; whereas horse milk contains lessthan 2% fat. Sheep milk has the highest protein con-tent (4.6%), and mare’s milk has the lowest (1.3%).This leads to differences in the quality of the yo-gurts. For example, a yogurt from sheep or buffalomilk will present a creamy texture and a buttery fla-vor associated with the high fat content (Aneja, 1991;Anifantakis, 1991). If the milk is not homogenized,a layer of cream will occur in the manufacture of set-type yogurt (Anifantakis, 1991). Yogurt from sheepmilk, because of the high protein content, does notrequire milk fortification (Muir and Tamime, 1993).On the other hand, a yogurt from mare’s milk willhave a very thin texture, and the blending with cowor sheep milk, or the addition of caseinates or thick-eners, is recommended to afford a convenient texture(Di Cagno et al., 2004). Figure 10.2 illustrates the ef-fect of milk source (cow, sheep, and goat) on yogurtviscosity and syneresis.

Finally, the content of minor components also hasan impact on the yogurt flavor. For example, a “goaty”

Table 10.1b. Heat Classification of Nonfat Dry Milk

Classification Whey Protein Nitrogen Index (mg/g) Solubility Application

High heat <1.5 Least Baked goods, meats confectionsMedium heat 1.51–5.99 Average Ice creamLow heat >6.0 Most Recombined milk dairy products,Source: ADPI Bulletin no. 916, 1990.

Table 10.2. Approximate Average Composition (%, w/w) of Milk of Different Species of MammalsUsed in Yogurt and Fermented Milk Manufacture

Specie Dry Matter Fat Casein Whey Protein Lactose Ash

Sheep 18.8 7.5 4.6 1 4.6 1Buffalo 17.5 7.5 3.6 0.7 4.8 0.8Camel 13.4 4.5 2.7 0.9 4.5 0.8Goat 13.3 4.5 3 0.6 4.3 0.8Cow 12.7 3.9 2.6 0.6 4.6 0.7Horse 10.8 1.7 1.3 1.2 6.0 0.5Source: After Walstra et al., 1999.

Figure 10.1. Effect of milk source on yogurt acidification. ——, cow milk; – – – –, sheep milk; ------, goat milk;——, camel milk. After Jumah et al., 2001.

Figure 10.2. Effect of milk source on yogurt apparent viscosity (A) and syneresis (B). Yogurt viscosity wasmeasured by Brookfield LV viscometer using spindle n◦ 3 at 0.6 rpm. Yogurt syneresis was determined by draining180 mL of yogurt on stretched cheese cloth. , sheep milk; , cow milk; �, goat milk. After Kehagias et al., 1986.

169


flavor noticeable in the yogurt from goat milk, hasbeen associated with a high amount of free fatty acidsin goat milk (Abrahamsen and Rysstad, 1991). Ac-etaldehyde is one of the major aromatic componentscharacteristic of yogurt flavor. It is produced mainlyfrom the conversion of threonine into acetaldehydeand glycine during fermentation. Threonine aldolaseis the key enzyme in this conversion. Low amount ofacetaldehyde observed in goat milk yogurt has beenattributed to high amount of free glycine in goat milk,which causes a feedback inhibition of the threoninealdolase (Rysstad et al., 1990). The addition of threo-nine to milk has been recommended in the manufac-ture of yogurt from goat milk (Rysstad et al., 1990),as well as mare’s milk (Di Cagno et al., 2004,) inorder to improve yogurt flavor.

Effect of the Breed and Genetic Variant onYogurt Properties

Table 10.3 shows the gross composition of milk pro-duced by four breeds of cows, Friesian, Holstein,Brown, and Jersey. Fat and protein content varies de-pending on the breed. This affects the textural prop-erties of the yogurt resulting due to the relationshipbetween protein content in milk and yogurt viscos-ity (Schkoda et al., 2001b). For example, Allmereet al. (1999) observed a strong difference in elasticmodulus for yogurts made with milk from individualcows from two breeding selection lines. An increaseof 40% was observed with yogurt made with milkfrom one selection line as compared to the other.This was correlated to a difference in protein con-tent (3.71% versus 3.37%). Furthermore, an effect ofthe genetic variants on the physical properties of yo-gurt has been demonstrated for �-lactoglobulin and�-casein variants. Allmere et al. (1998) and Bikkeret al. (2000) reported higher elastic modulus withmilk gels containing �-lactoglobulin B and C thanthe ones containing �-lactoglobulin A. For instance,Allmere et al. (1998) observed a 30% higher storagemodulus in acidified milk gels containing only the B

Table 10.3. Approximate Average Composition (%, w/w) of Milk of Different Breeds of Cow

Breed Dry Matter Fat Crude Protein Lactose Ash

Friesian (in the Netherlands) 13.3 4.4 3.4 4.6 0.75Holstein (in the US) 12.1 3.4 3.3 4.5 0.75Brown Swiss 12.9 4.0 3.3 4.7 0.72Jersey 15.1 5.3 4.0 4.9 0.72Source: After Walstra et al., 1999.

variant of �-lactoglobulin compared with those con-taining only the A variant. The use of milk containing�–casein variant AA or BB does not affect the vis-cosity or the texture of yogurts (Allmere et al., 1998;Muir et al., 1997). However, Muir et al. (1997) ob-served that the serum leakage was lower for yogurtsmade from milk with the �-casein variant AA thanyogurts containing the �-casein variant BB.

Effect of the Seasonal Variation in MilkComposition on Yogurt Properties

The composition of milk can vary across the seasons.For instance, approximately a 10% variation in fatand protein is observed in milk received in July andAugust (lowest level) compared to that received inOctober and November (highest level) in the UnitedStates (Chandan, 1997). These variations of compo-sition are known to affect the consistency and thequality of the manufactured dairy products. Seasonalvariation of sheep milk in Scotland has been shownto change viscosity, serum separation, and acidity inyogurts (Muir and Tamime, 1993). Seasonal variationof cow milk in Australia has been reported to affectthe viscosity and serum separation in both set andstirred yogurts (Cheng et al., 2002). Standardizationof the protein content by addition of milk protein invarious forms (powders or concentrates, fractionatedor whole milk protein) reduces the effects of milkseasonality in yogurt manufacture.

Cream

Yogurt can have a fat content ranging from 0% to10%, with most common values comprised between0.5% and 3.5% (Tamime and Robinson, 1999). In theUnited States, regulations distinguish three types ofyogurts: regular yogurts (more than 3.25% milkfat),low-fat yogurts (between 0.5% and 2% milkfat), andnon-fat yogurts (less than 0.5% milkfat).

The effect of cream addition on yogurt texture islinked to the integration of the fat globules into the

10 Milk and Milk-Based Dairy Ingredients 171

Figure 10.3. Simplified structure of full fat yogurt issued from homogenized milk. Note that fat globules areintegrated into the gel structure. After Schkoda et al., 2001a.

gel structure. This integration does not occur if thecream is added after the fermentation (Schkoda et al.,2001a), or if the milk is not homogenized (van Vlietand Dentener-Kikkert, 1982). In this case, addition ofcream decreases the viscosity of the yogurt, becausemilk fat globules act as “structure breakers” (Schkodaet al., 2001a; van Vliet and Dentener-Kikkert, 1982).On the other hand, when the cream is added in milkbefore fermentation, and when milk is then submit-ted to homogenization before inoculation with starterculture and acidified, which is the usual practice inyogurt manufacture, the addition of milk fat increasesthe yogurt viscosity and firmness, and decreases theserum separation. For instance, Martens (1972) re-ported an increase of 44% in the consistency scoreof stirred yogurt when the fat content varied from0% to 3.9%. Becker and Puhan (1989) found that gelfirmness was increased by 23% in whole milk yogurt(3.5% fats) compared to nonfat yogurt. De Lorenziet al. (1995) observed a higher (23%) apparent vis-cosity at 100 s−1 in full-fat yogurts (4% fat content)as compared to a nonfat yogurt. Finally, Becker andPuhan (1989) observed that yogurts made from wholemilk did not show any whey separation, while in 63nonfat yogurt samples, 15 showed a whey layer onthe surface after 14 days of storage.

The effect of cream addition on yogurt physicalproperties can be explained by the integration of themilk fat globules in the gel network. During homog-enization, the native milk fat globule membrane is

removed and a new membrane is formed, which sta-bilizes the homogenized fat globules. The new layercovering the fat globules is predominantly composedof micellar casein. Cano Ruiz and Richter (1997) de-termined the percentage distribution of proteins in themilk fat globule membrane of homogenized milk andfound a repartition between caseins, whey protein,and proteins from native membrane equal to 67%,10%, and 13%, respectively. The new layer of themilk fat globules interacts with the casein micellesduring acidification (Barrantes et al., 1996; Luceyet al., 1998) and acts as a “structure promoters” inthis case (van Vliet and Dentener-Kikkert, 1982), asreported in Figure 10. 3.

Milk Powders

Milk powders can be used to enrich the protein con-tent of the milk before fermentation and increase theviscosity of the yogurts. This allows the standard-ization of the protein content of the milk and helpsto maintain a constant quality of the products. Skimmilk powder or whole milk powder can be used. How-ever, it is more common to use skim milk powder,which has no effect on the fat content of the milkbase compared to whole milk powder. Hence, the fatcontent can be entirely controlled by the addition ofcream, while the addition of the milk powder allowsfor adjustment of the protein content.


The level of addition of milk powder determinesthe viscosity, gel strength, and ability to retain thewhey of the yogurt. Several studies have establisheda positive relationship between the addition of milkpowder, and the rheological and physical propertiesof yogurt (Becker and Puhan, 1989; Harwalkar andKalab, 1986; Rohm, 1993; Wacher-Rodarte et al.,1993). Rohm (1993) compared the viscosity of yo-gurts without adding skim milk powder and also with1%, 2%, and 3% of added skim milk powder. Theapparent viscosities measured at 10 s−1 were respec-tively, 0.53 Pa.s, 0.65 Pa.s, 0.77 Pa.s, and 0.91 Pa.s,for yogurts prepared with a classical yogurt culture.In this case, a 1%, 2%, and 3% skim milk powder ad-dition allows an increase of viscosity of respectively22%, 43%, and 70%. In another work, Becker andPuhan (1989) reported an increase in the gel strengthof 25% and an increase of viscosity as measured withthe posthumus funnel of 15% with an addition of 1%skim milk powder compared to yogurt made withoutadded skim milk powder. Finally, the susceptibilityto syneresis has been shown to be decreased with ahigher addition of milk powder. Harwalkar and Kalab(1986) reported a percentage of whey drained in adrainage test equal to 31%, 24.5%, 13.5%, and neg-ligible when the total solid content of the yogurt was10%, 12.5%, 15%, and 20%, respectively.

A low-heat or a medium-heat powder is usuallyrecommended for yogurt fortification (Tamime andRobinson, 1999). However, it has been reported thatrecombined milk from low-heat skim milk powdergives lactic gels with a lower elastic modulus as com-pared with lactic gels made from recombined milkfrom high-heat and medium-heat skim milk powder(50% decrease) (Cho et al., 1999). The reason is prob-ably the difference in the composition of the fat glob-ule surfaces. Fat globules stabilized by high-heat andmedium-heat skim milk powder have a higher con-centration of denatured whey protein on their sur-face compared to those stabilized by low-heat skimmilk powder. Higher denatured whey proteins pro-vide additional cross-links in the yogurt gel (Choet al., 1999). The type of the powder also can impactthe flavor of the yogurt. It has been demonstratedin yogurts fortified with four different commerciallow-heat skim milk powders that there were signif-icant differences of flavor according to the choiceof the skim milk powder (Drake, 2004). Among thefour milk powders tested, one presented an off-flavorcharacterized as animal/barny flavor. The acceptabil-ity of the yogurt fortified with the defected powderwas significantly lower than for the other samples.

Condensed Milk

Fresh liquid condensed skim milk can be used insteadof skim milk powder to enrich milk in yogurt man-ufacture. There is no difference in quality betweenthese two methods of enrichment (Guzman-Gonzalezet al., 1999). The choice between one and the other isdictated by the easiest way for providing the factorybetween these two ingredients. The incorporation ofcondensed milk, on a liquid form, into yogurt milk,is easier than the dissolution of skim milk powder.However, it requires specific equipment for storageand blending.

Buttermilk Powder

Buttermilk powder has been used successfully to re-place skim milk powder for milk fortification in yo-gurt manufacture (Guinee et al., 1995; Trachoo andMistry, 1998). No significant differences were ob-served in viscosity and water-holding capacity oflow-fat stirred yogurt stabilized with skim milk pow-der or buttermilk powder at a 5% protein content(Guinee et al., 1995). Trachoo and Mistry (1998)compared the firmness and sensorial properties ofnonfat and low-fat set yogurts enriched with skimmilk powder and buttermilk powder at a 3.7% and4.4% protein level, respectively. They reported thatfor the both types of yogurts, enrichment with butter-milk powder yielded a smoother product as comparedto yogurts enriched by addition of skim milk powder.Sensorial score for smoothness were respectively 8.2and 7.8 for nonfat yogurt, and 8.3 and 6.9 for low-fatyogurt. For the low-fat yogurt, the fortification withbuttermilk powder led to a slightly softer product ascompared with skim milk powder.

Milk Protein Concentrates

The replacement of skim milk powder by milk proteinconcentrates in yogurt manufacture has been stud-ied by Guzman-Gonzalez et al. (1999), Mistry andHassan (1990), Modler and Kalab (1983a), Modleret al. (1983b), and Rohm (1993). When the proteincontent of the yogurt is kept the same, the substi-tution of skim milk powder by milk protein con-centrates does not change the firmness (Mistry andHassan, 1990; Modler et al., 1983b), the viscosity(Guzman-Gonzalez et al., 1999; Rohm, 1993), thesyneresis (Modler et al., 1983b), the texture (Mistryand Hassan, 1992), and the flavor of the yogurts(Mistry and Hassan, 1992; Modler et al., 1983b). This


substitution does allow one to two-thirds reduction inthe amount of powder required for fortification, be-cause the protein content of milk protein concentratesis between 50% and 85%, as compared to 34–36%protein for a typical skim milk powder.

Another option is to use milk protein concentratedirectly as the yogurt milk. Some authors have stud-ied the properties of yogurts produced from ultra-filtered milk at protein levels varying from 3.3% to11.8% (Becker and Puhan, 1989; Biliaderis et al.,1992; Lankes et al., 1998; Savello and Dargan, 1995).When compared to the yogurts produced from milkfortified with skim milk powder at the same dry mat-ter level, the viscosity and firmness of yogurts pro-duced from ultrafiltered milks are higher because ofthe higher proportion of the protein in the milk base(Becker and Puhan, 1989; Biliaderis et al., 1992;Lankes et al., 1998). Biliaderis et al. (1992) noticed anincrease of elastic modulus from 511 Pa to 1220 Pabetween yogurt enriched to 14% dry matter by ad-dition of skim milk powder or by ultrafiltration ofskim milk, respectively. The corresponding proteinlevels were respectively 5.3% and 9.5%. Savello andDargan (1995) compared yogurts produced from ul-trafiltered milk and skim milk powder-fortified milkat a same protein content of 5%. They reported ahigher viscosity and higher gel strength (100% and50% increase, respectively) for the yogurt producedfrom the ultrafiltered milk. However, no explanationwas proposed to explain this phenomenon.

Whey Products

Whey Powders

The use of whey powder is limited in yogurt man-ufacture because it can be associated with some de-fects in texture, flavor, and appearance when addedat a high level. Nonetheless, because it is a relativelyinexpensive functional dairy solid, its use has beenwell-studied.

Shah et al. (1993) studied whey powder to replaceskim milk powder in yogurt prepared from reconsti-tuted milk. They reported that it was feasible to manu-facture yogurt with reconstituted skim milk and with25% of whey powder replacing the skim milk powder.Replacement of skim milk powder by 50% with wheypowder resulted in lower flavor scores and affectedbody and texture. Gonzalez-Martınez et al. (2003)reported a yellowish color developed in yogurt whenwhey powder was added, and the yellow color inten-sity was proportional to the amount of whey added.

When whey powder is used to substitute skim milkpowder on a dry matter basis, it decreases the firm-ness of the gel and lowers the viscosity of the yo-gurt because of the lower protein content of wheypowder (6% protein) as compared to skim milk pow-der (34% protein) (Bhullar et al., 2002; Dave andShah, 1998). For instance, for a plain set yogurt for-tified with 2% powder, whey powder-fortified yogurtwas less viscous than skim milk powder-fortified yo-gurt. The viscosity, as determined with a Brookfieldviscosimeter, was respectively 14 Pa.s and 25 Pa.s.However, at the same time, protein level was lower incase of the whey powder-fortified yogurt than in skimmilk powder-fortified yogurt, respectively 3.47% and3.70% protein (Bhullar et al., 2002).

When whey powder is used instead of skim milkpowder to fortify protein content of the milk, somedefects have been observed (yellow color, increasedsyneresis) (Gonzalez-Martınez et al., 2003). How-ever, texture defects are less pronounced, becausewhey proteins have a texturing effect in yogurt man-ufacture, where the high heat treatment applied al-lows their denaturation and their involvement in thebuilding of the protein network. Gonzalez-Martınezet al. (2003) reported that substitution of skim milkpowder by whey powder in a yogurt formulated at4.2% protein gives a more firm and viscous yogurt,showing better flow properties (more homogeneousfluid, without lumps) than the control. This has to beput in relation with the results of other works involv-ing whey protein concentrates demonstrating highergel strength when the ratio between casein and wheyprotein was lowered by the addition of whey pro-tein concentrates (Augustin et al., 2003; Cheng et al.,2000; Greig and Harris, 1983; Modler et al., 1983b;Puvanenthiran et al., 2002; Remeuf et al., 2003). Thepositive effect of whey protein on the firmness of thenetwork was attributed to the size of the particles con-stituting the gel network. They are larger in case ofaddition of whey protein because of the binding ofthe denatured whey protein on the casein micelles.These larger particles are suspected to absorb moreof an applied force by flexing without breaking theintraparticle cross-link bonds. This leads to highergel strength (Puvanenthiran et al., 2002).

Whey Protein Concentrates

Whey protein concentrates are very commonly usedin yogurt manufacture to replace skim milk powderbecause it can be less expensive than using the skimmilk powder. Furthermore, whey proteins are highly


Figure 10.4. Effect of source of proteinfortification on yogurt apparent viscosity.Apparent viscosity has been calculatedat 10 s−1 using the flow curveparameters. ––––, addition of skim milkprotein; ——, addition of Na-caseinate.After Rohm et al., 1993.

functional in yogurts. The substitution of skim milkpowder by whey protein concentrates in yogurts usu-ally increases the water-holding capacity of the yo-gurts and reduces ability to syneresis (Augustin et al.,2003; Cheng et al., 2000; Remeuf et al., 2003). How-ever, at a high level substitution (more than 1% on aprotein basis), defects as lack of bright and graininesshave been reported (Greig and Harris, 1983; Kailas-apathy and Supriadi, 1998; Remeuf et al., 2003).

The results on the texturing effect of whey proteinconcentrates in yogurt, as compared to skim milkpowder, on a constant protein basis, are contradic-tory in literature. Some report an increase of firm-ness and viscosity when fortification is done withwhey protein concentrates instead of skim milk pow-der (Augustin et al., 2003; Cheng et al., 2000; Greigand Harris, 1983; Modler et al., 1983b; Puvanen-thiran et al., 2002; Remeuf et al., 2003); whereasother researchers report a loss of consistency whenwhey protein concentrates are used to replace skimmilk powder in yogurt formulation (Greig and Harris,1983; Guinee et al., 1995; Guzman-Gonzalez et al.,1999; Modler et al., 1983b).

For instance, comparing the viscosity of yogurt for-tified at a 5% protein level with three different kindsof whey protein concentrates (35–75% protein) orwith skim milk powder, Guinee et al. (1995) reportedno difference of viscosity at 116 s−1 for yogurt forti-fied with skim milk powder or whey protein concen-trates at 45%, 60%, and 75% protein (viscosity 0.25–0.28 Pa.s). But a much lower viscosity (0.06 Pa.s) wasobserved when whey protein concentrate at 35% pro-tein was used to fortify the milk. On the other hand,

Remeuf et al. (2003) observed higher apparent vis-cosity at 10 s−1 in yogurt fortified at 4.5% proteinlevel with whey protein concentrates at 84% proteinthan in yogurt fortified with skim milk powder, re-spectively 3.5 Pa.s and 2 Pa.s.

This inconsistency between results in literaturecan be explained by differences between the reportsin quality of the whey protein concentrates (Augustinet al., 2003; Guinee et al., 1995; Sodini et al., 2005),level of addition of whey protein concentrates in milk(Greig and Harris, 1983), pH of the milk (Augustinet al., 2003; Vasbinder and De Kruif, 2003), and in-tensity of the heat treatment applied to the milk (Jelen,1997).

Whey protein concentrates can also be added inthe yogurt after the fermentation and gelation in thecase of stirred yogurt manufacture. In this case, it hasbeen shown that any texturing effect is very different.Patocka et al. (2004) reported a strong thinning effectof the addition of whey protein hydrolysate when itwas added from 2% to 8% level in a stirred yogurt.The thinning effect was not only due to dilution ofthe protein matrix, because the addition of sugar de-creased the viscosity to a lesser extent.

Microparticulated Whey Protein

A microparticulation process has been developed byKelco Ltd to produce microparticulated whey pro-tein (1�m average) enhancing the properties of low-fat foods. The commercial name of the product isSimplesse r©. Some works have demonstrated theirability to improve the consistency of nonfat (Tamimeet al., 1984) and low-fat yogurts (Sandoval-Castilla

(a)

(b)

(c)

Figure 10.5. Microstructure of yogurts obtained from milk base enriched with skim milk powder (a), whey proteinconcentrates (b), and Na-Caseinate (c). Bar-20 �m. After Remeuf et al., 2003.

175


et al., 2004). Tamime et al. (1984) and Sandoval-Castilla et al. (2004) showed the particles integratein the protein matrix of the yogurt; they were found tobe a part of the casein micelle chains or spanned ad-jacent chains. They were not freely dispersed into theaqueous phase, maintaining their corpuscular nature.The microparticulated whey protein seems to limitthe casein aggregation in clusters. A low-fat yogurtcontaining 1% microparticulated whey protein pre-sented the same profile analysis as a full fat yogurt(Sandoval-Castilla et al., 2004).

Caseinates

Na, Ca, or Na-Ca-caseinates have been used in yo-gurt formulation to increase the protein content, alone(Guinee et al., 1995; Guzman-Gonzalez et al., 2000;Modler and Kalab, 1983a; Modler et al., 1983b;Remeuf et al., 2003; Rohm, 1993; Tamime et al.,1984) or in combination with whey protein concen-trates (Guzman-Gonzalez et al., 2000; Remeuf et al.,2003) to control the casein/whey protein ratio.

When compared with skim milk powder enrich-ment, fortification with caseinate gave a more roughand less smooth yogurt texture (Modler et al., 1983b;Remeuf et al., 2003), with a higher gel firmness andviscosity (Guinee et al., 1995; Guzman-Gonzalezet al., 2000; Modler et al., 1983b; Remeuf et al.,2003; Rohm, 1993; Tamime et al., 1984). Figure10.4 reports the apparent viscosity of yogurts for-tified with skim milk powder or Na-caseinate. It hasbeen noticed by some researchers that texturing effectis different between Na- and Ca-caseinates. Higherviscosities were reported for Na-caseinates than Ca-caseinates fortified yogurts (Guzman-Gonzalez et al.,2000; Remeuf et al., 2003). For instance, Remeufet al. (2003) determined complex viscosities of40 Pa.s, 55 Pa.s, and 100 Pa.s respectively for yogurtsenriched to 4.5% protein with skim milk powder,Ca-caseinate, and Na-caseinate. Guzman-Gonzalezet al. (2000) showed yogurts enriched at 4.3% pro-tein with skim milk powder, Ca-caseinate and Na-caseinate had apparent viscosities of 34 Pa.s, 53 Pa.s,and 63 Pa.s, respectively.

Microstructure studies showed that the structure ofthe network is different when adding caseinates in-stead of skim milk, with a more open and loose struc-ture. This difference of structure explains while lowerwater holding capacity is reported in case of caseinatefortification (Guzman-Gonzalez et al., 2000; Remeufet al., 2003). Figure 10.5 reports the microstructure of

three yogurts fortified with skim milk powder, wheyprotein concentrates, and Na-caseinate. Large and ex-tensively fused casein are noticeable in Na-caseinatefortified yogurts (Fig. 10.5c), while a fine networkwith small pore size is observed in WPC-fortifiedyogurt (Fig. 10.5b), as compared to SMP-fortifiedyogurt (Fig. 10.5a). This can be explained by thecoverage of casein micelle by denatured whey pro-tein during the heat treatment, which is not the samedepending on the casein/whey protein ratio (Puva-nenthiran et al., 2002).

CONCLUSIONThere is a wide range of dairy ingredients that canimpact the properties of yogurt texture, flavor, andappearance. Continued advances in the technologiesfor fractionation and purification of milk into these in-gredients will offer yogurt manufacturers better toolsto manipulate and tailor the properties of yogurt forthe desired end use.

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Anifantakis, E. M. 1991. Manufacture of sheep’s milkproducts. In: Proceeding of the XXIII InternationalDairy Congress, Montreal, Canada. InternationalDairy Federation, Brussels, Belgium, pp. 420–432

Augustin MA, Cheng LJ, Glagovskaia O, Clarke PT,Lawrence A. 2003. Use of blends of skim milk andsweet whey protein concentrates in reconstitutedyogurt. Aust. J. Dairy Technol. 58:30–35.

Barrantes E, Tamime AY, Sword AM, Muir DD, KalabM. 1996. The manufacture of set-type natural


yoghurt containing different oils – 2. Rheologicalproperties and microstructure. Int. Dairy J.6:827–837.

Becker T, Puhan Z. 1989. Effect of different processesto increase the milk solids non fat content on therheological properties of yoghurt.Milchwissenschaft. 44:626–629.

Bhullar YS, Uddin MA, Shah NP. 2002. Effects ofingredients supplementation on texturalcharacteristics and microstructure of yoghurt.Milchwissenschaft. 57:328–332.

Bikker JF, Anema SG, Li Y, Hill JP. 2000. Rheologicalproperties of acid gels prepared from heated milkfortified with whey protein mixtures containing theA, B and C variants of beta-lactoglobulin. Int. DairyJ. 10:723–732.

Biliaderis CG, Khan MM, Blank G. 1992. Rheologicaland sensory properties of yogurt from skim milk andultrafiltered retentates. Int. Dairy J. 2:311–323.

Cano Ruiz ME, Richter RL. 1997. Effect ofhomogenization pressure on the milk fat globulemembrane proteins. J. Dairy Sci. 80:2732–2739.

Chandan R. 1997. Dairy-based ingredients. EaganPress, Saint-Paul, MN.

Cheng LJ, Augustin MA, Clarke PT. 2000. Yogurtsfrom skim milk – whey protein concentrate blends.Aust. J. Dairy Technol. 55:110.

Cheng LJ, Clarke PT, Augustin MA. 2002. Seasonalvariation in yogurt properties. Aust. J. DairyTechnol. 57:187–191.

ChoYH, Lucey JA, Singh H. 1999. Rheologicalproperties of acid milk gels as affected by the natureof the fat globule surface material and heat treatmentof milk. Int. Dairy J. 9:537–545.

Dave RI, Shah NP. 1998. The influence of ingredientsupplementation on the textural characteristics ofyogurt. Aust. J. Dairy Technol. 53:180–184.

De Lorenzi L, Pricl S, Torriano G. 1995. Rheologicalbehaviour of low-fat and full-fat stirred yoghurt. Int.Dairy Journal. 5:661–671.

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Drake MA. 2004. Flavor of dried dairy ingredients. In:Proceeding of the 4th International Symposium onRecombined Milk and Milk Products, Cancun,Mexico. U.S. Dairy Export Council, Arlington, VA.

El-Agamy EI. 2000. Effect of heat treatment on camelmilk proteins with respect to antimicrobial factors: acomparison with cows’ and buffalo milk proteins.Food Chemistry. 68:227–232.

Gonzalez-Martınez C, Chafer M, Albors A, Carot JM,Chiralt, A. 2003. Influence of substituting milk

powder for whey powder on yoghurt quality. Trendsin Food Sci. & Technol. 13:334–340.

Greig RIW, Harris AJ. 1983. Use of whey proteinconcentrate in yogurt. Dairy Industries Int.48:17–19.

Guinee TP, Mullins CG, Reville WJ, Cotter MP. 1995.Physical properties of stirred-curd unsweetenedyoghurts stabilised with different dairy ingredients.Milchwissenschaft. 50:196–200.

Guzman-Gonzalez M, Morais F, Amigo L. 2000.Influence of skimmed milk concentrate replacementby dry dairy products in a low-fat set-type yoghurtmodel system. Use of caseinates, co-precipitate andblended dairy powders. J. Sci. Food and Agric.80:433–438.

Guzman-Gonzalez M, Morais F, Ramos M, Amigo L.1999. Influence of skimmed milk concentratereplacement by dry dairy products in a low fatset-type yoghurt model system. I: Use of wheyprotein concentrates, milk protein concentrates andskimmed milk powder. J. Sci. Food and Agri.79:1117–1122.

Harwalkar VR, Kalab M. 1986. Relationship betweenmicrostructure and susceptibility to syneresis inyoghurt made from reconstituted nonfat dry milk.Food Microstructure. 5:287–294.

Jelen P. 1997. Texture of fermented milk products anddairy desserts. Trends in Food Sci. & Technol.8:345–347.

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Lankes H, Ozer HB, Robinson RK. 1998. Theeffect of elevated milk solids and incubationtemperature on the physical properties of naturalyoghurt. Milchwissenschaft Milk Sci. Int.53:510–513.

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Mistry VV, Hassan HN. 1990. Manufacture of low fatyogurt using a high protein powder. In: Proceedingof the XXIII International Dairy Congress,Montreal, Canada. International Dairy Federation,Brussels, Belgium, p. 518.

Mistry VV, Hassan HN. 1992. Manufacture of nonfatyogurt from a high milk protein powder. J. DairySci. 75:947–957.

Modler HW, Kalab M. 1983a. Microstructure of yogurtstabilized with milk proteins. J. Dairy Sci.66:430–437.

Modler, HW, Larmond ME, Lin CS, Froelich D,Emmons DB. 1983b. Physical and sensoryproperties of yogurt stabilized with milk proteins.J. Dairy Sci. 66:422–429.

Muir DD, Horne DS, West IG. 1997. Geneticpolymorphism of bovine kappa-casein: Effects ontextural properties and acceptability of plain, setyoghurt. In: Proceeding of the IDF Seminar on MilkProtein Polymorphism, Palmerston North, NewZealand. International Dairy Federation, Brussels,Belgium, pp. 182–184

Muir DD, Tamime AY. 1993. Ovine milk. 3. Effect ofseasonal variations on properties of set and stirredyogurts. Milchwissenschaft. 48:509–513.

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Puvanenthiran A, Williams RPW, Augustin MA. 2002.Structure and visco-elastic properties of set yoghurtwith altered casein to whey protein ratios. Int. DairyJ. 12:383–391.

Remeuf F, Mohammed S, Sodini I, Tissier JP. 2003.Preliminary observations on the effects of milkfortification and heating on microstructure andphysical properties of stirred yogurt. Int. DairyJ. 13:773–782.

Rohm H. 1993. Influence of dry matter fortification onflow properties of yogurt. 2. Time-dependentbehaviour. Milchwissenschaft. 48:614–617.

Rysstad G, Knutsen WJ, Abrahamsen RK. 1990. Effectof threonine and glycine on acetaldehyde formationin goats’ milk yogurt. J. Dairy Res. 57:401–411.

Sandoval-Castilla O, Lobato-Calleros C,Aguirre-Mandujano E, Vernon-Carter EJ. 2004.Microstructure and texture of yogurt as influencedby fat replacers. Int. Dairy J. 14:151–159.

Savello PA, Dargan RA. 1995. Improved yogurtphysical properties using ultrafiltration andvery-high temperature heating. Milchwissenschaft.50:86–89.

Schkoda P, Hechler A, Hinrichs J. 2001a. Improvedtexture of stirred fermented milk by integrating fatglobules into the gel structure. Milchwissenschaft.56:85–89.

Schkoda P, Hechler A, Hinrichs J. 2001b. Influence ofthe protein content on structural characteristics ofstirred fermented milk. Milchwissenschaft.56:19–22.

Shah NP, Spurgeon KR, Gilmore TM. 1993. Use ofdry whey and lactose hydrolysis in yogurt bases.Milchwissenschaft. 48:494–498.

Sodini I, Montella J, Tong PS. 2005. Physicalproperties of yogurt with various commercial wheyprotein concentrates. J. Sci. Food Agric.85:853–859.

Tamime AY, Kalab M, Davies G. 1984. Microstructureof set-style yoghurt manufacture from cow’s milkfortified by various methods. Food Microstructure.3:83–92.

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Trachoo N, Mistry VV. 1998. Application ofultrafiltered sweet buttermilk and sweet buttermilkpowder in the manufacture of nonfat and low fatyogurts. J. Dairy Sci. 81:3163–3171.

van Vliet T, Dentener-Kikkert A. 1982. Influenceof the composition of the milk fat globulemembrane on the rheological properties of acidmilk gels. Netherlands Milk and DairyJ. 36:261–265.

Vasbinder AJ, De Kruif CG. 2003. Casein-wheyprotein interactions in heated milk: the influence ofpH. Int. Dairy J. 13:669–677.

Wacher-Rodarte C, Galvan MV, Farres A, Gallardo F,Marshall VME, Garcia-Garibay M. 1993. Yoghurtproduction from reconstituted skim milk usingdifferent polymer and non polymer forming startercultures. J. Dairy Res. 60:247–254.

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11Ingredients for Yogurt Manufacture

Ramesh C. Chandan and Kevin R. O’Rell

Dairy Ingredients and Their OriginCondensed Skim MilkNonfat Dry MilkWhey SolidsMilk Protein Concentrate (MPC) (or Ultrafiltered Milk)SweetenersStabilizersNative and Modified StarchGums and Pectins

References

Previous chapters have offered valuable informationon the quality attributes, including chemical and mi-crobiological characteristics and specifications, ofthe raw materials used to formulate yogurt mixes.The manufacture of yogurt starts with a judicious se-lection of raw materials, accurate formulation, andprocessing of yogurt mix.

DAIRY INGREDIENTS ANDTHEIR ORIGINVarious dairy raw materials for formulating yogurtmixes consist of fresh milk, skim milk, cream, con-densed milk, and nonfat dry milk. In the UnitedStates, Yogurt is a Grade A product (United StatesDepartment of Health and Human Services, 1999).Chapter 3 details the requirements for milk produc-tion, transportation, and processing. Grade A impliesthat all dairy components used must come from TheFood and Drug Administration (FDA) supervisedGrade A dairy farms and Grade A manufacturingplants, as per regulations enunciated in PasteurizedMilk Ordinance. The basic raw material is milk. Itis emphasized that all dairy raw materials should be

selected for high bacteriological quality for secur-ing best flavor potential in yogurt. Milk should comefrom healthy cows that are fed wholesome feed andkept in clean surroundings. The flavor, consistency,and acid production is adversely affected by usingmilk from cows with infected udders (mastitis), gen-eral sickness, or in early or late stages of lactation, in-cluding milk containing high bacterial count, abnor-mal somatic cell count, and antibiotics, disinfectantsor sanitizers. This is related to the fact that growth ofyogurt culture is affected adversely in milk partiallyfermented by contaminating organisms and in milkcontaining high somatic cells, or antibiotics and sani-tizing chemical residues. Therefore, such milk cannotbe used for yogurt production. For the most part, inbulk milk, the adverse effects of the quality of milkfrom a single cow or a small herd of cows can bebalanced through dilution. Chapter 10 contains de-tailed information related to dairy ingredients usedin yogurt manufacture.

The major concern in milk for yogurt productionis the bacterial quality which is discussed in detailelsewhere (Chandan, 1982, 1997, 2004; Chandan andShahani, 1993, 1995; Tamime and Robinson, 1999)and the presence of inhibitors. The inhibitory ac-tion of antibiotics against lactic cultures has beenresponsible for production losses in the manufactureof cultured products. One of the two organisms inyogurt culture, Streptococcus thermophilus is par-ticularly sensitive to antibiotics (0.01–0.05 IU/ml ofpenicillin). Regular testing for antibiotics in milk inthe plant laboratory and other measures connectedwith the use of antimastitis drugs on the farm repre-sent a good system for controlling these residues.

In addition to antibiotics, residual disinfectants andsanitizing chemicals may inhibit the growth of starter

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cultures. Chlorine compounds such as hypochloritesand iodophors may partially inhibit starter cultures ata level of 6 mg/l to 10 mg/l of milk. Normal precau-tions regarding their use on the farm should greatlyreduce the chance of obtaining residual levels affect-ing yogurt cultures. On the other hand, quaternaryammonia compounds inhibit lactic acid bacteria atconcentrations as low as 0.1–1.0 mg/l, depending onparticular strain sensitivity. On the farm, these com-pounds should be used with great caution and theiruse followed by thorough drainage and rinsing withclean water. Preferably, these compounds should beavoided in plants manufacturing yogurt and cultureddairy products.

The microbiological quality of milk for yogurtshould contain a low bacterial count, coliform count,and mold and yeast count. Standard Plate count andcoliform tests should be performed on each load ofmilk to be used for yogurt production. A yeast andmold test should be done on a random basis. Althoughcoliform, yeast, and mold are readily destroyed bypasteurization, their presence along with significantnumber of bacteria is an indication that the milk washandled in unclean equipment, or held under warmconditions. When milk comes into contact with un-clean surroundings, it is very possible that it has be-come contaminated with thermoduric/thermophilicorganisms, which are capable of withstanding de-struction at pasteurization temperatures. If present,these bacteria will grow rapidly during the incuba-tion period of yogurt fermentation and compete withthe yogurt culture. This would result in slow fer-mentation time and/or weak body of the yogurt. Theformation of pin-point colonies on Standard Plate

count plates incubated at 32–35◦C is an indicationof thermophilic organisms, since they grow better at40–45◦C.

Also, if the milk has been contaminated with ahigh number of bacteria, it is possible that these bac-teria might be psychrophiles or psychrotrophs. Theseorganisms grow well in cold conditions. They growslowly in milk held at 3◦C, but the growth may berapid as the temperature rises to 10◦C or higher.Although psychrophiles are readily destroyed bypasteurization temperature, if allowed to grow insignificant numbers, they can produce heat-stableproteolytic enzymes, which would degrade the pro-tein. This protein degradation results in slow, weaksets, and possible off-flavors. There is a procedurefor detecting psychrofilic organisms outlined in theStandard Methods for Analysis of Dairy Products(American Public Health Association). However, aquicker modified version can be performed by incu-bating pour plates at 21◦C for 25 hours.

The procurement of all ingredients should be doneon the basis of specifications and standards, whichare checked and maintained with a systematic sam-pling and testing program by the quality controllaboratory.

Yogurt mix composition regarding milk fat andmilk solids nonfat is generally standardized fromwhole, partially defatted milk, condensed skim milk,cream, and/or nonfat dry milk. The chemical compo-sition of dairy ingredients commonly used in yogurtmanufacture is given in Table 11.1. Formulating yo-gurt mix to desired fat and milk solids-not-fat by theuse of these ingredients can be easily accomplishedby appropriate soft ware programs.

Table 11.1. Typical Chemical Composition of Dairy Ingredients Used in Formulating Yogurt Mix

Ingredient %Total Solids %Fat %Protein %Lactose %Ash

Whole milk 12.6 3.8 3.2 4.9 0.7Skim milk 9.1 0.1 3.3 5.1 0.7Whipping cream 42.7 36.8 2.2 3.2 0.5Condensed skim milk 40.1 0.4 14.4 22.3 3.0Nonfat dry milk 96.5 0.8 35.9 52.3 8.0WPCa–34 96.5 4.0 34.5 51.0 7.0WPC–50 96.5 4.0 50.5 36.0 6.0WPC–80 96.5 6.0 80.5 5.0 5.0Whey protein isolate 96.5 0.5 93.0 1.0 2.0Fluid UF milk 25–30 11–14 10–12 <5 >2.5Fluid UF skim milk 15–20 <0.5 10–12 <5 >2.5Fluid UF skim milk, with diafiltration 18–20 <0.5 16–17 <1 >1.5Adapted from Chandan, 1997.

a Whey Protein Concentrate

11 Ingredients for Yogurt Manufacture 181

The current FDA specification calls for a minimumof 8.25% nonfat milk solids (SNF) in the fermentedmix prior to fruit or flavor addition. In a typical nonfat,low fat, or full fat yogurt formulation, the total milkserum solids (or solids-not-fat) content of yogurt mixranges from 8.25% to 12%, depending on the choiceof stabilization. The serum solids associated with thefluid portion of milk is usually 8.8–9%. Additionalnonfat dry milk (NFDM) solids are added to the yo-gurt mix to build up the total solids and to increase theprotein content. In late spring and summer months,the protein content of milk is about 10% lower thanthe rest of the year. Consequently, the viscosity ofyogurt declines during this period unless additionalnonfat solids are added to compensate for the sea-sonal dip in protein content. Therefore, depending onthe stabilization system, additional 0.5–1.0% nonfatsolids may be needed to maintain the consistent vis-cosity of the finished product during late spring andsummer months.

In general, the level of added NFDM will vary,depending on the desired mouth feel of the finishedproduct, the processing conditions, the fat content,the culture, and type of stabilizer used, if any. Gen-erally, the addition of 2–4% NFDM solids raisesthe protein level sufficiently so that with the properheat treatment, there is an increase in bound wa-ter leading to improved firmness and consistencyof the coagulum. Another benefit is the control ofwheying-off or syneresis on the surface of yogurt.Thus, the consistency of yogurt is dependent on thenonfat solids portion, as well as the use of appropri-ate stabilizers and heat treatment of the mix. Gen-erally, the added NFDM solids will contribute toheavier mouth feel, which cannot be achieved withstabilizers alone. Higher nonfat solids will also pro-vide additional buffering capacity to the mix, whichin comparison with a mix containing lower non-fat solids would lead to higher lactic acid contentwhen the fermentation end point of the mix is deter-mined by the same pH. Therefore, the higher nonfatsolids mix will result in comparatively sourer tast-ing yogurt. In commercial practice in North Amer-ica, supplementation of milk solids-not-fat with somesolids from condensed skim milk or nonfat dry milkand/or whey protein concentrate is the most commonprocedure.

Removal of a significant portion of water from milkyields a series of dairy ingredients (Chandan, 1997).Details are given in Chapter 10. Consequently, theseingredients offer tangible savings in costs associ-ated with storage capacity, handling, packaging, andtransportation. A concentrated dairy ingredient used

in large yogurt manufacturing plants is condensedskim milk.

Condensed Skim Milk

Condensed skim milk process begins with liquid rawwhole milk, which is stored at the processing plantat temperatures below 7◦C. Raw whole milk has avariable fat content and is separated into cream andthe nonfat milk using a centrifugal separator. Thisseparation step facilitates standardization of the fatcontent prior to further processing. Centrifugal sepa-rators used also serve to further clarify the milk. Theskim milk is pasteurized (high-temperature, short-time) by heating to at least 71.7◦C, and holding at orabove this temperature for at least 15 seconds. In itsproduction, the original skim milk volume is reducedto about one-third to yield about 35–40% solids in thefinal product using energy efficient multieffect evap-orators that operate in high vacuum condition to boiloff water at moderate temperatures of 46–55◦C. Thecondensed milk is continuously separated from wa-ter vapor to achieve a desirable concentration of milksolids. It is cooled to 4◦C or below and pumped to in-sulated trucks for transportation to yogurt plants. Thecream produced from the separator is HTST pasteur-ized, cooled, and transferred to cream storage tanksfor use as a manufacturing ingredient.

Nonfat Dry Milk

Nonfat dry milk is made from condensed skim milk.Spray drying involves atomizing condensed milkinto a hot air stream at 180–200◦C. The atomizermay be either a pressure nozzle or a centrifugaldisc. By controlling the size of the droplets, theair temperature, and the airflow, it is possible toevaporate almost all the moisture while exposing thesolids to relatively low temperatures. Spray dryingyields concentrated and dry milk ingredients withexcellent solubility, flavor, and color. This is the mostcommon procedure for manufacturing concentratedand dry milk ingredients.

The spray drying process is typically a two-stageprocess that involves a spray dryer at the first stagewith a static fluid bed integrated in the base of thedrying chamber. The second stage is an external vi-brating fluid bed. The product is moved through thetwo-stage process quickly to prevent overheating ofthe powder. The powder leaves the dryer and entersa system of cyclones that simultaneously cools it.

Heat treatment affects the functional properties ofNFDM, so the temperature and time combinations


Table 11.2. Approximate Composition ofGrade A Nonfat Dry Milk

Constituents Amount Typical Range

Protein (N × 6.38)% 36.0 34.0–37.0Lactose (Milk sugar)% 51.0 49.0–52.0Fat% 0.7 0.6–1.25Moisture% 3.0 3.0–6.0Minerals (Ash)% 8.2 8.2–8.6Source: American Dry Milk Products Institute, with permis-sion.

can vary widely depending on the required proper-ties. The milk heat treatment determines the kind ofpowder produced. For nonfat dry milk produced bya “low-heat” method, the milk is simply pasteurizedand no preheating is done. However, heat treatmentfor a “high-heat” method requires heating milk to85–88◦C for 15 to 30 minutes in addition to pasteur-ization. Heat treatment in between pasteurization and“high-heat” treatment yields “medium-heat” powder.Tables 11.2, 11.3, and 11.4 contain information on thecharacteristics of nonfat dry milk, which are impor-tant from yogurt formulation standpoint.

Typical composition of nonfat dry milk is shown inTable 11.2. The standards for extra-grade spray-driednonfat dry milk are given in 11.3. The requirementsfor low-heat nonfat dry milk are shown in Table 11.4.

The extent of heat treatment can be measured bythe whey protein nitrogen index, which measures theamount of undenatured whey protein. For use in yo-gurt, only low-heat (WPN≥6.0 mg/g) NFDM is used.

Table 11.3. Standards for Extra Grade SprayDried Nonfat Dry Milk

Parameter Not Greater Than

Milkfat 1.25%Moisture 4.0%Titratable acidity 0.15%Solubility index 1.25 mla

Bacterial estimate 10,000 cfu per gScorched particles Disc B (15.0 mg)

a Except product designated as “high-heat” which shall notbe greater than 2.0 ml.Note: Extra Grade nonfat dry milk shall be entirely free fromlumps, except those that break up readily under slight pres-sure. The reliquefied product shall have a sweet and desirableflavor, but may possess the following flavors to a slight de-gree: chalky, cooked, feed, and flat.Source: American Dry Milk Products Institute, with permis-sion.

Whey Solids

The addition of whey solids in the form of sweetwhey or acid whey to replace NFDM in yogurt shouldbe avoided. Whey solids will contribute to the totalsolids content of yogurt mix; however, because oflower protein content (13–15%) for whey solids ascompared to 35–36% for NFDM solids, and lowerprotein functionality in terms of water binding ca-pacity, the addition of whey solids can be detrimen-tal to the consistency and firmness of the body ofyogurt.

On the other hand, whey protein concentrates(WPC), in relatively undenatured form, furnish excel-lent water binding properties and are a useful func-tional protein source in yogurt mix. Whey-proteinconcentrates are products derived from cheese wheyby removal of minerals and lactose. The processof protein concentration utilizes membrane filtration(ultrafiltration), which uses a semipermeable mem-brane of appropriate pore size to retain large proteinmolecules while letting small molecules consisting ofwater, lactose, minerals, small peptides, and aminoacids to selectively go into the permeate. On a drybasis, the WPC contains 34%, 50%, or 80% protein,and whey protein isolate contains at least 92% pro-tein. In addition, WPC-80 is available as gel type,which is designed to generate more viscosity in liq-uid foods. WPC-34 is commonly used in yogurt for-mulation, while WPC-50 is occasionally used. SinceWhey protein isolate and WPC-80 contain low levelsof lactose, they are important ingredients in the for-mulation of “low-carb” yogurt. The use of WPC-34allows the yogurt processor to reduce the ingredientcost and at the same time provides unique functionalproperties including desirable nutrients, namely, highquality whey proteins and calcium. Since yogurt isclassified as a Grade A product in the United States,only Grade A whey-protein concentrate produced ina Grade A cheese plant can be used. WPC helps inheat-set gelation. Whey protein gets denatured by theheat treatment used in yogurt mix preparation. Thedenatured protein has desirable water binding andadhesion characteristics. In addition, as a dairy prod-uct, it has a favorable image because of a clean label.WPC should be free of bixin or �-carotein colorantgenerally used in Cheddar cheese manufacture. Toremove the colorant, the whey is bleached with ben-zoyl peroxide during the WPC process. Cheese plantsmanufacturing Swiss and mozzarella cheese use nocolorants, but do use thermophilc cultures identical tothose used in yogurt production. Accordingly, there


Table 11.4. Heat–Treatment Classification of Nonfat Dry Milk

Undenatured Whey-ProteinClassification Processing Treatment Nitrogen a(mg/g)

Low heat Cumulative heat treatment of milk not over71.1◦C (160◦F) for 2 minutes

Over 6.0

Medium heat Preheat to 71.1◦C–79.4◦C (160◦–175◦F) for20 minutes

1.51–5.99

High heat Preheat to 87.8◦C (190◦F) for 30 minutes Under 1.5Adapted from: American Dry Milk Products Institute, with permission. Chandan 1997.

a Higher temperatures and/or extended holding times contribute directly to whey protein denaturation. This index is used asa measure of the cumulative heat effects during processing.

is a possibility of phage carryover from such cheesemanufacturing plants to yogurt production. To avoidphage contamination, WPC ingredient should comefrom cheese plants, where only mesophilic culturesare used, (e.g., Cheddar or Cheddar-type varieties.)

In general, whey proteins of WPC lack opacityand white appearance as compared to caseins presentin NFDM. However, whey proteins have fewer ten-dencies to mask flavor in yogurt than caseins. Ac-cordingly, more fruit flavor will be perceived in fruitflavored yogurt when skim milk solids are partiallyreplaced with WPC. In general, WPC (with 34%protein level) concentration in yogurt mix rangesfrom 0.5% to 1% level. In yogurt beverage, a higheramount up to 6% may be used.

Milk Protein Concentrate (MPC) (orUltrafiltered Milk)

Milk protein concentrate obtained by ultrafiltrationof skim milk is a functional ingredient to raise pro-tein level of the mix, but the main reason for its use isto reduce lactose content of the mix to produce “low-carb” yogurt. As yogurt is a Grade A product in theUnited States, the MPC must be derived from a GradeA process. The labeling for this ingredient is “ultrafil-tered skim milk.” It contains 80–85% water, 10–12%protein, <0.5% fat, <5% lactose, and >2.5% ash.

In the formulation of yogurt, the lactose level canbe reduced significantly, as much as 70%, by judi-cious use of lactose-reduced MPC and high-proteinWPC in the formulation, replacing milk and NFDM.To conform to the legislation in certain countries orto satisfy the consumer demand, yogurt with no sta-bilizers can be produced. In such products, the con-sistency and stability of texture are accomplished byaddition of nonfat dry milk, condensed skim milk,and/or whey protein concentrates. In rare practice,

milk may be partly concentrated by removal of15–20% water in a vacuum pan. In such a specialtyyogurt, the mix is formulated to contain high nonfatsolids as much as 12% to provide a desirable bodyand texture and freedom from syneresis.

Since yogurt is a manufactured product, its chem-ical composition is likely to vary depending on thequality standards established by marketing consider-ations. Nonetheless, it is extremely important to stan-dardize and control the day-to-day product to meetthe consumer expectations and regulatory obligationsassociated with a certain brand or label. The mix isformulated to predetermined milk fat and milk solids-not-fat content and the weights of each ingredient arecalculated with the aid of computer software. Mostyogurt plants are equipped with computer programsto calculate the amount of each ingredient neededto achieve target levels of milk fat, milk SNF, to-tal solids, sugar, stabilizers, and other ingredients.The program usually also calculates the cost of themix.

The level of milk fat found in commercial sam-ples of yogurt ranges from 0.05% to 3.60%. Gen-erally, consumers view milk fat negatively from thecaloric standpoint. Consequently, 90% of the refrig-erated cup yogurt sold in the United States today iseither low fat or nonfat. The fat level in yogurt has afavorable effect on texture quality of the yogurt. Milkfat also has a masking effect on the perception of yo-gurt acidity. It has been observed that nonfat yogurt(<0.5% fat) tastes more acidic and less mild than thesame pH yogurt with a fat content of >1.5%. There-fore, it is important to use a “mild” yogurt culture innonfat and 1% low-fat yogurt to maintain the finishedpH above 4.2 to please today’s consumer tastes. It hasalso been concluded that milk fat stabilizes the con-traction of the protein gel formed after fermentationof the yogurt mix and hinders whey separation. Thus,


in yogurt with little or no stabilizer, a low fat contentin milk encourages whey separation, while a highfat content prevents the separation. As the fat con-tent is increased, there is a significant improvementin flavor, viscosity, and taste. However, there is alsoan increase in the caloric value. In most low-fat andnonfat yogurts produced today, stabilizers are usedto compensate for the loss of the stabilizing effect ofmilk fat. For products produced in the United States,the milk fat levels are standardized to a minimum of3.25% before the addition of bulky flavors for full-fatyogurt. Low-fat yogurt is manufactured from the mixcontaining not less than 0.5%, nor more than 2.00%milk fat before the addition of bulky flavors. Nonfatyogurt mix has milk fat level not exceeding 0.5%.These fat levels correspond to the Food & Drug Ad-ministration requirement for nutritional labeling ofnonfat yogurt, low-fat yogurt and yogurt. (Chandan,1997, 2004).

Sweeteners

Nutritive Sweeteners

In the manufacture of flavored yogurt, it is usually de-sirable to add a sweetening agent to the yogurt base.The standard of identity for yogurt, low-fat yogurtand nonfat yogurt (FDA CFR Parts 131.200 to 206)specifies the allowable nutritive sweeteners that canbe used. The level of sweetness in the yogurt mix willdepend on the Brix of the fruit or flavoring ingredi-ent and the desired level of sweetness in the finishedproduct. Most fruit-flavored yogurts contain approx-imately 10–13% sugar equivalent, whereas flavoredyogurts (vanilla, lemon, coffee etc.) contain 8–10%sugar. The sweetener most commonly used in the in-dustry is sucrose in either liquid (65–67% total solids)or granulated form. When liquid sugar is used, theadded water is taken into consideration to avoid di-lution of the total solids of the mix. The total amountof sugar solids in yogurt mix should not exceed10–11% because of the inhibitory effect on the tradi-tional yogurt culture. Depending on the culture, someinhibitory effect will be seen with sugar solids con-tent between 7% and 10%. The addition of the sugargenerally occurs before pasteurization due to follow-ing reasons:

� Heat treatment of the milk destroys anyosmophilic yeasts and molds that might bepresent in the sugar ingredient.

� Potential source of postpasteurizationcontamination (HACCP).

� The consistency of yogurt is better when sugar isadded to the milk rather than into the coagulum,unless the formulation has been adjusted to allowfor this dilution.

If it is necessary to add sweeteners after fermenta-tion, only pasteurized liquid sugar or flavored sweet-ened syrups should be used. When using this method,the total solids of the yogurt mix must be adjusted forthe dilution associated with these liquid sweeteners.Also, Good Manufacturing Practices and HACCPcontrol should be practiced to minimize the potentialrisk of microbiological or physical contamination.

Refined crystalline sucrose is manufactured in-dustrially from sugar cane or sugar beet processing.Both sources give identical sucrose with no chemical,physical, or structural differences. Crystalline sugaris either refined from crude raw sugar or is processedfrom sugar cane juice. The first step is to extractjuice from sugar cane using a series of roller presses.Nonsugar impurities are removed by mechanical fil-tration, followed by lime-carbon dioxide purifica-tion step. The juice is allowed to settle and then fil-tered to get purified juice. In some factories, this stepinvolves lime-phosphoric acid floatation procedure.Furthermore, purification of the juice is achieved bytreatment with activated charcoal and ion exchangereactors. This juice (12–15% total solids, 91–92% pu-rity) is evaporated in multistage vacuum evaporatorsto get sugar concentrate containing 65–71% solids.Furthermore, crystallization of sugar is effected invacuum pans under controlled conditions of temper-ature, pressure, density, and viscosity. The resultingsugar crystals are separated from mother liquor bycentrifugation at 1,000–2,500 x g. The semidry sugaris rinsed with water and dried further with hot air in arotating drum, cooled, classified on vibrating screens,and packaged. The mother liquor goes through aseries of crystallization steps to harvest maximumyield of premium quality sugar. The left over liquoris a by-product of sugar industry, called blackstrapmolasses.

Refined cane sugar is also manufactured from rawsugar produced at the point of origin. In this case, rawsugar is refined by extracting cane sugar juice, clar-ification, concentration, and crystallization. Otherproducts from raw sugar production are white sugar,turbinado sugar, and various grades of molasses. Rawsugar is then shipped to sugar refineries where itis subjected to a series of purification steps, suchas centrifugation, filtration, decolorization, evapora-tion, and crystallization. The by-products of refining


Table 11.5. Various Sugar Products Used in Formulation of Foods

Sucrose Product Sucrose Content(%) Moisture Content(%)

High-purity sucrose 99.90–99.95 0.02–0.04Brown/soft sugars 92.00–98.00 3.5–4.0Raw sugar 96.50–97.50 0.5–0.7Blackstrap molasses 38.00–45.00 12–18Raw molasses 56.00–62.00 14–18

steps are brown sugar, refinery syrups, liquid sugar,and molasses.

Beet sugar is produced in a single step. Beets aresliced, followed by diffusion of sugar in water, clari-fication, concentration, and crystallization directly towhite sugar. Purity and moisture content of varioussucrose products are shown in Table 11.5.

When granulated sugar (High Purity) is used foryogurt production, it is purchased in 50–100 poundbags, 1,000–2,000 lb tote bags or in bulk. In largeplants, bulk sugar is stored in silos. The color ofsugar is measured by procedures approved by Inter-national Commission for Uniform Methods of SugarAnalysis. The procedure involves measuring the ab-sorbance of 50% sugar solution (filtered through 0.45micron membrane filter) at 420 nm wavelength. Theabsorbance is converted to International Color Units(ICU). The higher the ICU number, the darker is thesugar color. Generally, most granulated sugars fallbelow 35 ICU. The inorganic ash content of sugar isapproximately 0.02%.

The moisture level in sugar is less than 0.04%. Partof the moisture in sugar results from the syrup trappedwithin the crystal during its formation, which can beremoved only by grinding sugar crystals. Anothertype of moisture is bound water associated with sat-urated syrup enveloping the crystals. Free moistureis attributed to a supersaturated solution coating thesugar crystal during rapid drying process of sugarmanufacture. Furthermore, crystallization of super-saturated solution during the storage of sugar causesthe free water to be released in the surrounding air.The dried granulated sugar is conditioned by the man-ufacturer to reach equilibrium with the surroundingatmosphere.

The size of crystals is selected for quick dissolutionduring the mix preparation. The crystal size distribu-tion is normally defined by the percent of the crystalsretained on the standard U.S. mesh screen. The higherthe mesh number, the finer would be the crystal size.Regular fine and extra fine grade of sugar has finecrystals. The grain size ranges from U.S. #20/40 and

#100 mesh screens. It is preferred by yogurt proces-sors for its bulk handling properties and resistance tocaking or lumping during storage.

The rating for sweetness varies according to thecrystalline form and size. It is related to the stereo-chemistry of the structural units in the sugar.

Liquid Sugar

Many large yogurt plants prefer using liquid sugarbecause it lends itself to an efficient handling (meter-ing and pumping ability). Although liquid sugar maybe economically priced, conversion from dry sugarto liquid sugar set up requires capital cost for sugarstorage tanks, appropriate pumps, heaters, strainers,and meters. The storage space and the inventory con-trol of liquid sugar must be coordinated with plantproduction volumes. If the delivery of liquid sugar isby tank cars, storage capacity requirements are of theorder of at least 1.5 cars or 12,000 gallons. If truckdelivery is convenient, the volume per delivery maybe in the range of 1,000 to 3,000 gallons. To cope upwith emergencies like delays and increased usage,the inventory should be adjusted accordingly.

Liquid sugar is obtained by dissolving refinedgranulated sugar in water. Some cane sugar refiningplants produce liquid sugar directly prior to crystal-lization and drying. It is delivered in tanks and storedin yogurt plant in specific tanks equipped with ultra-violet light to control growth of yeasts and molds.Adequate ventilation of the tanks is necessary toavoid moisture condensation and resulting microbialgrowth. Storage temperature range is 30–32◦C. Thisingredient contains 66–67% solids (67◦Brix) consist-ing of minimum of 99.7% sucrose and invert sugarlevel <0.35%. The ash content is restricted to lessthan 0.04% and iron content may not exceed 0.5 ppm.The pH is within the range of 6.7–8.5. A gallon of liq-uid sugar has 7.42–7.55 pounds of solids and weighs11.08–11.12 pounds. The viscosity of liquid sugar isaround 2 poises. The color of liquid sugar is similarto that of granulated sugar (less than 35 ICU).


Conversion of mix formula from dry sugar to liquidsugar can be done as follows:

Pounds of liquid sugar required

= Pounds of dry sugar required

Percentage of solids in liquid sugar.

Normally, for 100 lbs of dry sugar, 149.25 lbs ofliquid sugar is needed to add the same amount ofsucrose in the formula.

More often, conversion of dry sugar to gallons ofliquid sugar is required. To calculate gallons of liq-uid sugar to replace dry sugar, divide the pounds ofdry sugar with pounds of sugar solids per gallon. Toreplace 100 lbs of dry sugar, gallons of liquid sugarrequired would be: 100/7.42 = 13.48 gallons of liq-uid sugar.

The level of sucrose in yogurt mix appears to affectthe production of lactic acid and flavor by yogurtculture. A decrease in characteristic flavor compound(acetaldehyde) production has been reported at 8% orhigher concentration of sucrose (Chandan, 2004), butcultures capable of growth at higher sugar levels areavailable.

Corn Sweeteners

Corn sweeteners are normally not used in the man-ufacture of yogurt per se, but are commonly theconstituents of frozen yogurt mixes, where they areblended after fermentation. They are also sweeten-ers of choice in the preparation of fruit-for-yogurt(Chapter 9). The corn sweeteners offer savings in in-gredient costs. Nonetheless, they do exert much moreinhibitory effect on fermentation rate as compared tosucrose. This is attributed to higher osmotic pressureexerted by monosaccharides contained in corn syrupsweeteners. In comparison, sucrose being a disac-charide is less inhibitory to yogurt culture growth.The corn-derived sweeteners, fructose and glucose,usually enter yogurt via the processed fruit flavor inwhich they are extensively used for cost efficiencyand flavor enhancing characteristics. It is desirablefor a yogurt manufacturer (especially if frozen yo-gurt is a part of the product profile or fruit-for-yogurtis a part of the plant operation) to be knowledgeableabout basics of corn sweeteners.

Sweeteners can be made by hydrolyzing any foodstarch. In the United States, corn starch is an econom-ical starting material to manufacture corn sweeteners.The 1, 4 glucoside linkages holding together dextrosemolecules in starch are broken down to smaller frag-ments and eventually to individual building blocks

consisting of monosaccharide glucose. The hydroly-sis is accomplished by treatment of starch slurry withhydrochloric acid, followed by enzymatic action of�-amylase. If the reaction is stopped at an intermedi-ate point, the end products are composed of an assort-ment of sugars and oligosaccharides (maltodextrins).The degree of hydrolysis or conversion is termed by anumber “dextrose equivalent,” (D.E.) which is used tosignify the percent reducing sugars calculated as dex-trose. Hydrolysis of each glucoside linkage liberatesa free aldehyde group that displays the same reducingability as dextrose (glucose). Thus, reducing abilityis an indicator of the progress of starch hydrolysis.For instance, 42 D.E. corn syrup is a product madefrom corn starch that has reducing sugars in such pro-portions as to be equivalent to 42% dextrose. If theconversion is complete at 100% D.E., the product isdextrose.

Maltodextrins

Maltodextrins are products of very low hydrolysis ofstarch. Their D.E. ranges from 4 to 20. They are onlyslightly sweet. Hydrolysis of starch is random result-ing in the formation of smaller chain oligosaccharidesto saccharide polymers of varying chain length. Theyare made from common corn starch, as well as fromwaxy starch. The maltodextrins from each of thesestarting materials display slightly different function-ality. In general, their pH value ranges from 4.4 to5.0 and moisture level is 5–6%. Maltodextrin 5 D.E.from waxy starch has an actual D.E. range of 5–8,contains <0.5% dextrose, 1% maltose, and >98.5%higher polymers of dextrose. On the other hand, Mal-todextrin 5 D.E. derived from common starch hasan actual D.E. range of 4–7 and contains <1% dex-trose, <1% maltose, and >98% higher polymers ofdextrose. Maltodextrins of 10 D.E. have actual D.E.range of 9–13 and contain 0.5–1.0% dextrose, 2%maltose, and 96–97% higher polymers of dextrose.Finally, maltodextrins D.E.15 have an actual D.E.range of 13–18 and contain 2% dextrose, 3% maltose,and >94% higher polymers of dextrose (Alexander,1997). It is good to remember that lower the D.E., thehigher the molecular weight of the product and lowerthe intensity of sweetness. To enhance dispersability,maltodextrins are agglomerated. Agglomeration ofcorn-derived 10 D.E. maltodextrins reduces the bulkdensity from 0.54 to 0.34 g/cc. In dry mixes, theypromote flowablity and reduce dust during handling.They are also good bulking agents in the formulationof low/non fat frozen yogurt.


Table 11.6. Properties of Liquid and Dry Corn Sugars

RelativeSweetness:

Type Actual DE % Moisture % Dextrose % Maltose DP3a Higher DPb Sucrose = 1

Corn syrup 36 D.E. 35–37 20 13–14 11–12 10 64–66 0.40Corn syrup 42 D.E. 41–43 18–20 19 13–14 12 55 0.50Corn syrup solids

36 D.E.34–38 4–5 13–14 11–12 10 64–66 0.40

Corn syrup solids42 D.E.

40–44 4–5 19 12–14 11–12 55–58 0.50

Dextrose 100 0.5 99.5 0 0 0 0.8Adapted from Alexander, 1997.

a Degree of polymerization, 3 dextrose units.b Degree of polymerization.

Corn syrups are defined as the products inwhich 20–70% of the glucoside linkages have beenhydrolyzed. Three types of corn sweeteners are com-mon in the frozen yogurt industry. They are classifiedas low conversion (28–38 D.E.), regular conversion(38–48 D.E.), intermediate conversion (48–58 D.E.)and high conversion (58–68 D.E.). High-conversionsyrups may be obtained by a combination of acidand enzyme action on starch. High maltose syrup ismade from a combination of acid and �-amylase hy-drolysis. The disaccharide maltose consists of twomolecules of glucose. Dry corn syrups are obtainedby spray drying partially hydrolyzed corn starch ofvarious D.E. Crystalline dry forms of refined dextroseand fructose are available. Generally, frozen yogurtproducers use 36 or 42 D.E. corn syrup in liquid formor as dry corn syrup solids. Since the liquid form isvery viscous, to facilitate their pumping and meter-ing, this ingredient is stored in heated tanks at 32◦C.

Corn syrup solids are economical to use. Theycontribute firmness and extend the shelf life of thefrozen dessert. The sweetness and other proper-ties of corn sweeteners are shown in Tables 11.6.The high-polymer content contributes adhesive andcohesive properties to mix (Marshall and Arbuckle,

1996). The corn syrup solids ingredient is a whitepowder and is susceptible to caking when exposedto moist air. Since too much corn syrup in the mixmay impart a flavor defect, its use in frozen dessertis limited to one-third of the total sweetener level.Crystalline dextrose is a white powder with 80% ofthe sweetening power of sucrose. Dextrose, being amonosaccharide of molecular weight nearly one-halfof sucrose, depresses the freezing point of the mixtwice as much as sucrose. Frozen yogurt from a mixcontaining corn syrup displays less stiff consistencyas it extrudes from the ice cream freezer. Accord-ingly, its usage level is adjusted not to exceed 25%of the total sweetener level.

High fructose corn syrups (HFCS) and crystallinefructose equal or exceed the sweetness of sucrose(Table 11.7). HFCS production involves dextroseconversion to fructose in corn syrup by enzymaticmeans. They also lower the freezing point of frozendessert mixes to the same extent as the original cornsyrups.

Crystalline fructose is commonly used to effectflavor improvement in light yogurt by rounding offsweet flavor of aspartame and other nonnutritivesweeteners.

Table 11.7. Properties of High Fructose Corn Syrups and Crystalline Fructose

Relative%Higher Sweetness:

Type of HFCS %Moisture %Fructose %Glucose Polymers Sucrose = 1

42 20–29 42 53 5 0.9–1.055 23 55 41 4 1.0–1.290 20 90 7 3 1.4–1.6Crystalline Fructose 0.05 99.5 0.5 0 1.2–1.6Source: Adapted from Alexander, 1997.


Other nutritive sweeteners for use in specialty yo-gurt manufacture are honey, maple sugar, and brownsugar. Honey is used in honey-flavored natural yo-gurt. Honey has a pH of 3.9 and consists of 17.1%moisture, 38.5% fructose, 31% glucose, 7.2% mal-tose, 1.5% sucrose, 4.2% higher chain sugars, 0.5%protein, 0.6% acids, and trace amounts of minerals,vitamins, enzymes and amino acids. Due to the highfructose content, honey is sweeter than sugar. Thecolors of honey form a continuous range from waterwhite to dark amber. In general the flavor of honeyis related to its color. Dark colored honey is moreintense in flavor while lighter honey is usually mild.Honey flavor is the result of a number of variablessuch as the floral source, the geographical region,sugars, acids, tannins, and volatile and nonvolatileconstituents. Honey can be used as the sole sweet-ener source or in combination with equal parts ofsucrose for a honey flavor in yogurt.

Maple sugar comes from the sap of sugar mapleand black maple trees. The sap is 98% water. The sapis concentrated in open kettles to 65.5% solids. Typ-ical composition of maple syrup is: 34% moisture,58–66% sucrose, 0–8% glucose, fructose and otherhexoses, 0.09% malic acid, 0.01% citric acid, and var-ious minerals. The flavor of maple syrup is attributedto ligneous materials present in sap and caramelizedsugars produced during the concentration step. Thecolor of maple syrup can range from light amber todark amber. Maple sugar is the end product of furtherevaporation of maple syrup and contains 92% solids.

Brown sugar is described in the sucrose section. Itis basically unrefined sugar and has flavor similar tomolasses.

Fruit and grain sweeteners are used in productsmarketed with a no added sugar label. They are con-centrates of apple, grape, and other juices. Syrupsmade from rice, oats, and other grains are used in yo-gurts identified as containing natural ingredients andno sugar added label.

Sweeteners such as crystalline fructose, glucose,lactose, invert sugar, or honey are not often used ex-cept in certain circumstances, such as manufactureof dietetic yogurt or yogurts marketed with an “allnatural” or health food appeal.

High Intensity Sweeteners

Because the U.S. standards of identity for yogurt,low-fat yogurt and nonfat yogurt do not allow non-nutritive sweeteners to be used, there are labeling op-tions that must be considered. Two of these options

include using a nonstandardized name for the food orusing the two-food concept (i.e., nonfat yogurt withaspartame). Currently these sweeteners are used toproduce “Light” and “low-carbohydrate” products.Today, the use of aspartame alone or in combinationwith crystalline fructose or other nonnutritive sweet-eners is common in the marketing of low-calorie or“low-carb” yogurt.

Regular low-fat and nonfat yogurts contain ap-proximately 43 g of sugar per 8 oz. cup. By replacingthe sucrose in yogurt, the sugar content drops to 13 g.This reduction in sugar content is of the order of 70%.The remaining sugar is lactose, part of which may beremoved by using 80% milk protein concentrate ob-tained by ultrafiltration and diafiltration of skim milk.This approach is the basis of “low-carbohydrate”yogurt. Concomitantly, reduction in sugar in yogurtresults in significant reduction in calories as well.Regular low-fat yogurt contains 230 calories per 8oz. cup. By replacing added sugar, the calories dropto 130. Similarly, the calories in nonfat yogurt dropfrom 207 to 102 per cup by sugar replacement.

The following high intensity sweeteners are ap-proved by the Food and Drug Administration for usein yogurt (Table 11.8).

Aspartame

Aspartame is a dipeptide. It is L-�-aspartyl-L phenylalanine methyl ester. Intestinal esterases hydrolyzeto individual peptides and methanol. The end prod-ucts do have calories, but since the level used is sosmall, the calorie contribution is essentially zero.The stability of aspartame to heat, yogurt fermen-tation and acidic conditions must be understood.Aspartame breaks down with excessive heat ex-posure to diketopiperazine, but is reasonably sta-ble at dairy processing temperatures. It is partiallymetabolized by yogurt cultures during fermenta-tion. Accordingly, pasteurized aspartame solution isblended with yogurt base after fermentation. Use of

Table 11.8. High Intensity SweetenersApproved by FDA for Use in Yogurt

Non-Nutritive Sweetness Factor,Sweetener Sucrose = 1

Aspartame 160–220Sucralose 600Acesulfame K 200Neotame 7,000–13,000


aspartame requires the statement “Phenylketonurics:Contains phenyl alanine.” Aspartame degradesslowly during storage and shelf life of yogurt. Studieshave shown that about 7% aspartame is inactivated inyogurt stored at 4◦C for 8 weeks. To compensate forexpected loss in sweetness, it is advisable to adjustaspartame level for incorporation into yogurt.

Granular or liquid aspartame preparations may beused in manufacturing light yogurt and smoothies.Aspartame is dissolved in water along with an acidu-lant (for example, citric acid). To obtain optimumsweetness control, it is preferable to add aspartamein the granular form at the first point of breaking andcooling the yogurt coagulum. It requires 30–45 min-utes of swept-surface agitation to properly dispersethe granular aspartame. A less preferred route is toincorporate aspartame in fruit preparation during thecooking step. Addition of this fruit adds appropri-ate level of aspartame to the fruit flavored yogurt orsmoothie. However, since the level of fruit prepa-ration in finished yogurt varies considerably due tomechanical variations in dosing of fruit preparation,the sweetness level in yogurt would vary accordingly.For processing yogurt fruit as a carrier of aspartame,cooking at 96◦C for 5 minutes, followed by quickcooling to 32◦C or lower maximizes the stability ofaspartame. The shelf life of the processed fruit is6 months at 4◦C or below.

Sucralose

Sucralose is another high intensity sweetener whichis truly nonnutritive. It is poorly absorbed in thegastrointestinal tract (11–27%). The absorbed sucra-lose is excreted intact in the urine; the unabsorbedportion is excreted in the feces. This is how it pro-vides no calories. It is synthesized from sucroseby replacing three hydroxyl groups with chlorine.Chemically speaking, it is 1,6-dichloro-1,6-di-deoxy-�-D-fructofuranosyl-4-chloro-4-deoxy-�-D-galactpyranoside. It is three times sweeter thanaspartame or 600 times sweeter than sucrose. It isstable to heat and acidic conditions prevalent in foodprocessing and storage. Currently, it is being usedin light and “low carbohydrate” yogurt, drinks andsmoothies.

Acesulfame-K

Acesulfame-K is 5.6-dimethyl-1,2,3,-oxathiazine-4(3H)-one-2,2-dioxide. In general, the potassium saltis used. It provides no calories because 95% or moreis excreted, unchanged in the urine. It is 200 timessweeter than sucrose. It is stable to baking and cook-ing temperature. It works well with other nonnutri-tive sweeteners by providing sweetness synergy andmasking unpleasant flavors.

NeotameTM

NeotameTM was approved by the Food and Drug Ad-ministration on July 5, 2002. It is 7,000 to 13,000times sweeter than sucrose. Like aspartame, it is aderivative of dipeptide of aspartic acid and pheny-lalanine. Since it is rapidly metabolized by esterasesand the end products are excreted in body wastes,it is noncaloric. Compared to aspartame, phenylala-nine released in plasma is not significant. Therefore,neotameTM requires no warning label for PKU. Itsflavor is clean and sweet with no off-flavors. It lacksmetallic flavor. It enhances other flavors. It is heatstable and can be incorporated directly in yogurtproducts. Alternatively, it can be incorporated in fruitpreparations and then blended with fermented yogurtbase. Adding the sweetener through fruit preparationis not preferred because of inconsistency of mechan-ical dosing of the fruit in each cup. Compared toaspartame, neotameTM is stable to yogurt process-ing temperature and fermentation conditions. Studieshave shown that 99% of neotameTM survived UHTpasteurization conditions and 88% survived after yo-gurt fermentation and subsequent storage for 5 weeksat 4◦C.

Usage level of neotameTM and aspartame toachieve 6–10% sucrose level in yogurt is shown inTable 11.9.

Saccharin

Saccharin is a synthetic compound that is 300 timessweeter than sucrose. It provides no calories. Itis excreted unchanged through the kidneys. It has

Table 11.9. Usage Levels of Neotame and Aspartame in Yogurt

Product NeotameTM Aspartame

Fruit flavored yogurt 0.0011–0.0017% (11–17 ppm) 0.055–0.08% (550–800 ppm)Fruit-for-yogurt preparation 0.006–0.012% (60–120 ppm) 0.25–0.35% (2500–3500 ppm)


relatively bitter taste but is widely used as sugar re-placer in beverages, cooking, and table top sweetener.However, it has little or no use in yogurt processing.

There are several nonnutritive sweeteners await-ing approval by the FDA. Alitame is a peptide ofL-aspartic acid and D-alanine with a C-terminal moi-ety. It is 2000 times sweeter than sucrose. It has nometallic or bitter taste. It blends with other high in-tensity sweeteners to maximize quality of sweetness.However, it is pending approval. Cyclamates are usedin 50 countries worldwide, but were banned by theFDA in 1969. Cyclamates are 30 times sweeter thansucrose. The application for reapproval is pendingwith the FDA. Neohespridene dihydrochalcone is aby-product of the citrus industry. It is 1500 timessweeter than sucrose. It has licorice flavor. It is ap-proved by the FDA as a flavor ingredient, but notas a sweetener. However, in the EU countries, itis approved as a sweetener. Another high-intensitysweetener, not yet approved by the FDA, is ste-via or stevioside. It is obtained from South Africanshrub. Similarly, thaumatin has Generally-Regarded-As-Safe status for use as flavor adjunct in the UnitedStates. It is a mixture of proteins with tight disulfidebonds. It has an intense sweet flavor but used as aflavor enhancer.

Current trend in the use of high-intensity sweeten-ers in yogurt is to blend two or more sweeteners tooptimize the flavor profile of yogurt. A combinationof acesulfame-K with aspartame, or sucralose can en-hance perceived sweetness, optimize flavor, reducecost, and improve sweetness stability. However, re-search is required to determine the right combinationand ratio in yogurt or fruit for yogurt formulation toachieve optimum sensory quality of the product.

Stabilizers

They are hydrocolloids of plant and animal origin. InNorth America, they are commonly used in the manu-facture of yogurt. The primary purpose of adding sta-bilizers in yogurt is to improve consistency and buildviscosity, to minimize whey separation and bind freewater, and to maintain the gel structure after pumping,mixing, and cooling. The stabilizer increases shelflife of the product and provides a reasonable degreeof uniformity from batch to batch. Stabilizers func-tion through their ability to form gel structures inwater, thereby leaving less free water for syneresis.

In addition, some stabilizers complex with casein.A good yogurt stabilizer should not impart any flavor,should be effective at low pH values, and should be

easily dispersed in the normal working temperaturesin a yogurt plant. In addition, the stabilizer should beeasily soluble, display good water holding capacity,and aid in forming stable emulsion. Furthermore, itshould promote stable foam formation (in whippedyogurt), gelation, and adhesion.

Preferably, the incorporation of the stabilizershould take place using a high shear-type blender thathas strong agitation resulting in complete dispersionand a uniform suspension (Chapters 5 and 13). An al-ternative method would be to use a pump and funnel,but care must be taken to avoid lumps. To minimizepotential lumps or “fish eyes,” it is best to dispersethe stabilizer in granulated sugar or NFDM duringaddition. Once dispersed in the mix, it is necessaryto have continuous agitation to keep the stabilizer insuspension until it is fully hydrated while receivingproper heat treatment.

There are many stabilizers and their combinationsavailable in the industry for use in yogurt. For choos-ing a stabilizer, the following areas should be consid-ered:

� Type of yogurt being produced: vat/cup set,Swiss/blended type or drink/smoothie,mousse/whipped type.

� Formulation: fat content, total solids.� Desired firmness and consistency of the finished

product as per marketing objectives.� Desired ingredient labeling (natural, organic,

kosher, etc.).� Processing equipment available: batch process

(ease of incorporation), continuous heatingsystem, in-line dosing and mixing, cooling, andpumping of coagulum.

� Possible masking effect on the flavoring system.

Gelatin

Gelatin has been extensively used as a stabilizer invarious styles of yogurt. It is derived by irreversiblehydrolysis of the proteins collagen, and ossein. Itis used at a level of 0.1–0.5%, depending on thefirmness desired in refrigerated yogurt. Gelatin is agood stabilizer for frozen yogurt as well. The termBloom refers to the gel strength as determined by aBloom gelometer under standard conditions. Gelatinof Bloom strength of 225 or 250 is commonly used.The gelatin level should be geared to the consistencystandards for yogurt. The amount of gelatin above0.35% tends to give yogurt of relatively high milksolids a curdy and lumpy appearance upon stirring.


Gelatin tends to degrade during processing at ul-trahigh temperatures and its activity is temperaturedependent. At temperatures below 10◦C, the yogurtacquires a pudding-like consistency. The yogurt geldeveloped by gelatin is considerably weakened by arise in temperature.

Gelatin is desirable because of its sheen-like ap-pearance and its ability to take a lot of abuse andstill produce a good product. However, when usingonly gelatin, the product could have a jelly-like bodywhich tends to stir out lumpy, which is undesirablein most markets. For this reason, it is more commonto use gelatin in combination with other stabilizers tolessen the stiff jelly effect and produce a body whichstirs out smooth and is free of lumps. Two combi-nations are commonly used: modified starch-gelatinand gelatin-pectin. When the objective is to producea “natural” Swiss style yogurt with medium viscos-ity without the use of conventional stabilizers, theaddition of WPC and MPC is helpful. Their addi-tion increases the protein content and water bindingcapacity.

The stabilizers generally used in yogurt are shownin Table 11.10.

For effective use of stabilizers, it is imperative tounderstand their interactions with milk constituentsfor possible synergy or interference with the ingredi-ents of yogurt mix.

Native and Modified Starch

A new technology has been developed for produc-ing native starches without chemical modificationthat have properties similar to modified starches forapplication in low to moderate temperature and shear

food systems. This functional native starch can be de-rived form corn or tapioca. They have been used aloneor in combination with WPC or gums in speciallymarketed yogurt products with some success. Al-though these specially processed native starches aredesigned to resemble the textural properties of modi-fied starches, they have both product and process lim-itations. For most applications, starch products thathave been subject to chemical and physical modifica-tion, result in starch gels that are made to withstandprocessing conditions involving high heat, shear, andacidic environment. Improvement in gelatinizationand pasting characteristics, solubility, and clarity arepossible with appropriate modification. Furthermore,modification of starch can lead to viscosity gener-ation or reduction, freeze-thaw stability, increasedgel strength and enhanced appearance, and synere-sis control, making them versatile for use in foodprocessing. Chemical modification is effected by es-terifying hydroxyl groups of starch with acetic anhy-dride, succinic anhydride, phosphoryl chloride, var-ious phosphates or by etherification with propyleneoxide, or by reaction with hydrochloric/sulfuric acid,or by bleaching with hydrogen peroxide, hypochlo-rite, etc. A combination of these treatments may beapplied. In addition, cross-linking of starch chainswith phosphate diester reduces the degree and rate ofgranule swelling, which helps stabilize the yogurt andprovide resistance to break down during mechanicalshearing.

Modified corn/tapioca starch suitable for use atlow pH is commonly used in yogurt formulation. Forinstance, stabilized and medium cross-linked waxymaize starch (hydroxypropyl distarch phosphate) isa viscosity generator and a stabilizer. It has a bland

Table 11.10. Common Stabilizers for Yogurt and Yogurt Drinks

Stabilizer (%) Concentration in Yogurt Mix

Whey protein concentrate (34%, 50%, or 80%protein) or/and milk-protein concentrate

0.7–1.5

Starch, modified (tapioca/corn) 0.8–2.0Gelatin (225/250 Bloom) 0.1–0.5Agar 0.25–0.70Pectin (low methoxy for yogurt) 0.08–0.20Pectin (high methoxy for yogurt beverages) 0.30–0.50Locust bean gum (in combination) 0.3–0.5Xanthan gum (in combination) 0.01–0.05Carrageenan (in combination) 0.01–0.05Natural corn starch 1.5–2.0Carboxymethyl cellulose 0.1–0.2


flavor, gives clear paste, smooth short texture, andcan withstand severe processing conditions of lowpH, high heat and extreme shear.

Gums and Pectins

Frozen yogurt contains plain yogurt of the order of10–20%, while the rest of the product is constitutedfrom ice milk mix. The ice milk mix is designed foroptimum freezing characteristics, as well as for de-sirable texture during shelf life of composite frozenyogurt product. Various gums are used to achievethese effects. The seaweed gums impart a desirableviscosity as well as gel structure to yogurt. Alginand sodium alginate are derived from giant sea kelp.Carrageenan is made from Irish moss and compareswith 250 Bloom gelatin in stabilizing value. Thesestabilizers are heat stable and promote stabilizationof the yogurt gel by complex formation with Ca+2

and casein.Pectins are commonly used alone or in combi-

nation with other hydrocolloids to stabilize stirredand set yogurt. The source, structure, and type ofpectins are discussed in Chapter 12. Low Methoxy(LM) pectin is the preferred type for (refrigerated)cup yogurt. Very small amount (0.07–0.15%) mod-ifies the consistency of the yogurt making it stifferand preventing any syneresis that might arise duringhandling, transportation, and distribution. LM pectinretains the lactoserum in a very flexible network thatis formed in reaction with calcium ions present in theyogurt. The maximum amount of pectin to be addedto yogurt is 0.20%, as higher concentrations couldresult in a chalky or sandy texture and decreased vis-cosity in stirred yogurt.

High Methoxy (HM) pectin is preferred to ensurestability and control viscosity in acidified milk drinks.HM pectin stabilizes the milk proteins to produceproducts without sedimentation and whey separationand ensures a smooth mouth feel without “sandi-ness.” The stabilization is obtained by absorption ofpectin onto the surface of the protein particles withthe proper application of shear force. The absorbedpectin imparts a similar charge to all particles caus-ing repulsion between particles preventing agglomer-ation that would result in sedimentation, separation,and a sandy texture. The optimum HM pectin levelis determined by:

� Protein concentration� Protein particle size

� Heat treatment� Length of shelf life

Among the seed gums, locust bean gum or carobgum is derived from the seeds of a leguminous tree.Carob gum is a neutral polysaccharide and therefore,pH has little effect on viscosity in the range pH 3–11.It is insoluble in cold water and must be heated tobe dissolved. It does not have gelling properties onits own and is used primarily in yogurt to add vis-cosity or increase gel strength in combination withother stabilizers. It is commonly used in frozen yo-gurt where its principal function is stabilizing and thebinding of water, which provides heat-shock resis-tance and a slow creamy meltdown. Guar gum is alsoobtained from seeds and can be used in stabilizer sys-tems for frozen yogurt. Guar gum is readily solublein cold water and is not affected by high temperaturesused in the pasteurization of yogurt mix. Guar gum isnongelling and is used mainly as a viscosity builder,stabilizer, and moisture-binding agent. Guar gum im-parts body, texture, chewiness, and heat-shock resis-tance to frozen yogurt. Carboxy methyl cellulose is aderivative of the natural product cellulose. It is readilysoluble in either hot or cold water and is effective athigh processing temperatures. Its primary function inyogurt would be as a thickener and moisture-bindingagent. In frozen yogurt, it functions to bind water,thus preventing the formation of large ice crystalsthat can develop during temperature fluctuations instorage. The result is a frozen yogurt with smoothertexture and improved melt down characteristics.

The stabilizer system used in yogurt mix prepara-tions is generally a combination of various vegetablestabilizers. Their ratios as well as the final concentra-tion (generally 0.5–2.00%) in the product are care-fully controlled to get desirable effects.

Other important ingredients used in yogurt man-ufacture are fruits and flavors. They are describedseparately in Chapter 9.

REFERENCESAlexander RJ. 1997. Sweeteners: Nutritive. Eagan

Press, St. Paul, MN, pp. 17–43.American Dairy Products Institute. 1990. Standards for

grades of dry milks including methods of analysis.Bulletin 916 (Revised). Elmhurst, IL, 60126.pp. 1–56.

Chandan RC. 1982. Fermented dairy products. In: GReed (Ed), Prescott & Dunn’s Industrial


Microbiology. Avi Publishing, Westport, CT,pp. 113–184.

Chandan RC. 1997. Dairy-Based Ingredients. EaganPress, St. Paul, MN, pp. 48–49.

Chandan RC. 2004. Dairy: yogurt. In: JS Smith, YHHui (Eds), Food Processing: Principles andApplications, Blackwell Publishing, Ames, IA,pp. 297–328.

Chandan RC, Shahani KM. 1993. Yogurt. In: YH Hui(Ed), Dairy Science and Technology Handbook, Vol.2. VCH Publishers, New York, New York, pp. 1–56.

Chandan RC, Shahani KM. 1995. Other fermenteddairy products. In: G Reed, TW Nagodawithana

(Eds), Biotechnology, Vol. 9, 2nd ed. VCHPublishers, Weinheim, Germany, pp. 386–418.

Marshall RT, Arbuckle WS. 1996. Ice Cream.Chapman and Hall, NY, pp. 317–318.

Tamime AY, Robinson RK. 1999. Yogurt Science &Technology, 2nd ed. Woodhead Publishing Limited,Cambridge, England and CRC Press, Boca Raton,Florida.

United States Department of Health and HumanServices. 1999. Public Health Services, Food andDrug Administration. Grade “A” Pasteurized MilkOrdinance. Revision. Publication no. 229.Washington, DC.

12Principles of Yogurt Processing


Mix PreparationHeat TreatmentHomogenizationYogurt Starter

Factors Influencing Growth of Yogurt StarterYogurt Strain SelectionChanges in Milk Constituents During Yogurt Production

References

Yogurt is a fermented, low to high acid semisolidcultured milk product (Chandan, 2002; Shah, 2003;Vedamuthu, 1991). The sequence of stages of pro-cessing in a yogurt plant is given in Table 12.1.

MIX PREPARATIONDuring standardization of the mix for yogurt man-ufacture, the contribution of common dairy ingredi-ents to the milk fat and milk solids-not-fat portionof yogurt mix is given in Chapter 11 (Table 11.1). Inmost yogurt formulations, standardization of milk forfat and solids-not-fat content results in fat reductionand a possible 30–35% increase in lactose, protein,mineral, and vitamin content (Chandan and Shahani,1993, 1995; Chandan, 1997, 2004). The nutrient den-sity of yogurt mix is thus increased over that of milk.Specific gravity changes from 1.03 to 1.04 at 20◦C.Addition of stabilizers (gelatin, starch, pectin) andsweeteners further impacts physical properties.

HEAT TREATMENTYogurt processing requires intense heat treatment,which destroys all the pathogenic flora and most veg-etative cells of all microorganisms contained therein.In addition, milk enzymes inherently present are

inactivated. From microbiological standpoint, de-struction of competitive organisms produces condi-tions conducive to the growth of desirable yogurt bac-teria. This contributes to the long shelf life as well asto food safety aspects of yogurt. Furthermore, theheat processing results in the expulsion of oxygen,creation of reducing conditions (sulfhydryl genera-tion), and production of protein-cleaved nitrogenouscompounds. All these effects enhance nutritional sta-tus of the medium for growth of the yogurt culture.

Physical changes in the proteins as a result of heattreatment have a profound effect on the viscosity ofyogurt (Shah, 2003). Optimum results are obtainedby using a heat treatment of 90–95◦C and a hold-ing time of 5–10 minutes (Robinson, 2003a). Con-sequently, whey protein denaturation of 70–95% en-hances water absorption capacity, thereby creatingsmooth consistency, high viscosity and stability fromwhey separation in yogurt.

Nutritional changes include ease of digestion ofdenatured whey proteins in the gastrointestinal tract,soft curd in the stomach, and rapid gastric emptyingrate attributed to viscous nature of yogurt.

Heat treatment of yogurt mix can be conductedusing a variety of methods:

� Jacketed mix/processing tank� Plate heat exchanger� Tubular heat exchanger� Scraped-surface heat exchanger.

In most yogurt manufacturing facilities today theheat treatment of the yogurt mix is accomplished us-ing plate heat exchangers. The plate heat exchangerconsists of a pack of stainless steel plates clamped ina frame. The frame may contain several plate packsor sections in which different stages of treatment such

195




Table 12.1. Sequence of Processing Stages in the Manufacture of Blended Style Yogurt.

Step Salient Feature

Milk procurement Sanitary production of Grade A milk from healthy cows is necessary. Formicrobiological control, refrigerated bulk milk tanks should cool to10◦C in 1 hour and <5◦C in 2 hours. Avoid unnecessary agitation toprevent lipolytic deterioration of milk flavor. Milk pickup from dairyfarm to processing plant is in insulated tanks at 48-hour intervals, asappropriate.

Milk reception and storagein manufacturing plant

Temperature of raw milk at this stage should not exceed 7◦C. Insulated orrefrigerated storage up to 72 hours helps in raw material and processflow management. Quality of milk is checked and controlled.

Centrifugal clarification andseparation

Leucocytes and sediment are removed. Milk is separated into cream andskim milk or standardized to desired fat level at 5◦C.

Mix preparation Various ingredients to secure desired formulation are blended together at5◦C in a mix tank equipped with powder funnel and an agitation system.

Heat treatment Using plate heat exchangers with regeneration systems, milk is heated totemperatures of 95–97◦C for 7–10 minutes, well above pasteurizationtreatment. Heating of milk kills contaminating and competitivemicroorganism, produces growth factors by breakdown of milk proteins,generates microaerophilic conditions for growth of lactic organisms,and creates desirable body and texture in the cultured dairy products.

Homogenization Mix is passed through extremely small orifice at a pressure of approx.1,700 MPa (2,000–2,500 psi), causing extensive physicochemicalchanges in the colloidal characteristics of milk. Consequently, creamingduring incubation and storage of yogurt mix is prevented. Thestabilizers and other components of a mix are thoroughly dispersed foroptimum textural effects.

Inoculation and incubation The homogenized mix is cooled to an optimum growth temperature(41–42◦C). Inoculation is generally at the rate of 0.5–5% and theoptimum temperature is maintained throughout incubation period toachieve a desired titratable acidity or pH. A pH of 4.5–4.6 is commonlyused as an endpoint of fermentation. Quiescent incubation is necessaryfor product texture and body development.

Cooling, fruit incorporationand packaging

The coagulated product is cooled down to 5–22◦C, depending upon thestyle of yogurt. Using fruit feeder or flavor tank, the desired level offruit and flavor is incorporated. The blended product is then packaged.

Storage and distribution Storage at 5◦C for 24–48 hours imparts in several yogurt productsdesirable body and texture. Low temperatures ensure desirable shelf lifeby slowing down physical, chemical, and microbiological degradation.

Source: Chandan, 2004.

as preheating, final heating, and cooling take place.The plates are corrugated in a pattern designed foroptimum heat transfer as the liquid product entersand leaves the channels on one side and the heatingor cooling medium on the opposite side. Most heatplate exchangers contain a section that is used for re-generation. Regeneration is a process using the heatof a hot liquid (yogurt mix) to preheat the cold in-coming liquid (yogurt mix). The cold liquid (yogurtmix) is also cooling the hot liquid (yogurt mix) saving

on water and energy. Regeneration efficiencies of upto 94–95% can be achieved using efficient plate heatexchangers. Proper heat treatment of the yogurt mixrequires that the mix be held for a specified time at adesired final heating temperature. This is usually ac-complished in an external holding tube. The holdingtube consists of stainless steel pipe arranged in eithera spiral or zigzag pattern. The tube can be insulatedor contained in an insulated box to minimize heat lossduring the extended hold time. The length of the pipe

12 Principles of Yogurt Processing 197

Figure 12.1. Stained cells of yogurt bacteriaunder microscope. 1,000 × magnification.

and flow rate is calculated to give the desired holdtime in the tube.

HOMOGENIZATIONHomogenization treatment reduces the fat globulesto an average of less than 1 �m in diameter and as-sures a uniform distribution of the milk fat in the yo-gurt. Consequently, no distinct creamy layer (crust)is observed on the surface of yogurt produced fromhomogenized mix. There is also an improvement inthe consistency of the yogurt and greater stabilityof the coagulum against whey separation. In gen-eral, homogenized milk produces soft coagulum inthe stomach, which may enhance digestibility.

Homogenization temperatures used are usuallyfrom 55◦C to 80◦C with homogenization pressuresbetween 10 and 20 MPa (100–250 bar). In generalthe homogenizer is placed after the first regenerativesection and before the final heating. This is becausehomogenization is most efficient when the fat phaseis in a liquid state.

Most yogurt facilities use a two-stage homoge-nizer to achieve optimal homogenization. Althoughhomogenization always takes place in the first stage,the second stage serves two basic functions: (a) It sup-plies a constant and controlled back-pressure to thefirst stage that improves homogenization efficiency;(b) it prevents the clumping of fat globules that canoccur immediately following the first-stage homog-enization.

Yogurt is traditionally made from fortified wholemilk, low-fat milk or skim milk to which a yogurtculture is added and allowed to grow. In general,

yogurt should have a custard-like or soft spoonableconsistency that is free from syneresis or wheyingoff. The coagulum should be smooth without grainsor lumpiness and break cleanly when spooned fromthe container. The coagulum should also have a closetexture with complete absence of any gas space oropen texture. The activity of yogurt culture plays akey role in getting the required texture and flavor. Thefermentation is carried out by yogurt starter.

YOGURT STARTERStarters for yogurt production are discussed in detailin Chapter 6. A starter culture consists of food-grademicroorganism(s), which when allowed to grow inmilk produce predictable attributes characterizingyogurt (Fig. 12.1).

The composition of yogurt starter is shown inTable 12.2.

Also, shown in this table are some additional or-ganisms found in yogurt or yogurt-like products mar-keted in various parts of the world.

All types of yogurt in the United States arefermented with the yogurt characterizing culturesmandated by FDA regulations. The yogurt culturecontains Streptococcus thermophilus (ST) and Lacto-bacillus delbrueckii subsp. bulgaricus (LB). Further-more, a majority of the yogurt sold contains optionalbacteria, especially those of intestinal origin. The op-tional organisms include Lactobacillus acidophilus,bifidobacteria, and other lactobacilli that are oftenreferred to as probiotic bacteria. Their inclusion inyogurt starter is motivated by their unique health-promoting effects. Such effects include improvement


Table 12.2. Required and OptionalComposition of Yogurt Bacteria.

Required by FDA Optional AdditionalStandard of Identity Bacteria Found in Yogurt

Streptococcus Lactobacillus acidophilusthermophilus (ST) Lactobacillus casei

Lactobacillus Lactobacillus casei subsp.delbrueckii subsp. rhamnosusbulgaricus (LB) Lactobacillus reuteri

Lactobacillus helveticusLactobacillus gasseri ADHLactobacillus plantarumLactobacillus lactisLactobacillus johnsoni

LA1Lactbacillus fermentumLactobacillus brevisBifidobacterium longumBifidobacterium breveBifidobacterium bifidumBifidobacterium

adolescentisBifidobacterium animalisBifidobacterium infantis

Source: Adapted from: Chandan, 1999, 2004.

in protein digestibility, alleviation of lactose intoler-ance, enhancement of mineral absorption, control ofintestinal health, lowering of serum cholesterol, an-tihypertensive effects, anticancer properties, and im-munity enhancement (Takano and Yamamoto, 2003).Some yogurt manufacturers incorporate them afteryogurt fermentation, whereas others coculture themwith yogurt organisms.

Both ST and LB are fairly compatible as wellas symbiotic for growth in milk medium. However,the optional organisms do not necessarily exhibitcompatibility with LB and ST. Judicious selectionof strains of LB, ST, and the optional organismsis necessary to insure survival and growth of allthe component organisms of the starter. Neverthe-less, product characteristics, especially flavor, maybe significantly altered from traditional yogurt fla-vor, when yogurt culture is cocultured with optionalbacteria, especially bifidobacteria. Normally, the yo-gurt culture, which is composed of LB and ST, isresponsible for the characteristic flavor and aromaof yogurt through the production of acetaldehyde,diacetyl, and acetic acid during the fermentation pro-cess. Lactic acid, being a nonvolatile substance, con-tributes to the acidic and refreshing taste of yogurt,

whereas the volatile by-products contribute to itspleasant and characteristic aroma. Of the volatileflavor components, acetaldehyde accounts for al-most 90%. However, bifidobacteria produce moreacetic acid than lactic acid. Therefore, if they areused in the culture makeup, the overall flavor pro-file will change as a result of higher acetic acidcontent.

With the advice of culture suppliers, the properculture can be selected that yields a finished yogurtwith desirable flavor and consistency and is suitablefor the plant equipment and production schedule.

The physiological state of a starter culture is deter-mined by microscopic examination of the dyed cellsof the culture. Cells of ST grown fresh in milk orbroth display pairs or long chains of spherical coccalshape (Figure 12.2). Under stressed condition of nu-trition and age (old cells, cells exposed to excessiveacid, solid media colonies, inhibitor containing milk),the cells appear oblong in straight chains, resemblingsomewhat like LB.

The acid producing ability is measured by pH dropand titratable acidity rise in 12% reconstituted nonfatdry milk medium (sterilized at 116◦C/18 minutes)incubated at 40◦C for 8 hours. A ratio of 3 parts ofST and 1 part of LB gives a pH of 4.20 and % TA of1.05 (Chandan and Shahani, 1993) under the aboveconditions.

Since starter cultures from culture suppliers areadded to the pasteurized yogurt mix, it is essen-tial that the commercial starter be contaminant-free.Commercial starter culture suppliers provide mi-crobiological specifications in terms of contaminanttolerances for their products. Accordingly, microbio-logical specifications of commercial cultures are out-lined (Sellars, 1989). In general, counts of mesophiliclactics, yeasts and molds, coliforms, anaerobic spore-formers, and salt-tolerant micrococci should notexceed 10 CFU/g. Escherichi coli, Enterococcusfaecium, and coagulase positive staphylococci shouldbe <1 CFU/g. The culture must be free of salmonella,listeria, and other pathogenic contaminants.

Data relative to various characteristics of bacteriamost commonly used for yogurt processing are pre-sented in Table 12.3.

Factors Influencing Growthof Yogurt Starter

Yogurt fermentation constitutes the most importantstep in its manufacture. To optimize the parametersfor yogurt production, an understanding of factors


Table 12.3. Certain Characteristics of Most Commonly Used Microorganisms in YogurtProduction.

Streptococcus Lactobacillus delbrueckiiCharacteristic thermophilus subsp. bulgaricus Lactobacillus acidophilus

Cell shape andconfiguration

Spherical to ovoid,pairs to chains

Rods with round ends,single, short chains,metachromaticgranules

Rods with round ends, single,pairs, short chains, nometachromatic granules

Catalase reaction − − −Growth temperature, ◦CMinimum 20 22 20–22Maximum 50 52 45–48Optimum 40–45 40–45 37Incubation temperature,◦C 40–45 42 37Heat tolerance

(60◦C/30 minutes)++ + −

Lactic acid productionin milk

0.7–0.8% 1.8% 2.0%

Lactic acid isomers L(+) D(−) DLAcetic acid Trace Trace +Gas (CO2) production − − −Proteolytic activity +/− + +/−Lipolytic activity +/− +/− +/−Citrate fermentation − − −Fermentation ability for

carbohydrates:Lactose + + +Glucose + + +Galactose − − +Sucrose + + +Fructose + + +

Aroma/flavor compounds ++ ++ +Hydrogen peroxide

production+/− + +

Mucopolysaccharideproduction

+ ++ −

Alcohol production − Trace TraceSalt tolerance: 2.0 2.0 6.5

% maximumSource: Compiled from: Chandan and Shahani, 1995; Surono and Hosono, 2003; Nauth, 2004.

involved in the growth of yogurt bacteria is importantto manage the uniformity of product quality and costeffectiveness of manufacturing operation.

Streptococcus thermophilus

Streptococcus thermophilus (ST) is characterized byits typical attributes, which distinguish it from lacto-cocci used in the manufacture of cheese, buttermilk,and sour cream. ST originates exclusively from the

dairy environment from which it can be easily iso-lated. ST (Fig. 12.2) is a Gram-positive, anaero-bic, nonmotile, and catalase negative organism withspherical/ovoid cells of 0.7–0.9 �m in diameter(Robinson, 2003b).

ST can survive 60◦C for 30 minutes (Nauth, 2004).It does not grow at 10◦C. Although the optimumgrowth temperature for ST is 37◦C, it grows wellin cooperation with LB at the yogurt incubationtemperature of 43◦C. During yogurt fermentation, the


Figure 12.2. Streptococcus thermophiluscells under microscope. 1,000 ×magnification.

initial need of ST for nitrogen source is fulfilled byfree amino acids present inherently in milk medium.As fermentation proceeds, the peptides generated byLB are hydrolyzed by the peptidases of ST to gener-ate free amino acids for its nutritional needs.

Milk is a good medium for its growth. ST can fer-ment glucose, fructose, mannose, sucrose, and lac-tose. Milk lactose is transported through the cellmembrane with the help of the enzyme galacto-side permease located in the membrane. The lac-tose in the cell is then hydrolyzed by lactase or�-galactsidase enzyme. ST produces significant lev-els of lactase, which catalyzes the hydrolysis of lac-tose to glucose and galactose. Glucose is convertedto pyruvate via Embden-Meyerhof pathway (Chap-ter 6). Pyruvate is metabolized to lactic acid by theenzyme lactic dehydrogenase. In most strains, glu-cose is readily utilized in milk medium while lacticacid and galactose accumulate. Some strains can uti-lize galactose. These strains display galactokinase ac-tivity converting galactose to galactose-1-phosphate,which is further converted to glucose-1-phosphateor galactose-6-phosphate and further metabolized tolactic acid (Robinson, 2003b). The lactic acid pro-duced by this organism is L (+) lactic acid. ST isinhibited by increasing levels of lactic acid and at ap-proximately 1% concentration (pH 4.3), its growthis arrested and cell numbers reach stability. At thisstage the fermented mass displays ST counts of log7–8 CFU/g.

The lactase activity of ST has a physiological sig-nificance in aiding the digestion of lactose in human

digestive tract following consumption of yogurt bylactose intolerant individuals.

When cultured in milk at 43◦C, many strains ap-pear as spherical occurring in pairs or long chains of10–20 cells. Most cells appear as diplococci. At highacidity levels in milk, if the cells are aged or if theculture is grown on solid media, ST may exhibit longchains. When plated on solid media, ST producespin-point colonies. The display of abnormal shapesof cells obtained from liquid media are indicators ofstress conditions on the organism, viz., bacteriophageattack, and inhibitors (sanitizers, antibiotics, cleaningcompounds, etc.) in the growth medium. ST is verysensitive to inhibitory substances, especially antibi-otics. It is readily inhibited by 0.005 IU penicillin/mlof milk. It should be noted that ST is more often at-tacked by bacteriophage than LB.

Lactobacillus delbrueckii subsp. bulgaricus

This organism was originally described by OrlaJensen in 1919 as Thermobacterium bulgaricum. Onthe basis of DNA homology studies, four subspeciesof Lb. delbrueckii are classified as bulgaricus, le-ichmannii, lactis, and delbrueckii. LB is a Gram-positive, catalase-negative, and nonmotile organism.(Fig. 12.3).

LB is an anaerobic/aerotolerant homofermentativeorganism that produces D (−) lactic acid and somehydrogen peroxide. It can produce a large quantityof lactic acid (up to 1.8%), but for yogurt produc-tion the strains, which are moderate acid producers


Figure 12.3. Lactobacillus delbrueckii spp.bulgaricus cells under microscope. 1,000 ×magnification.

are selected. Like ST, LB produces lactase enzymeto hydrolyze lactose to glucose and galactose. Glu-cose is metabolized to lactic acid, while galactoseaccumulates in the growth medium.

The cells of LB appear under microscope as slen-der rods with rounded ends. The cells occur singly orin chains of 3–4 short rods (0.5–0.8 × 2.0–9.0 �m)with rounded ends. In a young and vigorous state,the cells occur mainly singly or in pairs. Younger LBcells under microscopic examination do not show vo-lutin (metachromatic) granules. With increasing age(20–24 hours), the cells elongate and the volutin gran-ules become more visible. Nutritional stress leads tocopious granules in the rods. LB has a higher re-sistance to antibiotics than ST, but is inhibited by0.3–0.6 IU of penicillin/ml of milk.

The optimum growth temperature of LB is 45◦C,but for yogurt production, a temperature of 42–43◦Cis used to accommodate the lower optimum growthtemperature of ST. LB utilizes lactose, glucose, fruc-tose, and in some strains galactose to produce as highas 1.8% D(−) lactic acid. It tolerates low pH muchbetter than ST. Unlike ST, LB can hydrolyze casein(�-casein, preferentially) to peptides, using its cellwall bound proteinase (Argyle et al., 1976a, 1976b;Chandan et al., 1982). But to convert the resultingpeptides to free amino acids, LB has to rely on ST,which has active peptidase activity.

Collaborative Growth of ST and LB

Yogurt starter organisms display obligate symbioticrelationship during their growth in milk medium. The

rates of acid and flavor production by yogurt startercontaining both ST and LB are considerably higherthan by either of the two organisms grown separately(Loones, 1989; Robinson, 2003b). Although they cangrow independently, they utilize each other’s metabo-lites to effect remarkable efficiency in acid produc-tion. In general, LB has significantly more cell-boundproteolytic enzyme activity, producing stimulatorypeptides and amino acids (especially, valine) fromcasein protein for ST. The relatively high amino-peptidase and cell-free and cell-bound dipeptidaseactivity of ST is complementary to strong proteinaseand a low-peptidase activity of LB. ST in turn pro-duces formic acid and removes oxygen, which stim-ulates the growth of LB. In addition, urease activ-ity of ST produces CO2 which also stimulates LBgrowth. Concomitant with CO2 production, ureaseliberates ammonia, which acts as a weak buffer. Con-sequently, milk cultured by ST alone exhibits consid-erably low titratable acidity or high pH of coagulatedmass. Formic acid formed by ST as well as by heattreatment of milk accelerates LB growth. During theearly part of incubation, ST grows faster and outnum-bers LB by 3–4 to 1. However, in the later stages,(at pH 5.0), ST growth slows down due to adverseeffect of acid development and the numbers of LBgradually approach the population of ST. Therefore,acid production is accomplished in the first stage ofincubation predominantly by ST, and in the secondstage, mainly by LB.

Yogurt organisms are microaerophilic in nature.Heat treatment of milk drives out oxygen. It also de-stroys competitive flora. Furthermore, heat produced


Figure 12.4. Lactobacillus acidophilus cellsunder microscope. 1,000 × magnification.

sulfhdryl compounds tend to generate reducing con-ditions in the medium. Accordingly, rate of acidproduction in high heat-treated milk is considerablyhigher than in raw or pasteurized milk.

Viability of yogurt culture is an important attributefor consumer acceptance. The number of ST and LBcells in a sample of yogurt can be enumerated by stan-dard International Dairy Federation procedure (IDF,2003). Provided the fermentation conditions are opti-mal, the manufacturer of yogurt should achieve com-bined yogurt culture level of at least 100 millionCFU/g of the product.

Lactobacillus acidophilus

Lactobacillus acidophilus is an adjunct culture com-monly found in yogurt marketed in the United Statesand other countries with highly developed yogurtmarkets (Fig. 12.4).

There has been strong interest in the microfloraof the mammalian gastrointestinal (GI) tract and itsrole in promoting health of the host (Chandan, 1989;Chandan, 2002; Fernandes et al., 1992; Takano andYamamoto, 2003). Certain strains of this organismcan be implanted in the colon after surviving the harshconditions of low pH and surface active bile secre-tions in stomach and small intestine. These strainspossess properties required of probiotics and are con-sidered to be desirable dietary adjuncts. Probiotics aredefined as live microorganisms, which contribute tothe well being of human and animals by improvingtheir microbial balance in the GI tract. Probiotics arediscussed in Chapters 21 and 22. Consuming yogurtcontaining the probiotics allows continuous passage

of these organisms through the gut and the possibil-ity of obtaining the benefits associated with them.Such benefits include improvement of gastrointesti-nal health and overall prevention of disease. Researchstudies show that Lb. acidophilus in the formula re-sults in the improvement of nutritional profile for ba-bies and protects them from diarrheal episodes andassists in lactose digestion. Further benefits of con-suming the culture include control of intestinal infec-tions in the very young and very old, cancer preven-tion, and enhanced competence of immune function(Chandan, 1999). For efficacy, desirable acidophiluslevel in yogurt should exceed one million CFU/gat consumption stage. Other lactobacilli occasion-ally found in yogurt are Lactobacillus reuteri andLb casei.

Bifidobacteria

Other probiotic cultures frequently found in yogurtare species of bifidobacteria (Fig. 12.5).

They are a group of Y-shaped anaerobic organisms.Some are tolerant to oxygen and can be successfullyused as adjunct cultures in yogurt. They are character-ized by the production of 2 moles of L (+) lactic acidand 3 moles of acetic acid from 2 moles of glucose.Commonly used bifidobacteria are: Bifidobacteriumbifidum, B. infantis, B. adolescentis, and B. breve.

Although the adjunct organisms do not play an es-sential role in yogurt manufacturing, the yogurt fer-mented with these organisms generally tends to tastemilder in terms of acidity and flavor. Also, their usecan be declared on the label and ingredient statementto provide possible marketing advantage, particularly


Figure 12.5. Bifidobacteria cells undermicroscope. 1,000 × magnification.

for consumers familiar with the benefits of probioticbacteria.

Inhibiting Factors

As given in Chapter 6, proper selection of ST andLB strains is necessary to achieve maximum sym-biosis between the two organisms. Certain abnor-mal milks (mastitic cows, hydrolytic rancidity inmilk) are inhibitory to their growth. Seasonal vari-ations in milk composition resulting in lower mi-cronutrients (trace elements, nonprotein nitrogenouscompounds) may affect starter performance. Natu-ral inhibitors secreted in milk (lactoperoxidase thio-cyanate system, agglutinins, lysozyme) are gener-ally destroyed by proper heat treatment and thereforedo not pose a problem. Antibiotics residues in milkand entry of sanitation chemicals (quaternary com-pounds, iodophors, hypochlorites, hydrogen perox-ide) have profound inhibitory effect on the growth ofyogurt starter.

Yogurt mixes designed for manufacture of refriger-ated or frozen yogurt may contain appreciable quan-tities of sucrose, high fructose corn syrup, dextrose,and various DE corn syrups. The sweeteners exert os-motic pressure in the system, leading to progressiveinhibition and decline in the rate of acid production bythe culture. Being a colligative property, the osmotic-based inhibitory effect would be directly proportionalto concentration of the sweetener and inversely re-lated to the molecular weight of the solute. In thisregard, solutes inherently present in milk solids-not-fat part of yogurt mix accruing from starting milkand added milk solids and whey products would also

contribute toward the total potential inhibitory effecton yogurt culture growth.

Phage infections and accompanying loss in the rateof acid production by lactic cultures results in flavorand texture defects, as well as major product lossesin fermented dairy products. Serious economic losseshave been attributed to phage attack. It is known thatspecific phages affect ST and LB, and that ST is rel-atively more susceptible than LB.

Yogurt fermentation process is relatively fast(3–4 hours using bulk starter and 5–6 hours using di-rect set starter cultures). It is improbable that both STand LB would be simultaneously attacked by phagesspecific for the two organisms. In the likelihood of aphage attack on ST, acid production may be carried onby LB, causing little or no interruption in productionschedule. However, it may affect the flavour charac-teristic. In fact, lytic phage may lyse ST cells spillingcellular contents in the medium, which could con-ceivably supply stimulants for LB growth. Also, theuse of mixed strain yogurt starter cultures minimizesthe risk of production failure from a single phage at-tack. This rationale may explain partially why the yo-gurt industry has experienced low incidence of phageproblems. Nonetheless, most commercial strains ofyogurt cultures have been phage typed. Specificphage sensitivity has been determined to facilitatestarter rotation procedures as a practical way to avoidphage threats in yogurt plants. If the plant begins toexperience longer fermentation times, the starter cul-ture can be pulled out of production and replaced witha new starter that has different phage sensitivity.

The ST phage is destroyed by heat treatment of74◦C for 23 seconds. This phage proliferates much


faster at pH 6.0 than at pH 6.5 or pH 7.0. Methodsused for phage detection include plaque assay, inhi-bition of acid production (litmus color change), en-zyme immunoassay, ATP assay by bioluminescence,changes in impedance, and conductance measure-ment.

Phage problem in yogurt plants cannot be ignored.Accordingly, adherence to strict sanitation proce-dures and attention to proper air quality would insureprevention of phage attack.

Commercial production of yogurt relies heavilyon fermentation ability and characteristics impartedby the starter. By controlling the culture strains andbalance, the acidity and flavor development of yogurtcan be optimized. Traditionally, the ratio between STand LB was maintained between 1:1 and 3:2 in thefinished yogurt. With current technology and today’smarket toward a more mild yogurt acid and flavor,the ratio is maintained to favor ST around 80–90%of the total yogurt culture.

In yogurt, the ratio of yogurt bacteria, productionof lactic acid and aroma compounds, and body char-acteristics can be controlled to some degree by thefollowing factors:

Yogurt Strain Selection

The culture suppliers deliver frozen or freeze driedforms of cultures containing one or more types of se-lected strains which exhibit discreet properties. Sev-eral characteristics should be considered in selectingthe strains which are best suited to meet the marketingobjectives.

1. Acid production during fermentation and pH sta-bility during shelf life of yogurt. At present, theUS consumer shows a preference for yogurt withmild acidity (pH 4.2–4.4). A culture with strongacid production usually leads to overacidificationduring cooling and storage including shelf life.It is recommended to select a culture with weakto medium acid production ability. The use ofmixed strain cultures with mild acid productionis particularly important during the long shelf life(6–7 weeks) of the product. In particular, it as-sumes even more importance during interruptionin the refrigeration chain starting from product de-livery to grocery market ending with consumer re-frigerated storage. The ability of acid productionby the culture can be ascertained by plotting anacid curve (pH drop versus time).

2. Flavor and aroma production. The best methodfor determining the sensory quality is anorganoleptic evaluation 24–48 hours after pack-aging and at the end of code. It is also customaryto check the pH/titratable acidity and viscosity ofthe stored samples.

3. Mucopolysaccharide production. There are sev-eral strains producing polysaccharide or slime/ropiness within both ST and LB. Production ofsome polysaccharide by the culture is sometimesdesirable to improve the consistency and viscosityof yogurt, particularly cup-set yogurt, yogurt withlow solids or a “natural” product produced with-out the use of stabilizers. Excess ropiness shouldbe avoided since it tends to mask flavor and aroma,and imparts slick mouth-feel and an undesirablestringy consistency. The intensity of polysaccha-ride production can be controlled from none toheavy. Also, the temperature of incubation affectsthe degree of polysaccharide production by theculture. Low incubation temperature appears toinduce polysaccharide production.

4. Proteolysis. Protein hydrolysis favorably affectsthe digestibility of proteins in yogurt, but is detri-mental to the consistency and taste. Certain strainsof LB to avoid are those which produce bitter pep-tides from casein as a result of extensive proteindegradation by proteolysis. ST exhibits very weakproteolysis in milk.

5. Sugar resistance. Depending on culture strain, thesensitivity of yogurt culture to sucrose concentra-tion varies between 5% and 12%. In general, mostcultures show significant inhibition at 8–10% su-crose concentration. However, there are special-ized cultures, which can ferment yogurt mixescontaining sucrose levels as high as 10–13% with-out a significant slow down in acid development.

Ratio of ST and LB in the Culture

Depending on the type or form of yogurt culture usedin yogurt manufacture, the ratio of its constituent bac-teria may be controlled to enhance flavor, acid level,and texture.

Fresh Bulk Starter. Since bulk starter is producedand controlled by the yogurt manufacturer, it is moreeasily subject to variability in the culture-strain ra-tio. The manufacturer must strive to maintain con-sistent fermentation temperature and rate of coolingat the end of fermentation with bulk starter to assure


consistent yogurt production. However, the benefitsthat are obtainable from exact control of the culture-strain ratio are more difficult to accomplish at thislevel. This is one reason that most yogurt manufac-turers use direct set starter cultures.

Frozen Concentrated Cultures. Using direct setfrozen concentrated cultures provides more consis-tent yogurt production because the culture manufac-turer controls the strain ratio. However, there are stillsome limitations to frozen mixed strain cultures dueto their inability to utilize single-strain culture pro-duction. They have limited ability to “customize” cul-tures and control of downward shift in post fermenta-tion pH; also they are unable to alter ratios of ST: LB,all of which have desirable effects on the final yogurt.Furthermore, they are sensitive to temperature abuseduring shipping and storage.

Freeze-dried or Pelletized cultures. This newertechnology has greatly enhanced the functional ben-efits of these direct set products. The use of directset freeze-dried cultures provides the best opportu-nity to control strain ratios to optimize yogurt quality.This process combines defined single-strain culturewith the blending of specific freeze dried or pelletizedstrains in precise ratios. The advantages consist of:

� Ability to obtain abnormal ratios of ST: LB (50:1to 100:1) to produce mild yogurt.

� Exact control of viscosity and mouth feel.� Exact control of tartness and flavor intensity.� Control of post-processing acidification.� Possibility of developing new value added

yogurts containing bifidobacteria andLactobacillus acidophilus.

� Better protection of multiple strains frombacteriophage attack.

� Provide customized strain blends for specificfunctionalities.

Incubation Time. In general, the longer the in-cubation time, the higher the numbers of LB andmore chances of postprocessing acidification. Ac-cordingly, caution must be exercised so that the LBdoes not produce too much lactic acid to make yogurtbitter and too sour.

Incubation Temperature. The optimum growthtemperature for LB is 40–50◦C and for ST, it is 35–40◦C. The incubation temperature for yogurt cultureranges from 31◦C to 45◦C. However, most yogurt

base is incubated at 41–43◦C. When time permits, itis possible to use a low temperature (32–37◦C) withbulk starter for the production of vat incubated Swiss-style or blended-type yogurt. The lower tempera-ture range produces a steady acid development anda slightly fuller body with fewer tendencies towardwheying off, grainy texture, and over-acidification.For the production of cup-set Sundae-style yogurtwith bulk starter, it is preferable to use a temperaturerange of 41–43◦C to provide efficient use of incu-bation room. At temperatures higher than 45◦C, thefinished product can experience more wheying-offproblems, harsher flavors, and a grainy texture due torapid acid development. This is because rapid acidi-fication leads to a very dense aggregation of the pro-tein particles with a corresponding decrease of boundwater. Also, higher temperature (>45◦C) favors thedifferential growth of LB resulting in undesirable cul-ture ratio and flavor. When using direct set cultures,most manufacturers recommend a temperature rangeof 41–42◦C to achieve the benefits of the specificculture ratio maintained by the supplier.

Composition of the mix. The total solids in themix including sucrose content should be taken intoaccount for selection of the culture.

Amount of bulk starter. The rate of inoculumchanges the ratio of ST: LB in the finished yogurt,as shown below (Table 12.4).

Addition of too high level of culture may cause adefect in the structure and in the aroma of the finishedyogurt. The optimum amount of bulk starter shouldbe about 1.0–2.0% and may be increased to 4–5% ifsugar content of the mix is high (10–11%).

Both incubation temperature and inoculation rateinfluence the structure and properties of yogurt gel.In general, the conditions favoring faster acid pro-duction (higher temperature and higher inoculationrate) tend to produce weak gel and more whey sepa-ration. It appears that weak yogurt gel and syneresis

Table 12.4. Effect of Inoculum Size of BulkStarter on the Ratio of ST and LB.

%Inoculum Ratio of ST/LBa

0.5 3:11.0 2:12.0 3:25.0 2:3

a incubation to 0.85% titratable acidity


are related to rearrangement of casein particles in thegel network and the rate of solubilization of colloidalcalcium during fermentation (Lee and Lucey, 2004).

Changes in Milk ConstituentsDuring Yogurt Production

Biochemical and Microbiological ChangesDuring Fermentation

Conversion of milk base to yogurt is accompaniedby intense metabolic activity of the fermenting or-ganisms ST and LB. Yogurt is a unique product inthat it supplies the consumer vital nutrients of milk,as well as metabolic products of fermentation alongwith abundant quantities of live and active yogurtcultures. As a result of culture growth, transforma-tion of chemical, physical, microbiological, sensory,nutritional, and physiological attributes in basic milkmedium is noted. Changes during fermentation areprofound and many are relevant to the health at-tributes of yogurt.

Carbohydrate. Lactose content of yogurt mix isgenerally around 6%. During fermentation lactose isthe primary carbon source resulting in approximately30% reduction. However, a significant level of lac-tose (4.2%) remains unutilized. One mole of lactosegives rise to 1 mole of galactose, two moles of lacticacid, and energy for bacterial growth. Some strains ofST exhibit both �-galactosidase and phospho �-D-galactosidase activity. Therefore, these strains alsouse a phospho-enolypyruvate-phospho transferasesystem. Lactose is converted to lactose phosphate,which is hydrolyzed by phospho �-D-galactosidaseto galactose-6-phosphate and glucose and that on gly-colysis gives lactic acid (Chapter 6). Although lac-tose content is in excess in the fermentation medium,lactic acid build-up beyond 1.5% acts progressivelyas an inhibitor for further growth of yogurt bacte-ria. Normally, the fermentation period is terminatedby temperature drop to 4◦C. At this temperature, theculture is alive but its activity is drastically limited toallow fairly controlled flavor in marketing channels.

Lactic acid produced by ST is L (+) isomer, whichphysiologically is more digestible than the D (−) iso-mer produced by LB. It seems that the kidneys ofsmall infants are not capable of handling D (−) lac-tic acid. Yogurt contains both isomers. The L (+)isomer is normally 50–70% of the total lactic acid.Normal consumption level of yogurt does not posehazard from D (−) lactic acid, but relatively large

doses have been implicated in toxicity problems insmall infants.

Lactic acid production results in coagulation ofmilk beginning at pH 5.2–5.3, at the point where thecasein is first destabilized, and continues until com-pletion at pH 4.6. During lactic acid production, thereis a gradual removal of phosphorus and calcium thatis bound to the stable casein particle as tricalciumphosphate. Texture, body, and acid flavor of yogurtowe their origin to lactic acid produced during fer-mentation.

Small quantities of organoleptic moieties are gen-erated through carbohydrate catabolism, via volatilefatty acids, ethanol, acetoin, acetic acid, butanone, di-acetyl, and acetaldehyde. (See Chapter 6). Homolac-tic fermentation in yogurt yields lactic acid as 95% ofthe fermentation output. Lactic acid acts as a preser-vative.

Proteins. Aggregation of whey proteins in yogurthas been observed (Argyle et al., 1976a,b), whichcontributes to the consistency of yogurt during stor-age. Hydrolysis of milk proteins is easily measuredby liberation of −NH2 groups during fermentation.LB displays appreciable proteolytic activity in milk(Argyle et al., 1976a,b; Chandan et al., 1982). Inhis review, Loones (1989) reported that free aminogroups double in yogurt after 24 hours. The proteoly-sis continues during the shelf life of yogurt, doublingfree amino group again in 21 days storage at 7◦C. Themajor amino acids liberated are proline and glycine.The essential amino acids liberated increase 3.8–3.9fold during the storage of yogurt, indicating that vari-ous proteolytic enzymes and peptidases remain activethroughout the shelf life of yogurt. The proteolyticactivity of the two yogurt bacteria is moderate but isquite significant in relation to the symbiotic growthof the culture and production of flavor compounds.

Lipids. A weak lipase activity results in the lib-eration of minor amounts of free fatty acids, par-ticularly stearic and oleic acids. Individual esterasesand lipases of yogurt bacteria appear to be more ac-tive toward short-chain fatty acid glycerides than to-ward long-chain substrates (DeMoraes and Chandan,1982). Since nonfat and low fat yogurts comprisethe majority of yogurt marketed in the United States,lipid hydrolysis contributes little to the product at-tributes.

Formation of Yogurt Flavor Compounds. Lac-tic acid, acetaldehyde, acetone, diacetyl, and other


carbonyl compounds produced by fermentation con-stitute key flavor compounds of yogurt. Acetalde-hyde content varies from 4 to 60 ppm in yogurt. Di-acetyl varies from 0.1 to 0.3 ppm and acetic acidvaries from 50 to 200 ppm. These key compoundsare produced by yogurt bacteria. Certain amino acids(threonine, methionine) are known precursors of ac-etaldehyde. For example, threonine in the presenceof threonine aldolase yields glycine and acetalde-hyde. Acetaldehyde can arise from glucose, via acetylCoA or from nucleic acids, via thymidine of DNA.Diacetyl and acetoin are metabolic products of car-bohydrate metabolism in ST. Acetone and butane-2-one may develop in milk during prefermentationprocessing.

Several compounds contribute to yogurt aroma(Marsili, 2003). They include acetaldehyde,dimethyl sulfide, 2,3-butanedione, 2,3-pentanedione,2-methylthiophene, 3-methyl-2-butenal, 1-octen-3-one, dimethyl trisulfide, 1-nonen-3-one, acetic acid,methional, (cis,cis)-nonenal, 2-methyl tetrahydro-thiophen-3-one, 2-phenyacetaldehyde, 3-methyl-butyric acid, caproic acid, guaiacol, benzothiozoleand more.

Synthesis of Oligosaccharides and Polysaccha-rids. Both ST and LB are documented in the lit-erature to elaborate different oligosaccharides in theyogurt-mix medium. As much as 0.2% (by weight) ofmucopolysaccharides has been observed in 10 daysof storage period. In stirred yogurt, drinking yo-gurt, and reduced-fat yogurt, potential contributionof exo-polysaccharides to impart smooth texture,higher viscosity, lower synerisis, and better mechan-ical handling is possible. Excessive shear duringpumping destroys much of the textural advantage be-cause the viscosity-imparting function of the muco-polysaccharides is not shear resistant. Most of thepolysaccharides elaborated in yogurt contain glu-cose, galactose along with minor quantities of fruc-tose, mannose, rhamnose, xylose, arabinose, or N-acetylgalactosamine, individually or in combination.Molecular weight is of the order of 0.5–1 millionDaltons. Intrinsic viscosity range of 1.5–4.7 dl g−1

has been reported for exo-polysaccharides of ST andLB (Zourari et al., 1992). The polysaccharides form anetwork of filaments visible under the scanning elec-tron microscope. The bacterial cells are covered bypart of the polysaccharide and the filaments bind thecells and milk proteins. Upon shear treatment, the fil-aments rupture off from the cells, but maintain linkswith casein micelles. Ropy strains of ST and LB are

commercially available. They are especially appro-priate for stirred yogurt production.

It is conceivable that some of the exo-polysaccharides exert physiological role in humannutrition because of their chemical structure resem-bling dietary fiber.

Other Metabolites. Bacteriocins and several otherantimicrobial compounds are generated by yogurt or-ganisms. A bacteriocin called bulgarican is elabo-rated by LB that has been shown to possess antago-nistic property toward the growth of several spoilagebacteria (Reddy et al., 1984). Similarly, Lb. aci-dophilus produces acidophilin, which is shown toexhibit a wide spectrum activity against both Gram-positive and Gram-negative bacteria (Shahani et al.,1972). Benzoic acid (15–30 ppm) in yogurt has beendetected, which is associated with metabolic activityof the culture (Chandan et al., 1977). These metabo-lites tend to exert preservative effect by controllingthe growth of contaminating spoilage and pathogenicorganisms gaining postfermentation entry. As a re-sult, the product attains extension of shelf life andreasonable degree of safety from food borne illness.

Cell Mass. As a consequence of fermentation, yo-gurt organisms multiply to a count of 108 to 1010

CFU g−1. Yogurt bacteria occupy some 1% of vol-ume or mass of yogurt. These cells contain cell walls,enzymes, nucleic acids, cellular proteins, lipids, andcarbohydrates. Lactase or �-galactosidase has beenshown to contribute a major health-related property toyogurt. Clinical studies have concluded that live andactive culture containing yogurt can be consumed byseveral millions of lactose-deficient individuals with-out developing gastrointestinal distress or diarrhea.

Minerals. Yogurt is an excellent dietary source ofcalcium, phosphorus, magnesium, and zinc in humannutrition. Research has shown that bioavailability ofthe minerals from yogurt is essentially equal to thatfrom milk. Since yogurt is a low-pH product com-pared to milk, most of calcium and magnesium oc-curs in ionic form.

The complete conversion from colloidal form inmilk to ionic form in yogurt may have some bearingon the physiological efficiency of utilization of theminerals.

Vitamins. Yogurt bacteria during and after fer-mentation affect the B-vitamin content of yogurt.The processing parameters and subsequent storage


conditions influence the vitamin content at the timeof consumption of the products. Incubation temper-ature and fermentation time exert significant balancebetween vitamin synthesis and utilization by the cul-ture. In general, there is a decrease of vitamin B12,biotin, and pantothenic acid and an increase of folicacid during yogurt production. Nevertheless, yogurtis still an excellent source of vitamins inherent tomilk.

Postfermentation Changes

These changes refer to the shelf life period of yogurtfollowing manufacture.

Refrigerated Yogurt and Drinkables. The chaincomprised of distribution, marketing, and retail lead-ing to eventual consumption of product by theconsumer may require 4–7 weeks of shelf life. Nu-tritional quality is reasonably preserved by tempera-tures of 4–6◦C in this chain. Maintenance of productintegrity by appropriate packaging is achieved. How-ever, a slight increase in acidity (of the order of 0.2%)is noticeable during this period. Viability of the yo-gurt culture is also slightly reduced by one log cycle.These changes are relatively minor compared to thechanges observed during fermentation.

Soft Serve Mix and Soft Serve Yogurt. Soft servemix may be marketed refrigerated or frozen until dis-pensed as soft serve frozen yogurt by the operator.If marketed refrigerated, changes similar to those inrefrigerated yogurt are projected in the mix until ex-trusion through the soft serve freezer. If marketedfrozen, the mix has to be thawed prior to extrusion.A loss of 1–2 log cycles in viable cell counts of yo-gurt culture may be noticed by the freeze-thaw cycle.Furthermore, destruction of cell viability is possibleduring the freezing process through the soft servefreezer. Other than viable cell counts, no significantchanges are known.

Hard Pack Frozen Yogurt. Shelf-life require-ments of 6–12 months are normal for this type ofyogurt. A loss of 1–2 log cycles in viable counts ofyogurt bacteria may be attributed to the freezing pro-cess of the mix. During the shelf-life storage con-ditions, especially fluctuation in temperatures couldhave a deleterious effect on the viability and activityof yogurt cultures. The formation of crystals duringfrozen state conceivably may rupture bacterial cells,reducing live cell counts progressively.

REFERENCESArgyle P, Jones N, Chandan RC, Gordon JF. 1976a.

Aggregation of whey proteins during storage ofacidified milks. J. Dairy Research, 43:45–51.

Argyle P, Mathison GE, Chandan RC. 1976b.Production of cell-bound proteinase byLactobacillus bulgaricus and its location in thebacterial cell. J. App. Bact. 41:175–184.

Chandan RC (Ed). 1989. Yogurt: Nutritional andHealth Properties. National Yogurt Association,McLean, VA.

Chandan RC. 1997. Dairy-Based Ingredients. EaganPress, St. Paul, Minnesota, MN.


Chandan RC. 2002. Symposium: Benefits of livefermented milks: Present diversity of products. In:Proceedings of International Dairy Congress, Paris,France [Available in CD Rom].

Chandan RC. 2004. Dairy: Yogurt. In: JS Smith, YHHui (Eds), Food Processing: Principles andApplications. Blackwell Publishing, Ames, IA.pp. 297–328.

Chandan RC, Argyle PJ, Mathison GE. 1982. Actionof Lactobacillus bulgaricus protease preparations onmilk proteins. J.Dairy Sci. 65:1408–1413.

Chandan RC, Gordon JF, Morrison A. 1977. Naturalbenzoate content of dairy products.Milchwissenschaft 32(9):534–527.

Chandan RC, Shahani KM. 1993. Yogurt. In: YH Hui(Ed), Dairy Science and Technology Handbook, Vol.2. VCH Publishers, New York, pp. 1–56.

Chandan RC, Shahani KM. 1995. Other fermenteddairy products. In: G Reed, TW Nagodawithana(Ed), Biotechnology, 2nd ed., Vol. 9, VCHPublishers, Weinheim, Germany, pp. 386–418.

DeMoraes J, Chandan RC. 1982. Factors influencingthe production and activity of Sterptococcusthermophilus lipase. J. Food Sci. 47:1579–1583.


International Dairy Federation. 2003. Yogurt:Enumeration of Characteristic Organisms-ColonyCount Technique at 37 C. IDF Standard No. 117A,Brussels, Belgium.

Lee WJ, Lucey JA. 2004. Structure and physicalproperties of yogurt gels: Effect of inoculation rateand incubation temperature. J. Dairy Sci.87:3153–3164.

Loones A. 1989. Transformation of milk componentsduring yogurt fermentation. In: RC Chandan (Ed),


Yogurt: Nutritional and Health Properties. NationalYogurt Association, McLean, VA, pp.95–114.

Marsili R. 2003. Flavors and off-flavors in dairyproducts. In: H Roginski, JW Fuquay, PF Fox (Eds),Encyclopedia of Dairy Sciences,. Vol. 2. AcademicPress, New York, pp. 1069–1081.

Nauth KR. 2004. Yogurt. In: YH Hui, LMeunier-Goddik, AS Hansen, J Josephsen, W-KNip, PS Stanfield, F Toldra (Eds), Handbook ofFood and Beverage Fermentation Technology.Marcell Decker, New York, pp. 125–145.

Reddy G, Shahani KM, Friend BA, Chandan RC.1984. Natural antibiotic activity of Lactobacillusacidophilus and bulgaricus III. Production andPartial Purification of Bulgarican from Lactobacillusbulgaricus. Cultured Dairy Prod. J. 19(5):7–11.

Robinson RK. 2003a. Yogurt types and manufacture.In: H Roginski, JW Fuquay, PF Fox (Eds),Encyclopedia of Dairy Sciences, Vol. 2. AcademicPress, New York, pp. 1055–1058.

Robinson RK. 2003b. Yogurt, role of yogurt cultures.In: H Roginski, JW Fuquay, PF Fox (Eds),Encyclopedia of Dairy Sciences, Vol. 2. AcademicPress, New York, pp. 1059–101063.

Sellars RL. 1989. Health properties of yogurt. In: RCChandan (Ed), Yogurt: Nutritional and Health

Properties. National Yogurt Association, McLean,VA, pp. 115–144.

Shah N. 2003. Yogurt: The product and manufacture.In: B Caballero, L Truco, PM Finglas (Eds),Encyclopedia of Food Sciences and Nutrition,Vol. 10, 2nd ed. Academic Press, New York,pp. 6252–6259.

Shahani KM, Vakil JR, Chandan RC. September 5,1972. Antibiotic acidophilin and process forpreparing the same. United States Patent 3,689,640.

Surono I, Hosono A. 2003. Starter cultures.In: H Roginski, JW Fuquay, PF Fox (Eds),Encyclopedia of Dairy Sciences, Vol. 2. AcademicPress, New York, pp. 101023–101028.

Takano T, Yamamoto N. 2003. Health aspects offermented milks. In: H Roginski, JW Fuquay,PF Fox (Eds), Encyclopedia of Dairy Sciences,Vol. 2. Academic Press, New York, pp. 1063–1069.

Vedamuthu ER. 1991. The yogurt story—past, presentand future. Dairy, Food Environ. Sanit. 11:202–203,265–276, 371–374, 513–514.

Zourari A, Accolas J-P, Desmazeaud MJ. 1992.Metabolism and biochemical characteristics ofyogurt bacteria: A review. Le Lait. 72(1):1–34.

13Manufacture of Various

Types of YogurtRamesh C. Chandan and Kevin R. O’Rell

IntroductionGeneral Procedures Applicable to All Categories

Packaging Equipment and MaterialsProduction of Yogurt Starters

Yogurt Styles and DefinitionsMarket Statistics on Yogurt TradeManufacturing Processes for Major Types of YogurtGeneral Manufacturing Procedures

Plain YogurtFruit-Flavored YogurtVanilla-Flavored YogurtNatural YogurtOrganic YogurtYogurt Drink/SmoothiesYogurt Whips/MousseConcentrated/Greek-Style/Strained YogurtFrozen Yogurt

Postculturing Heat TreatmentAcknowledgmentReferencesBibliography

INTRODUCTIONThe yogurt market is highly sophisticated, complex,and diverse. The evolution of the yogurt markethas been dictated by market forces and consumerdemands. Different types or styles or categories(and subgroups) of yogurt have entered the market-place in response to consumer preference, changinglifestyles, and dietary adjustments. The first majorchange in the yogurt market was the entry of “flavoredyogurts.” Under this category different styles wereintroduced. This was followed by subcategories thatoffered dietary choices, for example, full-fat, low-fat, and fat-free types. Changing lifestyles gave riseto liquid yogurts and “snacking types” and “on-the-go tubular types.” The emphasis on “healthy” and

“natural” foods gave rise to entirely specializedgroups of products. These products will be discussedin this chapter.

The topics included in this chapter will be dis-cussed under the following headings: (a) Generalmanufacturing procedures applicable to all cate-gories, (b) yogurt types, styles, subcategories, anddefinitions, (c) market statistics on yogurt trade,and (d) manufacturing process for major yogurtcategories.

GENERAL PROCEDURESAPPLICABLE TO ALLCATEGORIESAs discussed in Chapter 3, in the United States, a yo-gurt plant must be a Grade A milk processing facility.All the equipment must conform to Grade A regula-tions for processing (FDA, 1999). The equipment fortransportation, handling, and storage must be madeof nontoxic, smooth, nonabsorbent, and corrosion-resistant materials. The construction of the process-ing equipment such as tanks, pumps, valves, heat ex-changers, piping, and others must be designed forcleaning in place (CIP) and sterilization. Grade Amilk and cream must be stored at 4◦C in vertical/silotanks for a period not to exceed 72 hours. The stor-age vessels must be equipped with agitators for slowagitation to prevent the separation of cream. Onemore legal requirement is the provision for accuratetemperature-indicating thermometers and an appro-priate recording system with charts.

Packaging Equipment and Materials

Most plants attempt to synchronize the packaginglines with the termination of the incubation period.

211




Generally, textural defects in yogurt products arecaused by excessive shear during pumping or agi-tation. Therefore, positive drive pumps are preferredover centrifugal pumps for moving the product afterculturing or ripening. For adding fruit to the product,it is advantageous to use a fruit feeder system. Vari-ous packaging machines of suitable speeds (up to 400cups/minute) are available to package various kindsand sizes of yogurt products. More details of pack-aging materials and containers for yogurt are givenin Chapter 8.

Yogurt is generally packaged in plastic containersvarying in size from 4 to 32 oz. Yogurt packaged intubes weighs even less per tube (2 to 3 oz). The ma-chines involve volumetric piston filling. The productis sold by weight and the machines delivering vol-umetric measure are standardized accordingly. Thepumping step of fermented and flavored yogurt baseexerts some shear on the body of yogurt. In somecases, specific shape of the cup characterizes certainproduct branding. Some plants use preformed cups.The cup may be formed by injection molding—aprocess in which beads of plastic are injected intoa mold at high temperature and pressure. In this typeof packaging, a die-cut foil lid is heat sealed on tothe cups. Foil lids are cut into circles and procuredby the plants from a supplier along with preformedcups. A plastic over-cap may be used. In some cases,partially formed cups are procured and assembled atthe plant. Some other plants use roll stock, which isused in form–fill–seal system of packaging. In thiscase, cups are fabricated in the plant by a processcalled thermoforming. This involves ramming a pluginto a sheet of heated plastic. Multipacks of yogurtare produced by this process. Following the forma-tion of cups, these are filled with appropriate volumeof yogurt and are heat-sealed with foil lid. These arethen placed in cases and transferred to a refrigeratedroom for cooling and distribution. For breakfast yo-gurt, a mixture of granola, nuts, chocolate bits, dryfruits, and cereal is packaged in a small cup and sealedwith a foil. Subsequently, the cereal cup in invertedand sealed on the top of yogurt cup. This package isdesigned to keep the ingredients isolated from yogurtuntil the time of consumption. This system helps tomaintain crispness in cereals and nuts, which oth-erwise would become soggy or interact adverselyif mixed with yogurt at the plant level, i.e., duringpackaging.

Some interesting innovations in yogurt packaginginclude spoon-in-the-cup lid and squeezable tubes.The former adds convenience in eating yogurt, while

the squeezable tubes add convenience, portability,and play value to children. In addition, yogurt in tubesis freeze–thaw stable, which adds another dimensionof convenience and versatility of its use.

Production of Yogurt Starters

The first step in the manufacture of yogurt is thepreparation of starter. The same procedures for starterpreparation are used regardless of the type or style ofyogurt being produced in the plant.

The starter is a crucial component in the produc-tion of high quality yogurt delivering consistent qual-ity attributes desired by consumers. The movementof personnel assigned to starter room and traffic be-tween the starter room and the rest of production areashould be strictly restricted. An effective sanitationprogram including filtered air and positive pressure inthe culture and fermentation area should significantlycontrol airborne contamination. The result would becontrolled fermentation time and consistently high-quality product (Chandan, 2004; Chandan and Sha-hani, 1993).

As discussed in Chapters 6 and 11, yogurt culturesare available from various culture suppliers as frozenconcentrates or freeze-dried concentrates for directinoculation into fermentation tanks. These offer con-venience of use and reliability of performance andfunctionality of the culture. However, for economicreasons, large manufacturers of yogurt may prefer tomake their own bulk starters.

The characterizing culture for yogurt manufac-ture consists of Lactobacillus delbrueckii subsp. bul-garicus (LB) and Streptococcus thermophilus (ST).Frozen/freeze-dried culture concentrates availablefrom commercial culture suppliers can be used fordirect inoculation into yogurt mix or making bulkstarters. Reasons for their use include convenience,ease of handling, dependable quality, and reliable ac-tivity. The frozen concentrates are shipped frozen indry ice and stored at the plant in special freezers at−40◦C or below for a limited period of time specifiedby the culture supplier. Presently, the freeze-driedconcentrates are preferred by many yogurt manufac-turers because these can be stored in a refrigerator(freezer) and do not require dry ice for shipping.

The starter area is segregated in most yogurt plantsfor maintaining a sanitary environment. It shouldhave positive pressure and HEPA-filtered (capturingparticles larger than 0.3 �m) air supply to preventpossible contamination from airborne bacteria andbacteriophages.

13 Manufacture of Various Types of Yogurt 213

Funnel

VAT

Valve Pump

Water

Dry milk

Figure 13.1. Equipment set up forreconstitution of nonfat dry milk (NFDM)using a “powder cone”/funnel/hopper.The vat on the right contains measuredvolume of water. The weighed NFDM isdeposited in the cone and the valve onthe vat is opened. The pump on the leftcirculates the reconstituted milk until allthe dry milk is dispersed.

For making bulk starter, Grade A skim milk is used.In most yogurt plants, it is Grade A, antibiotic-free,low-heat nonfat dry milk (NFDM). The dry milk isreconstituted in water and contains 9–12% solids.Mainly, two types of equipment are used for recon-stitution. One is cone/funnel/hopper type of set up(see Fig. 13.1). The other type of equipment is a highshear blender in which all the ingredients are weighedin and blended together (Fig. 13.2).

The practice of using fresh skim milk or pretestedreconstituted NFDM reduces the risk of off-flavorsbeing transferred to the finished yogurt from untestedor held-over milk used for making starter. Pretestingfor the absence of inhibitory principles (antibiotics,sanitizers) is also advisable to insure desirable growthof the starter in the medium. Another quality attributepreferred with the NFDM for starter preparation islow-heat powder with not less than 6.0 mg of wheyprotein nitrogen/g of powder (Chapters 10 and 11).

The starter medium is never fortified with growthactivators like yeast extract, beef extract, or proteinhydrolysates because they tend to impart undesirableflavor to the starter, which would be carried over toyogurt. Additionally, kosher requirements would pre-clude the use of such ingredients. Bulk starter is usu-ally made in specially designed aseptic tanks.

Figure 13.3 outlines the process for making bulkstarters. Following addition of fresh skim milk orreconstitution of NFDM in water in the tank, themedium is heated to 90–95◦C and held for 30–60 minutes. Such a heat treatment improves thegrowth properties of the medium by destroyingoriginal microorganisms and bacteriophages, and

facilitates the denaturation of the milk proteins andexpulsion of dissolved oxygen. The medium is thencooled in the tank to the inoculation temperature,42–43◦C. During cooling, the air drawn into the vatshould be free of airborne contaminants (phages, bac-teria, and yeast and mold spores). Accordingly, useof proper filters (e.g. HEPA) on the tanks to filter-sterilize incoming air is desirable.

The next step is inoculation of frozen orlyophilized (freeze-dried) culture concentrate (Fig.13.4). Instruction for handling the culture concentrateas prescribed by the supplier should be followed care-fully. When using the frozen culture concentrate, thecan is thawed by placing it in cold or lukewarm watercontaining a low level of sanitizer, preferably chlorine(quaternary ammonium compounds have a residualeffect), until the contents are partially thawed. Theculture cans are emptied into the starter vat as asepti-cally as possible and bulk starter medium is agitatedsufficiently to facilitate mixing and achieving uni-form dispersion of the culture. For freeze-dried cul-ture, the contents of the container are emptied intothe medium taking due precautions not to introducecontamination from improper handling, followed bysufficient agitation time, usually 20–30 minutes, as-suring proper dispersion of the culture.

Incubation period for yogurt bulk starter rangesfrom 4 to 6 hours and the proper temperature of 42–43◦C is maintained by holding hot water in the jacketof the tank. The fermentation must be quiescent(i.e., lack of agitation and vibrations) to avoid phaseseparation in the starter following incubation. Theprogress of fermentation is monitored by titratable


Figure 13.2. High shear mixer for blending dry milkand water. Courtesy: Tetra Pak.

acidity/pH measurements at regular intervals. Whenthe titratable acidity is 0.85–0.90% (or the pH is4.4–4.5), the fermentation is terminated by turningthe agitators on and replacing warm water in thejacket with chilled water. If the culture is going tobe used within next 4–6 hours, circulating chilledwater is used to drop the temperature of the starterto 10–12◦C. If the starter will not be used withinnext 6 hours, it is advisable to drop the temperatureto 4–5◦C. The starter is now ready to use. Occa-sionally, a microscopic examination of the culture

smear (stained with methylene blue dye) is helpful indetermining the physiological condition of the starterbacteria by observing the cell morphology as well asthe ST/LB ratio. In the earlier literature, a ratio of 1:1was considered desirable, but more recent trend is infavor of ST predomination (66–80%). An organolep-tic examination is also helpful to detect any unwantedflavors in the starter.

YOGURT STYLES ANDDEFINITIONSTo assist in the understanding of various types of yo-gurt available in the market, Fig. 13.5 shows classifi-cation of the yogurt category. We will discuss theirmanufacture later. All types of yogurts may be label-ed nonfat, low fat, or full fat, depending on the milk fatcontent of yogurt mix. Further, they may be preparedfor consumption by toddlers, children, or adults.

Table 13.1 lists various types of yogurt found inthe market in North America and Europe.

MARKET STATISTICS ONYOGURT TRADEIn the United States, the sale of refrigerated yo-gurt category in 2004 is $2.7 billion and is grow-ing. Its sales are up by 6% compared to that in 2003.Blended/Swiss style and single-serve product formsare the primary product types. The blended styleconstitutes 74% of the category, while fruit-on-the-bottom (FOB) style has shrunk to 8%. Drinkable yo-gurts form 12% of the market, whereas plain andyogurt with toppings constitute 5% and 1%, respec-tively. Compared to the previous year, the blendedyogurt, plain, and drinkables grew by 1%, 5.7%, and97.1%, respectively. The category decline was 13.6%in FOB and 3.9% in yogurt with toppings, respec-tively. The yogurt market is dominated by flavoredvarieties and plain yogurt is only a fraction of theyogurt sold. Among the flavored varieties, 10 flavorsaccount for 70% of the category volume.

Organic/natural yogurt experienced dramaticgrowth accounting for 22% sales increase in yogurtsold in regular grocery stores and 17% increase innatural yogurt sold in natural food grocery stores. Inthe refrigerated yogurt category based on packaging,the single serve package accounts for 62% with 2.8%growth over previous year. Multipacks are gaining inpopularity and have 20% share of the market with agrowth of 21.3% over the previous year. Large multi-serve packs have 10% of the market and have grown


Reconstitute and standardize to 10–12%solids non-fat. Batch pasteurize at 90˚Cfor 30-60 Minutes, Cool to 43˚C andadd yogurt culture. Incubate to pH 4.4–4.5. Agitate and cool to 4–5˚C

Frozen/lyophlizedYogurt culture

(add post pasteurization )

Grade A low-heatNFDM

Batch tank

Pumped to pasteurized unculturedstandardized yogurt base tanks

Figure 13.3. Preparation of bulk starter in yogurt plant.

Figure 13.4. Inoculation of freeze-driedculture concentrate during starter preparation.Courtesy: Tetra Pak.

7% over the previous year. Multipack tube market is8% and its share has declined 1.8% as compared toprevious year.

The total U.S. market for yogurt may be dividedinto three categories based on the fat content: non-fat, low fat, and full fat. All types of yogurt (Table13.1) are divided into one of these categories basedon milk fat content and the code of federal regulationsstandard of identity Title 21, Parts 131.200–131.206(FDA, 2003). In the year 2004, the estimated sales ofall types of full fat yogurt were $262.1 million (in-crease of 1.7% as compared to 2003), the low fat yo-gurt sales were $1,506.2 million (increase of 3.9%),and the fat-free/nonfat sales were $901.3 million (in-crease of 10.9%) (see Table 13.2).

Nonfat yogurt is available as plain, sugar sweet-ened with vanilla or with fruit preparations or withfruit flavor only. A significant share of nonfat yogurtis light yogurt, which is sweetened with aspartameand/or other high-intensity sweeteners.

The market share of full fat, low fat, and nonfatin all styles of yogurt is illustrated in Fig. 13.6. Fullfat yogurt has declined from 30% in 1985 to 10% in2004, whereas in the same period, low fat yogurt de-clined from 66% to 56% and nonfat yogurt increasedfrom 4% to 34%.

Figure 13.7 shows recent trend in full fat, low fat,and nonfat yogurt with respect to plain, blended, andFOB styles. At present, the blended/Swiss-style yo-gurt in the market consists of 11% full fat, 56% lowfat, and 33% fat-free. The corresponding data forFOB yogurt type is 2% full fat, 86% low fat, and


Yogurt

Fruit flavored

Vanilla

Natural

Organic

Drinks/ Smoothies

Whips/ Mousse

Concentrated

Frozen

Blended/ Stirred

Swiss

Fruit on- the-bottom

Traditional cup

Western style

French

Custard

Figure 13.5. Classification ofvarious types of yogurt.

12% fat-free; while for plain yogurt it is 19% full fat,31% low fat, and 50% is fat-free.

Lately, an extra-creamy yogurt has been intro-duced in the market. It contains fat content of theorder of 4.0–4.5%, but would still be characterizedas full fat yogurt by US Federal standards and mar-ket data tracking. This type of yogurt is characterizedby its mild and creamy taste. Also available in the

market are whipped yogurts, which are full fat yo-gurts with a mild and sweet flavor and a foamy/fluffytexture. Several yogurts are designed for children.The attributes preferred by children (darker colors,enhanced sweetness, fruit purees without fruit in-tegrity, thicker custard-like consistency) are built intosuch products. Yogurt drinks and smoothies are gain-ing market growth (Fig. 13.8).

Table 13.1. Major Styles of Commercial Yogurts and Their Definition

Style of Yogurt Definition

Plain Unflavored yogurt may be cultured in individual cups or cultured in avat and dispensed into cups. No sugar is added to the formulation.

Fruit flavored This type of yogurt is cultured in a vat or bulk and then flavored with afruit preparation. Styles consist of blended/stirred and fruit-on-thebottom.

Blended/stirred In this style, fermented base containing sugar is blended with fruitpreparation to disperse the fruit throughout the body of the yogurt.This style is further subdivided into Swiss- and French-styleblended yogurt.

Swiss/blended The fermented base is blended with fruit preparation to disperse thefruit throughout and packaged. On cooling, the product thickens andviscous custard-like texture is formed. The product containsstabilizers to assist in texture formation.

French/blended Similar to Swiss style, but is characterized by a distinctly less viscoustexture. Generally contains no stabilizers other than milk solids.

Light Nonfat yogurt in which no sugar is added to yogurt base and highintensity sweeteners are used, resulting in significant reduction incalories.

Lo carb Nonfat yogurt in which high intensity sweeteners are used in place ofsugar. Fruit preparations are replaced with fruit flavors. Lactosecontent of nonfat milk is reduced by membrane processing. Milkprotein concentrate and whey protein isolate are used to reduce thelactose content further.

Custard Designed for children. It has a very viscous body resembling custard.Only fruit puree/juice is used for fruit flavoring. Usually, fermentedin the cup.

Sundae/fruit-on-the-bottom The fruit is deposited on the bottom of the cup, followed by a top layerof unfermented or fermented yogurt. Before consumption it requiresblending to mix the fruit preparation.

Cup-incubated traditional sundae The fruit is layered in the bottom of the cup and unfermented(inoculated) yogurt mix is deposited on the top. The cups areincubated individually to desired pH and cooled quickly to controlfurther acid production.

Vat-incubated sundae The fruit is layered in the bottom of the cup and white fermentedyogurt base is deposited on the top. On cooling, the texture of thetop layer is developed.

Western sundae The fruit is layered on the bottom of the cup, and yogurt basefermented in vat is deposited on the top. It is characterized byspecial formulation of yogurt base in that corresponding color andflavor of the fruit-on-the-bottom is included in the top layer.

Vanilla flavored The yogurt may be cup- or vat-incubated. Following fermentation,yogurt base is mixed with vanilla flavor.

“Natural” Contains natural ingredients only. Generally, it does not containstabilizers, artificial colors, or flavors.

Organic Contains only ingredients certified as organic.Yogurt drink/smoothie Drinkable yogurt is fluid enough to drink. May be sweet and fruit

flavored. Smoothies are drinking yogurt, often fortified withminerals and vitamins, prebiotics and probiotics. Some may bedesigned as a meal replacement.

Continued

217

Table 13.1. (Continued)

Style of Yogurt Definition

Whips/mousse This yogurt contains up to 50% (by volume) of inert gas/air to create afluffy/light texture.

Yogurt with topping Sweetened fermented base is packaged separately in a cup and sealed.Topping consisting of cereals, nuts, or fruits and is packaged in asmaller cup and sealed. Then the smaller cup is inverted and placedon the larger yogurt cup. The two cups are tied together by plasticwrap. The consumer mixes the toppings prior to consumption.

Concentrated/Greek/strained It is relatively high in milk fat and milk solids-not-fat. It has a creamytexture and mild flavor as a result of whey removal bycentrifugal/membrane separation or by straining through cloth.

Frozen The fermented yogurt is blended with low fat/nonfat ice cream toobtain pH of 6.0. The yogurt mix is then extruded through a softserve machine at 50% overrun and garnished with nuts and otherfoods to get soft serve frozen yogurt. If the extruded frozen yogurt ishardened like ice cream, it is called hard frozen yogurt.

Table 13.2. Estimated Sales of Full Fat, Low Fat, and Nonfat Yogurts in the Overall United StatesRefrigerated Yogurt Market During 2004

Type of Yogurt

Full Fat Low Fat Fat-Free

Salesa 262.1 1,506.2 901.3Changeb +1.7% +3.9% +10.9%

a Million dollars.b Against year 2003.

30%

18%13%

10%

4%

10%

66%

72%

51%50% 52%56%

4%

10%

36%40%

44%

34%

0%

10%

20%

30%

40%

50%

60%

70%

80%

1980 1985 1990 1995 2000 2005

Year

% S

har

e of

mar

ket

Full fat yogurtLow fat yogurtNonfat yogurt

Figure 13.6. Recent trends in the U.S. market for full fat, low fat, and nonfat yogurts.

218

19

11

2

31

57

86

50

32

12

0

10

20

30

40

50

60

70

80

90

100

Plain Blended FOB

Style of yogurt

% M

ark

et s

har

e

Full fat

Low fat

Nonfat

Figure 13.7. Current market share of major styles of full fat, low fat, and nonfat yogurts with respect to plain,blended, and fruit-on-the-bottom varieties in the United States.

17.8

63.3

96.5

131.2

268.7

0

50

100

150

200

250

300

1998 1999 2000 2001 2002 2003 2004

Year

Sales, million $

Figure 13.8. Recent trend in the sales of yogurt drinks.

219


MANUFACTURING PROCESSESFOR MAJOR TYPES OF YOGURTThe sequence of stages for yogurt manufacture issummarized in the previous Chapter 12 in Table 12.1.The formulation of yogurt varies considerably, de-pending on the style that is being produced. Never-theless, the first step in the manufacture of yogurt isbasically the same regardless of the style made. Thestarting step is to make yogurt mix by blending var-ious ingredients. In this step, the formulation for aparticular yogurt production is calculated in terms ofthe weight/volume of each ingredient for the batchsize desired. At the time of manufacture, the liquiddairy ingredients like condensed milk, cream, wholemilk, low fat milk, or skim milk are pumped into aprocessing vat. Next, NFDM solids may be addedwith the aid of powder blender equipment consistingof a funnel and a circulating pump (Fig. 13.1) or ahigh shear type blender (Fig. 13.2).

The product is then pasteurized and then subjectedto high heat treatment to facilitate the growth of yo-gurt culture and to denature the milk protein aiding inthe formation of desirable body and texture in the yo-gurt. The mix is homogenized, cooled to incubationtemperature, and inoculated with the culture. Fromthis point, the process varies with the style of yogurtthat is being produced. The yogurt mix is either leftin the fermentation vat for incubation or pumped intoindividual cups and placed in the incubation room.The flavoring system used will also vary accordingto the style.

The following are the critical physical, chemical,and biological steps in yogurt technology.

1. Blending: In the mix preparation, it is necessary tohomogeneously disperse and dissolve the dry in-gredients in the liquid phase obtaining a uniformmixture. The following are important considera-tions during this step:(a) Sufficient agitation in the mix tank.(b) Incorporate dry ingredients using a pump and

funnel set-up or preferably a special highshear blending equipment.

Table 13.3. Denaturation of Whey Proteins as a Function of Heat Treatment

Temperature (◦C) Holding Period (min) Denaturation of Whey Proteins (%)

85 20–30 85–9085.0-90.6 30 85–9090.6 15 85–9090.6–93.3 2 70–7595. 8–10 90–95

(c) Minimize air incorporation.(d) Perform prepasteurization tests to conform to

chemical composition standards of butterfatand solids.

(e) Restandardize, if necessary.2. Pasteurization and Heat Treatment: Generally,

pasteurization of milk is carried out with the pur-pose of killing all the pathogenic microorganisms,and significantly reducing the majority of otherorganisms present and inactivating the inherentenzymes of milk. In the U.S. yogurt processingindustry, the FDA regulations require the plant op-erators to install legal pasteurization equipment,although the heat treatment of yogurt mix useshigher temperatures with a longer holding timethan legal milk pasteurization. Accordingly, thereare two sets of heat treatments: first one is to com-ply with the legal requirements and the secondone in tandem is more intense in temperature andholding time. The main purpose of this additionalheat treatment is to denature whey proteins and tocreate optimum conditions for the growth of yo-gurt culture. Proper denaturation of whey proteins(80–85%) increases their water binding capacity,which improves the consistency and viscosity ofyogurt and helps to prevent free whey separa-tion (syneresis). The level of desired denaturationdepends on the type of yogurt being processed.The manufacture of a “natural” yogurt, which hasno stabilizers, requires a greater denaturation ofserum or whey proteins. Studies have shown thatheating the mix at 85◦C for 20 minutes is opti-mum for maximum water binding capacity of milkproteins. This treatment gives minimum amountof drainage of whey from coagulated productwhen compared to lower or higher treatments ofthe milk. Other equivalent time–temperature heattreatments that are equally effective are given inTable 13.3.

Heat treatment exceeding the above-mentionedguidelines adversely affects the consistency of yo-gurt because of too much serum protein denaturation,


Figure 13.9. Principle of a homogenizer. Milk stream is forced from the right through a narrow orifice where fatglobules are split and homogenized milk exits from the left. Courtesy: Tetra Pak.

which results in yogurt that is weak set with signifi-cant syneresis.

Other kinds of yogurt containing increased milksolids content and stabilizers technically requirelower serum protein denaturation, since these de-pend on the higher solids and stabilizer to impartthe desired consistency and prevention of whey sep-aration. For these products, high-temperature–short-time systems can be used, provided that a tempera-ture of 90.6–93.3◦C can be obtained and the holdingperiod is at least 30 seconds. If this holding periodcan be extended using a special tube with a hold-ing period of 1–5 minutes, better consistency and in-creased protection from whey separation are usuallyobserved.

3. Homogenization: This process of mechanicallybreaking milk fat globules to smaller size alsohelps in more uniform dispersion of stabilizers inyogurt mix (Fig. 13.9 ). The homogenization ofyogurt mix with fat content greater than 1.5% hasthe following advantages:(a) No rising of cream during incubation, which is

the main purpose of homogenization. In some

Greek-style yogurts and natural whole milkyogurts, no homogenization is done because acream layer on the top is desired.

(b) Improvement of the consistency and viscosityof the yogurt because of uniform distributionof finely divided fat globules within the coag-ulum structure.

(c) Greater stability of the coagulum against wheyseparation. In addition it has been shown thata high temperature–pressure homogenizationbreaks up the casein micelles altering the hy-drogen bonds of the casein, increasing its hy-drophilic ability and denaturing serum pro-teins, both of which result in a more stabilizedprotein complex and increased whey retention.This procedure can be used in the productionof all “natural” yogurts with minimum or nostabilizer use.

Studies have shown that homogenization after pas-teurization favors better consistency in the final prod-uct. The optimum range for homogenization has beenfound to be 50–60◦C, with 35◦C as the minimum ef-fective temperature.


In the manufacture of “natural” yogurt with mini-mum stabilization (MSNF 11–13%), a high pressureof homogenization of approximately 23–28 MPa/6MPa (2000–2500/500 psi), double stage or 23–28 MPa (2000–2500 psi), single stage is used in orderto improve consistency and help prevent whey sepa-ration.

Yogurt with higher total solids content and/or sta-bilizers can use lower homogenization pressures ofthe order of 6–17 MPa (500–1500 psi). Improving theconsistency, viscosity, and prevention of whey sep-aration using homogenization is less important withthis type of yogurt because of the increased solidscontent and the effect of the stabilizer.

If the stabilizer that is being used contains a mod-ified starch, which is not resistant to shear, a mini-mum homogenization pressure should be consideredto prevent destruction of the starch structure resultingfrom severe shearing from the homogenizer. In thiscase, a homogenization pressure of 3–4 MPa (250–300 psi) single stage is recommended. Since homog-enization follows heat treatment, the need for utmostcare in cleaning and sanitation of the homogenizer isemphasized.

4. Coagulation: The protein content of yogurt milkconsists of casein, (comprising of 80% of the to-tal protein) and serum/whey proteins. Casein ispresent in milk in the form of micelles composedof a calcium–caseinate complex (Chapter 2).

These casein particles are very stable in fresh milkof normal composition partly because of their elec-trical charge. The charged particles repel each otherand stay in suspension. This stability is affected bychanges in milk composition relating to ionic balanceand salt concentration, by processing treatments, es-pecially by changes of the hydrogen ion concentra-tion.

During yogurt fermentation, lactic acid is producedas a result of bacterial growth. As the pH is lowereddue to acid production, there is a gradual removalof calcium and phosphorus (bound to casein as tri-calcium phosphate) from the casein particles. At thepH of 5.2–5.3, the caseinate particles are destabi-lized, initiating precipitation. Complete precipitationoccurs at a pH of 4.6–4.7, which represents the iso-electric point of casein. At this point casein is free ofbound calcium phosphate and the particles have nocharge to keep them repelled from each other leadingto their precipitation.

As mentioned earlier, denaturation of the serumproteins results in their decreased solubility in the

acidic range and coagulation is observed at pH 4.6–4.7. During heat processing, a major whey protein,�-lactoglobulin, interacts with �-casein and duringcoagulation this complex is coprecipitated as well.Thus, the coagulated proteins in the yogurt are a co-precipitate of casein and denatured whey proteinswith entrapped fat globules.

5. Cooling: The objective of cooling fermentedmass is to restrict the growth of yogurt cultureand its enzyme activity as quickly as possibleand maintain the desired pH, body, and texture.Under practical conditions, the introduction ofcooling yogurt mass after completed incubationdepends on(a) manufacturing conditions such as tempera-

ture of incubation or intensity of acidifica-tion.

(b) processing facilities available for cooling,such as cooling tunnel or cells, tube cooler, vatwith agitator, plate cooler, or scraped surfacecooler.

(c) type of yogurt produced, i.e., cup set, fruit fla-vored, vat set, and plain (natural).

(d) the desired organoleptic properties, such as fi-nal acidity and aroma production.

Generally, cooling in yogurt plants should takeplace at a pH of 4.5–4.65. Cooling with agitationat pH 4.7 or above can result in a grainy body andundesirable texture in the finished yogurt. The rate ofcooling should be steady but not too fast. Cooling toorapidly can bring unfavorable changes in the struc-ture of the coagulum contributing to whey separationin the finished yogurt. It is thought that this defectis probably due to the very rapid contractions of theprotein filaments and their disturbed hydration. Themethod of cooling depends on the style of yogurt thatis being produced. It is desirable to reach a tempera-ture of 18–20◦C within 1 hour to quickly stop furtherculture growth. Cup-incubated yogurt is cooled in theretail containers using a blast of cold circulated air ina cooling chamber/cell or a blast cold tunnel. High-velocity air creates simulated wind-chill conditions.

Vat-incubated yogurt is cooled using a special platecooler, a multitube cooler, or in some cases in a pro-cessing vat with the circulation of refrigeration waterin its jacket wall and agitation of the coagulum in thevat. When cooling in the vat, it is better to use a narrowhigh tank with swept surface agitation for quick cool-ing of the gel. Wide and high processing tanks witha propeller-type agitator are unfavorable for cool-ing. Many plants pump their cooled fermented base


through a back-pressure valve, a perforated stainlesssteel disk, a stainless steel mesh screen, or a “sourcream” cone in the line to insure a smooth texture inthe fermented mass.

In the vat-incubated yogurt, the temperature offilling varies according to the type of stabilizersused. Generally, it is desirable to cool the yogurt to7–13◦C.

6. Stirring: Stirring should not be too rigorous or toolong. This is especially important in the manu-facture of natural yogurts; however, it should alsobe considered in stabilized yogurt since excessivestirring may break down some of the stabiliza-tion and change the level of stabilizer needed toobtain desirable body. In order to obtain a homo-geneous gel, it is preferable to use a higher rateof stirring initially, reducing the rate of agitationas the temperature drops below 30◦C. Stirring atpH above 4.70 gives a partially formed gel result-ing in a grainy texture; therefore, stirring shouldcommence at pH 4.65 or below.

7. Pumping: Pumps are needed to transport stirredyogurt from fermentation tanks through pipes andpossibly a plate cooler to the filling machine. Theyoperate with different pressures, depending on thedesign. However, for this application only positivedrive pumps should be used. This insures a posi-tive displacement of the gel without impairing itsstructure. Centrifugal pumps should not be usedbecause the high centrifugal force produced bythe rotary propeller forces the product to leave thepump with high speed and high pressure, whichdamages the gel consistency resulting in a weakerbody.

GENERAL MANUFACTURINGPROCEDURESWe will now discuss general processes for majortypes of yogurt.

Plain Yogurt

Plain yogurt is gaining share of the refrigerated yo-gurt category. Its market share is currently around 5%of the total refrigerated yogurt category in the UnitedStates. Plain yogurt is made either by cup-incubationor by vat-incubation. It can be found in the marketas full fat, low fat, or nonfat yogurt. Formulationsvary widely and the total solids range from 12.50%to 14.0%. Plain yogurt is an integral component of the

manufacture of frozen yogurt. The steps involved inthe manufacturing of set-type and stirred-type plainyogurts are shown in Fig. 13.10.

Plain yogurt normally contains no added sugar orflavors in order to offer the consumer natural yogurtflavor for consumption or as an option of flavoringwith other food materials of the consumer’s choice.In addition, it may be used for cooking or for saladpreparation with fresh fruits or grated vegetables. Inmost recipes, plain yogurt is a substitute for sourcream providing a lower fat/calories alternative. Forthese reasons it is common to find plain yogurt pack-aged in larger multiserve containers.

Fruit-Flavored Yogurt

For the production of blended/Swiss style, the fer-mented yogurt base is mixed with various fruit prepa-rations. The fruit incorporation is conveniently doneusing a fruit feeder or metering pump at a 10–20%level followed by a static in-line mixer to assure ho-mogenous blending of the fruit with the yogurt base.Prior to flavoring, the texture of stirred-yogurt canbe made smoother by pumping it through a back-pressure valve or a stainless steel screen.

The second class of fruit-flavored yogurt is FOB.In this case the fruit is dispensed on the bottom ofthe cup and the top layer is that of fermented yogurtor cultured yogurt mix. In the latter case, individualcups are incubated, and then cooled. We will nowdiscuss all the types of fruit-flavored yogurts.

Blended or Swiss-Style Yogurt

This type of yogurt is the most popular and com-mands more share of the market than the other va-rieties. Its volume has grown consistently over theyears. There are two contributing factors for itsgrowth: First is the reformulation of the stabiliza-tion system that results in a smoother body and lessgel-like texture. Second is the incorporation of “mild”yogurt cultures, which produces a more pleasing mildtaste and very little or no acidification (lowering ofpH) during the entire shelf life. These yogurt at-tributes have gained broad consumer acceptance inthe market.

Swiss or blended yogurt is a homogeneous blendof fruit and/or fruit-flavored syrup with fermented yo-gurt base. This product is made using vat-incubationand almost always requires the use of stabilizers. Thestabilizers and their level can be varied to obtain thedesired product. The sugar solids vary, depending on


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Standardize mix to:0–2% fat, 10.5%

MSNF,

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Standardizing tank

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Milk/Skim Storage

Figure 13.10. Flow sheet for the manufacture of cup-set plain yogurt.

the sugar content of fruit preparation and flavoring.The fat content varies according to the desired prod-uct category, namely, full fat, low fat, or nonfat yogurt(see Table 13.4 for variations in the formulation).

One of the most common stabilizer blends used forblended yogurt consists of a combination of modi-fied food starch (0.6–1.5%) and gelatin of 225–250

Bloom (0.25–0.40%). It produces a creamy, firm yo-gurt, which is resistant to wheying-off and comes outsmooth and free of lumps. If a “natural” approachis desired, a gelatin–pectin stabilizer or agar–pectinstabilizer can be used. Again, other stabilizer com-binations can be used to meet specific marketing ormanufacturing needs.

Table 13.4. Typical Formulation of Blended/Swiss-Style Yogurt Base

Composition Nonfat Yogurt (%) Low Fat Yogurt (%) Full Fat Yogurt (%)

Milk fat 0.3–0.5 1.0–2.0 (>0.5–<2) 3.25–3.50Milk solids-not-fat 11.0–12.0 10.5–12.0 10.5–11.0Sugar solids 0–6.0 0–6.0 0–6.0Stabilizer 0.4–1.6 0.3–1.4 0.3–1.2


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Standardize mix to:0 - 3.25% fat, 9 -

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(45ºC, 4.5pH cut)

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(60º

C,

1500

psi

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Base StorageTank(4ºC)

Blended Style Yogurt

Standardizing Tank

Milk/Skim StorageFermentation Tank

Figure 13.11. Flow sheet for stirred/blended/Swiss style yogurt.

Over-stabilized yogurt possesses a solid-like con-sistency and lacks a refreshing character. Blended orSwiss-style yogurt should be spoonable and shouldnot be of flowing kind or have the consistencyof a drink. The steps involved in the manufac-ture of blended/Swiss-style yogurt are illustrated inFig. 13.11. A typical in-line fruit mixing is illustratedin Fig. 13.12.

Typical flavorings for stirred style yogurt are asfollows:

(a) Fruit preparations used at 10–18% level� degree Brix (◦Bx): 45–64� % fruit: 15–35� sweetener: sugar and/or corn sweeteners� stabilizer: pectin/modified food starch

(b) Flavored syrup or flavored concentrate and/orfruit juice� no visible fruit� lower calorie versus fruited yogurt� 8–9% sugar versus 10–12%

Figure 13.12. Fruit mixer built into the pipe. Courtesy:Tetra Pak.


(c) Combination of fruit preparation and flavoredsyrup or flavored concentrate� economy version� 6–10% fruit (40–50◦Bx)� 2–4% flavoring.

Details of the fruit preparation are given in Chap-ter 9.

Light Yogurt

This is made without the addition of sugar. High-intensity sweeteners are used to replace the sugar inthe formulation. The synthetic sweetener is added ei-ther in the fruit preparation or flavoring or directly tothe yogurt base. Light yogurts are stirred-style prod-ucts that use a special fruit preparation characterizedby 10–12◦Bx, 30–60% fruit content, and is designedfor use at 10–18% level.

Custard Style

This fruit-flavored yogurt is a reduced fat productcontaining enough starch to create custard-like con-sistency. Furthermore, it contains no fruit chunksand is preferred mostly by children. It is a cup-fermented product. Other children-directed yogurtscontain bright colors and are sweeter than regularyogurt. Some are packaged in a cup in such a mannerso as to produce multiple colored vertically depositedlayers during packaging. Other yogurts for childrenare packaged in plastic tubes.

French-Style Yogurt

This style of yogurt is more common in Europe. Inthe United States, it has been popular in the past, butnow its market is virtually nonexistent. It is a blendedyogurt similar to Swiss style in that it has fruit dis-persed throughout the body of yogurt, but it is char-acterized by distinctly weak set and creamy texture.The relatively runny body (low viscosity) style haslost popularity in the United States and has given wayto viscous pudding-like body and texture of Swissstyle. It is a vat-incubated product and depends on thetechnology of the stabilization system (hydrocolloidsor protein preparations) to develop its characteristicsoft body and texture. In some cases, it also employsthe use of selective culture strains, which produce a“ropy” body and/or special processing methods suchas evaporation, ultrafiltration, or reverse osmosis toconcentrate milk solids. Table 13.5 gives the typicalcomposition for a low fat French-style yogurt.

Table 13.5. Composition for a Low FatFrench-Style Yogurt

Ingredients %

Milk fat 1.5–2.00Milk solids-not-fat 8.62–8.66Added nonfat dry milk 3.85–5.00Sugar solids 3.00–3.60Stabilizera As neededTotal solids 17.00–20.00

a Gelatin–pectin (0.35–0.45%), modified starch–gelatin(0.60–0.90%), pectin, low methoxy (0.10–0.12%), agar–pectin (0.50–0.65), or whey protein concentrate (0.5–0.9%).

There are other typical processing methods usedin the manufacture of European and other special yo-gurts. Two of these processes for concentrating solidsand increasing protein concentration are reverse os-mosis and ultrafiltration.

Reverse osmosis (RO) is a pressure filtrationprocess that utilizes a semipermeable membranemade of cellulose acetate, vinyl, ceramic, or certainhigh-polymer materials. The membrane is charac-terized by the molecular weight and the size ofmolecules that are retained by it. With RO, watermolecules pass through the membrane while prac-tically all the dry matter is retained. RO is a high-pressure process and can concentrate skim milk intoa concentrate containing 5.4% protein, 7.2% lactose,and 1.1% ash. The concentrate is standardized withcream, homogenized, heat treated, and cultured.

Ultrafiltration is a similar kind of membrane fil-tration process that works at much lower pressuresthan RO process. It utilizes a specific semipermeablemembrane that is more porous than the membraneused in the RO process. With ultrafitration membrane,water molecules, lactose, and minerals pass throughthe membrane while proteins and fats are retained.Skim milk is concentrated to 6.8% protein, 4.9% lac-tose, and 1.0% ash. This concentrate (retentate) isthen blended with cream, homogenized, pasteurized,and cultured. The ultrafiltration concentrate can beused in various mixtures to increase the protein con-centration at different levels in the final product.

Sundae Style or Fruit-on-the-Bottom(FOB-)Style Yogurt

The popularity of this variety has significantly de-clined in recent years and has a market share of only8% of the total refrigerated yogurt category in the


Table 13.6. Formulation for a TraditionalSundae-Style Low Fat Yogurt Base That IsCup-Incubated

Ingredients %

Milk fat 1.00Milk solids-not-fat 8.64Added nonfat dry milk 4.00Stabilizers (optional)a 0.07−0.15Total solids 13.64+

a Usually pectin, agar, or gelatin.

United States. There are two types of sundae-style yo-gurt. First is the traditional style and the second is theWestern style. The traditional sundae style constitutesthe majority of sundae-style yogurt. The traditional-style product is made using plain yogurt on the topand fruit preparation on the bottom. The yogurt topphase can be produced by either incubation in thecontainer or adding vat-incubated yogurt.

(a) Cup-incubated traditional sundae-style yo-gurt: The largest percentage of sundae-styleyogurt is produced by incubation in the cupand can be formulated without a stabilizer byrelying on added nonfat milk solids, properheat treatment of the mix, and proper fer-mentation to obtain a semifirm body withoutwheying-off. However, with current trend to-ward increased code dates, warehouse distri-bution, and handling, the addition of a smallamount of pectin, agar, or gelatin to the yo-gurt will help maintain product consistencythroughout the product’s shelf-life. Table 13.6gives formulation for a traditional sundae-style low fat yogurt base that is cup-incubated.

In a typical traditional 8 oz cup of sundae-styleyogurt, 59 ml (2 oz) of special fruit preparation islayered at the bottom followed by 177 ml (6 oz) ofinoculated yogurt mix on the top. After the containersare sealed, incubation and setting of the yogurt takesplace in the individual cup. When a desirable pH of4.3–4.4 is attained, the cups are placed in refriger-ated rooms, or blast cooling tunnels or cells for rapidcooling. For consumption, the consumer mixes thefruit and yogurt layers. Flow sheet for the manufac-ture of traditional sundae-style yogurt is illustratedin Fig. 13.13.

(b) Vat-incubated sundae-style yogurt: If the yo-gurt is first incubated in the vat and thenpumped into the cup with fruit preparation on

the bottom, a stabilizer must be added to theyogurt base. Table 13.7 gives the formulationfor sundae-style yogurt that is vat-incubated.

(c) Western style sundae type yogurt: One specifickind of sundae-type yogurt is called “Westernstyle.” It is made with flavored sweetened yo-gurt on the top. The top layer may consist ofyogurt mix containing stabilizers, sweeteners,and the flavor and color indicative of the fruiton the bottom. The flavored yogurt on the topcan be made with or without color. The bot-tom layer consists of fruit. This yogurt can beeither incubated in the cup or the vat, but astabilizer is used regardless of the method ofincubation. The sugar solids in the yogurt basevary, depending on the Brix of fruit prepara-tion and top phase flavoring. Table 13.8 givesformulation for a typical low fat formulation.

Typical Flavorings for Sundae-Style Yogurt

(a) Fruit Preparations to be used at 18–23% level.� ◦Bx: 40–64� % fruit: 35–45� sweetener: sugar and corn sweeteners� stabilizer: modified food starch or pectin or

pectin–locust bean gum(b) Combination of flavored syrup or flavor con-

centrate and fruit preparation� Western style� 1–4% top phase flavoring� 12–14% FOB

Vanilla-Flavored Yogurt

Vanilla is the second largest selling flavor in the U.S.market with the sales of $240 million for 2004. Chap-ter 11 details the sourcing and manufacture of vanillaand its various forms used in the production of vanillayogurt. As discussed in Chapter 11, it is most com-mon to use vanilla extract added in yogurt productionafter fermentation for blended yogurts or added priorto fermentation for cup-set yogurt. When using purevanilla extract the usage rate will vary depending onthe fold or concentration of the extract, the sourceof the vanilla beans, and the desired flavor profile inthe finished yogurt. In yogurt production it is mosttypical to use vanilla extracts from 1× (1-fold) to3× (3-fold). The higher the fold or concentration ofthe vanilla extract, the lower the usage rate in theyogurt. For a 2× vanilla extract a typical usage rateis 0.45–0.60%. The vanilla extract supplier should

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Fruit placed in bottomof cup and yogurt

layered on top

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FOB Style Yogurt

Figure 13.13. Flow sheet for the manufacture of fruit-on-the-bottom yogurt.

Table 13.7. Formulation for Sundae-StyleYogurt That Is Vat-Incubated

Ingredients %

Milk fat 1.00Milk solids-not-fat 8.64Added nonfat dry milk 2.00 (2.0−4.0)Stabilizer 1.00 (0.45−1.40)Total solids 12.64 +

Table 13.8. Formulation for a Western StyleSundae Type Yogurt

Ingredients %

Milk fat 1.00Milk solids-not-fat 8.64Added nonfat dry milk 3.00 (2.00−4.00)Sugar solids 4.00 (3.0−6.0)Stabilizer∗ 1.20 (0.45−1.80)Total solids 17.64 +/−

* Typical gelatin or gelatin-modified starch combination.

228


be consulted to provide recommended starting usagesfor the various extracts. For economic reasons somemanufacturers might choose to blend a vanilla fla-vor or vanillin with pure vanilla extract to lower thecost. This would also impact the product label. Somemanufacturers prefer to obtain vanilla in processedsyrup (vanilla extract in liquid sugar syrup) from atypical fruit preparation supplier. With this syrup, itis possible to produce both vanilla and fruited yo-gurts using one plain yogurt base. Whether vanillayogurt is produced from pure vanilla extract or in a50–60◦Br syrup, the finished yogurt usually targetsa finished sugar content of 7–9%. This sugar levelgives the balance of sweetness and acidity in mostyogurts to deliver a well-rounded vanilla flavor forthe consumer.

Natural Yogurt

In the United States there is no definition for “natural”in food regulations. Since there is no legal definition,so called natural yogurts are defined by the consumer.In formulating yogurts for this market segment thereare certain guidelines that yogurt manufacturers havecome to use:

� Natural or WONF (with other natural flavors)flavorings.

� No added preservatives.� No high-intensity sweeteners or corn sweeteners;

preferred carbohydrate sources include sucrose,fructose, fruit juice concentrates, or honey.

� No stabilizers or the minimum use of acceptablegums like pectin, agar, or locust bean gum.

� No artificial colors; if colors are needed, it ispreferable to use extracts derived from vegetableor fruit sources (i.e., grapes, beet, annatto,blackberry).

In the processing of blended or cup-set natural yo-gurts, as discussed earlier, the heat treatment to ob-tain 80–90% protein denaturation is important to helpcontrol syneresis, since either no or minimal use ofstabilizers is preferred.

Organic Yogurt

The total sales for organic yogurt are approximately$179 million, representing 6.5% of the total refrig-erated yogurt category for the 52-week period end-ing in May 2004. The popularity of this category is

represented by its annual growth of 17.1% in the nat-ural market and 21.9% in grocery. The birth of theorganic regulations occurred when Congress passedthe Organic Foods Production Act (OFPA) in 1990.The OFPA required the USDA to develop nationalstandards for organically produced agricultural prod-ucts to assure consumers that the organic foods thatthey purchase are produced, processed, and certifiedto one consistent national organic standard. This wasaccomplished by the implementation of the NationalOrganic Program (NOP); Final Rule on October 21,2002. Yogurt that is sold, labeled, or represented asorganic will have to be produced and processed in ac-cordance with the NOP standards as defined in 7 CFRPart 205 (FDA, 2003).

Under the NOP standards, food products meetingthe requirements for “100% organic” and “organic”may display these terms and may use the USDA or-ganic seal. Products labeled as “100% organic” mustcontain (by weight, excluding water and salt) only100% organically produced ingredients, includingany processing aids. This product category is primar-ily found in produce, meat, or minimally processedfoods. Manufacturers of multiingredient foods, suchas yogurt, strive to achieve the organic label. Yogurt,as well as all products labeled “organic,” must con-sist of at least 95% organically produced ingredients(by weight, excluding and salt), and any remainingproduct ingredients must be organic compliant, thatis, consist of nonagricultural substances approved onthe National List (FDA, 7 CFR 205.605) or non-organically produced agricultural products that arenot commercially available in organic form (7 CFR205.606). Any yogurt, or other product, labeled asorganic must identify each organically produced in-gredient in the ingredient statement on the informa-tion panel. The regulations also prohibit the use ofgenetic engineering, ionizing radiation, and sewagesludge in organic production and handling.

A yogurt manufacturer interested in producingorganic products must be certified. Certificationstandards under the NOP regulations establish therequirements that organic production (crops and live-stock) and handling (processing) operations mustmeet the standards necessary to be certified bya USDA-accredited certifying agent. The informa-tion that an applicant must submit to the certifyingagent includes the applicant’s organic system plan.The organic system plan describes (among otherthings) practices and substances used in process-ing, record keeping procedures, practices to prevent


Table 13.9. Organic Ingredients for yogurt manufacture (as defined by 7 CFR 205)

Organic Ingredients (as defined by 7 CFR 205)Organic milk and creamOrganic Nonfat dry milkOrganic sugar or organic evaporated cane juiceOrganic agaveOrganic tapioca, rice, or corn starchOrganic fruits, fruit puree, and fruit juice/concentrate

Organic Compliant Ingredients (as defined by 7 CFR 205)Agar-agar: allowed 205.605 (a)Colors: allowed 205.605 (a) (5)—nonsynthetic sources onlyDairy cultures: allowed 205.605 (a) (6)Flavors: allowed 205.605 (a) (9)—nonsynthetic sources only and must not be produced using synthetic

solvents and carrier systems or any artificial preservativesAscorbic acid: allowed 205.605 (b) (4)Nutrient vitamins and minerals: allowed 205.605 (b) (19)—in accordance with 21 CFR 104.20, Nutritional

Quality Guidelines for FoodsLM pectin: allowed 205.605 (b) (21)Gelatin: approved by the National Organic Standards Board, pending listing in the Federal Register

commingling of organic and nonorganic products,and on-site inspections.

There are many available organic ingredients thatcan be used in the production of a certified organicyogurt, low fat yogurt, or nonfat yogurt. Table 13.9lists some of these agricultural organic ingredientsas well as some ingredients that can be found on theNational List and be used for the other 5% portion ofthe formulation.

Yogurt Drink/Smoothies

Yogurt drinks have registered a significant growth(Berry, 2004) in the current yogurt market (Fig. 13.9).This product is designed to be consumed as a drinkor shake. It consists of (a) refreshing low-milk-solidsdrink or (b) a health-promoting yogurt drink sup-plemented with prebiotics, probiotics, vitamins, andminerals. In order to be labeled as yogurt drink, thewhite mass (yogurt component) of the drink/beveragemust conform to the FDA standard of identity thatcalls for >8.25% milk solids-not-fat and fat levelto satisfy nonfat yogurt (<0.5%), low fat yogurt(2.00%), or yogurt (>3.25%) label (Chandan, 1997),prior to the addition of other ingredients. After theaddition of fruit and flavors, it does not have to meetthese standards. If a yogurt-based beverage is pro-duced that does not conform to these standards, itcan still be marketed given a fanciful name otherthan “yogurt” drink. Similarly, smoothies are notnecessarily standardized and some may not contain

yogurt at all. If the product contains descriptors suchas “a blend of yogurt and fruit juice,” it automaticallyrequires that the product use yogurt in its preparation.A descriptor “a blend of juice and milk” allows theuse of directly acidified milk (Roberts, 2004).

Typically, commercial drinkable yogurt is a low fat(<2.0% fat) drink containing 8.0–9.5% milk solids-not-fat and 8–12% sugar. Its pH varies from 4.0 to4.5. Low-calorie drinks are made with high-intensitysweeteners replacing all the sugar. Yogurt drinks gen-erally contain fruit juices or purees, although in somemarkets they may contain only sugar, with or with-out fruit flavors. The fruit content is generally in therange of 8–15%. In some markets the fruit juice rangemay be as high as 30–49%.

Yogurt drinkables and smoothies are of twotypes: regular and those fortified with prebiotics,probiotics, minerals, and vitamins. The prebioticfructo-oligosaccharides (FOS) or inulin, along withsynergistic probiotic cultures of Lactobacillus casei,Lactobacillus reuteri, and bifidobacteria are presentin addition to yogurt culture. The type and level ofstabilizer chosen is designed to keep the product fromsettling into two phases during its shelf life. The sta-bilizers prevent the milk protein from aggregationand subsequent separation of clear layer on the top.The stabilizers also help in appropriate viscosity ofthe drink. A mixture of hydrocolloids in the rangeof 0.01–0.5% is usually employed. High-methoxypectin is especially functional in imparting the re-quired viscosity and protein interaction to prevent


separation. Another important processing step is low-pressure homogenization (6 MPa (500 psi)) of fer-mented base to create small casein particles, whichinteract with pectin to stop aggregation of the proteinand creating thereby a stable suspension.

The production method for drinkables is simi-lar to that of blended/Swiss-style yogurt. The mixcontains milk solids, sugar, stabilizers, and optionalingredients consisting of mineral–vitamin supple-ment, fructo-oligosaccharide. This blended mix isheat-treated at 85◦C for 30 minutes or at 95◦C for10 minutes to create conditions favorable for culturegrowth and for viscosity generation. The mix is thencooled to 39–41◦C, inoculated with 1–2% of yogurtstarter and optional probiotic cultures, and incubatedin quiescent state until a pH of 4.3–4.4 is achieved.The curd is broken while cooling to 18–19◦C. Thenext step is distinctly different for yogurt drinks. Cer-tain processes require addition of pasteurized solu-tion of high-methoxy pectin to achieve 0.3% pectinlevel in the yogurt drink. The cooled fermented massis homogenized at low pressure (6 MPa (500 psi),single stage) to convert casein to low particle sizeand facilitate interaction with pectin to obtain desiredlow viscosity and to render stable suspension. At thispoint, fruit puree and flavoring or syrup may be in-corporated. Typical flavorings for yogurt smoothiesconsist of flavored syrups or flavor concentrate and/orfruit juices. After proper blending, the drink is readyfor packaging in paper cartons or bottles. Individualserving bottles are commonly used for yogurt drink-ables. When the yogurt drink is en route to the bottlefiller, it is desirable to cool it to 5◦C by passing itthrough a plate cooler. Prior to filling, the bottles areunscrambled and air-blown to remove any dust orforeign material. These are then turned upside down,rinsed, sterilized, and filled with required weight, fol-lowed by sealing with aluminum foil and applicationof a cap. The finished product is checked for pH, vis-cosity, and color at regular intervals. After coding andshrink-wrapping, the bottles are packed in cases andmechanically moved to cold room. These are thenplaced on pellets, shrink-wrapped, and transferred tothe cooler before being shipped out of the plant (Clarkand Plotka, 2004).

Aneja et al. (2002) and Chandan (2002) have givendetails for the manufacture of a long-life sweetenedyogurt drink (lassi). Table 13.10 gives the formula-tion for lassi.

The process used in the manufacture of this yogurtdrink includes pasteurization, homogenization, andculturing systems. The shelf life can be extended by

Table 13.10. Formulation for the Manufactureof a Long-Life Sweetened Yogurt Drink(Lassi )

Ingredients %

Milk fat 0.5–3.5Milk solids-not-fat 9.00Sugar 10–11Sodium dihydrogen phosphate 0.5High-methoxy pectin 0.5

UHT processing after fermentation and aseptic pack-aging. Wheying-off is controlled by using a suitablestabilizer and proper processing conditions. The pro-cess has been patented for the manufacture of long-life sweetened drink, which maintains phase stabilityand does not separate over extended storage in asep-tic packs. Standardized low fat milk (9–10% SNFand 0.5–1.0% milk fat) is heated to 85◦C for 30 min-utes or to 91◦C for 2.5–5 minutes and cultured withyogurt culture. It is then fermented to lower the pHto 4.5. The set curd is broken with the help of stir-rer while pasteurized sugar solution (30% in water)is added so as to give 8–12% sugar concentration inthe blend. The blend is then homogenized at 23 MPa(2000 psi) and UHT processed at 135–145◦C for 1–5seconds and packaged aseptically employing stan-dard equipment. A flow sheet for the production ofsweetened yogurt drink is shown in Fig. 13.14. Thefigure shows procedure for making drink with livecultures as well as for heat-treated and asepticallypackaged (extended-life) drink.

Yogurt Whips/Mousse

Whipped yogurt has unique eating quality in that it isfluffy and light textured and has a good mouth feel.It adds variety and new taste sensation to the prod-uct portfolio. The foam formation of the mix takesplace during processing. Compared to stirred-typeyogurt, the mix for whipped yogurt contains moresugar and stabilizers. Gelatin is an essential ingredi-ent of whipped yogurt. Low to regular fat mix whipsbetter than the nonfat mix. The stability of the foam isfacilitated by the use of suitable emulsifiers and stabi-lizers in the mix. An emulsifier aids in foam formationwhile stabilizer is responsible for viscosity, mouthfeel, and stability of the foam and emulsion struc-ture. The bubbles formed are prevented from col-lapsing by the action of stabilizer–emulsifier during


Ambient Distribution


He

at

Exc

ha

ng

er

(11

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se

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Pre

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at

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ºC)

Co

olin

g(C

oo

l to

40

ºC)

Ba

lan

ceT

K

Bottle Filling(Non Aseptic)

Vacu

um

Cham

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(80

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Hold Tank(Mix well, stand

1 hr.,5º C)

AsepticHold Tank

Carton Filling(Aseptic)

AmbientStorage

ColdStorage

SteamInjector

Holding Tube



Hom

ogeniz

er

(No

pre

ssu

re)

From Yogurt DrinkBatching

Yogurt Drink

Aseptic Yogurt Drink

Shear Pump

Shear Pump

Figure 13.14. Flow sheet of the manufacturing procedure for refrigerated and long-life sweetened yogurt drink.

the shelf life of the product. High altitude can affectthe stability of the foam as well. Generally, a sta-bilizer system includes starch, gelatin, carageenan,guar gum, xanthan gum, and locust bean gum. Theemulsifiers include mono- and diglycerides, espe-cially the lactylated type. The stabilizer–emulsifierblend is incorporated directly in the yogurt mix priorto the heat treatment. After fermentation, the mixis whipped using inert gas like nitrogen to increasethe volume of the mix by 50%. Thus, the whippedyogurt has an overrun of 50%. Thus, a 6-oz cupwill hold 4 oz of yogurt whip. During whipping, thehigh turbulence in the equipment results in fine gasbubbles dispersed in the aqueous phase. The mixinghead of the aeration machine disintegrates large gasbubbles into finer bubbles forming desirable foamstructure. The emulsifiers are surface-active agents.By reducing surface tension, they facilitate bubbleformation, while the stabilizers enhance viscosityand form a coating around the bubbles to give themstrength and capacity to resist from collapse. The

foam matrix consisting of fat globules, gas bubbles,and aqueous phase containing soluble and insolublecomponents of the mix is formed at low whippingtemperature.

Concentrated/Greek-Style/StrainedYogurt

This type of yogurt is more common in the UnitedKingdom and some other countries. The base forthis type of yogurt is whole milk, supplemented withcream to standardize the fat level to 7%. In tradi-tional process, after fermentation is complete, theyogurt is concentrated by straining through cheesecloth at 4◦C overnight. Because of the drainage ofwhey, the total solids increase from 14% to 21–23% (Tamime and Robinson, 1999; Robinson, 2003).The concentration step results in a remarkably thickviscous body. The fat content of this type of yo-gurt rises to approximately 10%. The high fat con-tent imparts very creamy flavor and moderates the


acid flavor. The fermented protein also concentratesand contributes to smooth texture. The traditionalmethod is labor intensive and lacks sanitation con-ditions for obtaining desirable shelf life of the prod-uct. Accordingly, modern processing procedures forwhey removal are employed. Drainage of the wheyis accomplished by ultrafiltration or is done whenthe fermented milk passes through Quarg/centrifugalseparators. The resulting concentrated yogurt is sub-sequently packaged.

Alternatively, Greek yogurt can also be found inthe UK market that does not involve the concentrationstep. Such Greek yogurt is formulated with high fatcontent of 7–10% and SNF content of 10–12%.

Frozen Yogurt

The sale of frozen yogurt category in the UnitedStates has been on the decline in recent years. For the52-week period ending on May 16, 2004, this cate-gory has shown a decline of 7.8% but still represents$195 million in sales. It remains a viable businessperhaps because of its low fat and nonfat attributeand the health image of yogurt. The frozen yogurtbase mix may be manufactured in a cultured dairyplant and shipped to a soft-serve operator or an icecream plant. Alternatively, the mix may be preparedand frozen in an ice cream plant. (For details, seeMarshall and Arbuckle, 1996.)

Currently, no Federal standards have been ap-proved for frozen yogurt. The product may be de-fined as a food prepared by freezing while stirring ablend of pasteurized nonfat or low fat ice cream mixand yogurt (Marshall and Arbuckle, 1996). Yogurtused for blending with ice milk mix must complywith the Federal and State compositional standardsfor yogurt. It must be cultured with LB and ST totitratable acidity of minimum of 0.85%. In general,

frozen yogurt mix obtained by blending yogurt andlow fat/nonfat ice cream has a pH of 6.0 or titratableacidity of 0.30%. Thus, the industry standards requireminimum titratable acidity of 0.30%, with a contri-bution of approximately 0.15% as a consequence offermentation by yogurt bacteria. Most manufacturersuse 10% of yogurt in their formulations. As a con-sequence, frozen yogurt tastes very similar to lowfat/nonfat ice cream, with a hint of yogurt flavor atthe end. This flavor attribute is preferred by the con-sumer because the perceived health attributes of yo-gurt bacteria are available along with the popular tasteof low fat/nonfat ice cream. Frozen yogurt is labeledaccording to the fat content of standard serving size(4 fl oz) used in the ice cream industry. Accordingly,the product containing >3 g of fat per 4 fl oz is labeledas frozen yogurt, the product containing 0.5–3.0 g per4 fl oz is low fat frozen yogurt, and the product with<0.5 g fat is labeled nonfat frozen yogurt.

A typical formulation of low fat frozen yogurt isgiven in Table 13.11. The table shows a mix com-posed of 10% nonfat sweetened plain yogurt and 90%low fat ice cream mix. If a lower pH (<6.0) is desiredin the finished product, the proportion of plain yogurtcan be increased to >10% and vice versa.

Some manufacturers may pasteurize the softfrozen yogurt mix, which is a low acid food, to en-hance its shelf life. Pasteurization also assures safetyof the food by destruction of possible contaminat-ing pathogens, including Listeria and Campylobac-ter. However, the label of the heat-treated productmust display the phrase “heat treated after culturing”on the package panel.

Figure 13.15 illustrates the typical process formaking frozen yogurt. Like ice cream, frozen yo-gurt is flavored and extruded from ice cream freezerat −8◦C to obtain soft serve frozen yogurt for imme-diate consumption.

Table 13.11. Formulation for Low Fat Frozen Yogurt

Component Yogurt 10% Ice Milk 90% Frozen Yogurt Mix

Milk fat 0.07 2.39 2.16Milk solids-not-fat 10.96 10.02 10.11Whey protein concentrate 34 (97% solids) 0.0 2.7 2.4Sucrose, (100% solids) 4.0 13.5 12.6Corn syrup solids, 36 or 42 DE (95% solids) 0.0 6.0 5.4Maltodextrin 10DE (96% solids) 0.0 4.0 3.6Stabilizer (90% solids) 0.0 0.7 0.6Total solids,% 15.03 36.04 33.94Titratable acidity,% 0.85 0.15 0.30pH 4.6 6.7 6.0


NFDM, Stabilizer,WPC-34, Sugar, 10DE Maltodextrins,and CSS 36 DE

Milk/Skim/CondensedStorage

Standardize mix box 2.4%fat, 10% MSNF, 13.5%sugar, 0.7% stabilizer,

maltodextrin, 2.7% WPC

Standardizing Tank


Palletizing

BlastFreezer(−40° C)

CartonFiller

ColdStorage

Fruit/Nut

Palletizing

Pre

-Hea

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Hea

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)

Baa

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TK

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el (

17M

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]

Plain Yogurt(11% MSNF,4% sugar) Mix Tank

(10% yogurt,6.0 pH)

Flavor/Color

Holding Tube

FrozenStorage

In-LineAddition

Bag inBox Filler

Frozen Distribution

Ice Cream Freezer

36 DE Corn Syrup Solids

(Extrude -6° C)

Frozen Yogurt

Soft Serve Mix

Figure 13.15. Flow diagram for the manufacture of soft serve mix and hard frozen yogurt.

Soft serve frozen yogurt may be garnished withnuts and other food materials to enhance its eating ex-perience. The extruded frozen yogurt may be packedin suitable containers and hardened at −25◦C to ob-tain hard pack frozen yogurt. The ice cream freezeris a scraped surface freezing barrel (heat exchanger)(Fig. 13.16). As the liquid mix is pumped through thebarrel, removal of the sensible and latent heat leads toformation of frozen mass. The dasher scrapes the in-ner surface of the barrel while the frozen mass movestoward the exit point. Simultaneously, air cells areformed as a result of whipping action of the dasherand the volume of the mix increases. Eventually, thesemifrozen yogurt mass exits from the barrel as foamwith a specific controllable degree of aeration. Theoverrun or the degree of air incorporated in the foamis around 50%. It implies that the original volume ofthe mix is increased by 50% in the finished frozenyogurt.

The calculation of overrun involves weighing a cupof the mix before freezing and determining the net

weight of the mix. Using the same cup, the frozenyogurt is packed and its net weight is determined.The overrun is calculated as follows:

% Overrun = (Density of mix − Density of frozen yogurt) × 100

Density of frozen yogurt

= 100 × (Net weight of mix − Net weight of frozen yogurt)

Net weight of frozen yogurt

Assuming the mix weighs 9 lb/gallon, and thefrozen yogurt has 50% overrun, a gallon of frozenyogurt would weigh 6 lb. Accordingly, one servingof one-half cup (or 4 fl oz) would weigh 85 g.

POSTCULTURING HEATTREATMENTThe shelf life of yogurt may be extended by heatingyogurt after culturing to inactivate the culture and theconstituent enzymes. Heating to 60–65◦C stabilizesthe product so the yogurt shelf life will be 8–12 weeks


Figure 13.16. An ice cream freezer used formanufacturing frozen yogurt. Courtesy: Tetra Pak.

at 12◦C. However, this treatment destroys the “live”nature of yogurt, which may be a desirable consumerattribute to retain (Chandan and Shahani, 1993; Shah,2003). Federal Standards of Identity for refrigeratedyogurt permit the thermal destruction of viable or-ganisms with the objective of shelf life extension,but the phrase “heat treated after culturing” must bedisplayed on the principle display panel of the pack-age. The postripening heat treatment may be designedto (1) ensure destruction of starter bacteria, contami-nating organisms, and enzymes and (2) redevelop thetexture and body of the yogurt by appropriate stabi-lizer and homogenization processes.

The heat-treated yogurt possibility is quite contro-versial in the United States. Although legal, the majorplayers in the yogurt industry believe that such prod-uct will not deliver live and active yogurt expectationof the consumers (Chandan, 1989, 1999; Fernandes

et al., 1992; Mistry, 2001; Tamime and Robinson,1999; Nauth, 2004). Indeed, the scientific evidencehas been compelling that the health properties ofyogurt are mostly lost by heat treatment (Chapters21 and 22). This issue has been debated around theworld. The Codex standard for yogurt does call forlive and active status to be labeled as yogurt. Further-more, if the product is heat-treated after culturing, ithas to be labeled as “heat-treated fermented milk.”A similar standard, which is awaiting clearance, hasbeen proposed by National Yogurt Association to USFDA. The standard would also require a minimumyogurt culture count of 10 million CFU/g in refriger-ated yogurt at the time of consumption to insure thelive and active status of the product.

ACKNOWLEDGMENTWe appreciate the contribution of Brent Cannell forpreparing flow sheet diagrams for this chapter.


2002. Technology of Indian Milk Products. DairyIndia Yearbook, New Delhi, India, pp. 158–182.

Berry, D. 2004. Cultured dairy foods: A world ofopportunity. Dairy Foods, April 2004.

Chandan RC (Ed). 1989. Yogurt: Nutritional andHealth Properties. National Yogurt Assoc, McLean,VA.

Chandan RC. 1997. Dairy-Based Ingredients. EaganPress, St. Paul, MN.


Chandan RC. 2002. Benefits of live fermented milks:Present diversity of products. In: Proceedings ofInternational Dairy Congress, Paris, France.[Available in CD-ROM.]

Chandan RC. 2004. Dairy: Yogurt. In: JS Smith, YHHui (Ed), Food Processing: Principles andApplications. Blackwell, Ames, IA, Ch 16.

Chandan RC, Shahani KM. 1993. Yogurt. In: YH Hui(Ed), Dairy Science and Technology Handbook, Vol.2. VCH Publ., New York, pp. 1–56.

Clarke S, Plotka VC. 2004. Yogurt and sour cream:Operational procedures and processing equipment.In: YH Hui, L Munier-Goddik, AS Hansen, JJosephson, W-K Nip, PS Stannfield, F. Toldra (Ed),Handbook of Food and Beverage FermentationTechnology. Marcel Dekker, New York,pp. 159–182.



Food and Drug Administration (FDA). 2003. UnitedStates Department of Health and Human Services,Public Health Services. 2002. Code of FederalRegulations. Title 21. Section 131. US GovernmentPublishing Office, Washington, DC.

Food and Drug Administration (FDA). 1999. UnitedStates Department of Health and Human Services,Public Health Services. Grade “A” Pasteurized MilkOrdinance. 1999 Revision. Publication No. 229. USGovernment Publishing Office, Washington, DC.

Marshall RT, Arbuckle WS. 1996. Ice Cream, 5th ed.Chapman and Hall, New York, pp. 317–318.

Mistry VV. 2001. Fermented milks and cream. In: EHMarth, JL Steele (Eds), Applied DairyMicrobiology, 2nd ed. . Marcel Dekker, New York,Ch 9, pp. 301–325.

Nauth KR. 2004. Yogurt. In: YH Hui, L Meunier-Goddik, AS Hansen, J Josephsen, W-K Nip, PS

Stanfield, F Toldra (Eds). Handbook of Food andBeverage Fermentation Technology. Marcel Dekker,New York, Ch 7, pp. 125–145.

Roberts B. 2004. Dairy Foods, June 2004, pp. 56.Robinson RK. 2003. Yogurt types and manufacture.

In: H Roginski, JW Fuquay, PF Fox (Eds),Encyclopedia of Dairy Sciences, Vol. 2. AcademicPress, New York, pp. 1055–1058.

Shah N. 2003. Yogurt: The product and manufacture.In: B Caballero, L Truco, PM Finglas (Eds),Encyclopedia of Food Sciences and Nutrition,Vol. 10, 2nd ed. Academic Press, New York,pp. 6252–6259.

Tamime AY, Robinson RK. 1999. Yogurt Science &Technology, 2nd ed. Woodhead Publ. Cambridge,England, and CRC Press, Boca Raton, FL.

BIBLIOGRAPHYDairy Management, Inc. (DMI). 2003. Concentratedand Dry Milk Ingredients. Dairy Ingredient Applica-tion Guide. DMI, Chicago, IL.

14Plant Cleaning and Sanitizing

Dennis Bogart

CleaningNormal SoilsSpecial SoilsManual CleaningFoam CleaningCOP CleaningCIP Cleaning

SanitizingBacteriophage (Phage) Control

Phage ControlA Final Thought

The concepts of cleaning and sanitizing in a yogurtprocessing plant are fairly simple and basic. Firstclean the soil from the surface, and then sanitizethe surface. Simple to look at, read about and talkabout; however, very difficult to accomplish on aregular basis. In fact, millions of dollars worth ofyogurt and other cultured dairy products have beenlost due to poor sanitation and it would be almost im-possible to calculate the number of good customerslost due to poor sanitation. There are a lot of compa-nies today that I call “used-to-bees.” Some of thesecompanies, at one time, were major players in thedairy industry and some were small independent op-erations. They all have one thing in common. Theyno longer exist. They are gone, a part of history andwe can think of many dairy companies that are “used-to-bees.” Some are “used-to-bees” because of the fi-nancial burden of business; however, far too manybecause of poor quality product.

The issues with the product not only involve top-ics such as shelf life, flavor, appearance, and otherquality issues but also product safety. The Center forDisease Control and Prevention (CDC) estimates that

approximately 75 million people in the United Stateshave food poisoning every year. That is roughly 25%of the population every year. Also CDC estimates thatover 5,000 people every year die from food poison-ing in the United States. This is a true tragedy and inmany cases could be prevented if the food-processingplants use good GMPs and sanitation. Simple thingssuch as washing hands for 20 seconds with soap, andcleaning and sanitizing the plant can go a long waytoward preserving a good company name.

In cleaning and sanitizing yogurt plants there area few ideas that need to be dismissed right away:

� Yogurt is a “safe product because the product’sacidity takes care of any ‘bad bugs’”—FALSE

� Sanitizers kill everything—FALSE� Phage will not attack yogurt as in other products

like buttermilk—FALSE� Cleaning removes all the bacteria and phage from

a surface—FALSE� The external environment is not

important—FALSE� Sanitizer rotation is important because we

develop “resistant” bacteria—FALSE� Quat sanitizers are too dangerous to use—FALSE

CLEANINGCleaning is simply the removal of soil from a sur-face (notice that this says nothing about killingmicroorganisms—that is for later). There are no gra-dients of clean. The surface is either clean or it isdirty. If all the soils are removed, the surface is clean.If the soil is not completely removed, it is still dirty.There are several types of soil with which we have

237




to be concerned. Some of these are called normal,whereas others can be called special.

Normal Soils

Fat–

All yogurts and other cutured dairy foods contain fat.Even nonfat products may contain up to 0.5% butter-fat, while others may contain 4% butterfat or more.The fat will coat the surfaces with a greasy film thatover time becomes rancid, attracts other soils, resistsrinsing and, as all other soils, protects microorgan-isms from the action of sanitizers. Oil (fat) and wa-ter do not mix. This is one reason we need to use agood detergent or soap (surfactants). A surfactant issimply a chemical that has two functional ends onits molecule. One end is hydrophilic and “likes wa-ter.” The other end is hydrophobic and “likes fats andoils.” When the surfactant is in a solution of waterand gets close to fat, it attaches itself to the water andon the other end to the oil. Thus the fat or oil mixeswith the water. If the cleaning procedures are prop-erly followed, the cleaner will remove the fat fromthe surface. There is also a very special circumstance,where it is very good that there is a little fat on thesurface, when the cleaning operation starts. This is es-pecially true for clean-out-of-place (COP), clean-in-place (CIP), and pasteurizer cleaning. The cleaningchemicals normally used for these applications usu-ally do not contain any surfactants. This is especiallytrue for the chlorinated CIP cleaners used in COP andCIP. Also caustic cleaners used to clean pasteurizersfrequently do not have surfactants in their formulas.So how is the fat removed? Chemically all of thesecleaners contain strong alkalis such as caustic soda(NaOH) or caustic potash (KOH). When these alka-lis are mixed with fats or oils in normal cleaning,the fat or oil will undergo a chemical process knownas saponification. In other words it makes good old-fashioned soap, a natural surfactant. This is a verydesirable reaction and greatly boosts the cleaning ac-tion of the cleaner. It is extremely important to havea vigorous prerinse to remove excess butterfat fromtanks and lines and an even more vigorous postrinseto thoroughly rinse the now dissolved or suspendedsoils from the system.

Sugars

The various sugars in yogurt are relatively easy toclean. Water will usually do the trick. Most of the

sugars such as lactose, sucrose, and fructose are eas-ily rinsed out with the prerinse. That is assuming thatthey are not all complexed within the other four soils.This will happen frequently and thus compounds theissues with the complex carbohydrates. Also thereis a very dangerous situation that develops insidetanks, silos, and other enclosed spaces. When lac-tose is mixed with caustics, carbon monoxide (CO)may be formed. There have been several incidenceswhere personnel have entered a tank after cleaningand succumbed to the colorless and odorless gas.

Complex Carbohydrates

Complex carbohydrates are actually a matrix of allthe soils together attached to the surface. Most of thetime this happens when the yogurt mix is pasteurizedand the soil is simply referred to as “burn-on.” Thesecond circumstance where this complex soil formsis on equipment that has not been properly cleanedand the soil keeps building upon itself. The additionof stabilizers and emulsifiers compound the soilingissue. The more ingredients added, the more likelya soil will form. As with butterfat, strong alkalinecleaners are needed to clean this tough soil from thesurface.

Proteins

Milk is an excellent source of protein and most cul-tured dairy products have added proteins and othermilk solids. Protein is the last and the hardest to re-move organic soil that we normally encounter. Theyare relatively easy to see on a surface because oftheir typical blue film. However, if the cleaning hasbeen neglected or the protein film has been allowedto thicken, it will change from a blue haze to an “ap-plesauce” appearance. Further development will leadto a serious white film that may be confused with amineral film. There are four common ways to re-move protein films and to keep them from buildingup. The first is in cleaning a pasteurizer. Extremelystrong (1–3%) caustic circulated hot (>170◦F) formore than 30 minutes will usually control the pro-tein film. The issue is that the protein is an extremelylong and complex molecule that is not soluble in wa-ter. The caustic acts to break this long molecule upinto shorter chains that are soluble in water and re-moved in the postrinse. As this treatment with caus-tic is neither feasible nor recommended in COP, CIP,foam, or manual cleaning, other ways need to be used

14 Plant Cleaning and Sanitizing 239

to break the protein molecule. The most common inNorth America is to add chlorine to the cleaner. Chlo-rine, at typical concentrations between 75 and 300ppm, will quickly remove protein soils. Other alter-natives including enzymes, hydrogen peroxide, andselected acids will also act to remove protein films.Protein films are especially important for they mayharbor phage that will destroy the yogurt during theculturing phase of production. One issue to be veryaware of is if chlorinated cleaners are being used,they will clean protein films, boost general cleaning,and deodorize. One thing that they will not do is tokill sufficient microorganisms to achieve sanitizing.The pH is too high for the chlorine to be active asa sanitizer. This is critical because you must alwaysclean prior to sanitizing.

Minerals–

Mineral films are formed in many ways. A commonindustry name for mineral films is “stone.” Thesestones are further referred to by their common ori-gin such as milkstone, beetstone, beerstone, water-stone, and soapstone. In the cultured dairy-productsindustry the three most common stones are milkstone,soapstone, and waterstone. All of these hard to cleanstones have one thing in common, they generally needto be cleaned with an acid. The food grade acids suchas phosphoric, nitric, sulfuric, and sulfamic are mostcommonly used. Normally the surface is cleaned withan alkaline detergent to remove all the organic soils,rinsed thoroughly with water, and then the acid isapplied.

Special Soils

Biofilms–

Biofilms are formed by many bacteria when they at-tach to a surface. They secrete a very viscous polysac-charide slime to cover for protection. This slime is acomplex carbohydrate film and can be cleaned withan alkaline cleaner. It is not easy to clean biofilms, asvigorous agitation may be needed. The significanceof these films is that they protect the bacteria from theaction of the sanitizer, thus the bacteria will survivesanitizing. To further emphasize the significance ofbiofilms, Listeria and Pseudomonas form biofilms.The first is a psychrotrophic pathogen and the sec-ond spoils probably more dairy products than anyother bacteria.

Bacteriophage–

In many ways, bacteriophage, the virus that attacksthe bacterial culture can be considered a soil. In aculture plant, phage (as it is more commonly known)is frequently associated with dirty equipment, air, orthe environmental surfaces. Controlling phage is aconstant battle for any cultured products plant andespecially a yogurt operation. To control phage, goodsanitation, adherence to GMPs, and culture rotationare needed.

As stated previously cleaning is the removal of soilfrom a surface and if any soil is left on the surface, thesurface will be dirty. There are three main principlesthat must be remembered when cleaning in a yogurtplant:

1. The prerinse is the most important step in the entirecleaning process.

2. The surface is either clean or it is dirty.3. You cannot sanitize a dirty surface.

The cleaning process is fairly simple. First, pre-rinse to remove all the gross soil; second, wash withan appropriate cleaner; and third, rinse off or removethe soil. These steps sound simple, but there are nu-merous ways to foul up the process in the four maincleaning methods: manual, foam, COP, and CIP.

Manual Cleaning

Manual cleaning is normally accomplished with abucket of suds and a brush or pad. It is a very commonmethod of cleaning and has been used in the dairy in-dustry for literally hundreds of years. Although man-ual cleaning is very common, there are issues thatoccur frequently:

� Failure to use the right detergent or cleaner.Manual cleaners are specifically designed to beactive at moderately hot temperatures(100–120◦F), to produce copious amounts ofstable foam and to be relatively mild to skin. Othertypes of cleaners, such as CIP or foam cleaners,may function quite differently and produce poorresults, possible corrosion of the surfaces, or betoo harsh to use even with gloves. Always followthe manufacturer’s recommendations as to whatproduct to use for manual cleaning.

� Failure to use the correct amount. If a little bit isgood, more is better. This idea has causednumerous problems in plants. It will cause poorrinsing, too strong a solution for operator’s skin,heavy streaking, and possibly corrosion issues.


Many times an operator will put far too muchdetergent in a bucket and just keeps adding waterto the bucket. Most powdered manual cleanerswill have directions to use approximately oneounce per gallon of water. Using more than thatlevel will not clean better but will wasteconsiderable money and will have all the otherconsequences listed above.

� Failure to use the right type of manual cleaner.The best type of manual cleaner for a yogurtoperation is a chlorinated alkaline cleaner. Thesetypes of cleaners come in powdered and liquidform and will do a very good job. They areespecially good at removing the protein films thatfrequently form on the product contact surfaces.The proper cleaning solutions will have a mildalkali and high foaming surfactants to remove anybutterfat and carbohydrate soils. The chlorine willbe present at between 60 and 200 ppm and willbreak up and help remove the very tough proteinfilms.

� Failure to use clean, fresh solutions. If thesolutions become too dirty or are more than30 minutes old, they loose their chlorine andtemperature and become very poor cleaners.Streaks, films, and poor rinsing will result.

� Failure to use the proper tools. Good brushes andpads are essential to good manual cleaning. Thebrushes need to be of the proper size and color(follow color coding system) and in goodcondition. Wood-handled brushes must never beused. Many operations use what are termed“green pads.” I strongly recommend against theiruse. Although they do clean well, they willseverely scratch stainless steel and their greencolor makes it very hard to tell when they need tobe replaced. I recommend that these “green pads”be replaced with “white pads.” These pads willnot scratch stainless steel as the green ones do andyou can tell when they need to be replaced.

� Failure to scrub. Manual cleaners are the mildestof all the commonly used cleaners. Because ofthis, they need heavy scrubbing and a little time todo their job. These cleaners will never “soak”clean a surface and therefore should never be usedin any other type of cleaning such as CIP or COP.

Foam Cleaning

Foam cleaning is a quick and effective method forcleaning surfaces that have a light or moderate soilload on them. The process is quite simple. First, and

most importantly, gross soils are rinsed from the sur-faces. After a thorough prerinse, a thin layer of foamcleaner is applied to the surface. After waiting 5 to10 minutes, the foam and soils are rinsed off the sur-face. As with manual cleaning, there are several is-sues that need to be addressed when you foam clean:

� Failure to use the proper detergent. Because foamcleaners are used with minimal scrubbing, theyare approximately 5–10 times stronger than amanual cleaner. The best type of foam cleaner in ayogurt operation for general cleaning isliquid-chlorinated alkaline foam cleaner. Thistype of cleaner removes all the organic soils andleaves the surface ready to sanitize. Occasionally,depending on water hardness and otherconditions, acid foam cleaner may also be used.This acid foam cleaning removes mineral filmsand leave the surface shinny. Take special notethat when you acid foam clean, it is always best touse it after an alkaline foam cleaner and be verycareful to avoid mixing the two cleaners in anyway.

� Failure to use the proper amount of cleaner.Always follow the manufacture’s directions forthe amount of product to use. If the directions aretoo vague, always ask your supplier to clarifywhat is the right amount. Typical usages arebetween 2 and 4 oz/gallon; however, someproducts are recommended outside of this range.

� Allowing the foam to dry. This is a primary failurein foam cleaning. If the foam dries on the surface,all the soils that the cleaner has removed will beredeposited on the surface. This redeposited soilis frequently referred to as “redep.” “Redep” isextremely hard to remove and will make itimpossible to sanitize the surface. Frequently anoperator will either foam too much equipmentand surfaces or will go on break after foaming.The worst situation is if the equipment is warm orhot, it quickly dries the foam. All of thesesituations must be avoided when foam cleaning.Only let the foam stay on a cool surface for5–10 minutes and rinse thoroughly.

� Failure to use the proper temperatures. Prerinsingand postrinsing with too hot water will “cook” thesoils on the surface and cause, at a minimum,streaking. For good cleaning, rinse waters shouldbe between 70◦F and 110◦F. This temperaturewill remove the soil and help eliminate streaking.The temperature of the water to generate the foamis also very important. Always use cool or cold


water for this purpose. If hot water is used, theproduct may not foam properly and may quicklydry and cause “redep.”

� Too wet or dry foam. The amount of water trappedin the foam determines if the foam is too dry ortoo wet. All foamers currently sold by reputablecompanies will have a method for adjusting thefoam. This is usually by adjusting the waterand/or air pressure or the air/solution mixture. Ifthe foam is too dry, there will not be enough waterin the foam for it to act as a good cleaner; and ifthe foam is too wet, it will be very heavy or soupyand fall from the equipment very fast. Good foamis similar to a wet shaving cream and will hang ona vertical surface for at least 5 minutes.

� Poor foaming technique. Here is the secondreason for foam cleaning to fail. If good foamingtechnique is not used, the operator will miss largeareas of the surfaces being cleaned. Always foamfrom the bottom up. Never foam from the topdown, and always have a plan as to how the foamwill be applied to the equipment.

� Failure to scrub difficult soils. Even as good asfoam cleaning is, it may not clean all the soil froma surface. There will be areas that need to havesome scrubbing to remove all the soil.

COP Cleaning

Clean-Out-of-Place (COP) cleaning is a wonderfulmethod to clean small parts, pipes, and other miscel-laneous items. The parts are rinsed and placed into aspecially designed tank that will circulate a cleaningsolution around and through all the parts. Again, aswith all types of cleaning, there are issues to address:

� Failure to use the proper detergent. COP tanksare not designed to tolerate foam. Foam in thesetanks causes the pump to cavitate, thus greatlyreducing the flow rate of the wash water. For thisreason only a cleaner designed to be a CIP cleaneris to be used. I strongly recommend a chlorinatedCIP cleaner for good soil removal. Remember toalways follow the manufacturer’s directions as tothe proper concentration.

� Improper cleaning temperature. If the cleaningtemperature is too cold the equipment will bedirty; and if it is too hot the equipment might bedamaged and it could be dangerous to theoperator. COP tanks are not “boil-out” tanks.Keeping the cleaning temperature at 145–160◦Fwill help in cleaning and saving energy.

� Failure to properly prerinse. All the parts that areto be cleaned in a COP vat must be thoroughlyrinsed prior to placing into the vat. Failure toproperly rinse might overload the detergent withsoil and may cause excess foaming. This is amajor reason that can cause COP cleaning to beineffective. Ensure that the prerinse is with coolor lukewarm (<120◦F) water or else there is a riskof “cooking” the soils onto the surface.

� Overloading the COP vat. This is the number tworeason for failure. Always leave some room in thevat for the water to properly circulate. COPcleaning depends upon temperature, time,chemical strength, and vigorous water circulation.If the vat is overloaded, there will be poorcirculation and the process will probably fail.Another situation I have frequently seen is anoperator trying to clean an 8-foot pipe in a 6-footCOP vat. Half of the pipe will stick out of the vatand never get cleaned. In fact, none of the pipeswill be cleaned because there is absolutely nocirculation of the cleaner in the pipe. Taking thepipe out and turning it around surely will not help.Long pipes need to be cleaned in a CIP system,pipe wash vat, or manually scrubbed with pipebrushes.

� Postrinse failure. In a COP vat when the cleaningtime is finished, the supply pump is turned off andthe tank is drained. Frequently, the soil that hasbeen removed off the equipment’s surface floatswhen the circulation of the cleaner ceases. Thisfloating soil redeposits onto the surfaces if the vatis simply drained at this time. Always add cool towarm water to the vat and overflow the floatingsoil. When doing so be very careful not to get anyof the cleaning chemicals on yourself or others.When the soil has overflowed, drain the tank andthoroughly rinse parts with either a cold waterhose or by refilling the vat with cold water.

� Failure to Disassemble. The number one reasonfor cleaning failures in a COP vat is notcompletely disassembling all the parts to becleaned. Any equipment that is not completelydisassembled will not clean and will be dirty.There is no exception to this rule. All gaskets,joints, and other assemblies must be taken apart.Small and/or delicate pieces should be placed intoa COP basket to facilitate cleaning and to protectthem. As stated, I have found this to be thenumber one cause for failure and I frequentlyrecommend that sanitation leaders andsupervisors not walk by a COP vat without


looking into it to verify that all the parts aredisassembled and that the vat is not overloaded.

CIP Cleaning

Generally prior to the mid 1940s, all equipment in adairy plant was completely taken down and manuallycleaned every day. It was usually left overnight to dryand reassembled the next workday. This worked rea-sonably well in small dedicated operations; however,this would be virtually impossible in today’s mas-sive processing plants where silos and tanks holding60,000 gallons or more are common and have milesof welded processing pipes and lines. A way of clean-ing this type of equipment had to be developed priorto the introduction of modern processing plants. Thatbreakthrough came in the mid 1940s and 1950s withthe advent of CIP cleaning. Today, CIP cleaning sys-tems range from simple manually operated systemsto huge systems completely run by powerful comput-ers. There are two fundamental CIP systems used inmodern cultured dairy product plants:

1. Reclaim CIP. The heart of a reclaim system is alarge tank used to reclaim the CIP cleaning so-lution for the next cycle. These systems can saveenergy and possibly water; however, the systems,by their very nature, will wash over and over withthe same wash water. This may cause contamina-tion to be spread throughout the plant if the systemis not running at top efficiency.

2. Single use CIP. A single-use CIP system alwaysuses fresh-wash water to wash each system. Mod-ern single use systems will not use excess wateror energy and can be an asset to the production ofhigh-quality products.

CIP systems offer an excellent way to clean if theyare properly designed and running well. They do, aswith other methods of cleaning, have a number ofissues that are critical to cleaning:

� Low flow rate. CIP cleaning totally depends uponthe flow of the cleaning solution for mechanicalaction. The flow rate through a pipe must be at aminimum of 5 ft/sec for the water to have enoughturbulence to clean. Any flow under this rateresults in the flow being too easy (laminar) toclean. Also tanks and silos must have proper flowdown the walls to clean. There is a simpleformula used to calculate the minimumflow—two times the circumference measured infeet. As an example, if the circumference is 40 ft,

the minimum flow to the spray device in the tankwill be 80 gal/min. This amount of water willcause a turbulent flow down the side of the tank.

� The wrong detergent. I recommend chlorinatedCIP cleaners for most CIP cleaning in a culturedplant. This will clean and leave the surfaces readyto be sanitized. If nonchlorinated cleaners areused, the equipment needs to be periodicallyinspected for a protein buildup. When using achlorinated cleaner, you not only have to measurethe concentration of the cleaner but also theconcentration of the chlorine. Both have to be atoptimal concentration. Always follow thesupplier’s recommendations for the cleaner andkeep the chlorine between 70 and 250 ppm. If areclaim system is used, extra chlorine may have tobe added.

� Too low or high a cleaning temperature. For mostcleaning of a processing plant, a temperature of140–170◦F should work well. If excesstemperature is used, the equipment may bedamaged and poor cleaning may result. Too low atemperature could leave the equipment dirty.

� System out of “balance.” “Balance” is a term usedto describe the CIP system’s hydraulics. A wellrunning system will have all the rinse and washwater following correct flow/time patterns. Asystem out of balance will loose water,contaminate solutions, mix chemicals, poorlyclean, and waste money. “Balance” is extremelyimportant and must be addressed. As a hint if theCIP supply pump has an air eliminator, the CIPsystem may be out of balance. Normally there isno need for an air eliminator on the CIP supplypump.

� Poor prerinse. The most important step in the CIPcleaning process is the prerinse. The CIP systemmust be programmed to thoroughly remove all thegross soils from the equipment. If the gross soilsare not removed, the cleaning solutions will beoverloaded with soil and the equipment willprobably be dirty.

Cleaning in a cultured plant is vital to the safe pro-duction of high-quality products. There is still thesimple truth that the surfaces are either clean or dirty.If the cleaning operations listed above are properlyperformed, the surfaces will be clean and ready tosanitize. I am frequently asked, “Why do we needto sanitize when we clean all the bacteria from thesurface?” This is a good question and the best wayto address it is that effective cleaning will remove


between 90% and 99% of the bacteria from the equip-ment’s surface. This is a very good reduction but notenough. Not enough to protect public health and toassure high-quality cultured products.

SANITIZINGSanitizing is the treatment of a cleaned surface with achemical or physical agent to destroy pathogenic mi-croorganisms and to reduce the total microbial vege-tative cell population to a safe level. Always note that“sanitizing” is not “sterilizing” and not all microor-ganisms are killed. Typically, sanitizing of a surfacewill reduce the microbial population by three logs.That is another 99.9% beyond what is accomplishedby cleaning. What is left on the surface is a matterof numbers. If there are a large number of microbeson a surface and the population is reduced by 99.9%,there could still be a substantial population of mi-crobes left. Vigorous cleaning and good sanitizingwill leave a surface with very few bacteria and othermicrobes. It is an accepted criterion that, after sani-tizing, there should be fewer than two microbes persquare centimeter of surface area. If the cleaning orsanitizing steps fail, there may be massive numbersleft on the surface and product quality will be com-promised.

There are a number of general rules for sanitizing:

� Only use sanitizers that are approved by theFederal EPA for use on food contact surfaces.

� Always follow label directions for use on foodcontact surfaces. It is a violation of Federal law ifthese directions are not followed.

� Pick the best sanitizers for your plant and then letthem do their job. Put 95% of your effort intoproperly cleaning the surface.

� Pick sanitizers based upon how they are to beused and the individual plant circumstances.

� In a cultured plant, never rinse the sanitizer fromfood contact surfaces with water.

� Constantly check the sanitizer concentrations.� Rotation of sanitizers because of “resistant bugs”

is not necessary. If there are problems, it is almostalways a cleaning issue.

� There is no sanitizer that can make up for poorcleaning.

� Sanitize open surfaces within 30 minutes of useand closed tanks within 3 hours of use.

� All sanitizers have broad-spectrum activity exceptquaternary ammonium compounds (Quats).

� Store all sanitizers out of direct sunlight in a cool,dry room with good ventilation.

There are numerous ways to sanitize cultured dairyplants. Various chemicals and heat have been usedover the years and I offer the following recommen-dations specifically designed for culture operations.

� For sanitizing in CIP systems and HTST units apara acetic acid sanitizer (PAA) is normallyrecommended. All reputable suppliers of cleanersand sanitizers will be able to supply anappropriate PAA sanitizer. Most PAA sanitizershave a fairly wide concentration range approvedfor food contact surfaces. It is recommended thatthe PAA sanitizer be used at maximum strength tohelp control yeast, mold, and bacteriophage. ForCIP systems, always use the products in coolwater and handle carefully. When used in HTSTunits, the heat of forward flow may cause gasketdamage and I recommend that Viton gaskets beused. They are more expensive than other gasketsbut will tolerate the PAA well. Because PAAsanitizers are not strong acids, the normalcleaning regimen may need to have an acidcleaning cycle. Always consult with yourchemical supplier regarding acid cleaning.

� COP vats are excellent vats in which to sanitizepreviously cleaned equipment. There are twogood sanitizers for use in a COP tank. The firstchoice is an iodine sanitizer. When using aniodine sanitizer, always make sure that theconcentration is set at 25 ppm and that the usesolution has a pH <4.5. Do not use an iodinesanitizer if the pH is over 5.5. A good iodinesanitizer is very effective on bacteria, yeast,and mold and is color-coded. The second choiceis to use a PAA sanitizer. I recommend thatthe strength be set at mid-range of the useconcentrations. Note: Only use iodine for soakinggaskets and other rubber parts to avoid excessivecorrosion.

� The best sanitizer for manual sanitizing of piecesand parts either by using a central sanitizer unit orin a bucket is iodine. Use a concentration of25 ppm and be sure the pH is acceptable. Iodine iswell accepted by operators. Its color makes it easyto judge the concentration and it does not have aharsh odor. I have heard that iodine will stainstainless steel. Under proper use, that does nothappen. What an iodine sanitizer will stain is soil,especially protein films. A second choice is to usePAA. It is a good sanitizer; however, it does have


a mildly offensive odor and is not tolerated wellby many operators.

� Now the topic comes up about what product touse for sanitizing environmental surfaces such asfloors, walls, drains, and doorway entrances. Irecommend that the best product for most of theseapplications is a Quat sanitizer, especially an acidQuat sanitizer. I am very well aware that there aremany people in the cultured products industrywho are very much against this type of sanitizerbecause it could kill the culture. There is sometruth that Quats, even small amounts like 5 ppm,are very effective against the Gram-positivebacteria that make up culture. For this reason, Irecommend Quats only for the environment. If theQuat that is on the floor ends up in the culture, theplant has a problem far worse than a dead culture.Quat sanitizers are excellent products forcontrolling yeast, mold, and pathogenic bacteriaon environmental surfaces. They have lowcorrosion and no offensive odor. I recommendusing a disinfecting strength of 500–1,000 ppmfor nonfood contact surfaces. Apply the Quat to aclean surface and do not rinse it off and it willform a residual effect that will help controlunwanted microbes. The most effective methodfor applying to the floor and building microbialbarriers at doorways is to use “door foamers.”They deposit sanitizing foam at the door forsanitizing shoes and fork lift wheels. Thisapproach is far superior to trying to use a footbath,which frequently becomes very dirty or dry.

To sum up the recommendations for sanitizers:

1. PAA for CIP2. Iodine for central sanitizer systems and manual

sanitizing3. Acid Quats for environmental sanitizing

BACTERIOPHAGE (PHAGE)CONTROLIn a dairy plant producing cultured dairy products,the term “phage” will cause even the most seasonedemployee to become immediately concerned for theirproduct. Phage (or phage particles) is a very specialtype of virus that only attacks bacteria. In the culturedplant, the phage can attack and destroy all the cultureneeded to make the product. Many vats of almostcheese and tanks of almost yogurt or buttermilk havefound their way to the drain or as other forms of wastebecause of phage.

What is a virus and how do they multiply? Are theyreally alive, dead, or somewhere in-between? Theseare really good questions. First of all a virus is thesmallest “living” thing that we know of, being muchsmaller than bacteria. The question, as to if they arealive, arises from the fact that a virus cannot multiplyor duplicate itself. To replicate, a virus will attack avery specific host cell. During this attack, the viruswill inject its DNA into the host cell and catastroph-ically change the complete function of the cell fromwhatever it was doing into becoming a virus man-ufacturing plant. After the host cell makes around30–200 new virus cells, the cell ruptures, thus releas-ing the viruses (lysing) and the process starts all over.As discussed above, phage is a virus that specificallyattacks bacteria, such as culture. Because of the rapidand massive multiplication of the phage in the culture,the phage will rapidly kill all the culture bacteria andruin the production. For example, a typical scenariowould be that after the culture is added to the mainproduct, the pH starts to drop from approximately 6.8toward the desired finished pH. However, about halfway to the desired pH, further acid production juststops and without quick intervention the productionis lost. The phage have completely taken over andkilled all the “good” bacteria.

Phage Control

There are four specific issues in controlling phagethat must be addressed:

� Culture and culture rotation� Sanitation� Emergency recovery� Plant design and condition

Environmental Sanitation. First of all, the envi-ronmental areas such as the HVAC, floors, walls, ceil-ings, drains, and doors need to be in good repair andof sanitary design. If these areas are neglected, it willbe very difficult to control phage. Install a floor san-itizing foam system on each doorway or entryway.The sanitizer of choice for these floor foamers is Quatat 800–1000 ppm. PAA may also be used followinglabel directions. For cleaning the environmental sur-faces, foam cleaning with chlorinated foam cleaner at3–4% concentration is recommended. If the plant hasa phage problem, add one quart of chlorine sanitizerto 15 gallons prediluted chlorinated foam solution in atank foamer and foam onto the surfaces. Let stand for15 minutes and thoroughly rinse. Foaming with the


added chlorine once a week will further help controlphage. Clean the drains every day with chlorinatedcleaner. After cleaning and thoroughly rinsing, san-itize all the surfaces with chlorine at 200 ppm. Fogsanitizing is of little use for phage control and wedo not recommend its use. If the HVAC is clean andproperly filtered, positive pressure maintained, andenvironmental surfaces cleaned and sanitized, phagewill not have anywhere to “hide.”

Open Cheese Vats. Clean the vats every day witha chlorinated cleaner using both foaming and handscrubbing. Thoroughly rinse the chlorinated cleanerand reclean with a manual acid cleaner and rinseagain. Prior to production, sanitize the vats with50–75 ppm chlorine sanitizer. Be very sure to alsocompletely clean and sanitize the vat superstructure,paddles, and knives.

Loose pieces and parts. Take every effort to han-dle these pieces and parts in a sanitary manner. Thisespecially includes gaskets, scoops, pipe joints, lu-bricant tubes, and other small items. After thoroughcleaning, store these items in sanitizer solutions, notlaid out or hung all over the plant. The best sanitizerfor long-term storage is iodine at 25 ppm. It will killphage and minimize any possible corrosion and is“kinder” on gaskets than other sanitizers. Change thesolution at least once a day.

CIP of Closed Vats, Tanks and Silos. After deter-mining that the CIP system is properly functioning,CIP all systems every day using a “built” chlorinatedCIP cleaner following manufacturing directions for

concentration. Following a thorough rinse, acid-washwith a surfactated CIP acid cleaner and rinse again.Sanitize prior to production with PAA followingmanufacturer’s recommendations.

Always remember that a surface must be abso-lutely clean prior to sanitizing and that most micro-biological issues, including phage, are cleaning is-sues not sanitizing issues. With thorough care andadherence to procedures, phage problems will be aproblem of the past.

A FINAL THOUGHTThe one factor that will make or break the sanitationprogram in a plant is people. For many years thecleanup crew has been made up of the newest, leasttrained, least supervised, and lowest paid employees.Yet these are the employees that totally control thefuture of the company. If this seems like a disconnect,it is. These employees need to be well trained andgiven all the tools they need to do their job. Thisincludes proper incentives to do a good jogg and tokeep good employees on the job. Many companiestoday have recognized the absolute importance oftheir cleanup crews and have addressed the issues inseveral ways. There are companies that have movedsanitation from third shift to first shift. Others paypremiums for sanitation or build in bonuses for goodperformance. There are other ways like shift rotationand other incentives that can make a difference. It isfair to say that if a company relegates sanitation toa third class operation, it is losing unrealized profitand will probably be a “USED-TO-BEE.”

15Yogurt Plant: Quality Assurance


Regulatory ObligationsFood & Drug Administration (FDA)Standard of IdentityFood Labeling in the United StatesAnalytical TestsQuality Control Programs

National Yogurt Association Criteria for Live and ActiveCulture Yogurt

Refrigerated YogurtFrozen Yogurt

Specification ProgramDefects and Trouble ShootingReferences

The quality assurance program for yogurt plant en-compasses various functions to assure the quality ofthe products produced. It also is designed to insurethat manufacturing plant meets all the state and fed-eral regulatory obligations in regard to package la-beling, proper ingredient usage, safety, and shelf liferequirements.

REGULATORY OBLIGATIONSMilk production, processing, marketing, and manu-facture of dairy products are all regulated by federal,state, and local authorities. The regulatory compo-sition for the manufacture of yogurt in the UnitedStates is discussed below. Chapter 3 includes detaileddiscussion of regulatory requirements for milk pro-duction, transportation, and processing.

Food & Drug Administration (FDA)

Production, transportation, and processing of GradeA dairy products are regulated by the Milk SafetyBranch of the FDA. Product safety, labeling,

packaging, and other product issues are included.In addition, other departments of the FDA are in-volved in product standards and labeling in generalunder the Fair Packaging and Labeling Act, and mat-ters related to overall compliance. Milk specialistsrepresent Milk Safety Branch’s regional offices andwork with the state regulatory agencies by provid-ing scientific, technical, and inspection assistance. Inthis manner, compliance with regulatory policies andprocedures is assured. Besides liaison with the FDA,the State Department of Agriculture (Dairy Divisionor Health Department) is also involved in regulatingmilk production and manufacturing in a particularstate. To assist States and municipalities in initiatingand maintaining effective programs for the preven-tion of milk borne disease, the Public health service,in 1924, developed a model regulation, known as theStandard Milk Ordinance for voluntary adoption byState and local milk control agencies. To provide forthe uniform interpretation of this Ordinance, an ac-companying code was published in 1927 that pro-vided administrative and technical details as to satis-factory compliance. This model regulation now titledthe Grade A Pasteurized Milk Ordinance (PMO)—Recommendations of the United States Public HealthService/Food and Drug Administration. The PMO isrecommended for legal adoption by States, counties,and municipalities, to encourage a greater uniformityand a higher level of excellence of milk sanitationpractice in the United States. An important purposeof this recommended standard is to facilitate the ship-ment and acceptance of high quality milk and milkproducts in interstate and intrastate commerce.

The Pasteurized Milk Ordinance describes the re-quirements for product safety, milk hauling, sani-tation, equipment, and labeling. The PMO is very

247




extensive and covers milk production at the farmto the manufacturing facility. The requirements forchemical, physical, bacteriological, and temperaturestandards are given in Table 3.3 in Chapter 3. Somesalient features include the following:

� Must contain the word Grade A on the container� Must contain the identity of the plant� Product standards of identity must be met� Temperature—cooled to 7◦C (45◦F) or less and

maintained there at� Bacterial limits not to exceed 300,000 CFU/ml in

commingled raw milk and 20,000 CFU/ml inpasteurized milk

� Coliforms—not to exceed 10 CFU/ml� Phosphatase test—less than 350 milliunits/liter

for pastcurized fluid products by the Fluorometeror Charm ALP or equivalent. The test representsdetection of 0.075% raw milk or less

� Drugs—no positive results on drug residue testingby approved procedures

National Conference of Interstate Milk Shippers(NCIMS) plays a key role in setting standards andregulations related to the PMO, methods of mak-ing sanitation ratings of milk supplies, and sanitationrequirements for Grade A condensed and dry milkproducts, including condensed and dry whey. Fur-thermore, NCIMS is involved in regulations pertain-ing to the fabrication of single service containers, andclosures for milk and milk products, and in the eval-uation of milk laboratories. The purpose of NCIMSis to promote the best possible milk supply for allthe people and to provide for unrestricted availabil-ity of milk and milk products in interstate shipment.The NCIMS operates to establish uniformity of prod-uct standards from state to state. Both producers andprocessors of milk are represented in NCIMS. Theyaddress issues related to laws and regulations gov-erning Grade A milk sanitation (storage, handling),reciprocity between regulatory jurisdictions and vio-lations of reciprocity.

Standard of Identity

All dairy products with standard of identity defini-tion must conform to the FDA standard and the reg-ulations published in Code of Federal Regulations(USDHHS FDA, 2003) (Table 15.1). Chapter 4 con-tains more information on this topic.

A few dairy products (e.g., butter and nonfat drymilk) are regulated by USDA grading and inspec-tion programs. The FDA has the authority to estab-lish standards of identity for foods whenever doing

Table 15.1. Code of Federal Regulations(21 CFR): Standard of Identity for Dairy Foods

CFR Part:

Dairy foodGeneral, definitions 130Milk and cream, definitions 131.3Milk 131.110Acidified milk 131.111Cultured milk 131.112Concentrated Milk 131.115Sweetened–condensed milk 131.120Sweetened–condensed skimmed

milk131.122

Low fat dry milk 131.123Nonfat dry milk 131.125Nonfat dry milk fortified with

vitamins A and D131.127

Evaporated milk 131.130Evaporated skimmed milk 131.132Low-fat milk 131.135Acidified low-fat milk 131.136Cultured low-fat milk 131.138Skim milk 131.143Acidified skim milk 131.144Cultured skim milk 131.146Dry whole milk 131.147Dry cream 131.149Light cream 131.155Light whipping cream 131.160Sour cream 131.157Acidified sour cream 131.162Eggnog 131.170Half-and-half 131.180Sour half-and-half 131.185Acidified sour half-and-half 131.187Yogurt 131.200Low-fat yogurt 131.203Nonfat yogurt 131.206

Frozen dessertsDefinitions 135.3Ice cream and frozen custard 135.110Goat’s milk ice cream 135.115Mellorine 135.130Sherbet 135.140Water ices 135.160

Food labelingFood labeling Part 101Nutritional quality guidelines for

foodPart 104

Current Good ManufacturingPractice in manufacturing,packaging holding human food

Part 110

Source: Adapted from USDHHS, FDA Revised April 1, 2003.http://www.cfsan.fda.gov/∼1rd/FCF131.html

15 Yogurt Plant: Quality Assurance 249

so will promote honesty and fair dealing in the in-terest of consumers. Standards generally specify thetypes of ingredients the food must contain (manda-tory ingredients), as well as those it may contain(optional ingredients). Standards also may set mini-mum and maximum content requirements for valu-able constituents as well as for fillers. FDA has es-tablished standards for staple food items, includingmilk, peanut butter, jams and jellies, and milk choco-late. The USDA’s Food Safety and Inspection Service(USDA/FSIS) also has standards for foods regulatedby that agency.

Food Labeling in the United States

Detailed discussion for food labeling regulations isdescribed in Chapter 4.

Under the Nutrition Labeling and Education Act of1990, the FDA promulgated new labeling regulationsthat became effective on May 8, 1994. Actual labelvalues depend on a particular formulation and actualnutrient analysis relative to the food being labeled.All the nutrients designated in dairy foods label aredeclared in relation to a standard reference amount(serving size) of the food. The label must declare theamounts per serving for calories, calories from fat,total fat, saturated fat, cholesterol, sodium, total car-bohydrates, sugars, dietary fiber, and protein. Also,percentage Daily Reference Values must be shownto a 2,000-calorie and 2,500-calories/day diets forthe above nutrients, as well as for vitamins A and C,and calcium and iron to make the label consumer-friendly and useful. Effective January 1, 2006, foodlabels will also be required to declare the content offat containing trans fatty acids.

Daily reference value (DRV) relative to variousdairy foods is based on an evaluation of scientificdata. For example, scientific data indicate that car-bohydrates should compose 60% of the daily calorieallowance. Therefore, the DRV for carbohydrates is300 grams, providing 1,200 calories. This amount ofcarbohydrate would furnish approximately 60% ofreference caloric intake for 2,000 calories per day.Accordingly, if a food serving contains 30 g of car-bohydrates, the DV percentage will be 10%.

Daily Reference Values used for calculations forNutritional Labeling are shown in Table 15.2. TheDRV for macronutrients is based on the daily diet of2,000 calories, except fats, carbohydrates, and fiber,which are based on 2,500-calorie diet. The referencedaily intakes (RDI) relates to micronutrients (vita-mins and minerals) regardless of caloric intake.

Certain claims on foods have also been defined forinclusion in the label. Table 15.3 lists these productdefinitions in terms of low fat, nonfat, and other terms.

The percentage value for a food label is calculatedas percent of the values shown in Nutritional labelfor yogurt (Fig. 15.1).

The calorie calculation is based on 4, 4, and 9 cal/gof carbohydrate, protein, and fat, respectively. All thecalculated numbers are rounded to the nearest wholenumber.

The FDA regulations also address health claims asshown below:

� Calcium and osteoporosis: Product must be highin calcium content

� Sodium and hypertension: Product must be lowsodium

� Food high in potassium and high blood pressure� Fat and cancer: Product must be low fat� Fat and heart disease: Product must be low fat,

low saturated fat, and low cholesterol� Soluble fiber from whole oats and coronary heart

disease� Soluble fiber from psyllium seed husk and

coronary heart disease� Whole grain foods and coronary heart disease� Fiber-containing grain products, fruits, and

vegetables and cancer� Fruits and vegetables (High in vitamins A and C)

and cancer� Fruits, vegetables, and grain products that contain

fiber, particularly soluble fiber and coronary heartdisease

� Folate and neural tube defects� Soy protein and risk of coronary heart disease

In addition, when making any health claims, theproduct must contain (before fortification) at least10% of one of the nutrients: Vitamin A, Vitamin C,calcium, iron, protein, or fiber.

Under the current standards, Vitamin A fortifica-tion to 2000 International Units (IU) (which is 500IU or 10 per cent of the daily value (DV) per 8 ounceserving) is optional for yogurt. When Vitamin D isadded, its level must be 400 IU per quart (100 IU or25% of the DV per serving). Because vitamins A andD are fat soluble, they get removed in the process offat removal from milk. As a result, nonfat and low-fat yogurt would be low in vitamins A and D contentas compared to full-fat yogurt. Therefore, additionof Vitamins A and D to low fat and nonfat yogurt ispracticed by some yogurt manufacturers.

The general standard also provides that, under cer-tain circumstances, safe and suitable ingredients that


Table 15.2. Daily Reference Values and Reference Daily Intakes for Nutrition Labeling (based ona 2000 calorie intake; for adults and children 4 or more years of age) in the United States

Macronutrient Daily Reference Values (DRV)

Total fata , maximum 65 gSaturated fatty acidsa , maximum 20 gCholesterola , maximum 300 mgSodiuma , maximum 2.4 gPotassiuma 3.5 gTotal carbohydratea 300 gFibera 25 gProteina 50 g

Micronutrient Reference Daily Intakes (RDI)Vitamin Aa 5000 IUVitamin Ca 60 mgCalciuma 1 gIrona 18 mgVitamin D 400 IUVitamin E 30 IUVitamin K 80 �gThiamin 1.5 mgRiboflavin 1.7 mgNiacin 20 mgVitamin B6 2 mgFolate 400 �gVitamin B12 6 �gBiotin 300 �gPantothenic acid 10 mgPhosphorus 1 gIodine 150 �gMagnesium 400 mgZinc 15 mgSelenium 70 �gCopper 2 mgManganese 2 mgChromium 120 �gMolybdenum 75 �gChloride 3.4 ga FDA regulations require these nutrients be listed in the Nutrition Facts panel. Labeling of other nutrients is optional.Source: Adapted from: http://www.cfsan.fda.gov/∼dms/flg-7a.html REV. Jan 30, 1998.

perform a technical effect (for example, thickenersand stabilizers) may be added to the modified foodsto maintain performance characteristics similar to thetraditional food.

In addition, the FDA permits certain qualifiedhealth claims. The following summarizes them:

1. Qualified Claims About Cancer Riska. Selenium & Cancerb. Antioxidant Vitamins & Cancer

2. Qualified Claims About Cardiovascular DiseaseRisk

a. Nuts & Heart Diseaseb. Walnuts & Heart Diseasec. Omega-3 Fatty Acids & Coronary Heart Dis-

eased. B Vitamins & Vascular Disease

3. Qualified Claims About Cognitive Functiona. Phosphatidylserine & Cognitive Dysfunction

and Dementia4. Qualified Claims About Neural Tube Birth De-

fectsa. 0.8 mg Folic Acid & Neural Tube Birth Defects

Tab

le15

.3.

Defi

nitio

nsof

Nut

rient

Con

tent

Cla

ims

Nut

rien

tFr

eeL

owR

educ

ed/L

ess

Com

men

ts

Cal

orie

s21

CFR

101.

60(b

)

Les

sth

an5

calp

erre

fere

nce

amou

ntan

dpe

rla

bele

dse

rvin

g

40ca

lor

less

per

refe

renc

eam

ount

(and

per

50g

ifre

fere

nce

amou

ntis

smal

l)M

eals

and

mai

ndi

shes

:120

calo

rle

sspe

r10

0g

Atl

east

25%

few

erca

lori

espe

rre

fere

nce

amou

ntth

anan

appr

opri

ate

refe

renc

efo

odR

efer

ence

food

may

notb

e“L

owC

alor

ie”

Use

ste

rm“F

ewer

”ra

ther

than

“Les

s”

“Lig

ht”

or“L

ite”:

If50

%or

mor

eof

the

calo

ries

are

from

fat,

fatm

ustb

ere

duce

dby

atle

ast5

0%pe

rre

fere

nce

amou

nt.I

fle

ssth

an50

%of

calo

ries

are

from

fat,

fat

mus

tbe

redu

ced

atle

ast5

0%or

calo

ries

redu

ced

atle

ast1

/3pe

rre

fere

nce

amou

nt“L

ight

”or

“Lite

”m

ealo

rm

ain

dish

prod

uct

mee

tsde

finiti

onf

“Low

Cal

orie

”or

“Low

Fat”

mea

land

isla

bele

dto

indi

cate

whi

chde

finiti

onis

met

For

diet

ary

supp

lem

ents

:Cal

orie

clai

ms

can

only

bem

ade

whe

nth

ere

fere

nce

prod

uct

isgr

eate

rth

an40

calo

ries

per

serv

ing

Tota

lFat

21C

FR10

1.62

(b)

Les

sth

an0.

5g

per

refe

renc

eam

ount

and

per

labe

led

serv

ing

(or

for

mea

lsan

dm

ain

dish

es,l

ess

than

0.5

gpe

rla

bele

dse

rvin

g)N

otde

fined

for

mea

lsor

mai

ndi

shes

3g

orle

sspe

rre

fere

nce

amou

nt(a

ndpe

r50

gif

refe

renc

eam

ount

issm

all)

Mea

lsan

dm

ain

dish

es:3

gor

less

per

100

gan

dno

tm

ore

than

30%

ofca

lori

esfr

omfa

t

Atl

east

25%

less

fat

per

refe

renc

eam

ount

than

anap

prop

riat

ere

fere

nce

food

Ref

eren

cefo

odm

ayno

tbe

“Low

Fat”

“%

FatF

ree”

:OK

ifm

eets

the

requ

irem

ents

for

“Low

Fat”

100%

FatF

ree:

food

mus

tbe

“Fat

Free

”“L

ight

”—se

eab

ove

For

diet

ary

supp

lem

ents

:cal

orie

clai

ms

cann

otbe

mad

efo

rpr

oduc

tsth

atar

e40

calo

ries

orle

sspe

rse

rvin

g

Satu

rate

dFa

t21

CFR

101.

62(c

)

Les

sth

an0.

5g

satu

rate

dfa

tand

less

than

0.5

gtr

ans

fatty

acid

spe

rre

fere

nce

amou

ntan

dpe

rla

bele

dse

rvin

g(o

rfo

rm

eals

and

mai

ndi

shes

,les

sth

an0.

5g

satu

rate

dfa

tand

less

than

0.5

gtr

ans

fatty

acid

spe

rla

bele

dse

rvin

g)N

oin

gred

ient

that

isun

ders

tood

toco

ntai

nsa

tura

ted

fate

xcep

tas

note

dbe

low

a

1g

orle

sspe

rre

fere

nce

amou

ntan

d15

%or

less

ofca

lori

esfr

omsa

tura

ted

fat

Mea

lsan

dm

ain

dish

es:1

gor

less

per

100

gan

dle

ssth

an10

%of

calo

ries

from

satu

rate

dfa

t

Atl

east

25%

less

satu

rate

dfa

tper

refe

renc

eam

ount

than

anap

prop

riat

ere

fere

nce

food

Ref

eren

cefo

odm

ayno

tbe

“Low

Satu

rate

dFa

t”

Nex

tto

alls

atur

ated

fatc

laim

s,m

ustd

ecla

reth

eam

ount

ofch

oles

tero

lif

2m

gor

mor

epe

rre

fere

nce

amou

nt;a

ndth

eam

ount

ofto

talf

atif

mor

eth

an3

gpe

rre

fere

nce

amou

nt(o

r0.

5g

orm

ore

ofto

talf

atfo

r“S

atur

ated

FatF

ree”

)Fo

rdi

etar

ysu

pple

men

ts:s

atur

ated

fatc

laim

sca

nnot

bem

ade

for

prod

ucts

that

are

40ca

lori

esor

less

per

serv

ing

Con

tinu

ed

251

Tab

le15

.3.

(Con

tinue

d)

Nut

rien

tFr

eeL

owR

educ

ed/L

ess

Com

men

ts

Cho

lest

erol

21C

FR10

1.62

(d)

Les

sth

an2

mg

per

refe

renc

eam

ount

and

per

labe

led

serv

ing

(or

for

mea

lsan

dm

ain

dish

es,l

ess

than

2m

gpe

rla

bele

dse

rvin

g)N

oin

gred

ient

that

cont

ains

chol

este

role

xcep

tas

note

dbe

low

a

Ifle

ssth

an2

mg

per

refe

renc

eam

ount

bysp

ecia

lpr

oces

sing

and

tota

lfat

exce

eds

13g

per

refe

renc

eam

ount

and

labe

led

serv

ing,

the

amou

ntof

chol

este

rol

mus

tbe

“Sub

stan

tially

Les

s”(2

5%)

than

ina

refe

renc

efo

odw

ithsi

gnifi

cant

mar

ket

shar

e(5

%of

mar

ket)

20m

gor

less

per

refe

renc

eam

ount

(and

per

50g

offo

odif

refe

renc

eam

ount

issm

all)

Ifqu

alifi

esby

spec

ialp

roce

ssin

gan

dto

talf

atex

ceed

s13

gpe

rre

fere

nce

and

labe

led

serv

ing,

the

amou

ntof

chol

este

rolm

ust

be“S

ubst

antia

llyL

ess”

(25%

)th

anin

are

fere

nce

food

with

sign

ifica

ntm

arke

tsha

re(5

%of

mar

ket)

Mea

lsan

dm

ain

dish

es:2

0m

gor

less

per

100

g

Atl

east

25%

less

chol

este

rolp

erre

fere

nce

amou

ntth

anan

appr

opri

ate

refe

renc

efo

odR

efer

ence

food

may

notb

e“L

owC

hole

ster

ol”

Cho

lest

erol

clai

ms

only

allo

wed

whe

nfo

odco

ntai

ns2

gor

less

satu

rate

dfa

tper

refe

renc

eam

ount

;or

for

mea

lsan

dm

ain

dish

prod

ucts

—pe

rla

bele

dse

rvin

gsi

zefo

r“F

ree”

clai

ms

orpe

r10

0g

for

“Low

”an

d“R

educ

ed/L

ess”

clai

ms

Mus

tdec

lare

the

amou

ntof

tota

lfat

next

toch

oles

tero

lcla

imw

hen

fate

xcee

ds13

gpe

rre

fere

nce

amou

ntan

dla

bele

dse

rvin

g(o

rpe

r50

gof

food

ifre

fere

nce

amou

ntis

smal

l),o

rw

hen

the

fate

xcee

ds19

.5g

per

labe

led

serv

ing

for

mai

ndi

shes

or26

gfo

rm

ealp

rodu

cts

For

diet

ary

supp

lem

ents

:cho

lest

erol

clai

ms

cann

otbe

mad

efo

rpr

oduc

tsth

atar

e40

calo

ries

orle

sspe

rse

rvin

g

Sodi

um21

CFR

101.

61

Les

sth

an5

mg

per

refe

renc

eam

ount

and

per

labe

led

serv

ing

(or

for

mea

lsan

dm

ain

dish

es,l

ess

than

5m

gpe

rla

bele

dse

rvin

gN

oin

gred

ient

that

isso

dium

chlo

ride

orge

nera

llyun

ders

tood

toco

ntai

nso

dium

exce

ptas

note

dbe

low

a

140

mg

orle

sspe

rre

fere

nce

amou

nt(a

ndpe

r50

gif

refe

renc

eam

ount

issm

all)

Mea

lsan

dm

ain

dish

es:1

40m

gor

less

per

100

g

Atl

east

25%

less

sodi

umpe

rre

fere

nce

amou

ntth

anan

appr

opri

ate

refe

renc

efo

odR

efer

ence

food

may

notb

e“L

owSo

dium

”

“Lig

ht”

(for

sodi

umre

duce

dpr

oduc

ts):

iffo

odis

“Low

Cal

orie

”an

d“L

owFa

t”an

dso

dium

isre

duce

dby

atle

ast5

0%“L

ight

inSo

dium

”:if

sodi

umis

redu

ced

byat

leas

t50%

per

refe

renc

eam

ount

.Ent

ire

term

“Lig

htin

Sodi

um”

mus

tbe

used

insa

me

type

,siz

e,co

lor

&pr

omin

ence

.L

ight

inSo

dium

for

mea

ls=

“Low

inSo

dium

”“V

ery

Low

Sodi

um”:

35m

gor

less

per

refe

renc

eam

ount

(and

per

50g

ifre

fere

nce

amou

ntis

smal

l).F

orm

eals

and

mai

ndi

shes

:35

mg

orle

sspe

r10

0g

252

.

“Sal

tFre

e”m

ustm

eetc

rite

rion

for

“Sod

ium

Free

”“N

oSa

ltA

dded

”an

d“U

nsal

ted”

mus

tco

nditi

ons

ofus

ean

dm

ustd

ecla

re“T

his

isN

otA

Sodi

umFr

eeFo

od”

onin

form

atio

npa

neli

ffo

odis

not“

Sodi

umFr

ee”

“Lig

htly

Salte

d”:5

0%le

ssso

dium

than

norm

ally

adde

dto

refe

renc

efo

odan

dif

not“

Low

Sodi

um”,

sola

bele

don

info

rmat

ion

pane

lSu

gars

21C

FR10

1.60

(c)

“Sug

arFr

ee”:

Les

sth

an0.

5g

suga

rspe

rre

fere

nce

amou

ntan

dpe

rla

bele

dse

rvin

g(o

rfo

rm

eals

and

mai

ndi

shes

,le

ssth

an0.

5g

per

labe

led

serv

ing)

No

ingr

edie

ntth

atis

asu

gar

orge

nera

llyun

ders

tood

toco

ntai

nsu

gars

exce

ptas

note

dbe

low

a

Dis

clos

eca

lori

epr

ofile

(e.g

.,“L

owC

alor

ie”)

Not

Defi

ned.

No

basi

sfo

rre

com

men

ded

inta

ke

Atl

east

25%

less

suga

rspe

rre

fere

nce

amou

ntth

anan

appr

opri

ate

refe

renc

efo

odM

ayno

tuse

this

clai

mon

diet

ary

supp

lem

ents

ofvi

tam

ins

and

min

eral

s

“No

Add

edSu

gars

”an

d“W

ithou

tAdd

edSu

gars

”ar

eal

low

edif

nosu

gar

orsu

gar

cont

aini

ngin

gred

ient

isad

ded

duri

ngpr

oces

sing

.Sta

teif

food

isno

t“L

ow”

or“R

educ

edC

alor

ie”

The

term

s“U

nsw

eete

ned”

and

“No

Add

edSw

eete

ners

”re

mai

nas

fact

uals

tate

men

tsC

laim

sab

outr

educ

ing

dent

alca

ries

are

impl

ied

heal

thcl

aim

sD

oes

noti

nclu

desu

gar

alco

hols

aE

xcep

tif

the

ingr

edie

ntlis

ted

inth

ein

gred

ient

stat

emen

thas

anas

teri

skth

atre

fers

tofo

otno

te(e

.g.,

“aad

dsa

triv

iala

mou

ntof

fat”

).N

ote:

“Ref

eren

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Nonfat Light YogurtYogurt With Aspartame andother Sweetener.Vitamins A & D Added

Low Fat1% Milk fatVitamins A & D added

Nutrition Facts Nutrition Facts

Serving Size 1 Container (170g) Serving Size 1 Container (170g)

Amount Per ServingCalories 100

Calories from Fat 0

% Daily Value % Daily Value

Total Fat 0g.

Saturated Fat 0g

Trans Fat 0g

Cholesterol

Less than 5mg

Sodium 85mg

Potassium 250mg

Total Carbohyrdrate 19g

Sugars 14g

Protein 5g Protein 5g

Vitamin A Vitamin A

Vitamin D Vitamin D

Calcium Calcium

Phosphorus Phosphorus

Not a significant source ofIron, Vitamin C and dietaryfiber.* Percent Daily Values arebased on a 2,000 caloriediet.

Not a significant source ofIron, Vitamin C and dietaryfiber.* Percent Daily Values arebased on a 2,000 caloriediet.

0%

0%

1%

4%

7%

6%

10%

15%

20%

20%

15%

15%

20%

20%

15%

11%

Total Fat 1.5g.

Saturated Fat 1g

Calories from Fat 15

Trans fat 0g

Cholesterol 10mg

Sodium 80mg

Potassium 260mg

Total Carbohyrdrate 33g

Sugars 27g

7%

11%

3%

3%

3%

8%

Amount Per ServingCalories 170

Figure 15.1. Typical nutrition facts label for light nonfat yogurt and low-fat yogurt. The format is shown in Chapter 4,page 67.

Analytical Tests

To conform to the regulatory standard of identityand company standards of quality, safety and cost,various analytical tests are performed in the in-dustry (Chandan and Shahani, 1993, 1995; Chris-ten, 1993; Tamime and Robinson, 1999). Chapter 7deals with the laboratory analysis of yogurt and fer-mented milks. In general, quality tests for milk anddairy products include analysis for chemical com-position, physical attributes, microbiological quality,

and sensory characteristics. Analytical tests for milkcomposition are for fat, total solids, protein, lactose,ash, vitamins, and minerals. Basic quality of milkis assessed by tests such as titratable acidity, addedwater, foreign materials, antibiotics, sanitizers, afla-toxins, pesticides, and other environmental contami-nants. Abnormal milk tests include Wisconsin andCalifornia somatic cell counts (SCC) for mastitis.SCC is a measure for white blood cells in the milkand is used as an indicator of herd health. Among the


microbiological tests for raw and pasteurized milk,total aerobic plate count gives a measure of total bac-teria present and is a good indicator of the overall milkquality. Coliform count is a marker of sanitary qual-ity of milk. Yeast and mold count is an indicator ofthe spoilage tendency of low pH products like yogurt,sour cream, and buttermilk. Pathogenic bacteria maygain entry in commercial dairy products as postpas-teurization contaminants or by cross contaminationwith raw milk. Dairy testing in the industry is typi-cally directed toward the incoming milk, cream, con-densed, and dry dairy ingredients to determine theirsuitability for use in the plant operations. Incomingtanker loads of raw milk are generally laboratory-pasteurized and subjected to organoleptic assess-ment (odor, flavor, and mouth-feel). Various testson raw milk include temperature check, sediment,fat content, moisture, total solids content, freezingpoint determination to detect adulteration with wa-ter and antibiotic tests. Freshly pasteurized milk andproduct mixes are tested for coliform count (violetred bile agar) as an overall index of sanitary qual-ity. Pathogenic organisms receiving attention includeSalmonella spp., Staphylococcus aureus, Yerseniaenterocolytica, E.coli 0157: H7, and Aeromonas hy-drophillia due to profound impact associated withtheir recent outbreaks of food-borne illness.

With a view to expedite the results of microbio-logical analyses and to implement corrective actionsin a timely manner, various rapid methods are be-ing developed. Accuracy, speed, simplicity, cost, andvalidity are the key factors in their development.

Procedures for Analytical Tests

Various physical, chemical, microbiological, andsensory analyses are typically conducted (See Chap-ter 7) in accordance with the standard official proce-dures, developed and updated by AOAC International(Horowitz, 2003) and American Public Health Asso-ciation (Marshall, 1993). For regulatory complianceof Standard of Identity, the FDA specifies certain an-alytical tests to be performed on a dairy food.

Quality Control Programs

General

A well planned quality control program must be ex-ecuted in the plant to consistently produce productswith high quality, to maximize keeping quality, and todeliver yogurt with the with most desirable attributesof flavor and texture to the consumer. As part of this

program, it is imperative to enforce a strict sanita-tion program along with good manufacturing prac-tices. Shelf-life expectations from commercial yogurtvary but generally approximate 30–55 days from thedate of manufacture provided the temperature duringdistribution and retail marketing channels does notexceed 10◦C (45◦F). Because lactic acid and someother metabolites produced in the fermentation pro-cess protect yogurt from most Gram-negative psy-chotrophic organisms, most quality issues in yogurtare not related to proliferation of spoilage bacteria.

Most problems related to yogurt spoilage are asso-ciated with yeast and molds, which are highly tolerantto low pH and can grow under refrigeration temper-atures.

The control of yeast contamination is done byaggressive sanitation procedures related to equip-ment, ingredients, and plant environment. Clean-in-place chemical solutions should be used with specialattention to their strength and proper temperature.Hypochlorites and iodophors are effective sanitizingcompounds for fungal control on the contact surfacesand in combating the environmental contamination.Hypochlorites at high concentrations are corrosive.Iodophors are preferred for their noncorrosive prop-erty as they are effective at relatively low concen-trations. For detailed discussion of sanitizing proce-dures, see Chapter 14.

Yeast and mold contamination may also arisefrom starter, fruit preparations, packaging materials,packaging equipment and overall plant environment.Organoleptic examination of yogurt starter may behelpful in eliminating the fungal contamination therefrom. If warranted, direct microscopic view of thestarter may reveal the presence of budding yeast cellsor mold mycelium filaments. Plating of the starter onacidified potato dextrose agar would confirm the re-sults. Avoiding contaminated starter for yogurt pro-duction is necessary.

Efficiency of equipment and environmental sani-tation can be verified by enumeration techniques in-volving exposure of poured plates to atmosphere inthe plant or making a smear of the contact surfaces ofthe equipment, followed by plating. Also, for a quickcheck of food contact surfaces prior to productionstart-up, ATP detection can be used. ATP swabs anduse of an ATP luminator provide an indirect mea-surement of microbes, food residue, or other biolog-ical material that is an indicator of the effectivenessof sanitation. In yogurt manufacturing a quick ATPswab on filler valves, fruit hoppers, blending tanks,etc., can identify low levels of contamination in a mat-ter of seconds. Filters on the air circulation system


should be on a maintenance schedule to be checkedand changed regularly. Walls and floors should becleaned and sanitized frequently and regularly.

The packaging materials should be stored in dust-free and humidity-free conditions. The filling roomshould be fogged with chlorine or iodine regularly.

Quality Control checks on fruit preparations, andflavorings (Chapter 9) should be performed (spotchecking) to minimize yeast and mold entry into fruitflavored yogurt. Certificate of analysis (COA’s) con-taining physical, chemical, and microbiological anal-ysis should be requested for each lot.

Quality Control in Yogurt Plant

Quality control programs for finished yogurt includecontrol of product viscosity, flavor, body and tex-ture, color, pH, and composition. In addition, dailychemical, physical, microbiological, and organolep-tic test programs must be in place for ingredients andfinished product. Also, the quality control programshould include a detailed “plan of control” for criti-cal processing parameters and milk receiving. All ofthese should be included in the product specificationsfor the plant. A summary of typical quality tests in ayogurt plant is outlined in Table 15.4.

There are many areas in formulation and process-ing that when overlooked lead to quality issues in yo-gurt. The most common flavor defects are generallydescribed as high acid, weak flavor, or unnatural fla-voring. The sweetness level may be excessive, weak,or may exhibit corn syrup flavor. The ingredients usedmay impart undesirable flavors like stale, metallic,old ingredients, oxidized, rancid, or unclean. Lackof control in processing procedures may cause over-cooked, caramelized, or excessively sour flavor notesin the product. Proper control of processing param-eters and ingredient quality assure a consistent goodflavor. Product standards for fat, total solids, viscos-ity, pH (or, titratable acidity) and organoleptic char-acteristics should be strictly followed. Wheying off orappearance of watery layer on the surface of yogurt isundesirable and can be controlled by judicious selec-tion of effective stabilizers and by following properprocessing conditions.

The evaluation of yogurt quality should be approx-imately 24 hours (D+1) after packaging. The follow-ing organoleptic evaluations are generally performed:

� Taste—Typical yogurt flavor, fruit flavor, andmouthfeel. Absence of any off-flavor.

� Aroma—Typical yogurt and fruit bouquet.

� Visual appearance—Color, fill of container,syneresis, fruit bleeding, white specks in theproduct, lumpiness, overall body and texture, fruitchunks/integrity.

In addition, the following laboratory analysisshould be conducted:

Titratable Acidity/pH Measurement. Titratableacidity (TA) is used as a measure of quality indairy products. %TA is obtained by titrating 9 g ofmilk/yogurt with a standard alkali to pH 8.6 or thephenolphthalein end point. It is expressed as % lacticacid. A standard procedure for titratable acidity mea-surement for yogurt is described in the InternationalDairy Federation publication (IDF1991a).

%TA = milliliters of 0.1 N alkali

10%TA is attributed to the constituents of serum

solids or milk solids-not-fat. In yogurt processing,TA is commonly used for following the progress offermentation, as well as a quality parameter in fin-ished yogurt product. TA is composed of “appar-ent” and “developed” acidities. Fresh milk should nothave any significant lactic acid content, since it hasnot been subjected to bacterial growth (acid produc-tion from lactose) or severe heat treatment. However,when fresh milk is titrated with a standard alkali, itrequires some alkali titer to reach phenolphthaleinendpoint. This is “apparent acidity,” which is due tosalts and proteins present in fresh milk. The approx-imate contribution of various constituents to TA is:carbon dioxide 0–0.01%; caseins 0.05–0.08%; wheyprotein 0.01–0.02%; phosphate 0.06%; and citrate0.01%. Accordingly, an apparent TA of 0.13–0.18%is contributed by milk constituents other than lacticacid.

Developed acidity is the portion of TA that is at-tributed to lactic acid produced as a result of bacterialfermentation of lactose under anaerobic conditionssuch as in yogurt. Certain yogurt plants prefer to usepH in place of TA. There is a correlation between%TA and pH. Depending on the milk solids-not-fatcontent of yogurt, a pH of 4.4 approximately corre-sponds to 0.85% TA in yogurt processing.

The current consumer preferred pH for yogurt isin the range of 4.2–4.4 at D+1 stage of shelf life. Ifincubation is not terminated in time to result in thispH range at D+1, the lactobacilli may continue togrow well below pH 4.2 during shelf life. When thisoccurs, the streptococci start to disappear, upsettingthe optimum bacterial ratio and resulting in a product,

Table 15.4. Summary of a Typical Yogurt Plant Quality Tests and Their Purpose

Incoming Material Test Purpose

Milk Direct microscopic countSensory (odor, flavor)Titratable acidity, freezing point

depression test, antibioticassay, fat and total solids tests

Temperature

Microbiological qualityGeneral qualityFreshness, handling practiceWater adulterationInsure absence of antibioticsVerify chemical compositionMeet company and Regulatory

requirementsStarter pH/titratable acidity, direct

microscopic examinationActivity and integrity of yogurt culture

Fruits, nuts, syrups,sweeteners

Yeasts and moldsOsmophilic yeasts

Microbial contaminationShelf life of the product

Packaging materials Sterility testing Safety/shelf life of the productVerify printing standards

Check print quality

Fresh ProductYogurt after 24 hours

of packagingpH/titratable acidityEvaluate flavor and textureMeasure Viscosity

Acidity controlAssure sensory quality

Yogurt after packaging(Day ofmanufacturing)

Coliform count Detecting unsanitary processing orpackaging conditions

Indicator of postpasteurizationcontamination

Yogurt 24 hours afterpackaging (D+1)

Preincubate product in itscontainer at 30◦C for 24hours, followed by yeast andmold count

Prediction of Shelf life

End of Code (storeshelf life samples at7.2◦C (45◦F)

SensorypHObserve spoilage

Assure quality standards are met at endof code

Inline Sampling andPlant Sanitation

Yogurt mix Fat and total solids after 10–15minutes of agitation.

Check on formulation

Yogurt mix infermentation tank

Titratable acidity/pH Follow progress and determine endpoint of fermentation

HTST/Filler orpackagingmachine/glycol orice water andequipment surfaces

Preincubation followed byStandard Plate Count andcoliform count

Contamination with Psychrotrophicorganisms and general sanitation

Environmental air andwater samples

Standard Plate Count andcoliform count

General sanitation practices

Filler Checks Seals, coding, record weights,fill temperature

Assure proper filing requirements andcoding

ATP Swabs FillerFruit hopper and/or blenderOther contact surfaces

Prestart up sanitation check of yogurtcontact surfaces

257


which is too high acid and weak in typical yogurtflavor.

Shelf-Life Test. As a check for shelf-life quality,incubate yogurt cups for 3 days at 30◦C to detectyeast contamination, and for 7 days at 20◦C for molddetection. This will give an indication of consumershelf-life issues. For large production runs it is recom-mended to take samples at the beginning, middle, andend for each flavor. It is also recommended to storeyogurt cups at 8–10◦C until the end of code life to de-tect any organoleptic changes in the product. Yeastand mold spoilage manifests on the surface. Yeastspoilage appears as colorless, flat, moist colonies andmold spoilage as white or blue-green spots with theeventual formation of film and overgrowth over thewhole surface. Also, the taste and smell of the productmight indicate typical bacterial/yeast/mold spoilageor enzymatic degradation. It is important to recordthe percentage of spoiled cups at the end of code life.

Compositional Analysis. Record the fat and totalsolids of plain yogurt and fermented base before theaddition of fruit to insure conformation to propri-etary and regulatory obligations. The fat content ismeasured by the AOAC procedure (Horowitz, 2003)and the total solids are determined by IDF procedure(IDF 1991b).

Viscosity Measurement. An instrument such aspenetrometer, Brookfield viscometer, or Rheomat,provides a quantitative value that can be assigned tothe viscosity of yogurt. An acceptable range can beestablished and maintained to help produce a moreconsistent body of yogurt from production batch tobatch.

Using Brookfield viscometer, the following proce-dure is suggested:

1. Temper yogurt sample in the cup to 3.3–4.4◦C.2. Use Brookfield Viscometer model RVT or equiva-

lent and Spindle #5 at 10 rpm. Attach the spindle.Place the yogurt cup on the counter and lower thespindle through the surface of yogurt to level thenotch on the spindle to the surface of yogurt.

3. Turn the viscometer on.4. Depress the lever after 25 seconds and take the

reading.5. Calculate the viscosity (in centipoises) of the sam-

ple by multiplying the reading with 400.

Typically, most commercial yogurts fall within therange of 12,000 cps to 30,000 cps.

Microscopic Examination. Occasionally, the ra-tio of yogurt culture bacteria (S. thermophilus (ST)and L. delbrueckii ssp bulgaricus (LB)) in the finalyogurt product should be evaluated to provide thehistory of culture performance. This check is alsouseful to detect slow down in acid production due toinhibitors or phage attack when one of the yogurt or-ganism ST may form abnormal shape and cell counts.

Microbiological Analysis. Generally, yogurt istested for coliforms, which indicates postpasteuriza-tion contamination, since coliforms do not survivepasteurization. This sanitation test is important inclearing yogurt for shipping and marketing.

Another test, which has a strong bearing on theshelf life of yogurt, is yeast and mold count, espe-cially in fruit flavored yogurt. This test should beconducted on yogurt samples that have been prein-cubated at 30◦C for 24 hours before plating.

Sensory Evaluation of Yogurt After 24 hours. Theplant should develop a quantitative rating scale on thebasis of marketing product objectives for flavor, con-sistency, and appearance. It is important to establishthe consumer “minimum acceptable” quality level.

Control of Overrun in Whipped Yogurt. In theproduction of whipped yogurt, the foam formation asa result of aeration of yogurt mix is called overrun.It is important in giving a fluffy texture to whippedyogurt and must be controlled during the aerationprocess. Overrun (OR) is the volume of yogurt ob-tained over and above the volume of yogurt mix usedand can be calculated as follows:

% OR = (Volume of whipped yogurt) − (Volume of yogurt mix used)

(Volume of mix used)

× 100 Equation 15b

On weight basis:

% OR = (Weight of cup of yogurt mix) − (Weight of cup of whipped yogurt)

(Weight of cup of whipped yogurt)

× 100

Frozen yogurt. In the production of frozen yogurtthe overrun (OR) is an important parameter of thefinished product texture and the overall eating quality.It can be calculated as shown in the section as abovefor whipped yogurt.

In hard-pack frozen yogurt, a coarse and icy tex-ture may be caused by the formation of ice crystalsdue to fluctuations in storage temperatures. Sandi-ness may be due to lactose crystals resulting from


too high levels of milk solids. A soggy or gummydefect is caused by too high milk solids-not-fat levelor too high sugar content. A weak body results fromtoo high overrun, insufficient total solids or improperstabilization.

Color defects may be caused by the lack of inten-sity or authenticity of hue and shade. Proper blendingof fruit preparations and yogurt mix is necessary foruniformity of color. The compositional control testsare: fat, total solids, pH, overrun, and microscopicexamination of yogurt culture to ensure desirable ra-tio in LB and ST. Also, good microbiological qualityof all ingredients is necessary.

NATIONAL YOGURTASSOCIATION CRITERIAFOR LIVE AND ACTIVECULTURE YOGURTNational Yogurt Association (NYA) is a nonprofitassociation of major yogurt producers in the UnitedStates. Their mission is to enhance consumption ofyogurt and to protect consumer perception and in-tegrity of yogurt. Accordingly, in the absence of FDArequirements for quantitative counts of yogurt bacte-ria in commercial yogurt, they have established cri-teria for live and active yogurt through their seal pro-gram. It should be noted that any yogurt manufacturerin the United States may declare “live & active” yo-gurt culture on the label without using the NYA pro-prietary seal provided that the statement is true andnot misleading. According to NYA, live and activeculture yogurt (refrigerated cup and frozen yogurt)is the food produced by culturing Grade A dairy in-gredients with a characterizing bacterial culture inaccordance with the standards of identity for yogurt(21 C.F.R. S 131.200), low-fat yogurt (21 C.F.R. S131.203), and nonfat yogurt (21 C.F.R. S 131.206).In addition to the use of the bacterial cultures re-quired by the referenced federal standards of identityand by the NYA criteria, live and active culture yo-gurt may contain other safe and suitable food gradebacterial cultures. The NYA offers a trademark sealfor use by its members for declaring the presenceof cultures of live and active yogurt cultures on thelabel.

According to the NYA, heat treatment of live andactive yogurt is inconsistent with the maintenanceof live and active cultures in the product. Accord-ingly, heat treatment, which is intended to kill the liveand active organisms should not be undertaken af-ter fermentation. Likewise, manufacturers of live and

active culture yogurt should undertake their best ef-forts to ensure that distribution practices, code dates,and handling instructions are conducive to the main-tenance of live and active cultures.

To meet these NYA criteria, live and active cultureyogurt must satisfy each of these requirements:

1. The product must be fermented with both L. del-brueckii subsp. bulgaricus and S. thermophilus.

2. For refrigerated yogurt, the total viable count at thetime of manufacture will be 108 CFU per gram.In the case of frozen yogurt, the total viable countat the time of manufacture will be 107 CFU pergram.

3. The cultures must be active at the end of the statedshelf life as determined by the activity test de-scribed in the NYA “Sampling and Analytical Pro-cedures.” Compliance with this requirement shallbe determined by meeting the criteria for the activ-ity test on two of the three representative samplesof yogurt, which have been stored at temperaturesbetween 0◦C (32◦F) and 7.2◦C (45◦F) for refrig-erated cup yogurt and at temperatures of −17.8◦C(0◦F) or colder for frozen yogurt for the entirestated shelf life of the product. The activity testis met if there is an increase of one log duringfermentation.

4. In the case of frozen yogurt, the product shall havea total titratable acidity expressed as lactic acid ofat least 0.3% at all times. At least 0.15% of totalacidity must be obtained by fermentation. This isconfirmed by demonstrating the presence of bothD & L forms of lactic acid.

The applicant should submit samples, each repre-senting a single line of product, ideally taken from thebeginning, middle, and end of a manufacturing runthat demonstrates that the yogurt has met the stan-dard. The samples should be analyzed according tothe following procedures:

Refrigerated Yogurt

1. Total viable yogurt counts will be enumerated bythe standard procedure (IDF, 2003a, 2003b). Thetotal viable count is the sum of colony formingunits of Streptococcus thermophilus and Lacto-bacillus delbrueckii subsp. bulgaricus per gramof the product.

2. At the end of the stated shelf life designated by theyogurt manufacturer, activity of the culture willbe reported for at least two of the three randomsamples on the NYA “Laboratory Report Form.”


The activity test is carried out by pasteurizing 12%solids nonfat dry milk at 92◦C (198◦F) for 7 minutes,cooling to 43◦C (110◦F), adding 3% inoculum of thematerial under test and fermenting at 43◦C (110)◦Ffor 4 hours. The total yogurt organisms in the in-oculated milk substrate are to be enumerated bothbefore and after fermentation by IDF methodology(2003a).

The activity test will be reported as log increase inyogurt organisms (CFU/g) following fermentation ofthe defined substrate under the standard condition atthe end of the stated shelf life.

Frozen Yogurt

1. The titratable acidity of samples, one each rep-resenting beginning, middle, and end of a man-ufacturing run, will be determined (IDF, 1991a).In addition, the manufacturer must certify that atleast 0.15% titratable acidity in the product wasderived from yogurt fermentation.

2. Total viable yogurt counts will be enumerated bythe IDF procedure (2003). The total viable countis the sum of colony forming units of Streptococ-cus thermophilus and Lactobacillus delbrueckiisubsp. bulgaricus per gram of the product.

3. At the end of the stated shelf life designated bythe manufacturer, activity of the culture will bereported for at least two of the three random sam-ples.

The activity test is carried out by pasteurizing 12%solid nonfat dry milk at 92◦C (198◦F) for 7 minutes,cooling to 43◦C (110◦F), adding 3% inoculum of thematerial under test and fermenting at 43◦C (110◦F)for 4 hours. The total yogurt organisms in the in-oculated milk substrate are to be enumerated bothbefore and after fermentation by IDF methodology(2003).

The activity will be reported as Log increase inyogurt organisms (CFU/g) following fermentation ofthe defined substrate under the standard conditions atthe end of the stated shelf life.

SPECIFICATION PROGRAMA specification program should include parametersfor raw materials, ingredients, and packaging mate-rials as well as the product formulation, processingsteps and plan of control in the plant. It should alsocover, milk receiving, HACCP, and rework controls,and product storage and shipping. As an example, thespecification for milk is shown below.

Raw Milk Quality Specifications

It involves several parameters as discussed below.

� Standard Plate Count (SPC) is a measure of thetotal bacteria count and measures the overallquality of milk. High SPC can cause reducedshelf life of the finished product and off flavorsfrom enzyme activity and elevated acidity.Federal Standards allow 100,000 CFU/mlmaximum for an individual producer (300,000CFU, commingled). However, some states maydiffer. For example, Idaho standard is 80,000CFU/ml maximum and California standard is50,000 CFU/ml maximum. It is recommended toset the standard at 50,000 CFU/ml.

� Coliform Bacteria Count is a measure of milksanitation. High coliform counts reflect poormilking practices and unsatisfactory cleanlinessof the dairy operation. Occasionally, coliformcount may indicate sick cows in smaller herds.Coliform is an indicator that food poisoningorganisms may possibly be present. There are noFederal Standards for coliform counts in rawmilk, but California does have a standard forcoliform (750 CFU/ml maximum). Arecommended standard is 500 CFU/ml.

� Laboratory Pasteurized Count (LPC) is a measureof heat-stable bacteria, which may survivepasteurization. It is performed by heat-treatinglaboratory samples to simulate batchpasteurization at 62.8◦C for 30 minutes andenumerating the bacteria that survive using theSPC method. High LPC results indicate potentialcontamination from soil and dirty equipment atthe dairy. High LPC will cause reduced shelf lifeof finished products. Bacillus cereus is a commonsoil microorganism that can survive pasteurizationresulting in a high LPC. There are no FederalStandards for LPC. However, California standardfor LPC is 750 CFU/ml maximum.A recommended standard is 500 CFU/ml.� Preliminary Incubation (PI) count is a measure

of bacteria that will grow in refrigeratedconditions. The test requires holding the sampleat 10◦C for 18 hours followed by a StandardPlate Count (SPC) test. PI type of bacteria willbe destroyed by pasteurization but can stillresult in lower quality milk due to enzymaticactivity on the protein. High PIs (3- to 4-foldshigher than SPCs) are generally associated withinadequate cleaning and sanitizing of either themilking system or cows and/or poor milkcooling.


There are no Federal Standards for PI results inraw milk. Since the type of bacteria and the initialcount of the SPC may vary, it is not possible to seta numerical standard for this test although countshigher than 50,000 CFU/ml are excessive for both PIand SPC. A recommended standard is less than twotimes the SPC count.

� Somatic Cell Count (SCC) is a measure of thewhite blood cells in the milk that is used as anindicator of herd health. High SCCs areundesirable because the yield of all culturedproducts is proportionally reduced, the flavorbecomes salty, development of oxidationincreases, and it usually relates to higher SPC in atime-lag process. Staphylococci and streptococciare heat-tolerant bacteria that normally causemastitis. Coliform bacteria that are easily killedby heat may also cause mastitis. FederalStandards allow 750,000 Cells/ml maximum.State standards vary. For example, Idaho standardis 750,000 Cells/ml maximum and Californiastandard is 600,000 Cells/ml maximum. Arecommended standard is 500,000 Cells /ml.

� Titratable Acidity (TA) is a measure of the lacticacid in milk. High bacteria counts will producelactic acid as the bacteria ferment lactose.Elevated temperatures for extended time willallow the bacteria to grow quickly and generate ahigher TA value. The normal range is0.13–0.16%. Lower values may indicate thatalkaline/ buffering chemicals are added to themilk. A recommended standard is0.13–0.16%.

� Temperature According to Federal Law, thetemperature of milk must never exceed7.2◦C. A recommended standard is 5.2◦C orless.

� Flavor is an important indicator of quality. Themilk should be fresh, clean and creamy. Elevatedbacteria counts can produce off flavors (i.e., acid,bitter). Feed flavors may vary from sweet to bitterand indicate the last items in a cow’s diet such aspoor feed, weeds, onion, or silage. Elevatedsomatic cell counts will render milk taste saltyand watery. Water in the milk will taste weak.Dirty, “barny,” and “cowy” flavors occur fromsanitation conditions and air quality at the dairyfarm. Oxidized or rancid flavors occur fromequipment operation and handling.

There are no federal standards for flavor. All re-ceiving plants should flavor milk (laboratory pasteur-ized) for defects before accepting it.

A recommended standard is that no off flavor ex-ists.

� Appearance is not a measured criterion but is asimportant as flavor for indications of quality.There are no federal standards for appearance.Most receiving plants will note any color ordebris defect in the milk before accepting it. Arecommended standard is “White, clean, nodebris, and filter screen of two or less (sedimenttest)”.

� Antibiotics and other drugs may not be present inmilk. All raw milk must conform to Grade A law.

To be considered organic, no milk can be usedfrom a cow that has been treated with antibiotics.For conventional milk, a treated cow will be withheldfrom the milking herd for about 5 days.

� Added Water is an adulteration. Testing thefreezing point of milk using a cyroscopeindicates if abnormal amounts of water exist inthe load. In most states it is illegal to have afreezing point above −0.530 Horvet scale. Arecommended standard should be −0.530 Horvetor less.

� Sediment is measured by drawing 1 pint of samplethrough a cotton disk and assigning a grade of 1(good) to 4 (bad) to the filter. A grade of 1 or 2 isacceptable. A processor also may monitor forsediment by screening the entire load through a3-inch mesh filter at the receiving line. There areno federal standards. Most receiving plants shouldrequire a filter grade of 1 or 2 although 3 may beaccepted.

A recommended standard is “No excessive mate-rial in a 3-in. sani-guide” filter.

� Fat and milk solids-not-fat (MSNF) Milk iscomposed approximately of 88% water, 3.5% fat,5.0% lactose, 3.5% protein, and <1% of minerals.MSNF is the percentage of total milk solidsminus the fat portion. The Standard of Identity formilk is 3.25% fat and 8.25% MSNF. This is therecommended standard.

Process and Product Specifications

Process and product specifications pertain to formu-lation, target processes, and a process plan of control.A manual for the plant should detail finished prod-uct characteristics, establish a target value, accept-able limits, and rejection values. The manual shouldinclude equipment and processing parameters, plan

Table 15.5. Defects in Yogurt and Their Causes

Defect Causes

Whey separation Low-fat contentWrong choice of modified starchInsufficient heat treatment of milkHeating or disturbing the coagulum during

incubation or thereafterAddition of rennetInsufficient acid formation, e.g., pH 4.8High incubation temperatures or too fast incubationHigh acidification before cooling, resulting in too low pH in

finished productMechanical shaking of the gelLow solids content in the mixAir incorporation in the stirred yogurtPoor culture

Weak body Too low pasteurizing temperature and timeToo fast incubationPoor cultureToo strong stirring of the gel or abuse in pumping

(high shear)Low solids content of yogurtInsufficient or improper addition of the stabilizerLow protein content of the milkMechanical shaking of the gel before completed coagulation

Sandy/Grainy body Poor cultureSevere heating of the milk causing unstable caseinHomogenization of the mix at high temperature and pressureExcessive addition of nonfat dry milkVibration during incubationToo fast set or incubationContainers disturbed before sufficiently cooledExcessive inoculation ratePoor distribution of starterWrong type of modified starch

“Ropy” Addition of slime producing strains of yogurt cultureToo low incubation temperature in the production

of the yogurt

Gummy The use of unsuitable stabilizerFaulty incorporation of stabilizersExcessive addition of stabilizers

Slow acid development Culture imbalanceToo low pasteurizing temperatureToo low incubation temperatureInsufficient inoculumWeak culturesToo high sugarInhibitors/antibiotics in milk supplyPhage infection

Fruity/fermented/yeasty flavor Growth of microbial contaminants

Oxidized flavor Effect of exposure to lightMetal catalyst

(Continued)

262


Table 15.5. (Continued )

Defect Causes

Lacking in flavor Culture imbalanceStarter growth slowed due to too low heat treatment

Bitter/ off flavor Culture imbalance (too many lactobacilli)Poor quality milkMicrobiological contamination.Poor quality flavoring used

Color of flavoring fading Microbiological contaminationHeavy metal contaminationColor unstable at low pH

of controlling them, and finished packaging param-eters. In addition, the manual should include qualitycontrol test methods and procedures, as well as clean-ing and sanitizing procedures.

Similarly, specifications should be set up for fruitpreparations, dairy ingredients, and dry milk (DMI,2003) (Chapter 9, 10, and 11, respectively).

Weight Control Program. To conform to weightsand measure regulations, it is imperative to set upa program on the basis of tolerances of the yogurtfillers. Based on the variations in the weight of filledcups from the weight set on the filling machine, astatistical model is set up to calculate standard devia-tions for the weights of product contained in the cups.Final setting on the filler is then made to achieve agiven confidence limit, say 95–99% confidence level.To minimize give away of the product, some compa-nies decide to set up fillers to deliver the weight de-clared on the cup plus two standard deviations, giving95% confidence limits.

DEFECTS AND TROUBLESHOOTINGWhen using poor ingredients or improper process-ing methods or improper formulation, several de-fects can develop in the finished yogurt. Some of themore common defects and their causes are shown inTable 15.5.

Finally, in the consistent manufacture of high-quality yogurt, it is important to give full considera-tion to the following key areas:

� The use of high-quality milk with adequateprotein content.

� Correct heat treatment and homogenization ofyogurt mix.

� Absolutely clean processing and packagingequipment.

� Proper inoculation of active pure cultures.� Maintenance of proper incubation time and

temperature.� Use of high-quality ingredients and flavors.� Storage of yogurt in a temperature below 4◦C.

REFERENCESChandan RC. 1997. Dairy-Based Ingredients. Eagan

Press, St. Paul, MN. pp. 48–49.Chandan RC, Shahani KM. 1993. Yogurt. In: YH Hui

(Ed), Dairy Science and Technology Handbook,Vol. 2. VCH Publishers, New York, pp. 1–56.

Chandan RC, Shahani KM. 1995. Other fermenteddairy products. In: G Reed, TW Nagodawithana(Eds), Biotechnology, Vol. 9, 2nd ed. VCHPublishers, Weinheim, Germany, pp. 386–418.

Christen GL. 1993. Analyses in Dairy Science andTechnology Handbook vol. I. Y.H. Hui, Editor. VCHPublishers, Inc. N.Y. pp. 83–156.

Dairy Management, Inc. (DMI). 2003. Concentratedand Dry Milk Ingredients. Dairy IngredientApplication Guide. Chicago, IL.

Horowitz W. 2003. Official Methods of Analysis, 17thed., 2nd Rev. AOAC International, Gaithersburg,MD.

International Dairy Federation. 1991a. Yogurt:Determination of Titratable Acidity. IDF/ISO/AOACStandard 150:1991.Brussels, Belgium.

International Dairy Federation. 1991b. Yogurt:Determination of total solids content.IDF/ISO/AOAC Standard 151:1991. Brussels,Belgium.

International Dairy Federation. 2003a. Yogurt:Enumeration of characteristicmicroorganisms-Colony Count Technique at 37◦C.IDF 117/ISO 7889 Standard, Brussels, Belgium.


International Dairy Federation. 2003b. Yogurt:Identification of characteristic microorganisms(Lactobacillus delbrueckii subsp. bulgaricus andStreptococcus thermophilus. IDF 146/ISO 9232Standard 150:1991.

Marshall, RT (Ed). 1993. Standard Methods for theExamination of Dairy Products. 16th ed. AmericanPublic Health Association, Washington, DC.

Tamime AY, Robinson RK (1999). Yogurt Science &Technology, 2nd ed. Woodhead Publishing Limited,Cambridge, England and CRC Press, Boca Raton,FL.

United States Department of Health and HumanServices, Public Health Services, Food and DrugAdministration. Grade “A” Pasteurized MilkOrdinance. 1999 Revision. Publication no. 229.Washington, DC.

United States Department of Health and HumanServices, Public Health Services, Food and DrugAdministration (USDHHS FDA). 2003. Code ofFederal Regulations. Title 21. Section 131. USGovernment Publishing Office. Washington, DC.

USDHHS, FDA Revised April 1,2003.http://www.cfsan.fda.gov/∼1rd/FCF131.html

16Sensory Analysis of Yogurt

Yonca Karagul-Yuceer and MaryAnne Drake

IntroductionSensory Analysis TechniquesSensory Analysis of YogurtConclusionsReferences

INTRODUCTIONSensory qualities (flavor and texture/mouthfeel) arecrucial for consumer acceptance. As such, under-standing and measuring sensory properties of dairyproducts is important. Although sensory science is arelatively young field (ca 1940), the importance offlavor and texture to the consumer has existed sinceproducts were first traded and sold in the market-place. This chapter will focus on a brief review ofsensory techniques followed by specific applicationsto yogurt and other fresh fermented dairy products.

SENSORY ANALYSISTECHNIQUESThe dairy industry has long recognized the impor-tance of sensory quality and developed tools to assessthese parameters before mainstream sensory scienceevolved. These traditional tools are grading and judg-ing of dairy products (ADSA, 1987; Bodyfelt et al.,1988). Both of these tools are still used today forspecific applications in the industry. These tools arenot advised for research and product development, asthey are not quantitative nor completely qualitative innature (Drake 2004; Singh et al., 2003). Both gradingand judging were developed in the early 1900s (1913and 1916, respectively) and were designed to rapidlyassess the overall product quality based on the pres-ence or absence of predetermined defects. Product

quality is evaluated on the basis of reference to theindividual’s ideal product. In the case of grading agrade is issued; in the case of judging a numericalquality score is issued.

Grading is still conducted by the US Depart-ment of Agriculture through the Agricultural MarketService (www.ams.usda.gov). Any dairy product cantheoretically be graded,;however, grading has tra-ditionally been conducted on Cheddar cheese, but-ter, and skim milk powder. Standards also exist forwhey and buttermilk powder, condensed milk; andSwiss, Emmentaler, Colby, Monterey Jack, and bulkAmerican cheese. Specific grading criteria do not ex-ist for other dairy products; however, they may stillreceive a USDA quality approval rating. The USDAquality approval rating can be used on retail pack-aging as with USDA grades and is based on USDAinspection of the product and facility where it wasproduced. A set of standards for yogurt to receivethe USDA Quality Approved Inspection Shield waspublished by the AMS in 2001 (www.ams.usda.gov).

The primary function of grading is to provide aspecific set of criteria for quality, which can be ap-praised by an impartial individual (USDA grader).Such criteria can be useful for marketing productsand promoting product uniformity. A list of defectsand grading criteria for skim milk powder are listedin Table 16.1.

The flavor and texture guidelines published for yo-gurt are listed in Table 16.2. These criteria are gen-eral, and not specific. Products can have quite a dis-tinct flavor and/or texture properties and still receiveuniform grades. This discrepancy has been demon-strated with Cheddar cheese and skim milk powders(Drake, 2004). This does not devalue the applica-tion of grading to the industry uniformity, but it does

265




Table 16.1. US Standards for Grades of Nonfat Dry Milk (Spray Process).

Ideal Flavor—Reconstituted nonfat dry milk shall possess a sweet, pleasing, and desirable flavor, but maypossess slight intensities of the following attributes: Cooked, feed, flat and chalky

Flavor Defect US Extra Grade US Standard Grade

Bitter Not permitted SlightChalky slight DefiniteCooked slight DefiniteFeed slight DefiniteFlat slight DefiniteOxidized Not permitted SlightScorched Not permitted SlightStorage Not permitted SlightUtensil Not permitted SlightNot permitted—sensory attribute not allowed in product for this grade; slight—slight intensity allowed for this grade; definite—definite intensity allowed for this grade www.ams.usda.gov

mean that grading is not an appropriate tool for prod-uct research where very subtle differences can impactexperimental conclusions and consumer acceptance.

Dairy products judging or scorecard judging wasdeveloped to stimulate and promote student inter-est in sensory quality of dairy products. Similar tograding, products receive a score based on the pres-ence or absence of specific defined defects (Bodyfeltet al., 1988). Butter was the first product included inthe contest. Today, six products are evaluated includ-ing strawberry yogurt. A list of judging criteria forstrawberry yogurt are listed in Table 16.3. As withgrading, product judging is a useful skill and canprovide valuable insight when troubleshooting in amanufacturing facility. Neither of these approachesare optimal tools for product research for several rea-sons. Quality scores generated are not discriminatingof subtle differences (both qualitative and quantita-tive) among products. This means that products may

receive identical or very similar quality scores and yetstill display very distinct specific flavor and/or texturedifferences that the scoring criteria do not take intoaccount. Scores are not uniformly spaced or assignedand thus cannot be subjected to parametric statisticalanalysis. Finally, judgments are generally made by afew individuals, typically one or two and are not repli-cated. Even highly experienced or trained individualscan vary from day-to-day in their sensory acuity andjudgment. As a result, larger numbers of panelists arerecommended for sensitive, reproducible results. Al-though the use of both grading and judging, as wellas other overall quality-based analysis criteria canbe found in research literature and will be addressedin this chapter, mainstream sensory techniques havegreat and powerful application to dairy products re-search and should be used.

Grading and dairy products judging were de-veloped in the United States. The International

Table 16.2. Quality Guidelines for USDA Specifications for Yogurt

FlavorShall possess a clean acid flavor, free from undesirable flavors such as bitter, rancid, oxidized, stale, yeasty,

and unclean. Flavoring ingredients shall be uniformly distributed, flavor shall be pleasing andcharacteristic of the flavoring used. Flavor shall not be harsh or unnatural.

Body/textureShall possess a firm, custard-like body with a smooth homogenous texture. A spoonful shall maintain its

form without displaying sharp edges, flavoring ingredients shall be uniformly distributed throughout theproduct.

Color/appearanceShall present a clean, natural color with a smooth velvety appearance. Unflavored yogurt may be a bright

white to off-white color. Surface should appear smooth and not exhibit excess whey separation or surfacegrowth or discoloration. Flavoring ingredients shall be uniform in size, distribution, and color.

www.ams.usda.gov

16 Sensory Analysis of Yogurt 267

Table 16.3. Quality Judging Criteria for Strawberry Yogurt—Approved by the American DairyScience Association

Attribute Defects Scoring

Appearance Atypical colorColor leachingExcess fruitLacks fruitLumpyFree wheyShrunkenSurface growth

Perfect score (no defects) is 5Different deductions are subtracted based on the

specific defect and the intensity (slight, definite,or pronounced) of the defect

Body/texture Gel-likeToo firmWeakGrainyRopy



Flavor High acidLow acidAcetaldehydeCookedLacks fine flavorToo high flavorUnnatural flavorLacks sweetnessToo sweetStabilizer flavorLacks freshnessUncleanOxidizedRancidStorage



Source: Bodyfelt et al., 1988.

Dairy Federation has also developed a quality-basedmethod for sensory evaluation of fermented dairyproducts (IDF, 1997), which covers the evalua-tion of appearance, consistency, and flavor (Table16.4). Products are given scores based on their vari-ability from a previously established specification.A numerical interval scale is used to demonstratethe magnitude of the possible deviation from thepreestablished sensory product specification. The fol-lowing scale shows the magnitude of the deviation foreach attribute in scoring:

Points

5 conformity with the preestablished sensoryspecification

4 minimal deviation from the preestablishedsensory specification

3 noticeable deviation from the preestablishedsensory specification

2 considerable deviation from the preestablishedsensory specification

1 very considerable deviation from thepreestablished sensory specification

0 unfit for human consumption

1. The evaluation of appearance can be carried outsimultaneously by the whole panel with separatescoring; involving the filling and the surface of theproduct, color, visible purity, presence of foreignmatters, spots of mold, seepage of whey, and phaseseparation. The evaluation is made by examinationin the opened package, if necessary by pouring outthe product from the package.

2. The evaluation of consistency involves thick-ness, stickiness, and coarseness. Evaluation canbe made by blending the product with a (black)spoon before evaluating the sample in the mouth.

3. The evaluation of flavor is made by smelling andtasting the product.


Table 16.4. Fermented Milk Product Quality Terms

Appearance Consistency Flavor

Overfilled Setting WateryUnderfilled Lumps or flakes FlatShrunken Dripping BitterHeterogeneous surface Uneven CookedUntypical color Gritty BurntBrown color Sticky SmokedNon-uniform color Too thick OilyMarbled Too fluid Chemical flavorAir bubbles Ropy/stringy Feed flavorForeign matter Dried Foreign flavorSeparation of whey Brittle Light-induced flavorMould Gelatinous Defective aromatizationYeast Defective ingredientsSeparation of phases CheesySedimentation MaltyLack of, or poor distribution Metallic

of ingredients MustyOxidizedAcidSharpHarshSourTallowyYeastyRancidAstringentUncleanStale/oldToo sweetToo saltySoapy, alkaline

Source: IDF, 1997.

The IDF quality terms developed for fermentedmilk products are listed in Table 16.4.

Mainstream sensory techniques, applicable to allproducts, both food and nonfood items, include a va-riety of tools to explore and define sensory propertiesand consumer perceptions. These groups of tools arecomprised of two basic groupings: analytical and af-fective tests. Several comprehensive textbooks areavailable on these topics (Lawless and Heymann,1998; Meilgaard et al., 1999). Analytical tests in-volve the use of screened or trained panelists whoseresponses are treated as instrumental data. Such testsinclude discriminatory tests (difference and thresh-old) and the most powerful tool in the sensory arse-nal: descriptive analysis.

Discrimination tests comprise of tests that are de-signed to answer the question: Does a difference exist

between samples? These tests are often used to de-termine the effect of specific processing parametersor ingredient substitutions. They can provide usefulinformation when a trained descriptive panel is not anoption. Two common examples are the triangle testand the duo–trio test. Both tests are designed to com-pare two products at a time (as are most differencetests). If more than two products or treatments areinvolved, multiple pairwise comparisons will needto be conducted. The triangle test involves the pre-sentation of three randomly coded products. Two ofthe products are the same; one is different. The pan-elist is asked to indicate which of the three productsis different. For the duo-trio test three products arepresented as with the triangle test, but one of theproducts is labeled as a reference, and the panelistsare asked to choose the product that is the same as


the reference. Correct results are tabulated and a bi-nomial calculation or statistical tables (provided inmost sensory textbooks) are used to determine if asignificant difference exists. A minimum of 15 in-dividuals are recommended for these tests and thediscriminatory power is improved if larger numbersare used. Several things are important to note aboutthese types of tests. First preference or acceptancequestions are not asked in conjunction with a differ-ence determination. Such a question is meaninglessas panelists do not even know if the product theychoose is actually the different product. Second, dif-ference tests provide evidence that a difference existsbetween products. They do not provide informationon the type of difference nor the amount of differ-ence. Finally lack of a statistical difference does notmean that two products are identical.

Attribute difference tests can be applied when morespecific information is desired, but again extensivepanel training is not an option. Some examples in-clude paired comparison tests and ranking tests. Apaired comparison test allows comparison of one par-ticular attribute between two samples. Ranking testsinvolve ranking a group of products based on the in-tensity of a single selected attribute (highest to low-est, most to least). An example would be ranking aset of yogurts based on perceived thickness. Distinctdifferences for a particular attribute can be providedbut results are not quantitative. How close the prod-ucts are to one another in that particular attribute isnot known. Numbers of panelists used are similarto those used for difference tests. Threshold tests canbe used to determine the concentration of a particularcompound (such as a desirable or undesirable flavorof a particular ingredient) that can be added for sen-sory detection. There are several types of thresholdsand the reader is referred to a sensory textbook forcomplete definitions. Testing for thresholds are moretime-consuming than other discriminatory tests pri-marily because to obtain a realistic threshold, largenumbers of panelists are required (at least 50) andtesting must cover the threshold range, which re-quires multiple presentations. Difference, ranking,threshold, and paired comparison tests can be used asstand-alone sensory tools to solve research problemsbut they can also be used as quick preliminary testsprior to descriptive sensory analysis.

The purpose of descriptive analysis is to traina group of individuals to evaluate specific sensoryproperties analytically. Descriptive analysis is thetool of choice for qualitatively and quantitatively dif-ferentiating foods. Descriptive analysis of any food

requires a descriptive technique and a lexicon orlanguage to describe the sensory properties. Thereare several valid approaches to descriptive analysis(Murray et al., 2001; Drake and Civille, 2003). Theseapproaches include flavor profile method, quantita-tive descriptive analysis (QDA), the Spectrum tech-nique, and other techniques, which have been takenfrom two or more parts of the previous methods. Sen-sory languages can be identified for any dairy foodand/or dairy food property of interest using any ofthese approaches. Many sensory languages have beenidentified for cheeses (Delahunty and Drake, 2004),and sensory languages have also been developed forfluid milk (Chapman et al., 2001), dried dairy in-gredients (Drake et al., 2003), and chocolate milk(Thompson et al., 2004).

Panelist selection scales and scale usage, and train-ing are critical parts of any descriptive analysisapproach. These specifics are reviewed elsewhere(Drake and Civille, 2003; Meilgaard et al., 1999).A panel or a group of individuals (generally 8–12)is used for descriptive sensory analysis rather thanone or two experts. A panel of individuals is used asfactors such as age, saliva flow, and onset of fatiguevary between them. Panelists also vary in sensitiv-ity to a particular stimuli, and it is highly probablethat they also vary in their concentration responsefunctions. Panelists, even highly trained panelists orexperts, can vary in sensory function daily. Thus, agroup or panel is used rather than one or two in-dividuals for consistent results. Training a descrip-tive panel requires time, persistence, practice, andgroup effort. The amount of time varies with themodality and number of attributes. Visual attributesare generally quicker to train than texture attributes,which are generally quicker to train than flavor orodor attributes. Trained panelists are components ofthe sensory instrument (the panel). Thus, replicationby each panelist is required for statistical analysisof results. Trained panelists as instrumental compo-nents are not consumers. Thus, liking and preferencemeasurements from these individuals have little orno meaning. Descriptive sensory analysis provides apowerful platform for enhanced product understand-ing, identifying chemical sources of specific flavor,and understanding consumer results.

Affective tests involve the use of untrained con-sumers and measure consumer responses. Such testsevaluate consumer liking, attitudes, and perceptions.Focus groups involve qualitative analysis of con-sumer perceptions, whereas quantitative question-naires and ballots can be used to probe consumer


intensity and liking of specific attributes and/or con-cepts. Focus groups involve guided discussion withsmall groups of screened and selected consumers(n = 10–12). The moderator is experienced in guid-ing such discussions. Sessions are generally observedthrough a two-way mirror or are taped for transcrib-ing and observation of nonverbal as well as ver-bal cues from participants. Focus groups can pro-vide powerful qualitative information for marketing,product development, and product positioning. Theyare not used often for research. Quantitative ques-tionnaires and ballots probing liking and other at-tributes are most commonly used in product research.A large number of consumers need to be polled ifa reasonable projection of consumer response is tobe obtained. A minimum of 50 (untrained) individu-als is recommended for these types of evaluations,and more commonly 100 or more individuals arepolled. Acceptance and consumer perception of spe-cific product attribute intensities can be quantitativelymeasured using line or category scales (Lawless andHeymann, 1998). The 9-point hedonic scale is byfar the best-known and established scale for measur-ing consumer responses. Following analysis of vari-ance, product preference can be inferred from specificdifferences in product liking. Alternatively, prefer-ence can be directly determined using a preferencequestion. Numerous questions including overall ac-ceptance, liking, and intensity perception of specificproduct attributes and preferences can be asked onone consumer ballot. As mentioned previously, mea-suring hedonic responses of a trained panel provideslittle useful information and violates the basis for bothanalytical and affective testing. They are differenttypes of tests and use different groups of respondents.

Consumers provide information on product likesand dislikes. Understanding what specific productattributes drive their likes and dislikes requires theapplication of descriptive analysis as well as con-sumer testing. This approach is called preferencemapping. Preference mapping is a commonly usedtool in understanding the descriptive sensory at-tributes that drive consumer preferences (McEwan,1996; Schlich, 1995). The procedure requires anobjective characterization of product sensory at-tributes, achieved by descriptive analysis, which isthen related to preference ratings for the product ob-tained from a representative sample of consumers(Murray and Delahunty, 2000). Both internal andexternal preference mapping techniques have beenimplemented in a number of studies with a varietyof products, including dairy products (Young et al.,

2004; Thompson et al., 2004; Hough and Sanchez,1998; Richardson-Harman et al., 2000). Similarapproaches can be used to explore sensory and in-strumental relationships.

SENSORY ANALYSIS OF YOGURTSeveral studies have addressed sensory properties ofyogurts. Quality judging, although far from ideal,has been used prevalently (Tamime and Robinson1987). Karagul-Yuceer et al. (1999) investigated sen-sory properties of sweetened low fat (1%) plain yo-gurt and Swiss-style strawberry and lemon yogurtswith/without carbon dioxide treatment. Stored yo-gurts were evaluated for flavor and texture qualityafter 7, 21, and 45 days refrigeration. Preference test-ing with consumers was subsequently used to deter-mine preference. McGregor and White (1986) like-wise used dairy product judging to evaluate flavorand texture quality of fruit flavored yogurts with dif-ferent sweeteners. Farooq and Haque (1991) usedquality judging to demonstrate that sucrose esters im-proved quality of nonfat low calorie yogurt. Penna etal. (1997) used sensory quality assessments of ap-pearance, texture, and flavor to optimize the amountof whey powder that could be added to yogurts with-out detrimental sensory effects. Quality assessmentswere used to determine sensory properties of plainyogurts with added oat fiber and fructose (Fernandez-Garcia et al., 1998), drinkable yogurts (Penna et al.,2001), the effect of milk somatic cell counts (Olivieraet al., 2002), and to characterize application of butter-milk powder in yogurts (Trachoo and Mistry, 1998).

Discrimination tests have been used to identify theeffects of specific parameters. Triangle tests followedby consumer testing were applied to evaluate sensoryproperties of yogurts with and without added fiberfrom different sources (Dello Staffolo et al., 2004).Pairwise difference tests were conducted to estab-lish if differences existed between products with andwithout added fibers. Subsequently, consumers eval-uated overall acceptance of products. Triangle testswere also used to determine the effects of differenthigh-pressure treatments on yogurt mix prior to fer-mentation (de Ancos et al., 2000), to determine theeffect of carbon dioxide treatment of milk used foryogurt (Gueimonde et al., 2002), and to evaluate theeffect of pasteurization and the addition of hydrogenperoxide on labneh (strained or concentrated yogurt)quality (Dagher and Ali, 1985).

Descriptive analysis has also been recently ap-plied to yogurts. Al-Kadamany et al. (2003) used a


panel trained to score the intensity of yeasty flavor todetermine the shelf life of labneh. To conduct thesensory analysis, seven panelists (four females, threemales; age 22–32 years) were selected. The panelistswere served with commercial labneh samples, storedfor different periods of time, and asked through groupdiscussion to determine and agree on sensory fail-ure attributes. During training sessions, yeasty fla-vor was detected at an earlier stage than yeasty odor.Thus, yeasty flavor was selected as a key attributefor determining labneh quality. Panelists were thentrained to rate the intensity of yeasty flavor. At eachsampling time, panelists were presented with a freshsample labeled a control, fresh sample designated asa control, duplicate samples from a stored pack, anda blind control coded with three-digit random num-bers. Panelists used a 7-point intensity scale to ratethe magnitude of difference of yeasty flavor of thecoded samples from the fresh control product.Theshelf life of labneh ranged between 18.5 and 18.9; 8and 9.5; and 2.7 and 3.1 days at 5◦C, 15◦C, and 25◦C,respectively.

In many cases, sensory attributes evaluated are pro-vided but have not been defined (Table 16.5), whereas

in other studies they have been defined and referencesprovided (Table 16.6). The use of specific definitionsand references greatly enhances the application andthe ability to reproduce published results. Drake et al.,(1999) used descriptive analysis of aroma to char-acterize the sensory impact of different lactobacilli.The effect of varying levels of sugar (18, 20, 22%)and fruit concentrations (15, 20, 25%) on the sensoryproperties of frozen yogurt was investigated (Guvenand Karaca, 2002). Sensory evaluation of the prod-ucts was performed on a 20-point scale by five ex-perienced panel members. The attributes asked forpanelists to evaluate were “color and appearance,”“structure and consistency,” “taste and smell,” and“totals.” The results indicated that frozen yogurtswith 25% strawberry, 20% sugar, and 22% sugar hadthe potential for consumer acceptance.

Skriver et al. (1999) investigated the sensory tex-ture and instrumental rheological characteristics ofstirred yogurts varying in fermentation temperature,heat treatment of milk, dry matter content, and com-position of bacterial cultures. Basically two sen-sory texture attributes, nonoral and oral viscosity,were evaluated. For sensory analysis a modified

Table 16.5. Sensory Descriptors Used for the Characterization of Fermented Milks and Yogurtsfor Which Definitions and References Were not Published

Appearance andOdor Texture on the Spoon Flavor/Taste Mouthfeel Aftertaste

Intensity Yellowish Intensity Light PersistentMilky Bubbles Creamy Thick MilkyYogurt Heterogeneous Buttery Floury Sour milkCottage cheese Compact Cottage cheese Sandy AcidSour milk Lumpy Acid Small lumps LemonPungent Thick Sweet Graininess AstringentOnion Smooth/coarse Cooked Firm BitterCooked Bitter SlimyAcid Astringent CreamySulfur Sour milk SmoothnessAcetaldehyde SourSharp WateryFruity FlatUnclean YogurtDiacetyl GrassyCheddar FreshSweet BlandSweaty Old ingredientBandaidFusel oilWheySource: Ott et al., 2000; Drake et al., 1999; Biliaderis et al., 1992; Lorenzen et al., 2002; Lee et al., 1990; Modler et al., 1983.


Table 16.6. Sensory Attributes and References Used to Describe Sweetened Unflavored andFlavored Yogurts

Attribute Reference

Color (light to dark) Visual appearance ranging from light to dark, plain low-fatyogurt is the light reference

Dairy aroma/flavor Plain low-fat yogurtDairy/culture ButtermilkAcid/sharp Lactic acidAcetaldehyde 0.66 and 2 ppm acetaldehyde in milkCooked milk 2% milk heated to 90◦C for 30 secondsCaramel Kraft caramelsMilky 2% milkButtery ButterCheesy Parmesan cheeseYeasty 0.1% baking yeast in waterFruity/sulfur CantaloupeRotten/sulfur Boiled eggsCreamy Whipping cream/fat-free cream cheeseSour cream Sour creamCottage cheese Low-fat cottage cheeseFresh fruit strawberry (strawberry yogurt) Fresh frozen strawberriesJammy strawberry (strawberry yogurt) Smuckers strawberry jamArtificial strawberry (strawberry yogurt) Premixed strawberry KoolaidFresh lemon (lemon yogurt) Fresh wedge of lemonLemon juice (lemon yogurt) Lemon juiceArtificial lemon (lemon yogurt) Lemon jelloMetallic Ferrous sulfate −0.1% in waterChalky Amount of chalk-like particulates perceived in the mouth,

reference is yogurt with 7% added soy protein concentrateRopy The degree to which a strand/rope forms when a spoon is

dipped into the product and slowly pulled outThickness Force required to push tongue up through product against

palate and then back downSweet (sucrose) Sucrose −7.3% in water, 5 and 10% sucrose in waterSweet (aspartame) (APM) APM −400 ppm in waterBitter Caffeine, 0.08% caffeine in waterSour Lactic acid, 0.32% lactic acid in water, 0.08 and 0.15%

citric acid in waterSalty 0.2% NaCl in waterAstringent Alum −0.1% in water, soak 10 tea bags in 1 qt boiling

water for 1 hourAftertaste (after 30 seconds) Overall aftertaste-driven by APMSource: Harper et al., 1991; King et al., 2000; Barnes et al., 1991a; Drake et al., 2000.

quantitative descriptive analysis was conducted. Thesamples were evaluated by a trained panel of asses-sors. A 150-mm unstructured line scale with anchorpoints placed at 15 and 135 mm from the left was usedto score nonoral viscosity and oral viscosity. The at-tributes were defined thus, enhancing the clarity ofthe study.

Nonoral Viscosity (The panel chose “gel firmness,”but the alternative term was used for clarity). Thiswas assessed by penetrating the yogurt gel with a tea-spoon, placing about 5 ml on the surface of the undis-turbed yogurt and observing how fast this dissipated.A high disappearance rate of the mounded spoonfulindicated a low nonoral viscosity.


Oral Viscosity (The panel chose “mouthfeel,” butthe alternative term was used for clarity). Thiswas assessed as the perceived degree of thicknesswhen the yogurt was placed in the mouth.

The results indicated that nonoral viscosity was re-lated to low deformation tests (G* from oscillationmeasurements and Brookfield viscosity) and oral vis-cosity to large deformation tests (posthumus viscos-ity and thixotropic behavior).

The rheological, sensory, and chemical charac-teristics of yogurts made from skim milk (SM)and ultrafiltered (UF) SM retentates were compared(Biliaderis et al., 1992). Quantitative descriptive anal-ysis was used to profile selected sensory properties(thickness, graininess, sourness) of yogurt by seventrained panelists. Sensory results indicated a differ-ence between the UF versus SM yogurt samples inperceived thickness and graininess, but not in sour-ness when examined at similar solids level.

The sensory properties of traditional acidic andmild, less acidic yogurts were determined by a trainedpanel using descriptive sensory analysis (Ott et al.,2000). For sensory evaluation, odor, taste, and flavorterms were used:

Odor refers to the organoleptic attribute percep-tible by the olfactory organ (nose) on sniffing cer-tain volatile substances. The term “aroma” was usedthereafter, like the term “odor,” without any hedonicaspect.

Taste refers to sensations perceived by the tasteorgan (tongue) when stimulated by certain solublesubstances.

Flavor refers to a complex combination of theolfactory, gustatory, and trigeminal sensations per-ceived during tasting.

Panel training and language development werewell-characterized. During the first panel trainingsession, panelists were served four samples of yo-gurt prepared with strains of Str. thermophilus and Lb.delbrueckii ssp. bulgaricus and were asked to list theterms appropriate to describe the appearance, texturewith spoon, aroma, flavor, mouthfeel, and aftertasteof the samples. A total of 55 terms were generated.Additional training sessions were used to (a) exposepanelists to more yogurt samples, and possibly iden-tify new terms; (b) present other dairy foods (e.g.,cottage cheese, kefir) to help panelists characterizesome specific descriptive terms; (c) reduce the totalnumber of terms by eliminating redundant ones orthose for which the panel could not reach a consensus;(d) agree on precise definitions of the terms and onthe tasting protocol; (e) practice the use of the rating

scale and make sure that panelists rated samples co-herently. After training, the panel agreed on a list of33 terms and an evaluation protocol.

To prepare samples for sensory evaluation, thesamples were vigorously shaken until the yogurt washomogeneous, and then poured into small glass pots,which were closed to contain volatiles. Before serv-ing, the samples were equilibrated to room temper-ature. In each session four samples were presentedmonadically to the panelists with random three-digitcodes and in a balanced presentation order. Panelistswere asked to open the lid and to evaluate odor firstand then the appearance and texture with the spoon.After placing product in the mouth, flavor and textureattributes in the mouth were rated. Finally, 10 secondsafter swallowing the sample, they evaluated aftertasteattributes. Each attribute was associated with a 12 cmunstructured linear intensity scale with two anchorsat 3 mm from each extremity. Rating marks on thescale were converted to numerical values (left anchor= 0; right anchor = 100).

Descriptive sensory analysis and time inten-sity measures were investigated to measure flavorchanges and perceived sweetness in yogurt madewith three concentrations of aspartame (APM) andfat (200, 400 or 600 ppm APM and 1% or 2% fatrespectively) (King et al., 2000). Twelve panelistswere trained in descriptive methodology and time-intensity evaluation techniques. For descriptive sen-sory analysis, panelists rated samples using a 15cm anchored line scale. For time-intensity measure-ments, panelists consumed a single tsp of sample,swirled it in their mouth for 5 seconds, and thenswallowed. After swallowing assessors began to ratethe sweetness aftertaste intensity for a total of 1minute. The results of this study showed that as-partame concentration had a greater effect on flavorcharacteristics and sweetness aftertaste than did fatcontent. Addition of aspartame reduced the yogurt-based related flavor properties, while enhancing thesweetness and aftertaste in the product. Addition offat reduced some of the sweetness impact demon-strating that fat has the potential of reducing some ofthe lingering sweetness that may be objectionable toconsumers.

Sensory analysis was used to compare flavor andtexture properties of milk-based yogurt to soymilkyogurt (Lee et al., 1990). Soymilk yogurts were char-acterized by a lack of acidity and typical yogurt fla-vors. Drake et al. (2000) used descriptive analysis todetermine sensory properties of low-fat yogurts for-tified with 0, 1, 2.5, or 5% soy protein concentrate


during 1-month storage at 5◦C. Descriptive analysiswas conducted on the yogurts following theSpectrumTM procedures. During training, the pan-elists were asked to identify and define appearance,flavor, and texture terms for the yogurts. Panelistswere presented with an array of yogurts with andwithout added soy protein to generate the descrip-tive terms with definitions and references. Attributesfor appearance (color, free whey), aroma (fermenteddairy, soy), flavor/taste/feeling factors (soy, fer-mented dairy, acidity, sweetness, astringency),and texture (ropiness, chalkiness, thickness) wereselected.

Evaluations were divided into three categories in-cluding visual, flavor/aroma, and texture evaluation.Panelists evaluated sample sets for visual attributesfollowed by evaluation of separate sample sets for fla-vor/aroma evaluation and texture evaluation. Yogurtwith 5% soy protein was darker, chalkier, and lesssweet compared to control yogurt with lower con-centrations of soy protein. In addition, yogurts with1 or 2.5% soy protein were most similar to controlyogurt. Descriptive analysis was subsequently usedto explore the specific effects of soy protein addition,sweetener type, and fruit flavoring on dairy yogurts(Drake et al., 2001).

Trained-panel sensory analysis of appearance andtexture demonstrated that whey protein concentratesproduced yogurts with improved sensory attributescompared to yogurts stabilized with casein-basedproducts (Modler et al., 1983). Trained panelists eval-uated sensory properties of milks fermented withdifferent mesophilic starter cultures as part of alarger study to characterize the effect of different cul-tures on fermented milk properties (Kniefel et al.,1992). Texture profiling (a form of descriptive tex-ture analysis) was used to profile the texture prop-erties of yogurts made using exopolysaccharide-producing starter cultures (Marshall and Rawson,1999). Lorenzen et al. (2000) used attribute profilingwith experienced assessors to determine the effect ofenzymatic cross-linking of milk proteins on yogurtodor, flavor, and consistency. Hekmat and McMahon(1997) used trained panelists to characterize the ef-fect of iron fortification of yogurts on specific sensoryattributes (oxidized and metallic flavors, bitter taste).Trained panelist analysis of yogurt has also been usedas a model system to study the effect of fat on flavorrelease and texture perception (Brauss et al., 1999).

Many of the previously mentioned studiesevaluated consumer acceptance using untrained

consumers following analytical sensory testing.However, consumer testing alone can be a usefultool provided a large enough sample of consumersis polled. Carbonated and strawberry flavored yogurtdrink was produced to attract customers who wouldnormally not enjoy a traditional yogurt product (Choiand Kosikowski, 1985). For this purpose yogurt andsoft drink consumers evaluated products using a 7-point hedonic scale (where 1 = dislike very much to7 = like very much). Carbon dioxide had no effect onspecific sensory properties through 45 days of storageor consumer preference. Adhikari et al. (2000) usedconsumer testing to determine acceptability of plainyogurts with and without encapsulated Bifidobacte-ria. Consumers (n = 547) were used to ascertainacceptance and attitudes toward soy-fortified dairyyogurts (Drake and Gerard, 2003).

Harper et al. (1991) used a combined approach ofdescriptive analysis and consumer testing to evalu-ate the sensory properties of commercial plain yo-gurts. Seventeen plain yogurts (whole, low fat, andfat free) were evaluated. Consumers (n = 153) eval-uated yogurts for liking attributes using a 9-point he-donic scale while sweetness, sourness, and thicknesswere evaluated for “just right” intensities using a 7-point just right scale. Wide variability in attributeintensities was noted among the yogurts. Consumerresults indicated that consumers preferred plain yo-gurts that were less sour and more sweet in taste.Laye et al. (1993) likewise demonstrated that un-trained consumers could differentiate between freshplain yogurts. A similar descriptive and consumerpanel study was also conducted with strawberry andlemon yogurts (Barnes et al., 1991a). Acceptance ofcommercial flavored yogurts differed for men andwomen, but trained panel sweet taste was correlatedwith consumer acceptance. In a subsequent study, thesame lab used descriptive analysis of sweet and sourtastes in combination with consumer testing to ex-plore relationships between trained panel sweet andsour taste scores and consumer acceptance of plain,strawberry, raspberry, and lemon yogurts (Barnes etal., 1991b). Trained panel sweet and sour taste scoreswere useful in predicting consumer liking of fruit-flavored yogurts.

CONCLUSIONSSensory quality (appearance, texture, flavor) ulti-mately determines consumer acceptance. The useof appropriately designed sensory tests, tools, and


statistical analyses is a powerful technique for mea-suring the specific sensory effects of processing pa-rameters and ingredients. Testing with appropriatenumbers of consumers provides compelling informa-tion on consumer acceptance. Many recently devel-oped sensory tools have been effectively applied toother dairy foods. Future sensory work with yogurtshould focus on the application of these recent andpowerful tests.

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Viability of micro-encapsulated Bifidobacteria in setyogurt during refrigerated storage. J. Dairy Sci.83:1946–1951.

ADSA. 1987. Committee on Evaluation of DairyProducts. Score Card and Guide for Cottage Cheese.Amer. Dairy Sci. Assoc., Champaign, IL.

Al-Kadamany E, Khattar M, Haddad T, Toufeili I.2003. Estimation of shelf-life of concentrated yogurtby monitoring selected microbiological andphysicochemical changes during storage. LebenWiss Technol. 36:407–414.

Barnes DL, Harper SJ, Bodyfelt FW, McDaniel M.1991a. Correlation of descriptive and consumerpanel flavor ratings for commercial pre-stirredstrawberry and lemon yogurts. J. Dairy Sci.74:2089–2099.

Barnes DL, Harper SJ, Bodyfelt FW, McDaniel M.1991b. Prediction of consumer acceptability ofyogurt by sensory and analytical measures ofsweetness and sourness. J. Dairy Sci. 74:3746–3754.

Biliaderis CG, Khan MM, Blank G. 1992. Rheologicaland sensory properties of yogurt from skim milk andultrafiltered retentates. Int. Dairy J. 2:311–323.

Bodyfelt FW, Tobias J, Trout GM. 1988. Sensoryevaluation of cultured milk products. The SensoryEvaluation of Dairy Products. AVI Publishers, NewYork.

Brauss MS, Linforth RST, Cayeux I, Harvey B, TaylorAJ. 1999. Altering the fat content affects the flavorrelease in a model yogurt system. J. Agric. FoodChem. 47:2055–2059.

Chapman KW, Lawless HT, Boor KJ. 2001.Quantitative descriptive analysis and principalcomponent analysis for sensory characterization ofultra-pasteurized milk. J Dairy Sci. 84:12–20.

Choi HS, Kosikowski FV. 1985. Sweetened plain andflavored carbonated yogurt beverages. J. Dairy Sci.68:613–619.

Dagher S, Ali A. 1985. Effect of pasteurization,centrifugation and additives on quality of

concentrated yogurt (labneh). J. Food Prot.48:300–302.

de Ancos B, Cano MP, Gomez R. 2000. Characteristicsof stirred low-fat yogurt as affected by highpressure. Int. Dairy J. 10:105–111.

Delahunty CM, Drake MA. 2004. Sensory character ofcheese and its evaluation. In: PF Fox, PLHMcSweeney, TM Cogan, TP Guinee (Eds), Cheese:Chemistry, Physics and Microbiology, Vol. 1,General Aspects, 3rd ed. Elsevier, London, pp.455–487.

Dello Staffoloa M, Bertolaa N, Martinoa M,Bevilacqua A. 2004. Influence of dietary fiberaddition on sensory and rheological properties ofyogurt. Int. Dairy J. 14:263–268.

Drake MA. 2004. Defining dairy flavors. J. Dairy Sci.87:777–784.

Drake MA, Chen XQ, Tamarapu S, Leenanon B. 2000.Soy protein fortification affects sensory, chemicaland microbiological properties of dairy yogurts. J.Food Sci. 65:1244–1247.

Drake MA, Civille GV. 2003. Flavor lexicons. Compr.Rev. Food Sci. 2(1):33–40.

Drake MA, Gerard PD. 2003. Consumer attitudes andacceptability of soy fortified yogurts. J. FoodScience. 68(3):1118–1112.

Drake MA, Gerard PD, Chen XQ. 2001. Effects ofsweetener, sweetener concentration and fruit flavoron sensory properties of soy fortified yogurt.J. Sensory Stud. 16:393–406.

Drake MA, Karagul-Yuceer Y, Cadwallader KR,Civille GV, Tong PS. 2003. Determination of thesensory attributes of dried milk powders and dairyingredients. J. Sensory Stud. 18:199–216.

Drake MA, Karagul-Yuceer Y, Chen XQ, CadwalladerKR. 1999. Characterization of desirable andundesirable lactobacilli from cheese in fermentedmilk. Leben Wissen Technol. 32:433–439.

Farooq K, Haque ZU. 1991. Effect of sucrose esters onthe textural properties of nonfat low calorie yogurt.J. Dairy Sci. 75:2676–2680.

Fernandez-Garcia E, McGregor JU, Traylor S. 1998.The addition of oat fiber and natural alternativesweeteners in the manufacture of plain yogurt.J. Dairy Sci. 81:655–663.

Gueimonde M, Alonso L, Delgado T, Bada-GancedoJC, Reyes-Gavilan CG. 2002. Quality of plainyoghurt made from refrigerated and CO2-treatedmilk. Food Res. Int. 36:43–48.

Guven M, Karaca OB. 2002. The effects of varyingsugar content and fruit concentration on the physicalproperties of vanilla and fruit ice cream-type frozenyogurts. Int. Dairy Technol. 55:27–31.


Harper SJ, Barnes DL, Bodyfelt FW, McDaniel MR.1991. Sensory ratings of commercial plain yogurtsby consumer and descriptive panels. J. Dairy Sci.74:2927–2935.

Hekmat S, McMahon DJ. 1997. Manufacture andquality of iron-fortified yogurt. J. Dairy Sci.80:3114–3122.

Hough G, Sanchez R. 1998. Descriptive analysis andexternal preference mapping of powdered chocolatemilk. Food Qual. Pref. 9(4):197–204.

IDF. 1997. Sensory Evaluation of Dairy Products byScoring—Reference Method. International IDFStandard. 99C:1997. Brussels: Belgium.

Karagul-Yuceer Y, Coggins PC, Wilson JC, White CH.1999. Carbonated yogurt: Sensory properties andconsumer acceptance. J. Dairy Sci. 82:1394–1398.

King SC, Lawler PJ, Adams JK. 2000. Effect ofaspartame and fat on sweetness perception inyogurt. J. Food Sci. 1056–1059.

Kniefel W, Kaufmann M, Fleischer A, Ulberth F. 1992.Screening of commercially available mesophilicdairy starter cultures: Biochemical, sensory, andmicrobiological properties. J. Dairy Sci.75:3158–3166.

Lawless HT, Heymann H. 1998. Sensory Evaluation ofFood: Practices and Principals. Chapman and Hall,NY.

Laye I, Karleskind D, Morr CV. 1993. Chemical,microbiological, and sensory properties of plainnonfat yogurt. J. Food Sci. 58:991–995.

Lee SY, Morr CV, Seo A. 1990. Comparison ofmilk-based and soymilk-based yogurt. J. Food Sci.55:532–536.

Lorenzen PC, Neve H, Mautner A, Schlimme E. 2002.Effect of enzymatic cross-linking of milk proteinsfunctional properties of set-style yogurt. Int. J. DairyTechnol. 55:152–157.

Marshall VM, Rawson HL. 1999. Effects ofexopolysaccharide-producing strains ofthermophilic lactic acid bacteria on the texture ofstirred yogurt. Int. J. Food Sci. Technol. 34:137–143.

McEwan JA. 1996. Preference mapping for productoptimization. In: T Naes, E Risvik (Eds),Multivariate Analysis of Data in Sensory Science.Elsevier, Amsterdam, pp. 71–80.

McGregor JU, White CH. 1986. Effect of sweetenerson the quality and acceptability of yogurt. J. DairySci. 69:698–703.

Meilgaard MC, Civille GV, Carr BT. 1999. SensoryEvaluation Techniques, 3rd ed. CRC Press, BocaRaton, FL.

Modler HW, Larmond ME, Lin CS, Froehlich D,Emmons DB. 1983. Physical and sensory properties

of yogurt stabilized with milk proteins. J. Dairy Sci.66:422–429.

Murray JM, Delahunty CM. 2000. Mapping consumerpreference for the sensory and packaging attributesfor Cheddar cheese. Food Qual. Pref. 11:419–35.

Murray JM, Delahunty CM, Baxter IA. 2001.Descriptive sensory analysis: present and future.Food Res. Int. 34:461–471.

Oliviera CA, Fernandes AM, Neta OCC, Fonseca LFL,Silva EOT, Balian SC. 2002. Composition andsensory evaluation of whole yogurt produced frommilk with different somatic cell counts. Austr. J.Dairy Technol. 57:192–196.

Ott A, Hugi A, Baumgartner M, Chaintreau A. 2000.Sensory investigation of yogurt flavor perception:Mutual influence of volatiles and acidity. J. Agric.Food Chem. 48:441–450.

Penna ALB, Sivieri K, Oliveira MN. 1997.Optimization of yogurt production usingdemineralized whey. J. Food Sci. 62:846–850.

Penna ALB, Sivieri K, Oliveira MN. 2001. Relationbetween quality and rheological properties of lacticbeverages. J. Food Eng. 49:7–13.

Richardson-Harman NJ, Stevens R, Walker S, GambleJ, Miller M, Wong M, McPherson A. 2000. Mappingconsumer perceptions of creaminess and liking forliquid dairy products. Food Qual. Pref.11:239–246.

Schlich P. 1995. Preference mapping: Relatingconsumer preferences to sensory or instrumentalmeasurements. In: P Etievant, P Schreier (Eds),Bioflavour=95. Analysis/Precursor Studies/Biotechnology. INRA Editions, Versailles, pp.231–245.

Singh T, Drake MA, Cadwallader KR. 2003. Flavor ofCheddar cheese: A chemical and sensoryperspective. Compr. Rev. Food Sci. 2:139–162.

Skriver A, Holstborg J, Qvist KB. 1999. Relationbetween sensory texture analysis and rheologicalproperties of stirred yogurt. J. Dairy Res.66:609–618.

Tamime AY, Robinson RK. 1987. Yoghurt Science andTechnology. Oxford: Pergamon Press.

Thompson JL, Drake MA, Lopetcharat K and YatesMD. 2004. Preference mapping of commercialchocolate milks. J. Food Sci 69(11/12):S406–S413.

Trachoo N, Mistry VV. 1998. Application ofultrafiltered sweet buttermilk and sweet buttermilkpowder in the manufacture of nonfat and low fatyogurts. J. Dairy Sci. 81:3163–3171.

Young ND, Drake MA, Lopetcharat K, McDaniel MR.2004. Preference mapping of Cheddar cheese withvarying maturity levels. J. Dairy Sci. 87:11–19.

Part IIIManufacture of Fermented Milks



17Cultured Buttermilk

Charles H. White

Milk SupplyProcessing of MilkButtermilk Starter CultureBreaking, Cooling, Bottling, and DistributionAcknowledgmentReferences

The term buttermilk can be somewhat confusing inthat buttermilk can mean:

1. The liquid remaining after cream is churned intobutter.

2. The milk product made by adding a bacterial cul-ture to fat free, low fat, reduced fat, or whole milk.

The second product is a topic that merits ourdiscussion. The product has great popularity as abaking aid but also as a satisfying milk beverage. Asa milk beverage, it is a product that fits the image ofa nutritious food that can be extremely refreshing.Vedamuthu (1985) stressed the sales potential forbuttermilk by considering:

� Buttermilk contains all the high-quality nutrientsthat are found in milk. It is rich in calcium, andunlike cheeses, there is no loss of the high-qualitywhey proteins in its production.

� There is little or no milk fat in buttermilk, since itis made from skim milk (buttermilk can be madewith milk of varying fat content, which can eventaste better than that made from skim).

� Unless salted, which in many cases isunnecessary, buttermilk can be labeled as asodium free or low sodium product (many peopleagree that buttermilk tastes better with added salt).

� There is about 15% less lactose in buttermilk ascompared with milk.

� Buttermilk provides an excellent base for makingvarious kinds of dressings and baked goods,which require a smooth, tangy flavor.

Buttermilk has steadily declined in per capita con-sumption from 4.7 pounds in 1975 to 2.1 in 2001(USDA-IDFA). Some of this decline is because ofmore interest in buttermilk for baking purposes ratherthan just for drinking. Also, the unfamiliarity withcultured buttermilk as a refreshing drink has spreadin the current generation. As a result, the poor qualityof some buttermilk has caused first-time consumersto not want to become a repeat consumer. A lack ofgood refrigerated temperature control results in poorquality buttermilk in many restaurants. The Ameri-can Cultured Dairy Products Institute has held an-nual product clinics. At these clinics, cultured dairyproducts of members would be evaluated by expertsensory judges. During a 4-year period (1972–1975),of 87 samples of buttermilk, 55 (63%) were found tohave a flavor of only fair or poor quality. Only onesample was judged to be excellent. Since that time,the flavor quality of buttermilk has not changed ap-preciably. From a technical point of view, buttermilkshould be the easiest cultured dairy product to make;however, this product consistently scores lower thanother cultured products in product clinics.

Many people judge a dairy processor based on thequality of buttermilk produced, since this product canbe the showcase of a dairy. The thinking tends to bethat if a company produces good buttermilk, the otherproducts also have to be good. Vedamuthu (1985) in-dicates that the successful marketability of buttermilkis based on four major product characteristics:

1. Body—Thick body2. Texture—Smooth texture

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280 Part III: Manufacture of Fermented Milks

3. Flavor—Good blend of acid, diacetyl, and somecarbonation, and

4. Freshness—Shelf-life or keeping quality

Many times body and texture are put together butthey are different characteristics. Flavor is extremelyimportant and can actually consist of more than justtaste. Aroma is a big part of flavor as are mouthfeeland aftertaste.

Lundstedt (1975) suggested that there are fivephases, which must be considered in the manufac-ture of cultured buttermilk:

1. Quality of the milk2. Preparation of the milk for buttermilk3. Cultures and ripening of the milk4. Cooling and pumping the buttermilk to the filling

machine5. Storage and distribution of the buttermilk

In looking more specifically at these major phases,White (1977, 1979) outlined the key steps in goodbuttermilk manufacture:

Key Steps in the Manufacture of Cultured Buttermilk

1. Milk supplya. Never use returned milkb. Free of inhibitory substances (antibiotics and

sanitizers)c. High bacterial qualityd. Needs some fat, 1.0–1.8% minimume. Standardized milk solids-not-fat content

2. Processing of milka. Standardizationb. Homogenizationc. Heating

85◦C (185◦F) for 30 minutes88–91◦C (190–195◦F) for 2.5–5.0 minutes

3. Addition and development (acidity and flavor) oflactic starter culture

4. Breaking, cooling, bottling, and distribution

MILK SUPPLYButtermilk may contain cream, milk, partiallyskimmed milk, or skim used alone or in combination.It may also be made from concentrated skim, nonfatdry milk (NFDM), or other milk derived ingredientsto increase the nonfat solids content of the food (CFR,2000). Not just the raw milk but all ingredients usedin making buttermilk must be of high quality. Suchingredients include salt, sodium citrate (a source ofdiacetyl for the flavor producing bacteria), NFDM,

and/or whey protein concentrate (WPC) as a sourceof added milk solids, stabilizer, and culture.

Fresh fluid milk should be used whenever possible.When using milk powder, fat should be incorporatedto approximately 1% with 40% cream, which appearsto be superior to whole milk as a source of fat. The fatcontent of buttermilk ranges all the way from approx-imately 0.05% to 3.5% milkfat. For optimal flavor,most processors find that milk with at least 1.0–1.8%fat produces the most acceptable product.

Regardless of the source of solids, there must be theabsence of any stale or “off” note, which will almostcertainly carryover into the finished product. Caremust be taken to ensure a consistent product withregard to the body and viscosity when using differentsources of fat and solids. Seasonal variations can alsoreflect changes in the body and flavor of buttermilk.Solids may be added in high-volume periods to keepthe body constant.

Sodium citrate may be added as a basis for di-acetyl production. A recommended level of additionis 0.10% w/w (legal maximum is 0.15% w/w). Intimes of the year, when solids are reduced more, cit-rate may be required for good diacetyl productionthan is naturally present in the raw milk. Many pro-cessors add sodium citrate on a regular basis to en-sure a ready source of citrate for the Leuconostocs or“flavor producers” (Petersen, 1997). Diacetyl is a keyflavor compound, which can result in excellent but-termilk. In the past some processors did not believethat one needed to add stabilizer to make good but-termilk. These thoughts have changed due to longerdistribution chains and buttermilk being packaged inclear plastic containers. Extensive syneresis or whey-ing off can look very unattractive in the dairy case.One should avoid using too much stabilizer to elim-inate the possibility of a “slick” body. Follow therecommendation of the stabilizer supplier for best re-sults. In an excellent overview of buttermilk, Danisco(2003) summarizes the commonly used stabilizers inmaking cultured buttermilk.

1. Food starch or modified food starch—Added to in-crease viscosity, the modified product is reportedto give better water-binding properties, improvedacid tolerance, and shear stability.

2. Locust bean gum—Increases viscosity. Synergis-tic with carrageenan.

3. Carregeenan—Added to reduce tendency of but-termilk to whey-off.

The direct microscopic count and the standardplate count are still the most commonly used methods

17 Cultured Buttermilk 281

to evaluate the microbial quality of the raw milk. Al-though the legal maximum for commingled raw milkin the United States is 300,000 cfu/ml, a lower stan-dard should be utilized by the processor to furtherensure that only high-quality milk is being used. Thecoliform test can also provide meaningful informa-tion as to the quality of the raw milk. Although moststates do not have coliform standards for raw milk,high numbers can indicate that the milk has beenhandled in an unsanitary manner, e.g., improperlycleaned/sanitized equipment. Just as with pasteurizedproducts, coliforms are “indicator” organisms, in thattheir presence indicates that conditions are suitablefor the presence of enteric pathogens. A reasonablegoal would be <100 coliforms per milliliter of milk.

At any rate, the quality of raw milk must be high.Each raw milk load should be tested for the following(at a minimum) prior to unloading the milk:

� Direct microscopic count (DMC)� Inhibitory substances (antibiotics)� Temperature� Sensory evaluation (aroma and taste after lab

pasteurization)� Sediment

Other tests may be run after the milk has beenpumped into the silo storage tanks. These could benormal compositional tests or troubleshooting testssuch as the acid degree value (for rancid milk),lab pasteurization count (for thermodurics), titratableacidity, etc. If there is a high psychrotrophic popula-tion in the raw milk, heat-stable proteases and lipasescan cause flavor problems in any type of dairy food.Some estimate of the psychrotophs needs to be doneon a regular basis.

PROCESSING OF MILKThe milk should be standardized to a minimum of9.0% solids-not-fat if fresh skim is being used. Ifusing a low-heat powder, a 10% SNF should be re-quired (White, 1979). The firmer the body desired,the higher the SNF level needed. In no case should thetotal solids of the buttermilk be allowed to fall under10% if full-bodied buttermilk is desired. Salt shouldbe added prior to pasteurization to get the desiredtaste. A level of 0.10–0.20% by total batch weightis common and yields a recognizable and desirablediacetyl flavor (Danisco 2003).

Following standardization/fortification, milk issubjected to a heat treatment. To achieve the desiredeffects of denaturing the whey proteins (to achieve

the desired viscosity) and destroying the microbialcontaminants, milk should be heated either to 85◦C(185◦F) for 30 minutes or 88–91◦C (190–195◦F) for2.5–5 minutes. Although most processors using thebatch method claim a better body in the finished but-termilk, heating to higher temperatures at the samehold results in a thinner body. Extended holding tubeson the high-temperature-short-time (HTST) pasteur-izing give plants more flexibility with regard to theirheating capabilities.

Prior to final heating, the milk should be homog-enized at approximately 1800 psi to improve thebody/viscosity of the finished product. The tempera-ture of the milk at the homogenizer should be main-tained approximately at 49◦C (120◦F).

It has been reported (Danisco, 2003) that the pump-ing and cooling steps can have the biggest influenceon the final viscosity. These reports indicated thatintermittent cooling with side swept agitation is thebest. In moving the buttermilk from the buttermilkvat/tank to the filler, avoid the use of a centrifugalpump, which adds air and reduces the product vis-cosity.

BUTTERMILK STARTERCULTUREAfter processing, the milk is cooled to a temperaturefrom 22.2◦C (72◦F) to 23.3◦C (74◦F) and pumpedto the buttermilk vat/tank when it is ready to be in-oculated with the starter culture. The culture manu-facturer’s directions for storage and handling of thestarter should be strictly followed. To understand thetemperature and time of product inoculation requiredfor good flavor and body characteristics, one must re-alize the characteristics of the bacteria in the starterculture. There are two types of bacteria:

1. Lactic acid producers. Typically Lactococcus(formerly streptococcus) lactis subsp. cremorisand Lactococcus lactis subsp. lactis are used.These two bacteria with many different strains arehomofermentative, since they convert lactose toonly lactic acid (Harrits, 1997). Their optimumtemperature is 30◦C (86◦F).

2. Flavor (diacetyl) producers. Leuconostoc mesen-teroides subsp. cremoris. This is a heterofermenta-tive bacterium with an optimum growth tempera-ture of 20–22◦C (70–72◦F) (Harrits, 1997). Strainsof this species metabolize the sodium citrate dis-cussed previously to produce diacetyl and CO2

(Harrits, 1997).


Thus, with the two types of bacteria in the starterculture, it is imperative to select a temperature thatwould be compatible for both. If the incubation tem-perature is too high, the lactic acid producers are fa-vored. As a result, an acid flavor predominates and apleasing culture flavor is lacking. On the other hand,if the incubation temperature is too low, the growth ofthe leuconostocs are favored, but the acid productionwill take significantly longer, which can further inter-fere with processing schedules. Therefore, a commonground is needed and 22.2◦C (72◦F) to 23.3◦C (74◦F)appears to provide the opportunity to maximize bothbacterial types.

The primary flavor problem seen in buttermilks inthe United States is a “high acid” and “lacks culturedflavor.” Normally, this occurs due to incubation at toohigh a temperature and too short an incubation time.The temperature must be low enough to allow for thesecondary growth (after pH drop) of the leuconos-tocs. Also, there needs to be sufficient sodium citrateas a source of diacetyl. Vedamuthu (1985) reportedthat the increase in diacetyl concentration slows downas the citric acid content decreases and the maximumlevel of diacetyl is attained in 14–18 hours of incu-bation. The exact time is determined by:

� The culture used� The citric acid concentration of the raw milk� The temperature of incubation

Vedamuthu (1985) listed five ways to prevent theloss of diacetyl in buttermilk:

1. Rapidly cool the vat once the desired acidity isreached. He indicated that when the buttermilk iscooled, the diacetyl destroying enzyme (diacetylreductase) is retarded and the high level of flavorconcentration is preserved. Diacetyl reductase actsrapidly at the incubation temperature of culturedbuttermilk, but slows down considerably at lowertemperature, e.g., 3.3◦C (38◦F) to 4.4◦C (40◦F).

2. Fortify the vat milk with sodium citrate. This helpsdue to the fact that fortification evens out any sea-sonal variations or deficiencies in citric acid con-tent of raw milk.

3. Slow, gentle agitation during cooling. Oxygen orair that is worked into the buttermilk greatly in-hibits diacetyl reductase.

4. Holding the buttermilk in a cooler for one or twodays. This step will also enhance the diacetyl level.Due to the longer distribution system, this stepmay not be feasible.

5. Strict sanitation during the filling operation. Psy-chotrophic bacteria are known for having a high

diacetyl reductase activity even at low tempera-tures. Filling machines are probably the largestsingle source of contamination microorganisms.

Following addition of the starter, the mixtureshould be agitated at high speed for 15–30 minutes,depending upon the type of tank and agitation em-ployed.

The buttermilk should be checked after 12–14hours for acidity and flavor (taste plus aroma). Manyprocessors have a rule on “breaking” the buttermilkat pH 4.50–4.60, plus desired aroma or flavor. Alltoo often though, the only criterion is acidity withoutproper regard for flavor development. Many times in-cubation for an additional hour or two will result inthe delicate aroma and flavor desired.

If “breaking” buttermilk on titratable acidity (TA)consider that this measurement is dependent on thesolids content. Since a minimum total of solids of10.0–10.5% is desired, a “breaking” TA of 0.90%should be the rule.

BREAKING, COOLING,BOTTLING, AND DISTRIBUTIONKnowing when to “break” a tank of buttermilk ismany times the difference between a good and poorproduct. As a rule, there will be several small pocketsor bubbles of whey on top of the buttermilk when thetank is ready. When the decision is made (based onpH/acidity reading and aroma evaluation) that furtherincubation would be injurious to the quality of theproduct, the ice water is circulated through the jacket10–15 minutes prior to turning on the agitator. Witha two-speed agitator, the agitator should be turnedon high speed until the product is moving easily inthe vat and the body is smooth–this is “breaking”the buttermilk (White, 1976, Personal communica-tion). The agitator should then be switched to lowspeed and cooled to 17◦C (45◦F) for bottling. Rapidcooling is essential to retard further bacterial ac-tion and stop excessive acid development. Agitationshould be stopped when bottling to prevent any exces-sive air incorporation and adverse effects to the finalviscosity. As indicated previously, air incorporationcauses shrinkage during storage and contributes tosyneresis.

The cooled buttermilk should be pumped to thefiller with a positive pump. After packaging, the but-termilk should be held at a temperature of less than4.4◦C (40◦F). This will retard the continued acidproduction and help keep the growth of microbialcontaminants to a minimum. Temperature control

17 Cultured Buttermilk 283

must be maintained throughout the storage and dis-tribution system.

Finished product testing is needed to ensure thatspecifications are attained. The following test shouldprovide the manufacturer adequate control (oneshould not feel limited to these and these alone):

1. Sensory evaluation—Taste samples at the follow-ing:a. At “breaking”b. When bottled—Packaging operatorc. Daily production samples—QA staff

2. Milk fat—Prior to inoculation and bottled product3. Coliform—Goal should be <1 coliform/ml4. pH/titratable acidity5. Viscosity—Use of a Zahn cup or equivalent is rec-

ommended. A minimum of at least 25 seconds in a#2 Zahn cup at 10◦C (50◦F) yields desirable prod-uct viscosity

6. Temperature7. Shelf life—Measured at 7◦C (45◦F)8. Competitor product evaluation—Evaluate blind

samples to ensure competitive properties of fin-ished product

Custer (1982) reviewed the sensory evaluationdefects of buttermilk. He mentioned the cause/prevention of each defect.

1. Flavor defects(a) Green (yogurt flavor)

Cause. Accumulation of acetaldehydePrevention. Avoid starters containing Lacto-

coccus lactis subsp. diacetylactis(b) Lacks flavor

Cause. High incubation temperature, insuffi-cient citric acid in milk, low acid develop-ment

Prevention. Incubate at 22◦C (72◦F) to 23.3◦C(74◦F) to obtain a “balanced” growth of acidproducers, as well as aroma bacteria. To in-sure sufficient citric acid in the milk for thestarter bacteria add 227 g sodium citrate per379 liters (100 gallons) of milk. To preventlow acid development increase the incubat-ing time, increase the amount of starter, becertain the incubation temperature is notlower than 22◦C (72◦F) minimum.

(c) BitterCause. Poor quality milk, temperature fluctu-

ation during handling, psychrotrophic con-tamination

Prevention. Use only fresh-quality milk; elim-inate excessive acid production, which

results in the starter bacteria breaking downthe protein in the milk. Bitter flavor is usu-ally more pronounced as the age of the prod-uct increases. Check for improperly cleanedequipment, especially from the buttermilkvat through the filler and eliminate psy-chrotrophic contamination.

(d) AcidCause. Over-ripening, inadequate, and/or

slow coolingPrevention. Determine the solids-not-fat con-

tent of the milk and break at the proper titrat-able acidity or pH (9.0% SNF → 0.85% TA;10.0% SNF → 0.90% TA: 11.0% SNF →0.95% TA)

(e) StaleCause. Use of old powdered milk. Use of whey

powder along with nonfat dry milk.Prevention. Check the quality of the fresh milk

powder. Check the rotation of the inventoryof powder especially if the defect occursonly occasionally. Never use whey solids.

(f) CheesyCause. Due to psychrotrophic contamination.Prevention. Never use returned dumped milk

for making buttermilk.(g) Unclean

Cause. Usually caused by bacterial contam-ination at some point such as poor qual-ity starter milk, poor quality skim, and es-pecially poor quality cream when used asa source of milk fat for buttermilk. Dirtyequipment almost always results in bacte-rial contamination.

Prevention. Use only excellent quality, freshdairy ingredients in the manufacture of but-termilk. Clean all equipment thoroughly.

(h) CookedCause. Excessive heat treatment either in milk

or more commonly in reconstituted milkpowder.

Prevention. If NDM is used, ensure proper ro-tation. Avoid over heating of milk.

2. Body and texture(a) Weak

Cause. Low level of milk solids not fat in themilk. Low heat treatment. Low acid devel-opment.

Prevention. Use proper level of milk solids(at least 9.0%.) This provides sufficient ca-sein, which is a natural stabilizer involvedin coagulation as well as water retention.Use of sufficient high-heat treatment of milk


partially denatures the whey proteins. Thiscontributes to the thickening of the butter-milk body.

(b) SlickCause. Excessive use of stabilizer. Bacterial

contamination.Prevention. Cut back on use of stabilizer or

eliminate stabilizer completely. Check forpsychrotrophic bacterial contamination.

(c) GrainyCauses. Excessive acidity, undissolved salt, or

milk powder, high incubation temperature,poor-quality milk.

Prevention. Check acidity or pH of butter-milk at both top of vat and outlet valve.Break buttermilk at correct acidity (9.0%SNF → .95% TA; 10.0% SNF → .90%TA etc.) and cool rapidly. Too high incu-bation temperature results primarily in fastacid development and the tendency of ca-sein precipitation in a similar manner asin the manufacture of cottage cheese. Useof poor-quality milk, which causes physi-cal casein precipitation during the heatingprocess.

Although the procedures in the manufacture of but-termilk seem fairly straightforward and simple, stillvery poor-quality buttermilks are seen. Companieswith multiple processing plants may have the samebasic formula and very similar equipment. Thus, theonly variable (other than the raw milk) remaining isthe “people-factor.” No matter how basic the steps, tomake good buttermilk, there must be that one personwho “cares” enough to do the right thing at the righttime. In this regard, it is very important to keep dailyrecords to ensure that each “right thing” is in fact

done at the “right time.” When the correct manufac-turing procedure coincides consistently with peoplewho care about quality, the customer will recognizethese attributes and the sales of this nutritious anddelicately flavored product will likely increase.

ACKNOWLEDGMENTApproved for publication as Book Chapter No. BC-10613 of the Mississippi Agricultural and ForestryExperiment Station, Mississippi State University.

REFERENCESCode of Federal Regulations. 2002. Part 131.112.Custer EW. 1982. Cultured dairy foods: Quality

improvement manual. Am. Cult. Prod. Inst.Orlando, FL.

Danisco. Fall. 2003. Dairy News. Cultured products.Cultured buttermilk. Danisco USA Inc., NewCentury, KS 66031.

Harrits J. 1997. Culture nomenclature. In: Cultures forthe Manufacture of Dairy Products, Chr. Hansen,Milwaukee, WI, pp. 18–26.

Lundstedt E. 1975. All you wanted to know aboutbuttermilk. Cult. Dairy Prod. J. 10:18–22.

Petersen LW. 1997. Buttermilk, sour cream and relatedproducts. In: Cultures for the Manufacture of DairyProducts, Chr. Hansen, Milwaukee, WI,pp. 106–110.

Vedamuthu ER. Better buttermilk. 1985. MicrolifeTechnics, Sarasota, FL, 34230

White CH. 1977. Manufacturing better buttermilk.Cult. Dairy Prod. J. (Feb.) 12:16–20.

White CH. 1979. Buttermilk—Love it or leave it.Am. Dairy Review. (July) 41:34–38.

White, HW. 1976. Personal Communication.

18Cultured/Sour Cream

Bill Born

Early HistoryPresent Standards

Summary of ProceduresProblems and Correction

Sour Cream ProductsReferences

EARLY HISTORYHistorians speculate that man began domesticationof animals around 10,000 years ago. With the adventof herding and milking mammals, sour milk foodscame about naturally (Pariser, 1975). Milking was byhand and there was no such thing as sanitation. Milkthat was not consumed with in a few hours turnedsour. The type of fermentation that took place wasdetermined by temperature and type of organisms inthe milk. As mammals grazed though pastures, theypicked up organisms from plants and soil on theirudders. During hand milking, these organisms wereimparted to the milk. Lactic bacteria are found onplant blossoms and are usually the predominant flora,although pathogens could be picked up from the mudof streambeds and manure. Rapid souring of milk bylactic organisms allowed them to dominate the fer-mentation (Clark and Goldblith, 1975). Prompted byhunger and guided by his nose, man began to con-sume sour milk products. Through ingenuity, trial,and error, samples of good sour milks were added tonew milk to improve the chance of an eatable producton the next batch. Techniques and information werepassed on and cultured dairy products evolved.

In the ancient city of Ur, archaeologists unearthedfrieze dating 2900 bc. A part of the frieze depictsa man milking while other workers make sour milkproducts in pottery containers. The menu of a dinner

party held during this period in Ur consisted of an ap-petizer of garlic in sour cream, Tigris salmon, roastpig or lamb, unleavened bread, dates, goat cheese,and plenty of beer and wine (Editors of Life, 1961).By this time agriculture and dairy products had beenwell-established and somewhat refined. As the artof making sour milk foods was carried from tribeto tribe though Europe, each local artesian put anindividual touch to his work and a variety of prod-ucts evolved. Some of those products surviving todayare “quark” of Germany, “creme fraiche” of France,“clotted cream” of England, and “yogurt” from theMediterranean area (Food News Service, 2003).

While dairy cows arrived at the Jamestown Colonyin 1611, sour cream, as we know it today, had notdeveloped to its present form until 1890 to 1900(FarMore, 2003). First sour cream products wereeither incubated in the package or in a ten-galloncan. Invention of homogenization in 1919 greatlyhelped give sour cream a more uniform body and tex-ture (International Dairy Foods Association, 2003a).This was a time of entrepreneurs, and in 1919, HarryBovarnick developed his secret process for makingheavily bodied sour cream, and he would allow noone in the room when he prepared the mix. Harry’ssecret was to add 0.5 ml of rennet per ten gallonsof sour cream mix (Fig. 18.1). Breakstone Broth-ers in Walton, New York bought Harry’s process in1923. Then Breakstone was bought by Kraft in 1928,and Breakstone/Kraft became one of the largest pro-ducers of sour cream and cream cheese in the world(Lundstedt, 1977). In the mid 1940s Martin Kloserof Bowman Dairies in Chicago eliminated ten-galloncans for incubation and set sour cream in a largetank. When the product reached correct acidity, itwas pushed out of the tank with 5 lb air pressure to

285




Figure 18.1. Sour cream production in the 1920s.

force the sour cream through a stainless steel screento smooth the product as it was packaged. At thattime consumer packages were glass jars that werereturned, washed, and used again.

Some East Coast dairy manufacturers made bothcream cheese and sour cream. It was a logical stepfor them to use the processing procedures from creamcheese to make a hot-pack, long shelf-life sour cream.After sour cream was fermented to pH 4.5, it wasstirred and heated to kill all organisms, pumpedthrough a homogenizer, and packaged hot into her-metically sealed glass containers. As the productcools, a vacuum forms producing a stable product thatmaintains its quality up to 12 months. When exposedto light, the glass-packed sour cream did develop anoxidized flavor. Hot-pack sour cream differed fromcream cheese processing in that it was not drainedand no salt was added. Hot-pack sour cream flavordiffers from conventional sour cream in that it has nodiacetyl or carbon dioxide (CO2) and has a cooked,lactic acid flavor (Kosikowski and Mistry, 1997).

The first sour cream stabilizer was gelatin andthis did a reasonably good job. In the 1930s ArthurAmbrose of the Kraft-Phoenix Cheese Company,while working on ice cream stabilizers, tried somegum combinations in sour cream. He discoveredthat a mixture of 60% locust bean gum, 25% Irish

Moss, and 15% Karaya gum was a good substi-tute for gelatin, which was more expensive. ArthurAmbrose’s pioneer work was followed by profes-sional stabilizer manufacturers, which developedsour cream stabilizers that greatly improved body,texture, and palatability of sour cream (Lundstedt,1977).

University researchers developed considerableknowledge of sour cream technology for the dairy in-dustry to use. Some of the hallmark names that set thestandards for our present sour cream processing andcomposition are: FJ Doan and CD Dahle, Pennsyl-vania Agricultural Station; LD Hilker, ES Gutherie,and FV Kosikowski, Cornell University; HE Calbert,University of Wisconsin; and S Tuckey, Universityof Illinois (Tuckey, 1963).

Gutherie (1952) developed a method to measurethe body strength of sour cream using a plummet ofgiven weight and dropped from a given height. Theplummet was divided in ten equal segments and wasused to measure body strength by depth of penetrationinto a sour cream sample. This was used to evaluateresults from their experiments on factors effectingsour cream. Their experiments encompassed fat con-tent, time and temperature of pasteurization, homog-enization techniques, use of rennet, addition of milksolids not fat (MSNF), effect of stirring, and cooling

18 Cultured/Sour Cream 287

sour cream to 40◦F after incubation. They found thatsour cream could be made by either vat pasteurizationor high temperature/short time (HTST). A composi-tion of 18% fat, 9.5% MSNF, and addition of ren-net gave the most desirable consistency. It was alsofound that cooling the incubated product to 40◦F be-fore packaging weakened the body (Gutherie, 1963).The work of these early researchers set the standardsfor our present sour cream.

PRESENT STANDARDSFederal standards require that sour cream be 18%butterfat (International Dairy Foods Association,2003b). Acidification may be by a lactic culture or bydirect acid addition using an approved blend of acids.The acid blend most often used is a combination oflactic and citric acid. Other food grade acids, such asacetic, propionic, or phosphoric are commonly usedto achieve a particular flavor or improve keeping qual-ity. Lactic, acetic, and propionic have bacterial staticeffects, while citric can be fermented by many organ-isms, and if used in high levels or out of proportionwith other acids can cause excessive gas productionwhich will result in bloated cartons. One advantageof direct acidification is extended an shelf life. Directacidified sour cream and dips do not have the fineflavor of cultured sour cream for the first 2 weeksof shelf life. Starting on about the 15th day, depend-ing on storage temperature, enzymes from the culturewill start producing a noticeable “aged” flavor similarto aging Cheddar or other cured cheeses. Proteolysisbecomes apparent as bitter, cheesy, and stale flavors.The action of culture enzymes on dip spices becomesparticularly unpleasant. If sour cream is made by di-rect acidification, it must be so labeled.

Body and texture of sour cream, which does notcontain stabilizer, is determined by composition andprocessing. Mix should contain high-quality creamand high-protein MSNF. Natural solids-not-fat con-tent of an 18% cream will be between 7.1% and7.5%. To produce an optimum quality sour cream,solids-not-fat should be increased to 9.0–9.5%, us-ing high protein condensed skim milk or non-fat drymilk (NFDM). Standardized mix, ready for process-ing, should test 18.5% fat and 27.5–28.5% total solids(Calbert, 1961).

Processing can be accomplished by different meth-ods. Mix is heat treated by vat or HTST pasteuriza-tion. In both cases, time and temperature of heatingshould denature a consistent amount of whey pro-teins, which then coprecipitates with casein during

fermentation to produce a smooth body with im-proved moisture binding properties. Vat pasteuriza-tion at 73.9–79.4◦C (165–175◦F) for 30 minutes orHTST at 82.2–85◦C (180–185◦F) for 3–4 minuteshold will denature sufficient whey proteins. Vat pas-teurization lower than 65.6◦C (150◦F) or more than85◦C (185◦F ) for 30 minutes will produce a weakerbody that is more susceptible to syneresis when prod-uct is stressed. Firmness of body is also determined bymethods of homogenization. Temperature and pres-sures of homogenization are key factors in the bodyof sour cream. A long used method, giving an ex-cellent body and texture, is two single-stage 2500 psipasses using a Manton–Gaulin homogenizer. This re-quires two available tanks and much processing time.The same effect can be accomplished by HTST witha long hold tube and two homogenizers positionedin line after the holding tube. This system requiresone pass and saves much processing time and tankspace (Gutherie, 1963). Mix goes back through theregeneration and cooling section where it is cooledto 21.1–23.9◦C (70–75◦F) and on to the fermentationtank for setting. The high heat treatment and homog-enization technique produces enough free fat crystal-lization and fat clumping to form a firm-bodied sourcream without the use of stabilizers.

As the popularity and sales of sour cream in-creased, the use of stabilizers allowed the produc-ers to simplify processing and install larger, higherspeed operations. Stabilizer companies have met thedemands of cultured product manufacturers for sta-bilizers to produce sour cream with excellent bodyand texture. Stabilizers may be composed of gums,gelatin, modified food starch, whey proteins, and pro-tein conditioners such as phosphates. A stabilizer spe-cialist can furnish stabilizers to give the body andtexture of sour cream for a particular market.

The majority of sour cream is incubated in largetanks rather than 10-gallon cans, as was done inthe early history of cultured products. Usual incu-bation temperature is between 22.2◦C (72◦F) and23.9◦C (75◦F). This temperature range produces agood balance between organic acids and aromatic fla-vor compounds. Higher temperatures produce moreacid flavor and less aromatic flavor. In sour creamsfor industrial applications that do not require a fineflavor such as in baking and dips, incubation tem-peratures of 26.7–31.1◦C (80–88◦F) are often usedto reduce set times of 14–18 hours to 6–8 hours.A good sour cream culture is a blend of Lactococ-cus lactis and cremoris plus leuconostoc or Lc. lactissp diacetylactis. For fast-set industrial sour cream,


cottage cheese cultures containing no flavor organ-isms are often used at 31.1◦C (88◦F) to give setsas fast as 4–5 hours. Citric acid or sodium citrateis often added to consumer sour cream to enhanceflavor and produce a small amount of CO2. Exces-sive CO2 can cause problems. Since sour cream isusually packaged at incubation temperatures, culturecontinues to ferment citrate until the product cools. Ifcooling is slow, which often happens when the caseis corrugated and palletized, excess carbon dioxidewill swell carton and pop lids. This is particularlysevere when cartons have a gas tight seal and CO2

cannot escape. Customers think that swelled cartonsindicate spoilage. Culture should produce enough di-acetyl for a balanced flavor without overcarboniza-tion. The high fat content of sour cream smoothesout the sharp acid flavors that would be noticeable inbuttermilk. Some manufacturers take advantage ofthis trait to shorten incubation time by increasing settemperature to 29.4–31.1◦C (85–88◦F). Product willhave a clean acid flavor, but will lack the pleasant lin-gering aroma produced at lower incubation tempera-ture. Direct set cultures work very well to inoculatesour cream. These are the most reliable methods andare consistently balanced between acid and flavor-producing organisms.

Rennet may be added at set time to produce a firmerbody. If sour cream is to be used for dips, salt contentof dip seasonings will cause product to thin if stabi-lizers or rennet are not used. Usage level of single-strength rennet varies between 0.5 and 50 ml per 100-gallon mix. The upper level is close to that used forCheddar cheese and is not recommended. The usuallevel is 5 ml per 100 gallon. Even at this level cautionmust be taken to have rennet well diluted with cold,pure water and limit agitation after addition so thatproduct is quiescent before rennet coagulates casein.If rennet reacts with casein, while mix is still in mo-tion, a grainy texture will develop and whey-off mayoccur. Rennet should be added after culture is added.At 22.2–23.9◦C (72–75◦F), usual incubation time is14–18 hours.

The automated mix blending operation shown inFigure 18.2 is for a sour cream and dip base. Tanksare on load cells, liquid ingredients are metered intotanks, and dry ingredients are added through a liq-uefier. Mix is circulated through a shear pump un-til uniform. It is analyzed for fat and solids beforeprocessing through HTST and homogenization. Mixgoes to a fermentation tank at 22.2◦C (72◦F) for fer-mentation to pH 4.5.

Sour cream may be incubated in the cup, 10-galloncan, or tank. Most large volume operations incubate

in the tank. End point of fermentation is determinedby titratable acidity or pH (pH is preferred). The titrat-able acidity will range from 0.70 to 0.90% dependingon the amount of MSNF used in mix. The pH shouldbe 4.45–4.5. Proper level of MSNF added to mixbuffers acid development so that it is rare for sourcream to develop a harsh acid flavor. When correctacid is developed, cup sets are placed in a cooler andtank incubated product is broken with a slow-sweepagitator. Agitation should be used only intermittentlyduring packaging. Tank sets are not usually cooledbelow 18.3◦C (65◦F) before packaging because bodywill be thin. Cups are filled at 22.2–23.9◦C (72–75◦F)and product is cooled while quiescent in package.With tank-set sour cream, a positive pump is usedto pump the product through a screen, backpressurevalve, or similar devise to smooth out the texture.When pumping at 18.3◦C (65◦F) or above, body willresist thinning by shear. As temperature is reducedbelow 18.3◦C (65◦F), viscosity is reduced and bodydoes not reset firmly in the cup. Warming cups to21.1◦C (70◦F) and cooling again will restore somebody. This procedure would only be used to correcta mistake.

Summary of Procedures

A summary of sour cream processing is availablein Gourmetsleuth (2001). Use only those ingredientsthat are free of defects. Do not try to salvage old andoff-flavored ingredients by using them in culturedproducts. Best advertising dollars are spent on qualityproducts.

1. Standardize mix to 18.5% fat and 27.5% totalsolids. Avoid incorporation of air while blendingmix.

2. Vat pasteurize at 73.9–79.4◦C (165–175◦F) for 30minutes or HTST 82.2–85◦C (180–185◦F) for 3to 4 minute hold.

3. To produce a firm-bodied sour cream, homogenizetwo single-stage 2500 psi passes. High-speed op-erations that use the same homogenizer for milkand sour cream processing and two-pass systemcannot be used. A stabilizer will be required togive a proper viscosity to the sour cream.

4. Cool to 21.1–23.9◦C n(70–75◦F) and set with di-rect set or bulk sour cream culture. Use 5 ml rennetper 100-gallon mix.

5. Break at pH 4.5 with slow-sweep agitation, thenturn off agitator and start packaging. Turn agitatoron periodically during packaging to blend in anypockets of whey. Agitation should be automatedso each batch is consistent.


Figure 18.2. Automated mix blending inmodern sour cream plant.

6. Pump sour cream with positive pump through ascreen, backpressure valve, or similar smoothingdevise to packaging machine.

7. Package at incubation temperature and cool inpackage for maximum body firmness.

Problems and Correction

Simple mistakes account for many problems but areoften the most difficult to find. People do not liketo admit a mistake especially if they think their jobis in jeopardy. Because of incubation time, culturedproducts are usually made at the end of the day or atnight when supervision is minimal and low senioritypersonnel are working; therefore, good methods ofcommunication are essential in determining and pre-venting problems. Working atmosphere should en-courage workers to tell a supervisor immediately ifa problem is suspected. Problems can often be cor-rected if found early.

Body and Texture

1. Weak bodya. Stabilizer or milk solids left out of mix: (have

a check list for mix personnel)

b. Agitator left on through part or all of incuba-tion: (tank set)

c. Low casein milk: (spring and summer milk)d. Homogenizer difficulty: (bad valves, type of

valve, pressure not correct)e. Excessive agitation before packaging and pack-

aging sour cream too coldf. Excessive heat treatmentg. Consistently weak-bodied: (basic mix formula

should be changed and processing methodsevaluated)

2. Weak body at beginning of packaging and heavily-bodied at end: (often fat test is low on first productand high at end of packaging)a. Steam valve leaked on tank during incubation

causing bottom of tank to be warm. Whey formsin bottom and fat rises to top. Often pH is differ-ent in top and bottom of the tank because of tem-perature difference. Sweep agitation will notcompletely blend viscous mass. Double valvesshould be used on steam and refrigerated linesto insure no leakage

b. Some homogenizer systems will promote fatclumping sever enough that fat will rise beforeacid is sufficient for coagulation

c. Excessive agitation at set can cause fat to churnand rise to top of tank


3. Different pH on top and bottom of tanka. Temperature is different at top and bottom of

tank. Steam valve or refrigerated water valvesleak

b. Excessive air incorporation in mix. Air risesto top of tank. Cultures are microaerophilicand will work faster at bottom of tank thantop

4. Grainy texturea. Excessive rennet, which was insufficiently di-

luted with water when added to mix, will coag-ulate casein before mix is quiescent

b. Excessive heat treatment of mixc. Culture agglutination: (should not occur if heat

treatment is sufficient)d. Stabilizer reaction with milk protein: (certain

pectin, algin, and carrageenan will react withmilk protein unfavorably)

e. Screen or backpressure device left out of linebetween tank and filler

f. Fat churning due to excessive agitation at set5. Free whey on packaged product

a. Packaged sour cream has suffered physicaland/or temperature shock

b. Improper heat treatment of mixc. Insufficient acid development: (above pH 4.6 at

packaging)d. Wrong stabilizere. Low solids mix: (low casein resulting in weak,

fragile body)6. Slick texture or gummy body

a. Wrong or too much stabilizerb. Using a culture that produces high levels of

polysaccharides

Flavor Defects

1. Lacks flavora. Incorrect incubation temperatureb. Not enough acid developmentc. Culture does not contain flavor-producing or-

ganismsd. Low citrate levele. Flavor mask by high level or wrong stabilizer

2. Green flavor (like a green apple flavor, occurswhen diacetyl is reduced to acetaldehyde)a. Wrong culture selectionb. High temperature and over incubation

3. Oxidizeda. Mix exposed to copper in processing systemb. Product exposed to sunlight or fluorescent

light

4. Bittera. Lactic culture that produces high levels of pro-

teolytic enzymesb. High psychrotrophic bacteria counts in raw

milk supply5. Rancid

a. Raw milk contains heat-stable lipolytic en-zymes

b. Old and poorly handled cream6. Absorbed and unnatural flavors

a. Sour cream stored next to fruits, vegetables,solvents, cleaning supplies, etc.

b. Mix contaminated with sanitizers or otheragents used in plant

SOUR CREAM PRODUCTSIn the beginning it was determined that 18% fat madethe optimum sour cream and the Food and Drug Ad-ministration (FDA) set this as the standard. Thosewere the days when butter was the king and skimmilk was a by-product. Later came heart disease re-search that indicated butterfat was a potential villain.Media-hyped various nutritional papers denouncingany food containing high fat and high cholesterol andthis redirected the diet of the general populous. Dairymarketing people requested products to satisfy publicdemand for low fat and low cholesterol products. Thisled the way to development of lower fat sour creamproducts. In November 1996 the FDA changed thestandard of identity for sour cream to cover productslower than 18% fat. To give the consumer a wideselection, sour cream was divided into lower fat cat-egories. Sour half and half, reduced fat, light sourcream, and nonfat or fat free are some names now inuse (refer to FDA standards for labeling). Sour skimmilk is identified as fat-free sour cream, and it must bestabilized heavily enough to have a sour cream-typebody otherwise it is buttermilk. Replacing butterfatwith vegetable fat is called a filled sour cream. Tak-ing it a step further, replacing butterfat with vegetablefat and skim milk solid with sodium caseinate pro-duces an imitation sour cream. It must be noted thatsome vegetable fats do more damage to the humancirculatory system than butterfat.

Producing a firm-bodied reduced fat sour creamis not a difficult project. By increasing NFDM andselection of the correct stabilizer blend, reduced fatsour cream can be made that is about comparableto 18% sour cream. Making a good fat-free sourcream is difficult. Skim milk solids must be increasedwith NFDM, whey solids or whey protein, and a


Figure 18.3. Production of sour cream dips.

compatible stabilizer blend is essential to give a bodyclose to sour cream. Correct selection of emulsifierscan produce a texture similar to milk fat, but the fi-nal product still falls short of 18% fat sour cream.Culture selection is also more critical for no fat sourcream. Because of high levels of MSNF, cultures pro-duce excessive amounts of CO2 giving a sharp biteto the product. If the product is packaged with a gas-tight seal, the carton puffs up and alarms consumersthat something may be wrong with it. Making an ac-ceptable no fat sour cream requires close attention toevery detail, but there are acceptable products in themarket.

Filled sour creams have found a niche in the sys-tem. By selecting the correct vegetable oil and com-patible emulsifier system, a heart-healthy sour creamproduct can be produced that is pleasing to eat. An-other large volume use for filled sour cream is in themanufacturing of chip dips (Fig. 18.4). For the first2 weeks of shelf life, there is nothing better than adip made with butterfat. Then bacteria and enzymesfrom dip seasonings start to decompose butterfat andunpleasant flavors develop. Chip dips often have ashelf life of over 90 days. Using direct acid in placeof cultures and vegetable fat in place of butterfat, dip

bases can be formulated to keep a fresh flavor forlong periods of time and stand up to abuses receivedin the distribution chain. Three flavor blending tanksare shown at center left in Figure 18.3. Dry dip spicesare palletized on deck to be added to each tank.

To make an acceptable imitation sour cream re-quires skilled research. Correct vegetable fats, emul-sifiers, sodium casein, whey powder, whey proteins,and some times corn syrup solids and other bodybuilders are used to develop a usable formula. Thevegetable fat and emulsifier must produce a creamyconsistency, which resist crystallization when heatshocked. Some imitation sour creams on the mar-ket have a body more like lard than sour cream dueto excessive fat crystallization. Body building solidsshould work together to give coagulation similar toMSNF and without off-flavors. Caseins in particularcan produce off-flavors tasting like glue. When allelements are compatibly put together, a reasonablyeatable product can be made. But why make an imi-tation sour cream when the others will usually makea better product? There is a small market for peo-ple with specific health problems, and people whowill not eat animal products of any kind. Also animitation sour cream can be made to meet Orthodox


Figure 18.4. Production of filled sour cream dips.

Jewish laws. (Note that kosher gelatin is available, butmixing any animal gelatin with milk is not kosher).Imitation sour cream has found favor with some in-dustrial bakers, dessert, and salad makers because itis cheap and fat crystallization produces a firm bodywhen mixed with other ingredients.

Sour cream’s popularity has grown logarithmicallysince its development on the East Coast in early1900. Homemakers and professional chefs have de-veloped thousands of recipes using sour cream. Manyof the products that were developed became verypopular and are now manufactured by large foodcompanies (i.e., sour cream for cheesecake toppings,sour cream for herring, sour cream in salad dress-ings, freeze/thaw-stable sour cream, and sour creamthat can stand temperature and agitation of ultra-hightemperature [UHT] sterilization). Each of these ap-plications requires the research person to find thecorrect combinations of stabilizer, starch, and emul-sifier for the specific conditions. If sour cream is tobe combined with other ingredients containing amy-lase, starch cannot be used because it will be degradedand the product becomes thin with free whey present.UHT destroys the protein structure of sour cream;therefore, body must be achieved with a combinationof gums and special modified starches. To get sour

cream to adhere to an oily piece of fish requires acombination of emulsifiers and starch. Each applica-tion of sour cream is an individual challenge, whichwhen met with expertise, will increase sales. The fu-ture sour cream, in many forms, will continue to growas these challenges are met.

REFERENCESCalbert H. 1961. Cultured sour cream. Manufacturers’

Conference, University of Wisconsin, Madison.January.

Clark J, Goldblith S. 1975. Processing foods in ancientRome. Food Technol. 29(1):30–32.

Editors of Life. 1961. The epic of man. Time, Inc. p. 76.FarMore F. 2003. Milk history: Milestones of milk

history in the United States. Retrieved February2004 from http://www.wegotmilk.com/milk history.html

Food News Service. 2003. Ochef—Questions: Whatare all the dairy products under the sun? RetrievedFebruary 2004 from http://www.ochef.com/100.htm

GourmetSleuth. 2001. How to make sour cream.Retrieved February 2004. Available at http://www.gourmetsleuth.com/recipe sourcream.htm.


Gutherie E. 1952. Study of the body of cultured cream.Bull. 880, Cornell University, Ithaca, NY.

Gutherie E. 1963. Further studies of the body ofcultured cream. Bull. 986, Cornell University,Ithaca, NY.

International Dairy Foods Association. 2003a. Industryfacts-milk: Milestones of milk history in the U.S.Washington, DC: Milk Facts, 2002 ed. RetrievedFebruary 2004. Available at http://www.idfa.org/facts/milk.cfm

International Dairy Foods Association. 2003b. Industryfacts-milk: Definitions of fluid milk and milkproducts. Washington, DC: Milk Facts, 2002 ed.

Retrieved February 2004 from. Available athttp://www.idfa.org/facts/milk.cfm

Kosikowski FV, Mistry VV. 1997. Cheese andfermented milk foods: Origins and principles.Vol. 1, 3rd ed. Westport, CT. p. 82.

Lundstedt E. 1977. Manufacture of superior sourcream. Cult. Dairy Prod. J., 10(1):20–22.

Pariser E. 1975. Food in ancient Egypt and classicalGreece. Food Technol. 29(1):23–27.

Tuckey S. October, 1963. Sour cream processing.Dairy Conference, University of Illinois,Urbana.Available at http://em.wilipedia.org/wikicream.

19Other Fermented and

Culture-Containing MilksEbenezer R. Vedamuthu

IntroductionDahi

HistoryProduction and PackagingProduct Description and Keeping QualityMicrobiology

KefirHistoryProduction, and PackagingProduct Description and QualityMicrobiology

KoumissHistoryProductionProduct DescriptionMicrobiology

Acidophilus Milk and Sweet Acidophilus MilkHistoryProduction of Acidophilus MilkProduction of Sweet Acidophilus MilkQuality StandardsMicrobiology

Probiotic MilksHistoryProduction of Probiotic MilksQuality Standards

Bulgarian MilkSkyrVilii

MicrobiologyReferences

INTRODUCTIONDahi, Kefir, Koumiss, Acidophilus Milk, Probi-otic Milk, and other cultured milks represent thegreat diversity of cultured dairy products producedaround the world. The diversity not only reflects the

geographical region of their origin but also the typesof milk used in their production, the gradation in thetechnology employed, the cultural conditions, andthe types and species of microflora involved in thosefermentations. Short descriptions of the various cul-tured milks in the following paragraphs illustrate thatdiversity:

Dahi is a semisolid cultured product popularthroughout South Asia, but there are subtle variationsin the body and flavor of Dahi made in different partsof the subcontinent. In a large portion of the coun-try, Dahi is made from cow milk. There are pock-ets where a mixture of cow milk and buffalo milkis used, and in certain areas buffalo milk is almostexclusively used. Buffalo milk being high in solidscontent, yields a very firm product, while cow milkDahi is a relatively softer product. In terms of fla-vor, in certain regions a mildly acidic, yeasty-sweetproduct is desired, whereas in other regions a moreacidic Dahi is preferred. Because of the higher solidscontent of buffalo milk, the acidity of buffalo milkDahi is higher. There is general agreement amongthe scientific community that the microorganisms in-volved in Dahi fermentation consist of dairy lacto-cocci , leuconostocs, and certain yeasts (Rangappaand Achaya ,1975) although the yeasts may be con-sidered as secondary contaminants that are carriedover by the extensive “back-slopping” that is prac-ticed in households and cottage industry involved inDahi production. Back-slopping is the practice ofusing a small remnant of the previous day’s prod-uct to inoculate a fresh batch. The Bureau of IndianStandards recognizes a category called “Sour Dahi”for which additional secondary flora consisting ofthemotolerant “coccus-rod” mixtures used in Yogurtmay be included (Aneja et al., 2002).

295




Kefir is popular in Russia, and originated in the areaabutting the Caucasus mountain range. TraditionalKefir is produced using Kefir grains as inoculum.The incubation is at room temperature. Kefir is anacidic–alcoholic product as both lactic acid bacteriaand yeasts are involved in the fermentation. Accord-ing to Kosikowski and Mistry (1997), in Russia, Kefirmay be made from goat, sheep, or cow milk. The lac-tic acid content is usually around 0.8% and alcoholiclevel about 1.0%. Carbon dioxide is the other ma-jor fermentation byproduct in Kefir. Modern produc-tion of Kefir in Russia and other European countrieswhere it is popular varies from the traditional pro-cess. The microflora involved in Kefir fermentation iscomplex.

Koumiss is acidic–alcoholic cultured milk that hasconsiderable commercial and public health signif-icance in Russia (Kosikowski and Mistry, 1997).Koumiss is made from mare’s milk. Koumiss has amilky white appearance with a grayish tint. Unlikemost other cultured milk products, which form co-agula of different consistencies, Koumiss remains afluid even after the fermentation is complete. Theprotein in mare’s milk is different from the pro-tein in milk from other species, and does not coag-ulate even with increase in acidity or when rennetis added (Kosikowski and Mistry, 1997). Accordingto Vedamuthu (1982), mare’s milk does not coag-ulate at the isoelectric point of casein and hence,Koumiss, which may contain about 0.7–1.8% lacticacid and 1.0–2.5% ethanol, is not a curdled product.Robinson et al. (2002) report that Koumiss orKoumiss-like products carrying names such as Airag,Arrag, Chige or Chigo are produced in Mongolia andWestern Chinese provinces.

Vedamuthu (1982) defines Acidophilus milk thus,“Acidophilus milk or reform yogurt is the productobtained by fermenting milk with an authentic cul-ture of Lactobacillus acidophilus.” Acidophilus milkmay be considered the prototype of all the present dayprobiotic milks. One of the unique features of Lacto-bacillus acidophilus is its ability to survive the severeenvironmental conditions found in the intestinal tractof man, animals, and birds. This bacterium is com-monly a part of the total microbial flora of healthyhumans. Scientific evidence has been steadily accu-mulating to establish that the normal intestinal floracontributes in no small measure to gut health. Tradi-tional Acidophilus milk is an extremely sour productand does not contain other balancing flavors. Hence,it has not been a popular product. Accordingly,alternative means to deliver gut health promoting

Lactobacillus acidophilus bacteria have been de-signed. These products are generally called “Sweetacidophilus milks” (Foster et al., 1957).

The definition for the term “probiotics” varies froma general description such as, “live microorganismsadministered in adequate amounts that confer a healtheffect on the host” (Skovsende, 2003) to a morenarrow specification, which states, “probiotics arelive microbial food supplements, which benefit thehealth of consumers by maintaining, or improvingtheir intestinal balance” (Mattila-Sandholm et al.,2002). Several species comprising the genera Lac-tobacillus and Bifidobacterium are normal inhabi-tants of healthy human gut, and have been shownto play a regulatory role in the ecology and the mi-crobial flora of the gut (Sanders and Huis in’t Veld,1999). Regular intake of probiotic-rich foods maycontribute to maintaining intestinal health and gen-eral well-being. Various other health benefits, suchas improvement of lactose metabolism, reduction inserum cholesterol, antimicrobial, anticarcinogenic,antimutagenic effects, and immune stimulation havebeen ascribed to the regular intake of probiotics(Shah, 2001). Skovsende (2003) has cited other re-ported benefits. The scientific evidence, however,is stronger and more equivocal with respect to themaintenance of intestinal health. Although severalfood products other than dairy foods like sausages,breakfast cereals, health food bars have been ex-plored as vehicles for the delivery of probiotics, byfar the greatest success has been with dairy prod-ucts, especially fluid milk (Skovsende, 2003). A morecomprehensive discussion of the benefits of addingprobiotics to milk is found in Chandan’s review(1999).

Besides the products discussed in the foregoingparagraphs, there are few other cultured dairy prod-ucts that are either confined to limited geographicalareas or little known beyond the areas where they areproduced and consumed.

Bulgarian milk is cultured milk that is popular inthe Eastern European countries. This product maybe considered to be the forerunner of the present daytraditional Yogurt. The appellation “Bulgarian” cameabout because the product originated in Bulgaria. Forthe product produced in Bulgaria, only Lactobacillusdelbrueckii ssp. bulgaricus (rod) is used as starter.In other places, the “coccus” (Streptococcus ther-mophilus) may be included along with the “rod.” Itis believed that the species name “bulgaricus” wasderived from Bulgarian milk from which the Lacto-bacillus species was first isolated. It is a highly acidic

19 Other Fermented and Culture-Containing Milks 297

product with a green acetaldehyde flavor reminiscentof traditional Yogurt.

In Scandinavian countries unique cultured milk isconsumed. The well known among those products isViili, also known as Pitkapiima, or just Piima andFiili. This product is popular in Finland. In otherScandinavian countries, similar products carry namessuch as Langfil, Taettemelk, and Keldermilk. Theunique feature about those milks is their ropy, stringy,and viscous texture. When a spoon is inserted intoone of those products and lifted out, the coagulumclings to the spoon and forms long stringy threadsas the spoon is drawn away from the surface of thecurdled mass. Special capsular slime-forming dairylactococci are included along with noncapsular lac-tococci in starters for those products. The FinnishViili also has a thin layer of mold on the surface.The mold, Geotrichum candidum is considered toimpart a unique flavor to the product. The immediatelayer below the surface of the mold, is less acidic, be-cause Geotrichum candidum metabolizes lactic acidformed by the lactococci.

Skyr is Icelandic cultured milk. It has been in-troduced in Denmark. The product is a variation ofYogurt. It may be considered as a concentrated Yo-gurt. The starter flora for Skyr is similar to Yogurt, andconsists of a symbiotic combination of “rod” (Lac-tobacillus delbrueckii ssp. bulgaricus) and “coccus”(Streptococcus thermophilus). Skim milk is used inits production and the concentration of the coagu-lum is achieved by removing sufficient whey to in-crease the solids level in the product from 18% to20%, which increases the initial acidity range from1.4–1.6% to 2.5–3.0% (Foster et al., 1957).

There are other concentrated variations of Yogurt,and other cultured milks made with mesophilic dairylactococci known by different local nomenclatures,and are listed in Chapter 1.

DAHIHistory

The origin of Dahi is shrouded in antiquity. Accord-ing to Aneja et al. (2002), numerous references toDahi are found in Vedic literature, which comprisethe sacred books of Hinduism. In the major sacredbook, the Rig Veda, various means of curdling milk(for Dahi) with a starter consisting of a small portionof an earlier stock, or by introducing greens from theputika creeper, the bark from palasha plant or the fruitof the kuvala (Ziziphus spp.) are mentioned. People

of those times presumably were aware that greenplants are the natural habitat for lactic acid bacteria.In many of the art forms of India depicting the mytho-logical legends of the exploits of Lord Krishna (incar-nate of Lord Vishnu), show young Krishna stealingDahi curd from earthen pots in the larder, or frolick-ing with milkmaids carrying earthenware, containingDahi.

In Vedic times as well as at present, Dahi is madefor consumption as such or as a starting material forsecondary products. In Southern India, Dahi may beeaten as curds or mixed with rice. Sometimes, a va-riety of spices and condiments cooked in hot edibleoil are added to Dahi, and the mixture is used to fla-vor the rice staple. Plain Dahi or the product embel-lished with hot spice-oil mixture may be used as saladdressing (raitha, the modern equivalent of rayata—royal food item of Vedic times). A doughnut shaped,deep fat-fried product made from a batter consistingof cereal-legume mixture called “vada” soaked inplain Dahi or Dahi containing hot spice-oil mixture,is served in Indian homes as “Dahi vada.”

In Northern India, where wheat is the staple, Dahiis eaten with flat wheat breads of different kinds. An-other favorite in Northern India is salty or sweet lassi,which is Dahi mixed and whipped with cold water,spices and salt (for salty lassi) or sugar (for sweetlassi). This drink is popular to quench the thirst dur-ing hot summer months. The South Indian equivalentis “buttermilk” (or moar). Dahi is also the interme-diate in the production of desi butter or makhan. Forconversion into makhan, the dahi curd with or with-out the addition of cold water is churned with a man-ual wooden paddle until the butter granules separatefrom the serum. The granules are collected and con-solidated to form a lump or a pat. The serum portionand the residual solid is consumed as a refreshingdrink, or mixed with rice and consumed. Desi butteris largely used for making ghee, the preferred short-ening in Indian cooking. In some homes, the uppercream layer on the surface of Dahi made from wholemilk is removed and stored until enough material isgathered, for churning into makhan. Another impor-tant product made from dahi is Shrikhand, popularin the Western States of India. Srikhand is a con-centrated curd of dahi by draining off the whey, andfortifying the concentrated curd with sugar and fla-vorings like nutmeg and cardamom.

Besides the foregoing, there are various other dahiderivatives. Those products are discussed by Anejaet al. (2002), Rangappa and Achaya (1975), and Pra-japati (2003).


Production and Packaging

Dahi is largely made in individual households forthe immediate needs of the family. In villages andtowns, the product is often made on a cottage in-dustry scale for sale, as such or for converting it tomakhan, and ultimately to ghee. Ghee is essentiallyclarified butter oil, which is made by evaporating themoisture off the desi butter by heating on an openfire. The heat treatment and the drastic reduction inmoisture content render the shortening a relativelystable product under ambient conditions, which couldbe easily transported to urban markets. Greater careis exercised in making dahi for direct consumptionthan for conversion into butter or ghee (Rangappaand Achaya, 1975).

In preparing dahi in households and in cottagescale production centers, milk is boiled to destroycontaminants, and after cooling to body or ambienttemperature in a covered vessel, is inoculated with aportion of the previous day’s product. The vessel maybe left undisturbed in a warm place (next to a warmoven) or wrapped with a cloth or straw and placed ina straw box to prevent loss of warmth by radiationfor anywhere from 6 to 24 hours depending upon theambient temperature. Rangappa and Achaya (1975)state that the amount of inoculum would vary de-pending upon the ambient temperature. In very coldweather, 5–10% by volume may be used, and dur-ing summer about 1–2% may be used. During veryhot summer months, the vessel containing the in-oculated milk may be wrapped in a moist cloth tokeep the content insulated from getting too warm.The authors further opine that the seed used is nevera pure culture but mixed with the predominance oflactic acid bacteria. The final acidity after incuba-tion may range from 0.7% to 1.0%. And, for gooddahi, Rangappa and Achaya (1975) suggest a finalpH range of 4.6 to 5.2. After incubation and attainingthe desired curd formation and acidity, the product iskept in a cold spot or held in clean, covered earth-enware to achieve evaporative cooling, or immersedin a shallow pan containing cold water. A similarprocess is mentioned by Aneja et al. (2002). In vil-lage markets and bazaars in towns, dahi portionedout in small pottery is offered for sale. The productmay also be ladled out of a large earthen vessel intoreceptacles brought to the market or bazaar by thecustomers.

To cater to the urban populace of India withgreater purchasing power, dahi is also made on anindustrial scale. The volume is, however, relatively

small. The manufacturing process and the equip-ment used are similar to other cultured dairy prod-ucts in the West. Double-jacketed stainless steel vatsequipped with suitable agitators and in-place heatingand cooling design, and incorporating cleaning-in-place (CIP) piping and equipment are used. Milk maybe vat pasteurized or run through a high- temperature-short- time (HTST) or an ultra high temperature(UHT) equipment and piped into stainless steel vatsequipped with thermostatic temperature controls (forincubation and cooling). To monitor the course offermentation, the vats may have sanitary ports forpH probes coupled with a recording chart, or sam-ple ports. After incubation is completed, the curd isgently broken by turning on the agitators and con-comitantly cooling the curd mass by circulating chillwater (sweet water) in the vat jacket. After sufficientcooling, the curd is gently conveyed to a filling ma-chine. To preserve the desired body and texture, grav-ity flow is desirable. If pumping is necessary, a posi-tive displacement pump with a back-pressure deviceis recommended. Plastic cups with lids and display-ing attractive graphic designs are used for packagingindustrially manufactured dahi. For a more detaileddescription of the equipment and processes used inindustrial production of dahi, the reader is referredto Aneja et al. (2002).

There are definite differences in process parame-ters between the small-scale and industrial-scale pro-duction of dahi. These differences relate to the heattreatment of milk, the incubation temperature andthe starter flora. Another variation is the homoge-nization of the milk or the sweetener containing mix.Homogenization ensures uniformity in body and tex-ture, and prevents the formation of the “cream line.”In small-scale production, the milk is brought to acomplete boil before it is slowly cooled down with-out any external coolant to body or ambient temper-ature. On an industrial scale, by low temperature—long hold (LTLH) procedure, milk is heated to 63◦Cand held at that temperature for 30 minutes; and,when sweeteners are added to milk, the mixtureheated to, and held at 66◦C for 30 minutes. Thisis usually vat pasteurization. For HTST treatment,milk is heated to 73◦C and held for 15 seconds, andmilk with sweetener is heated to 75◦C and held for15 seconds. The temperature-time parameters forUHT treatment may range from >90◦C to 148◦Cfor 2 seconds. When direct culinary steam injectionheating is practiced, the temperature attained is 94◦Cwith suitable adjustments made for dilution of the mixby condensation of steam (Aneja et al., 2002). On an


industrial scale, after heating, the milk/mix is cooledrapidly to the desired temperature by external coolingdevices.

The incubation for cottage industry preparation ofdahi is at ambient temperatures, which may rangefrom 28◦C to 30◦C during summer, and in wintermonths, the temperatures may vary from 20◦C to24◦C. Aneja et al. (2002) report that in industrialproduction of dahi, the incubation temperature is37◦C, and is thermostatically controlled. Because ofthe accelerated growth at higher temperatures, theincubation period is shorter for industrial produc-tion. Shorter incubation probably fits with rapid turnover of equipment and work schedules needed forindustrial operations. At the end of fermentation,in industrial operations, the dahi is rapidly cooledto <5◦C to arrest excessive acid development and“whey-off.”

Product Description and KeepingQuality

Rangappa and Achaya (1975) describe dahi as,“Good dahi is a weak gel, like junket.” That is a verygood description. The coagulum is soft and “livery.”The body of dahi may be termed as somewhat lumpy,and the texture as smooth. Dahi made from buffalomilk tends to be somewhat firmer than the productmade with cow milk or a mixture of cow and buffalomilk. Limited volume of dahi made from goat milkalso displays a firmer curd than cow milk product.Those differences are reflective of higher solids con-tent of buffalo and goat milks. Dahi made industriallyusually contains added solids and sweetener, and themix is homogenized. The coagulum made from suchfortified mixes is firmer, which is desired because,postfermentation operations such as breaking of thecoagulum, pumping and filling, tend to weaken thecurd structure, and loss of desired body characteris-tics. The firmer body attained industrially compen-sates for such postfermentation losses in body char-acteristics.

The Pure Food Act in India defines dahi or curd“as a semisolid product, obtained from pasteurizedor boiled milk by souring (natural or otherwise),using a harmless lactic acid or other bacterial cul-tures. Dahi may contain additional cane sugar. Itshould have the same minimum percentage of fat andsolids-not-fat as the milk from which it is prepared.Where dahi or curd, other than skimmed milk dahi,is sold or offered for sale without any indication ofthe class of milk, the standards prescribed for dahi

prepared from buffalo milk shall apply” (Aneja et al.,2002).

The keeping quality of dahi made in the unor-ganized sector varies considerably. Normally, dahimade in individual homes and sold in unorganizedsector is consumed immediately, with a small portionretained for inoculating the next batch. If properlyhandled and refrigerated, dahi made in unorganizedsector may have a shelf life of 2 to 3 days. Industri-ally manufactured, packaged dahi would have a shelflife of 7 to 10 days when properly refrigerated andhandled.

Dahi is often described as the Indian equivalentof yogurt. In reality, however, there are distinct dif-ferences between the two products. Plain yogurt cur-rently made is a firm, smooth product that can bespooned without much distortion of the curd bodyand structure. This is attained by the fortification ofthe mix with additional milk solids and (or) the useof stabilizers. Dahi, on the other hand, is a soft coag-ulum that is lumpy, and would display jagged edgeswhen the curd is broken, and exude whey near thecut edges. While yogurt mixes are homogenized togive a smooth body, lack of homogenization and sta-bilizers in dahi manufacture (except in industrial pro-duction) give dahi a lumpy texture and tendency forwhey off. In terms of flavor, yogurt is characterizedby sharp acid tartness (recent trends in yogurt showa preference for mild acidity) and the characteristic“green,” acataldehyde flavor (lately, a barely percep-tible greenness is preferred). Dahi, on the other hand,is mildly acidic, and diacetyl is the prominent fla-vor compound. The difference in the flavor betweenyogurt and dahi is because of the starter flora used.This will be addressed in the next section. Indus-trial scale dahi, where coccus or coccus-rod combi-nation is used, the product will have a flavor typicalof yogurt. Those aspects are discussed by Aneja etal. (2002).

Microbiology

The predominant bacteria in dahi starter culturesconsist of dairy lactococci and leuconostocs. Thedairy lactococci are homofermentative, and produce>99% lactic acid from lactose. The dairy leuconos-tocs are herterofermentative, and produce about 70%lactic acid from sugars, and the remaining 30% ofthe byproducts are made up of acetic acid, ethyl al-cohol, and carbon dioxide. The dairy leuconostocsalso metabolize the citrate present in milk to form di-acetyl and its reduced derivatives. While lactic acid


imparts the pleasant, mild acidic flavor, diacetyl con-tributes to a buttery, nut-meat like flavor. The othercomponents (acetic acid, alcohol, and carbon diox-ide) impart a balanced rounded flavor to dahi, muchlike Cultured Buttermilk. The presence of Strepto-coccus thermophilus and Lactobacillus delbrueckiisubsp. bulgaricus in factory scale dahi starters, leadsto the formation of acetaldehyde as in yogurt. Thecharacteristics and the roles played by the starter floraof dahi and yogurt are summarized by Aneja et al.(2002).

Because dahi is largely made in the unorganizedsector, where back-slopping is widely practiced, andcontrolled process conditions are not used, the bacte-rial flora of dahi is highly variable. Those aspects arediscussed in detail by Rangappa and Achaya (1975).Because dahi is a cultured dairy product, bacterialcount such as Standard Plate Count on a general me-dia is unsuitable to provide the index of quality. Be-ing an acid food, coliform count on dahi is unsuit-able as a sanitary index. Count for enterococci wouldbe more applicable as a sanitary index. In addition,yeast and mold count would be more relevant in qual-ity attributes of dahi. For microbiological examina-tion of dahi and its significance, the methods and thediscussion provided for fermented dairy products inthe Compendium of Methods for the Microbiologi-cal Examination of Foods (Richter and Vedamuthu,2001) should be consulted. Aneja et al. (2002) havealso detailed the procedures for chemical and micro-biological quality control of dahi.

Dahi, being an acid food containing lactic acid bac-teria, is not a conducive menstruum for the growthand survival of pathogens. Unless grossly contami-nated with pathogens, from a public health viewpoint,dahi is a relatively safe product.

KEFIRHistory

Kefir is made using kefir grains. Although the ori-gin of kefir grains is unknown, the prevailing legendattributes that the grains were given to people inhab-iting the region around Caucasus mountain range byProphet Mohammed (Koroleva, 1991). Kosikowskiand Mistry (1997) state that the grains, which sus-tain kefir fermentation were called “the gift of thegods.” Kefir may be made with milk from differentanimal species. Kosikowski and Mistry (1997) men-tion that milk from the sheep, goat, and cow maybe used for that product. Traditional fermentation

for kefir was carried out in a leather bag made ofgoat hide on a continuous basis by periodic with-drawal of a portion of the fermented product andreplenishing the container with fresh milk. Duringwarm months of the year, the fermentation bag washung outdoors, and brought indoors during winter tokeep it warm. An interesting practice was to hang theleather bag containing the fermenting milk near thedoor step, so that each person going past can kick orshake the bag to keep the contents mixed (Foster etal., 1957). Now, kefir is popular all over Russia, andthe annual per capita consumption amounts to 4 to5 kilograms.

Production, and Packaging

The complete starter flora of kefir is contained withinand on the surface of the kefir grains. Kefir grainsvary in size and may measure from 0.5 to 3.5 cm indiameter. The grains are gelatinous white- or cream-colored irregular granules ranging in size from thatof a wheat grain to a walnut. They have convolutedirregular folded surfaces resembling cauliflower flo-rets and an elastic consistency (Robinson et al.,2002; Vedamuthu, 1982; Kosikowski and Mistry,1997). Vedamuthu (1982) states that the granules arelargely composed of a polysaccharide called kifran ,which according to Kosikowski and Mistry (1997) ismade up of glucose-galactose heteropolymer. Therecould be some denatured milk protein associatedwith kifran matrix. The grains are insoluble in waterand resistant to enzymes. When soaked in water, thegrains swell and turn to a slimy, jelly-like product.Within the involutions or folds of the grains, bacteriaand yeasts that form the characteristic flora of kefirare found, and there appears to be a symbiotic as-sociation between the bacteria and the yeasts in thatecological niche (Vedamuthu, 1982).

The attractive feature about kefir grains is that theycould be reused several times if proper sanitation isobserved in recovering, drying, and storing the grainsfrom batch to batch. When kefir curd is agitated, thegrains migrate to the surface carried up by the en-trapped carbon dioxide. The grains are strained out,rinsed in chill water, and either could be stored andrefrigerated in cold water or drained and dried in awarm oven and stored in foil pouches. Wet-storedgrains last up to 8 to 10 days without loss of ac-tivity, while dried grains may be active as long as18 months (Kosikowski and Mistry, 1997). Dried ke-fir grains need to be activated by three consecutivepasses in milk.


In traditional manufacture of kefir, whole milk pas-teurized at 85◦C for 30 minutes is cooled to 22◦C,and inoculated with kefir grains. After overnight in-cubation at that temperature, a smooth curd is ob-tained. The curdled milk is run through a wire sieveto recover the grains. The product is then chilled andis ready for consumption (Kosikowski and Mistry,1997). Commercial manufacture of kefir is describedby Robinson et al. (2002). The process essentiallyconsists of pasteurizing whole milk at 95◦C for5 minutes, and cooling the milk to 23◦C. Incubationat 23◦C follows inoculation with kefir grains. After20-hour incubation, the grains are removed, and thecurdled milk is used as a bulk starter for fresh batches.The bulk starter is added to the pasteurized (95◦C for5 minutes), tempered milk (at 23◦C) at 3.5% (v/v).The inoculated milk is incubated at the same tem-perature for 20 hours. After cooling to <7◦C, theproduct is held at that temperature for several hoursto “ripen.” Ripening imparts “stability” to the prod-uct. After a sufficient period of ripening, the curd isgently broken and packaged to preserve the viscositypreferred by consumers.

Variations of that basic procedure are used whenlyophilized kefir cultures (without kefir grains) serveas the inocula. For further details on the variationsused in the manufacture of kefir, the reader is referredto Robinson et al. (2002).

Product Description and Quality

Good quality kefir is distinguished by a smooth softcurd, and a thick body preferred by discerning cus-tomers. When agitated, kefir fizzes and foams likebeer (Kosikowski and Mistry, 1997). The flavor ofkefir may be described as mildly alcholic, yeasty-sour with a tangy effervescence (Vedamuthu, 1982).The effervescence and foaming is caused by the es-caping carbon dioxide entrapped within the curd. Thecarbon dioxide is generated by the yeasts and hetero-fermentative lactic acid bacteria present in the kefirgrains.

The quality and characteristics of kefir are highlyvariable. According to Robinson et al. (2002), thequality is greatly influenced by the origin and mi-croflora of kefir grains used and the quality and typeof milk (sheep, goat, or cow) used for its manufac-ture. With storage, there is a progressive increasein the concentration of lactic acid, ethanol and car-bon dioxide in kefir. The peptide level also increaseswith aging. With the exception of the accumulationof the metabolic byproducts of fermentation, and a

decrease in the concentration of lactose and milkproteins, the composition of kefir does not differfrom the milk used in its preparation. For further de-tails, the chapter by Robinson et al. (2002) should beconsulted.

Microbiology

The microflora of kefir grains are complex and highlyvariable. The flora associated with the grains variesfrom one geographical region to another and of-ten within the same region. Sanitation during han-dling of the grain also introduces variability in theflora. Robinson et al. (2002) state that the microfloraof kefir grains consists of an undefined mixture ofspecies of bacteria and yeasts. The bacterial speciesinclude members of the genera Lactobacillus, Lacto-coccus, Leuconostoc, Acetobacter, and Streptococ-cus thermophilus. Often the mold, Geotrichum can-didum is also found. In some countries where kefiris consumed, the presence of Acetobacter aceti and(or) Acetobacter rasens and Geotrichum candidumis considered to be as undesirable contaminants insome areas, although in other areas, their presence isdesired. The authors report that several species be-longing to different yeast genera are present in kefirgrains. The complexity of the microflora associatedwith kefir grains as depicted by the authors is repro-duced in Figure 19.1.

Kosikowski and Mistry (1997) also attest to thevariability in the flora associated with kefir, but statethat the dominant yeasts are Saccharomyces kefir,Torula or Candida kefir. The dominant bacteria in-clude Lactobacillus kefir, Lactococcus spp. and Leu-conostoc spp. They also mention Acetobacter spp.and Geotrichum candidum. Furthermore, they statethat frequently the kefir grains are found to be coveredwith white cottony mycelia of Geotrichum candidum,which does not affect the quality of kefir producedfrom such grains. Improper handling of the grainsintroduces contaminants like coliforms, micrococci,and bacilli, which cause rapid spoilage of kefir.

Other bacteria reported to be present in ke-fir grains are Lactobacillus brevis and a capsularpolysaccharide-producing strain of Lactobacillus ki-firanofaciens (Robinson et al., 2002). The architec-ture of the kefir grains appears to consist of highlyconvoluted laminar sheets of yeasts, with the periph-eral sheets dominated by various bacteria and the in-ner core dominated by yeasts.

Kefir made in Russia and the neighboring EastEuropean countries makes use of the traditional kefir


Saccharomyces spp.Kluyveromyces spp.Candida spp.Mycotorula spp.Torulopsis spp.Cryptococcus spp.Pichia spp.Torulaspora spp.

Geotrichum spp.Pediococcus spp.Micrococcus spp.Bacillus spp.Escherichia spp.Enterococcus spp.

Lactobacillus spp.Lactococcus spp.S. thermophilusLeuconostoc spp.

Acetobacter acetirasens

MICROFLORA OFKEFIR GRAINS

YEASTSLACTIC ACID

BACTERIA

ACETIC ACIDBACTERIA

CONTAMINANTS

Figure 19.1. Microflora of Kefir grains. FromDairy Industries International, 1999. 65(5),32–33. Reproduced with permission.

grains. Recently, however, several nonyeast contain-ing flavored and unflavored fermented milks bearingthe label kefir have appeared in several Western coun-tries including the United States. Such products donot qualify as “traditional” kefir. There is no standarddefinition for kefir. Most of the nontraditional kefirsfound in the Western markets are cultured with a mix-ture of dairy lactobacilli, lactococci, Streptococcusthermophilus, and a few probiotic bacterial species.

KOUMISSHistory

The name Koumiss may be spelt differently in litera-ture. The various spellings used are Kumiss, Kumys,and Coomys (Robinson et al., 2002). Although theproduct is fermented and has a titratable acidity rang-ing from 0.54% to 1.08% it is a liquid product show-ing no curdling. Koumiss is made from mare’s milk.It is believed to have originated among the Tartars,and spread across the Asiatic Steppes to Western re-gions of China and Mangolia. In China, the product isknown by different names as mentioned in an earliersection.

Production

Traditional production was carried out by fillingsmoked horse’s hide with raw mare’s milk, andincubating at ambient temperatures. The smokedhorse-hide used for Koumiss production was called

tursuks or burduks. The microflora adhering to thehides served as the inoculum. After sufficient lengthof incubation, the product was drained out of thehide containers and refilled with another batch ofmare’s milk, essentially employing a back-sloppingprocess (Robinson et al., 2002). Kosikowski andMistry (1997) add that when mare’s milk incubatedin hide containers fails to ferment properly, a pieceof fresh horse skin, a tendon of a dead horse or a cop-per coin encrusted with copper sulfate verdigris wereadded to impel the progress of fermentation. Theyspeculate that those materials probably contained theneeded flora.

Several different commercial processes have beendeveloped in the last four decades. Most of thosemethods use cow’s milk as the starting material. Inone of the processes, skimmed cow’s milk fortifiedwith 2.5% sucrose, and heated at 90◦ C for 2 to3 minutes, was cooled to 28◦C. Tempered milk wasinoculated with starter culture consisting of Lacto-bacillus delbrueckii ssp. bulgaricus and a strain ofTorula yeast at the rate of about 10% (v/v). After mix-ing for 15 to 20 minutes, the mix was incubated at26◦C, until the titratable acidity reached about 0.9%.Other blends that were used as starting materials con-sisted of a mixture of whole and skim milk and wheypowders, a mixture made up of five parts of cow’smilk and eight parts of ultrafiltered rennet whey (with2-fold concentration of whey proteins), and a thirdblend made up of a 50/50 mixture of cow’s milk andclarified whey (Robinson et al., 2002).


Kosikowski and Mistry (1997) have described acommercial process using mare’s milk alone or amixture of cow’s milk and mare’s milk. They havealso described other variations in the manufacturingprocedures. In addition to Lactobacillus delbrueckiissp. bulgaricus, they also mention the inclusion ofLactobacillus acidophilus and Saccharomyces lactisinstead of Torula spp. as starter flora for Koumissproduction from cow’s milk.

Product Description

Traditional Koumiss is characterized by its milky graycolor, with no tendency for “wheying off.” The taste isdescribed as, “sharp alcoholic and acidic” (Robinsonet al., 2002). The main byproducts of Koumiss fer-mentation are lactic acid, ethanol, and carbon diox-ide. Carbon dioxide gives the “fizziness” in the fin-ished product. The viable bacterial counts in Koumissmay attain 50 million/ml and the yeast cell countabout 14 million/ml. Depending on the extent of fer-mentation, the product is classified as weak, medium,and strong. The percent titratable acidity will varyfrom 0.54 to 0.72, 0.73 to 0.90, and 0.91 to 1.08 forweak, medium, and strong categories, respectively.Alcohol content in percentage will vary from 0.7 to1.0, 1.1 to 1.8, and 1.8 to 2.5 for weak, medium,and strong categories, respectively (Robinson et al.,2002; Kosikowski and Mistry 1997).

Koumiss is prized as a therapeutic drink inRussia, and has been claimed to have curative prop-erties for pulmonary tuberculosis (Kosikowski andMistry, 1997).

Microbiology

The microflora of Koumiss is highly variable fromregion to region. In general, the bacterial speciesconsist of lactobacilli (Lactobacillus delbrueckii ssp.bulgaricus and Lactobacillus acidophilus), lactose-fermenting yeasts (Sacchamyces sp. and Torulakoumiss), nonlactose-fermenting Sacchromyces car-tilaginosus, and Mycoderma spp. which do not fer-ment carbohydrate substrates. In Koumiss made inMongolia, lactococci have been isolated, but theirpresence is undesirable, because of their rapid acid-generating property, which retards the developmentof yeasts that are necessary to give the characteris-tic properties of finished Koumiss (Robinson et al.,2002).

Most of the starter cultures developed was forKoumiss made from cow’s milk. Such cultures

included different blends of lactobacilli and yeasts,which were mainly chosen for their ability to func-tion in that substrate. A microbial survey of Koumissmade in Kazakhstan, showed the predominant pres-ence of a galactose-fermenting Saccharomyces unis-porus. That yeast, however, does not ferment lactose.The latter characteristic leads to slower fermentation,and a variety of metabolic byproducts such as glyc-erol, succinic acid, and acetic acid, which impart off-flavors to Koumiss.

In Koumiss (known as Chigo) made in innerMangolia and China, the majority of lactobacillifound were identified as Lactobacillus paracasei ssp.paracasei and ssp. tolerans and Lactobacillus cur-vatus. The yeast species found were Kluveromycesmarxianus ssp. lactis and Candida kefyr (Robinsonet al., 2002).

ACIDOPHILUS MILK ANDSWEET ACIDOPHILUS MILKHistory

Original Acidophilus Milk is a highly acidic, acridproduct with no balancing flavors. The acidity in theproduct may range from 1.5% to 2.0%. Because ofits acidic flavor, it is not generally relished by mostconsumers. Physicians in the United States have pre-scribed Acidophilus Milk in the diet of persons suffer-ing from either constipation or diarrhea and also forpersons who experience intestinal distress on con-suming ordinary milk. The latter effect is mainlyrelated to the alleviation of lactose malabsorption.Lactobacillus acidophilus is found in large numbersin the intestines of normal, healthy individuals. Thereis some difference among strains of Lactobacillusacidophilus to establish in the human intestine. Thestrains capable of establishing in the human intestineexhibit the ability to survive and grow in the pres-ence of normal levels of surface tension-depressingbile salts found in the enteric environment. Overthe years, regular intake of Acidophilus Milk wasfound to be an excellent means of maintaining in-testinal health. And, research showed that ingest-ing high numbers of selected, viable Lactobacillusacidophilus bacteria provided similar enteric-healtheffects. To promote wider consumption of such bene-ficial bacteria, modifications in the delivery of the mi-croorganisms via milk were sought. That search gaverise to a product called “Sweet Acidophilus Milk.”(Foster et al., 1957). Actual widespread commer-cialization of Sweet Acidophilus Milk came about in


1970s. This was the forerunner of Probiotic Milkswidely prevalent today.

Production of Acidophilus Milk

Traditional Acidophilus Milk is made from low-fat(partially skimmed) milk. The milk is sterilized at120◦C for 15 minutes to stimulate Lactobacillus aci-dophilus, which is used as a pure culture. Lactobacil-lus acidophilus lacks a good proteolytic system forhydrolyzing milk proteins. The high heat treatmentused denatures and releases peptides from milk pro-teins, which helps the growth of the organism. Afterheat treatment, the milk is tempered to 37 to 38◦C,and inoculated with a milk starter at the rate of 5%.The inoculated milk is gently stirred to mix the in-oculum, avoiding much incorporation of air, and in-cubated quiescently for 18 to 24 hours. When theacidity reaches 1.0%, the product is cooled to lessthan 7◦C, and bottled (Vedamuthu, 1982). A simi-lar process is described by Kosikowski and Mistry(1997).

Production of Sweet AcidophilusMilk

The original idea for delivering health-impartingLactobacillus acidophilus bacteria in unfermentedsweet milk was mooted by Myers in 1931 (Myers,1931). He reported that Lactobacillus acidophilusis inhibited by storage temperatures between 18◦Cand 20◦C, and the development of acid is entirelyprevented in milk held below 10◦C. He also foundthat milk containing Lactobacillus acidophilus cellscould be kept “sweet” for as long as 7 days if keptrefrigerated at 2 to 5◦C. The first prototype of theproduct that was commercialized in the 1970s wasmade in Oregon State University and was describedby Duggan et al. (1959). That product was made byadding a concentrated cell suspension of the organ-ism to cold (5◦C), pasteurized milk, mixing to ob-tain homogenous distribution of the culture, bottling,storing, and enumerating the bacterial numbers in themilk held under refrigeration. The Lactobacillus aci-dophilus cells retained their viability, when handledthus for a week, but did not cause any fall in the pHof the milk.

The idea was revived in the 1970s, and a strainof Lactobacillus acidophilus isolated from a humansubject, was subjected to taxonomic regime requiredto confirm its identity. The strain was further testedfor resistance to low pH and bile levels encountered in

human enteric system and intensively studied in thelaboratory at North Carolina State University. A re-liable fermentation procedure to propagate the strainin a food compatible medium to high numbers wasdeveloped. Further work was pursued to concentratethe cells, preserve the cell concentrate by freezing,and testing the cells for viability in cold, pasteurizedmilk over 15 to 21 day storage under normal refriger-ation conditions prevalent during distribution chan-nels in retail trade. Based upon the results, a suitableusage rate was established. The bacterial strain des-ignated Lactobacillus acidophilus NCFM, and thetechnology developed in the laboratory was licensedby the North Carolina State University Foundationto a marketing firm. The name “Sweet AcidophilusMilk” was registered as a trademark. The market-ing company under an exclusive licensing agreementwith a commercial starter company popularized thesale of the branded name product. An arbitrary mini-mum cell count of 2 million colony forming units permilliliter (cfu/ml) was recommended in “Sweet Aci-dophilus Milk” over the normal “open dating” periodused in the industry for pasteurized low-fat and skimmilk (usually 14 days). This stipulation was adoptedby most States in the United States, and the State ofCalifornia later amended the requirement to 4 millioncfu/ml throughout a 14-day shelf life.

Other starter companies also sold frozen concen-trated cultures for making a similar product. Productsmade with cultures from nonlicensed culture manu-facturers were not allowed to use the registered trade-mark, “Sweet Acidophilus Milk.” The frozen cultureconcentrate (also in pelletilized form) was sold in170 to 200 gram containers for inoculation into 2000liters of cold pasteurized milk. The manufacturingprocess was simple and consisted of adding the re-quired amount of frozen culture concentrate to coldpasteurized low fat or skim milk, mixing to distributethe cells evenly, and bottling the product.

Quality Standards

There were no definite standard counting proceduresfor establishing the viable count of Lactobacillus aci-dophilus cells in Sweet Acidophilus Milk, when theproduct was first introduced in the market. The proce-dure(s) adopted by State regulatory agencies gradu-ally evolved over time. Early procedure used plating-suitable dilutions (according to Standard Methodsfor the Examination of Dairy Products—APHA) of awell-mixed sample of milk on deMan/Ragosa/Sharpeagar (MRS agar) and incubating the plates in an


anaerobic jar at 35 to 37◦C for 72 hours. Later, themethod called for the use of MRS agar containing0.15% bile salts (Ox bile Salts). Certain establish-ments required the use of a more stringent Ragosaagar (or acidified Lactobacilli Selective agar) con-taining 0.15% bile salts.

Microbiology

There has been a considerable discussion among theacademic, industrial, and regulatory circles of theneed to establish the exact species identity, strainhistory, and salient characteristics that distinguishtheir suitability for enteric therapy of various cellconcentrates offered for sale to produce Sweet Aci-dophilus Milk. That led Sanders et al. (1996) to ex-amine several commercial cultures on the marketfor the aforementioned features. The problem hasbeen compounded by the introduction of “ProbioticMilks” recently, which contain several different bac-terial strains and species. Those aspects will be dis-cussed later.

The most widely studied Lactobacillus aci-dophilus strain for enteric therapy is Lactobacillusacidophilus NCFM. The published findings are sum-marized by Sanders and Klaenhammer (2001).

PROBIOTIC MILKSHistory

Probiotic Milks came into prominence over the lasttwo decades. The term probiotic is of a relatively re-cent origin. Currently, probiotics form a distinct cat-egory under “Functional Foods.” Functional foods(or nutraceuticals) are food components that pro-vide demonstrated physiological benefits or reducethe risk of chronic disease beyond their basic nutri-tional functions (Shah, 2001). According to the U.N.Agency, Food and Agriculture Organization, “probi-otics are live microorganisms, which, when adminis-tered in adequate amounts, confer a health benefit onthe host” (Shelke, 2003). The benefits of regular in-take of probiotics are many, including alleviation oflactose maldigestion, reduction in serum cholesterol,immune stimulation, antimicrobial, antimutagenic,and anticarcinogenic effects, maintaining intestinalhealth and general well-being (Shah, 2000). Otherpurported benefits are discussed by Sanders and Huisin’t Veld (1999), Chandan (1999), and others. Bacte-ria, especially species belonging to the genera, Lacto-bacillus and Bifidobacterium are almost exclusively

used as probiotics (Chandan, 1999; Sanders and Huisin’t Veld, 1999; Shah, 2001). Members of the aforementioned two-bacterial genera are normal inhabi-tants of healthy human gut, and have been shown toplay a regulatory role in the ecology and microbialflora of the gut (Chandan, 1999; Sanders and Huis in’tVeld, 1999). Among the various benefits reported forthe intake of probiotics, the evidence for maintenanceof gut health is equivocal. For extensive discussion ofthe role of those bacteria in maintaining gut health,the reviews by Sandine (1972), Speck (1976, 1978),Vaughan et. al (2002), and Hopkins (2003) should beconsulted.

One of the earliest marketed Probiotic Milkscontained Lactobacillus acidophilus and Bifidobac-terium spp., and bore the trade name A/B Milk.Presently, several Probiotic Milks with differentbrand names containing a variety of lactobacilli andbifidobacteria are available in the market in NorthAmerica, Europe, and the Far East (Sanders and Huisin’t Veld, 1999; Shelke, 2003). Every passing day,purported new clinically proven probiotic strains arebeing added to the list.

Production of Probiotic Milks

Probiotic Milks are made in the same manner as SweetAcidophilus Milk. Probiotic cultures in concentratedform are added to cold pasteurized low fat or skimmilk to give the desired numbers in the milk overthe normal open dating target period. After mixingto get uniform distribution of the cells, the milk isbottled. Several different probiotic strains are addedpresently.

Quality Standards

There are no regulatory standards for Probiotic Milksexcept those that apply to pasteurized milk. For A/Btype milk, the consensus in the industry was to re-quire a viable cell count of 2 million cfu/ml forLactobacillus acidophilus and Bifidobacterium spp.respectively. When products with multiple strainsappeared in the market, there was confusion in thetrade as to the exact requirements that should be stipu-lated to meet an “informal standard.” Guidelines havebeen developed by regulatory agencies with respectto “health claims” that could be made on the labels onthe packages. Presently, most Probiotic Milks in themarket list the cultures present in the milk on theirlabels. The technological challenges in the selection,propagation, preservation, and handling of cultures


for probiotic applications are extensively discussedby Mattila-Sandholm et al. (2002).

A major hurdle in fixing the exact viable cellcounts (cfu/ml) for each of the probiotic strains isthe lack of a reliable, accurate, reproducible, androutinely usable method(s) to get differential countsof the strains/species added to the milk. Several at-tempts have been made in developing suitable meth-ods (Shah, 2000), but so far none is adequate forregulatory purposes.

As referred to earlier, one of the primary concernsis establishing the exact identity of the strains/speciesused and declared on the labels of Probiotic Milks.Bacterial taxonomy has undergone rapid changeswith the advent of genetic probes, and with that devel-opment, the taxonomic status of many strains/specieshas eroded and in many cases entirely altered. Re-alizing the need for establishing modern criteria toestablish the taxonomic status of strains/species usedin Probiotic Milks, Yeung et al. (2002) examined alarge number of cultures using newly developed ge-netic probes, and published a status paper on the sub-ject. Their work would go a long way in establishingthe credibility of the industry in marketing a trulyprobiotic product.

BULGARIAN MILKBulgarian Milk is also known as Bulgarian Butter-milk. As the name suggests the product originatedin Bulgaria. The longevity enjoyed by people in andaround Bulgaria, who regularly consumed BulgarianMilk prompted one of Elias Metchinkoff’s associateto study that product. He isolated a Lactobacillus cul-ture from that product, which was later assigned thenomenclature, Lactobacillus bulgaricus (now, Lac-tobacillus delbrueckii ssp. bulgaricus). Metchinkoffstudied the organism for its therapeutic value. Fromhis observations, Metchinkoff postulated that highacid produced by the isolate had a suppressive effecton toxin-producing organisms in the large intestines,and prevented putrefaction and autotoxification in theindividual consuming fermented milk rich in Lacto-bacillus delbrueckii ssp. bulgaricus. Later, he wrotea book, entitled, The Prolongation of Life. His obser-vations laid the foundation for the present interest inprobiotics (Kosikowski and Mistry, 1997).

In the production of Bulgarian Milk, milk is heatedat 82–85◦C for 30 minutes, and cooled to 37◦C.An inoculum of a pure culture of Lactobacillus del-brueckii ssp. bulgaricus made in sterile milk (incu-bated at 37◦C, and a final acidity of 1.0% or slightly

higher), is used to seed a bulk starter made up ofmilk. Bulk starter is added at the rate of 1–2% to theprepared milk tempered at 37◦C, incubated till theacidity reaches 1.0%, cooled to 5–7◦C, and packaged.Most consumers do not relish acidities >1.0% inBulgarian Milk offered for sale (Foster et al., 1957,Kosikowski and Mistry, 1997).

SKYRSkyr has been produced in Iceland from the tenthcentury. The product was introduced into Denmarkin the mid-1900. It is actually a concentrated formof Yogurt curd. The manufacturing procedure is verysimilar to the production of Yogurt. In commercialproduction, skim milk heated to 93◦C for a few min-utes, is tempered at 42–44◦C, and inoculated witha mixture of Streptococcus thermophilus and Lacto-bacillus delbrueckii ssp. bulgaricus (0.1–0.5%). Thisis followed by the addition of 0.005% rennet. Afteruniform distribution of the additives, the seeded milkis incubated at 42–44◦C. Under those conditions, co-agulation is achieved in 3–4 hours. When the acidityreaches 1.4–1.6% (after approximately 20–24 hours),the curd is transferred into cloth bags for the drain-ing of sufficient whey to achieve a curd-solid contentof 18–20%, and a titratable acidity of 2.5–3.0%. Theproduct is then packaged and cooled (Foster et al.,1957).

Robinson et al. (2002) report that lactose-fermenting yeasts and Lactobacillus helveticus areoften found in starters used for Skyr. They have alsodescribed three mechanized processes, where the useof a nozzle separator and membrane filtration of curdcould be used for concentration of solids. Anothervariation involves the preformulation of milk solidsand fat to attain the desired solids concentration, be-fore the fermentation step.

VIILIViili is known by several different names in theScandinavian countries. The product is extremelypopular in Finland. It is a mildly acidic product madewith specially selected exopolysaccharide (capsularslime) producing strains of dairy lactococci. Suchstrains develop a mucoid and (or) stringy (ropy) coag-ulum. Often Geotrium candidum, a mold is includedin the starter. Being strictly aerobic, the mold formsa fuzzy mat on the surface of the product. The moldmetabolizes lactic acid generated by the lactococci


in the curd layers immediately below the mycelialmat. The product is often eaten with the addition ofpowdered cinnamon.

The product is produced from whole or low-fatmilk. After heat treatment at 80◦C for 30 minutesor modified HTST pasteurization (78◦C for 2 min-utes), the milk is cooled to 20–21◦C and 1.0% starteris added, and mixed. The seeded milk is filled intopackages. The filled packages are rolled into a walk-in incubator held at 20–21◦C. When the pH reaches4.6, the containers are rolled into a cooler.

Microbiology

Starter culture for Viili consists of a mixture of ropy(mucoid) and nonropy (nonmucoid) strains of Lac-tococcus lactis ssp. lactis and cremoris. Many ofthe mucoid lactococci are sluggish acid producers.To compensate, nonmucoid, relatively rapid acid-generating lactococci are included in the starters.

Mucoid lactococci are as susceptible to phages asnonmucoid types (Deveau et al., 2002). Because ofthe likelihood of phage infection of lactococci in in-dustrial settings, phage-unrelated strains are used instarter rotations. There is a paucity of suitable mucoidlactoccal strains for use in starter rotations for Viilimanufacture. Exopolysaccharide production amonglactococci is an unstable characteristic. Exopolysac-charide production is easily lost upon repeatedtransfer of cultures, high-temperature incubation,and abuse during propagation. Some of the genesassociated with exopolysaccharide production arefound on plasmids (Vedamuthu and Neville, 1986).Technology for converting nonmucoid (Muc−) lac-tococcal strains to muciod phenotypes (Muc+)through conjugative transfer of plasmid-carryingmucoid genes (Muc–plasmid) has been patented(Vedamuthu, 1989). The entire molecular charac-terization of exopolysaccharide production amonglactococci was elucidated by van Kranenburg(1999).


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Robinson RK, Tamime AY, Wszolek M. 2002.Microbiology of Fermented Milks. In: RK Robinson(Ed), Dairy microbiology handbook: Themicrobiology of milk and milk products, 3rd ed.Wiley-Interscience, John Wiley & Sons, New York,pp. 367–430.

Sanders ME, Huisin’t VJ. 1999. Bringing aprobiotic-containing functional food to the market:microbiological, product, regulatory and labelingissues. Antonie van Leeuwenhoek 76:293–315.


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Part IVHealth Benefits



20Functional Foods and Disease

PreventionRamesh C. Chandan and Nagendra P. Shah

IntroductionFunctional FoodsBioactive Dairy Ingredients

Milk ProteinsBioactive PeptidesLactoseMilk FatMinerals and Vitamins

ProbioticsBeneficial MicrofloraHealth Benefits of Probiotic ProductsRequirements for Effective ProbioticsProduction of Enzymes, Vitamins, and BacteriocinsBioavailability of CalciumReduction in Serum CholesterolPrevention of Diarrhea, Vaginitis and DermatitisAnticarcigoenesisImmunomodulatory roleManufacture of Probiotics for Use as Food Supplements

FortificationPhysiologically Active IngredientsReferences

INTRODUCTIONThe foods that contain significant levels of biologi-cally active components that impart health benefitsbeyond basic nutrition are generally referred to asfunctional foods. The driving forces behind the de-velopment of functional foods are ascribed to: (a)Scientific advances in our understanding of the rolethat foods play in disease prevention. Six out of theten leading causes of death in the Western world canbe linked to diet, e.g., cancer, coronary heart dis-ease, stroke, diabetes, atherosclerosis, and liver dis-eases; (b) The finding that 70% of certain cancers areprimarily caused by dietary factors; (c) Consumer

demands. Consumers are starting to regard foods as“miracle medicine;” (d) Increasing cost of healthcare. Accordingly, prevention rather than cure, isincreasingly being recognized; (e) Increases in theproportion of older persons in general population;(f) Technical advances in the food industry leadingto a shift in focus from removing harmful compo-nents to replacing or enhancing positive components;(g) Changes in regulatory attitudes. The struggle be-tween the Food and Drug Administration and thefood industry in relation to health claims for foodsis a good example; (h) The recent discovery of phy-tochemicals and probiotcs has boosted the search forand the development of functional foods.

Depending on the supplement, the functional foodscan be called designer foods, nutraceutical, phar-mafood, or phytochemical food (Goldberg, 1994;Shah, 2004). With the current emphasis on cost-effective health care, the importance of dietarychanges to optimize health continues to gain recogni-tion and acceptance. As a result, the food industry isresponding to consumer demands for a more health-ful food supply by developing nutrient-rich foodproducts, including products lower in fat and sodiumthat are consistent with the U.S. dietary guidelines forAmericans. In another effort to help the public makesound dietary choices, the nutrition labeling and edu-cation act has resulted in more responsible labeling ofall food items. Food labels provide a reliable sourceof applicable nutrition information for consumers tohelp them make informed purchase decisions.

Nutrient-rich foods can be developed either by for-tifying a component that improves the nutritionalvalue or by effective plant breeding by genetically en-gineering of the plants. Success is already seen in pro-duction of oranges with high vitamin C content and

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312 Part IV: Health Benefits

high phytochemical broccoflower (Goldberg, 1994).Yet another potential area to generate an array ofproducts that fit into the current consumer demandfor health driven foods is the milk-based dairy prod-ucts (Chandan, 1999). The reader is referred to a booktitled Functional Dairy Products, edited by Mattila-Sandholm and Saarela (2003) for comprehensive in-formation on this topic.

Diet-health link is now an integral part of a healthylife style. The role of diet and specific foods for theprevention and treatment of disease and improvementof body functions is now being recognized. Presentday consumers prefer foods that promote good healthand prevent disease. Such foods need to fit into cur-rent lifestyles providing convenience of use, goodtaste, and acceptable price-value ratio. The dairy in-dustry offers foods with established health-relatedbenefits and therefore constitutes a family of natu-ral functional foods.

This chapter presents an overview of functionalfoods and various bioactive ingredients present inmilk and fermented milks. Current trend is to of-fer products or ingredients specifically enriched forapplication in various foods to enhance their func-tional spectrum. Furthermore, the use of probiotics isdiscussed briefly as a means to supplement the func-tional attributes in milk products. For detailed dis-cussion of probiotics, the reader is referred to Chap-ter 22. Possible health benefits of consuming culturedand culture-containing milks have been briefly sum-marized in this chapter.

FUNCTIONAL FOODSThe current trend to provide specific health bene-fits beyond sustenance accorded by food intake hasroots in ancient medicine systems. The preventionand management of disease was recognized in In-dia some 5,000 years ago with the development ofAyurvedic (Science of Life) system of medicine. Useof active ingredients isolated from plants, herbs, min-erals, and animals formed the core of this medicalpractice to prevent disease and treat certain disor-ders. The emphasis was prevention and managementof common disorders by following specific dietarypattern in response to individual body requirements.Later, in third century bc, Chinese emperor ShenNong discovered that certain plants and herbs have amedicinal value.

Currently, an interactive discipline of nutrition andfood science has produced an array of food prod-ucts that represent a vibrant, dynamic, and emerging

segment of the food industry. Such foods in diet fur-nish traditionally recognized nutrients and in addi-tion provide specific health benefits. The objective ofconsuming these foods is to rectify or manage certaindisease states, reduce the risk of disease, or maintaingood health. This category of foods includes medicalfoods, supplements, biofoods, performance foods,special infant formulas, as well as foods specially for-mulated to deliver ingredients such as insoluble andsoluble fiber, vitamins and minerals, antioxidants,phytosterols, concentrates of specific dairy proteins,soy preparations, probiotics, and healthy fats and oils.

The epidemiological, experimental, and clinicalresearch has shown that consumption of diets highin fiber lowers the risk of colorectal cancer andcardiovascular disease. For example, a diet contain-ing viscous polysaccharides lowers the low-densitylipoproteins (LDL) and total serum cholesterol bybile acid turnover and lipid absorption. Furthermore,the beneficial effect may be ascribed to slow down incarbohydrate absorption, increase in stool bulk, andproduction of short-chain fatty acids in the colon.It is now known that factors in diet influencing thereduction in cardiovascular disease are generallyconstituents of plant foods including antioxidants,phenolics, carotenoids, and flavonoids. The phy-toestrogens (namely, coumesterol) of certain beansmay reduce bone loss. Isoflavones present in soyare recognized to be beneficial in reducing risk ofcancer and heart disease.

Vitamin E and folic acid are now considered to beimportant for their role in preventing heart disease.Folic acid is also important in lowering the risk ofneural tube defect in babies. Thus, new diet strategiesfor optimum health involve consumption of muchhigher level of fruits, vegetables, legumes, nuts, andwhole grains than previously believed.

BIOACTIVE DAIRYINGREDIENTSMilk has been described as nature’s nearly perfectfood as it provides vital nutrients including proteins,essential fatty acids, minerals, and lactose in bal-anced proportions. Leading nutrition experts recog-nize milk and milk products as important constituentsof a well-balanced and nutritionally adequate diet. Inthis regard, milk products complement and supple-ment nutrients available from grains, legumes, veg-etables, fruits, meat, seafood, and poultry.

Milk is composed of a unique set of constituents.More information on the composition of milk is given

20 Functional Foods and Disease Prevention 313

Milk solids12.6%

Milk solids-not-fat, 9%

Milk fat3.6%

Water87. 4%

Milk

Lactose4.9%

Minerals0.7%

Proteins3.4%

Caseins2.7%

Whey proteins0.7%

Figure 20.1. Nutritional composition of milk.

in Chapter 2. The major components are shown inFig. 20.1. It is necessary to understand the nutritionalcomposition of milk to comprehend the functionalaspects of its constituents.

These constituents perform nutritional function aswell as physiological functions. They act indepen-dently and synergistically with each other. The roleof major and minor constituents in human nutritionis intertwined with newly discovered physiologicalbenefits. We will briefly highlight both nutritionaland physiological benefits of consuming yogurt andfermented milks.

Typical nutritional profile of yogurt is shown inTable 20.1.

Milk Proteins

The major proteins of milk are casein and whey pro-teins in the ratio of 80 to 20. Casein further consistsof various fractions including �S1- and �S2-casein,�-casein and �-casein (Table 20.2). Also shown arethe major whey proteins of milk.

Nutritional value of milk proteins has been recog-nized for many years. Table 20.3 shows the nutritionalvalue of milk proteins compared with other proteins.

The protein efficiency ratio of whey protein isslightly lower than that of whole egg protein, whichis considered as the best protein. Compared to plantproteins, dairy proteins provide highest quality andabsorption characteristics. In other words, to achievethe requisite amino acids, our requirement for proteinis much lower when milk proteins are included in ourdiet. Table 20.4 illustrates this point.

It is apparent from this table that minimum require-ment for lactalbumin is lower than that of potato, buta combination of 30 parts of potato and 70 parts oflactalbumin balances the amino acids in a synergisticway and the requirement of the mixture is lower thanthat of either potato or lactalbumin. Thus, a combina-tion of whey protein and cereal-based food or potatocan enhance the nutritional profile.

Various milk constituents contribute to the phys-iological effects. Table 20.5 illustrates some of thepotential benefits.

Both caseins and whey proteins of milk possessbiological and physiological properties. For more in-formation on the physical and chemical character-istics of milk proteins, refer to Chapter 2. Hutchet al. (2004) have examined the emerging role ofdairy proteins and bioactive peptides in nutrition


Table 20.1. Typical Nutritional Profile of Yogurt

Nutrient Plain Fruit-Flavored Light, Vanilla

(Per 8 oz. serving = 227 g) Nonfat Low Fat Whole Milk Nonfat Low Fat Nonfat

Moisture 85 85 88 75 74 87Calories (kcal) 127 144 139 213 231 98Protein (g) 13 12 8 10 10 9Total fat (g) 0.5 4 7 Tr 2 TrSaturated fatty acids (g) 0.3 2.3 4.8 0.3 1.6 0.3Monosaturated fatty acids (g) 0.1 1.0 2.0 0.1 0.7 0.1Polyunsaturated fatty acids (g) Tr 0.1 0.2 Tr 0.1 TrCholesterol (mg) 4 14 29 5 10 5Carbohydrate (g) 17 16 11 43 43 17Total dietary fiber (g) 0 0 0 0 0 0Calcium (mg) 452 415 274 345 345 325Iron (mg) 0.2 0.2 0.1 0.2 0.2 0.3Potassium (mg) 579 531 351 440 442 402Sodium (mg) 174 159 105 132 133 134Vitamin A (IU) 16 150 279 16 104 0Thiamin (mg) 0.11 0.1 0.07 0.09 0.08 0.08Riboflavin (g) 0.53 0.49 0.32 0.41 0.40 0.37Niacin (mg) 0.3 0.3 0.2 0.2 0.2 0.2Ascorbic acid (mg) 2 2 1 2 2 2Note: Data is for yogurts fortified with nonfat dry milk, except for plain whole milk yogurt (Chandan, 2004).Source: United States Department of Agriculture, 2002.

Table 20.2. Casein Fractions and WheyProteins of Cow’s Milk

ConcentrationCasein Fractions (g/liter)

�-s1-Casein 10.3�-s2-Casein 2.7�-Casein 9.7�-Casein 3.5C-terminal �-Casein

fragments0.8

ConcentrationWhey Proteins Fractions (g/liter)

N-terminal �-caseinfragments

0.8

�-Lactoglobulin 3.4�-Lactalbumin 1.3Immunoglobulins 0.8Bovine Serum Albumin 0.4Lactoferrin 0.02–0.2Lactoperoxidase 0.03Lysozyme 130 �g/literAdapted from: Chandan, 1999; Schaafsma and Steijns,2000.

and health. The biological properties of milk proteinsare summarized in Table 20.6.

In studies with mice, it has been shown thatwhey proteins enhance humoral immune response.The sulfhydryl containing aminoacids, cysteine andglutathione, are related to immune response. Wheyproteins are rich in cysteine. �-Lactoglobulin con-tains 33 mg of cysteine per gram protein, while�-lactalbumin and bovine serum albumin contain 68and 69 mg cysteine per gram protein, respectively.The –SH compounds are also involved in quenchingtoxic-free radicals.

�-Lactalbumin is a calcium binding protein andthereby enhances calcium absorption. It is an excel-lent source of essential amino acids such as tryp-tophan and cysteine. Tryptophan regulates appetite,sleep-waking rhythm, and pain perception. Cys-teine is important in functions of –SH compounds.�-Lactalbumin interacts with galactosyltransferaseenzyme to promote transfer of galactose from UDP-galactose to glucose to form lactose in the mammarygland.

The immunoglobulins of milk are important forimparting immune defense for the host. IgG1 is amajor component. Milk contains 0.6 g/liter of IgG1,


Table 20.3. Comparative Nutritional Value of Proteins

Protein PERa AASb BVc PDd PDCAASe

Milk protein 3.1 1.27 91 0.95 1.21Casein 2.9 1.24 77 0.99 1.23Whey proteins 3.6 1.16 104 0.99 1.15Whole egg 3.8 1.21 100 0.98 1.18Soya 2.1 0.96 – 0.95 0.91Wheat 1.5 0.47 – 0.91 0.42

aPER (Protein Efficiency ratio). Gain in body weight divided by weight of protein consumed by growing rats fed 10% (w/w)of test or reference protein.

bAAS (Amino Acid Score). Content of the first limiting essential amino acid of the test protein compared with the content ofthat essential amino acid in a reference pattern of essential amino acids.

cBV (Biological value). Proportion of absorbed protein that is retained for body maintenance and/or growth.d PD (Protein Digestibility). Proportion of food protein absorbed.ePDCAAS (Protein Digestibility Corrected Amino Acid Score). Ratio of mg of limiting amino acids in 1 g of test protein and

mg of the same amino acid in reference requirement pattern multiplied with True Digestibility.

True Digestibility = I (F − f)

I

Where I = nitrogen intake, F = total fecal nitrogen excretion, and f = fecal nitrogen excretion on a protein-free diet.Adapted from: Schaafsma and Steijns, 2000.

whereas colostrum contains substantially higher levelof 48 g/liter of IgG1. Other fractions are IgG2, IgA,IgM, all of which provide passive immunity.

A number of colostrum products are being mar-keted to improve functionality of milk. Colostrumcontains several functional constituents including an-tibodies, lactoferrin, lactoperoxidase, cytokines, andgrowth factors. The antibodies act as antimicrobialagents against infection from rotavirus (which causesdiarrhea), Escherichia coli (which causes food poi-soning), Candida albicans (which causes yeast in-fection), Streptococcus mutans (which causes dentalcaries), Clostridium difficile (which causes antibioticassociated diarrhea), Cryptosporium parvum (whichcauses food poisoning), and Helicobacter pylori

Table 20.4. Minimum Requirements ofVarious Proteins (g/kg body weight) inHumans

Protein Requirement

Lactalbumin 0.480Potato 0.512Potato, 30% + Lactalbumin, 70% 0.374Cow’s milk 0.568Casein 0.699Wheat flour 0.892Adapted from Schaafsma and Steijns, 2000.

(which causes ulcer, gastritis). Colostrum stimulatesactive immune system by enhancing the activity ofnatural killer cells and phagocytes. The colostrumpowder is manufactured by drying process to insureactivity. Milk protein concentrate prepared from themilk of hyperimmunized cows is now commerciallyavailable, and is claimed to relieve joint pains ofarthritis by complementing the body’s naturally oc-curring antiinflammatory substances.

Lactoferrin has a role in nonspecific defense of thehost against invading pathogens. It is active againstseveral Gram-positive and Gram-negative bacteria,yeasts, fungi, and viruses. Its iron-binding character-istic aids in enhancing iron absorption. It stimulatesand protects cells involved in host defense mecha-nism. Furthermore, it controls cytokine response.

Lactoperoxidase is an enzyme that breaks downhydrogen peroxide and exerts an antibacterial effect.Therefore, it is considered to be a natural preserva-tive. It is being incorporated in toothpastes to preventcavities. Another suggested use of lactoperoxidaseis to control the acid development in stored yogurtknown as postacidification. Lysozyme has antimicro-bial activity against Gram-positive bacteria and it actsby lysis of cell walls. Bifidobacteria flora of colonimparts health-promoting properties and healthy gutecology to the host.

Fermented milks are enhanced functional foodsbecause of the fact that they contain nutrients of milk,


Table 20.5. Milk Constituents with Putative Physiological Effects

Component Health Effect

Butyric acid Reduce colon cancer riskCLA (Conjugated linoleic acid) Modulate immune function, reduce risk of cancer (stomach, colon,

breast and prostate)Sphingolipids May reduce risk of colon cancerStearic acid May modulate blood lipids to reduce risk of cardiovascular and

heart diseaseTriglycerides May enhance long-chain fatty acid and calcium absorptionWhey proteins May modulate immune system, reduce risk of heart disease and

cancer, lower blood pressureGlycomacropeptide Prevent dental caries, gingivitis, antiviral, antibacterial, bifidogenicImmunoglobulins Antibodies against diarrhea and GI tract disturbancesLactoferrin Toxin binding, antibacterial, immune modulating, anticarcinogenic,

antioxidant, iron absorptionLactoperoxidase AntimicrobialLysozyme Antimicrobial, synergistic with immunoglobulins and lactoferrinLactose Calcium absorptionCalcium Prevent osteoporosis and cancer, control hypertensionAdapted from: Chandan, 1999; Hoolihan, 2004.

as well products of metabolic activities of startermicroorganisms in the product. Furthermore, theycontain live and active cultures in significant num-bers to effect physiological benefits to the consumer.

In general, yogurt contains more protein, calcium,and other nutrients than milk, reflecting the extrasolids-not-fat content. Bacterial mass content and theproducts of the lactic fermentation further distinguish

Table 20.6. Some Functional Properties of Major Milk Proteins and Bioactive Peptides DerivedFrom Them

Protein Function

Caseins- Precursors of bioactive peptides,iron carrier (Ca, Fe,Zn, Cu)

Casomorphins from �- and �-caseinsCasoxins from �-casein Opoid agonistsCasokinins from �- and �-caseins Opoid agonistsCasoplatelins from �-casein and transferring AntihypertensiveCasecidin from �- and �-caseins AntithromboticIsracidin from �-caseinImmunopeptides from �- and �-caseins AntimicrobialPhosphopeptides from �- and �-caseins AntimicrobialGlycomacropeptide from �-casein Immunostimulants

Mineral carriersAntistress effects

�-Lactalbumin�-Lactorphin

Ca carrier, Lactose synthesis in mammary gland,antocarcinogenic and immonomodulatory effects

Opoid agonists�-Lactoglobulin Possible antioxidant, retinol carrier, fatty acid binding�-Lactorphin Opoid agonistsImmunoglobulis A, M and G Protectection of immune system, provide antibodiesLactoferricin from Lactoferrin Opoid agonistsAdapted from: Saxelin et al., 2003; Aimutis, 2004.


yogurt from milk. Fat content is standardized to com-mensurate with consumer demand for low-fat to fat-free foods.

Bioactive Peptides

Functional peptides are generated during digestiveprocesses in the body and during the fermentationprocesses used in fermented dairy foods. They arisefrom casein as well as from whey proteins (Table20.6). These peptides are inactive in the native pro-teins but assume activity after they are released fromthem. They contain 3 to 64 amino acids and largelydisplay a hydrophobic character and are resistant tohydrolysis in the gastrointestinal tract. They can beabsorbed in their intact form to exert various phys-iological effects locally in the gut or may have asystemic effect after entry into circulatory system.Casomorphins and lactophorins derived from milkproteins are known to be opoid agonists, whereaslactoferroxins and casooxins act as opoid antagonists.The opoids have analgesic properties similar to as-pirin. Casokinins are antihypertensive (lower bloodpressure), casoplatelins are antithrombotic (reduceblood clotting), immunopeptides are immunostimu-lants (enhance immune properties), and phosphopep-tides are mineral carriers.

Casein phosphopeptides may aid in bioavailabilityof calcium, phosphorus, and magnesium for optimumbone health. They may also be helpful in preventingdental caries. They may also have a role in secretionof entero-hormones and immune enhancement. Thecasein peptides also offer a promising role in reg-ulating blood pressure. Conversion of angiotensin-Ito angiotensin-II is inhibited by certain hydrolyzatesof casein and whey proteins. Since Angiotensin-IIraises blood pressure by constricting blood vessels,its inhibition causes lowering of blood pressure. ThisACE inhibitory activity would therefore make dairyfoods a natural functional food for controlling hy-pertension. A commercial ingredient derived by thehydrolysis of milk protein, has an anxiolytic bioactivepeptide with antistress effects. Psychometric tests andmeasurement of specific hormonal markers have dis-played their antistress effect. The ingredient may beincorporated in milk, cheese, or ice cream.

The glycomacropeptide released from �-casein asresult of proteolysis may be involved in regulatingdigestion, as well as in modulating platelet functionand thrombosis in a beneficial way. It is reported tosuppress appetite by stimulating CCK hormone. Con-sequently, it may be a significant ingredient of sati-ety diets designed for weight reduction. Furthermore,

this peptide may inhibit binding of toxin in the gas-trointestinal tract.

Some miscellaneous bioactive factors are beingdiscovered. Specific proteins for binding VitaminB12, folic acid, and riboflavin may assist in enhancingbioavailablity from milk and other foods. Fat globulemembrane protein called butyrophilin is a part of theimmune system. Other growth factors in milk mayhelp gut repair after radiation or chemotherapy.

Lactose

Lactose, the milk sugar stimulates the absorption ofcalcium and magnesium. It has a relatively lowerglycemic index as compared to glucose or sucrose,hence making it suitable for diabetics. It is less cario-genic than other sugars. Lactose stimulates bifidobac-teria in the colon and thereby prevents infection andimproves intestinal health.

Lactose absorption in humans is catalyzed by theenzyme lactase or �-D-galactosidase. Lactase is anonpersistent enzyme in certain individuals, resultingin distressing symptoms of bloating, flatulence, anddiarrhea following milk intake. Most individuals cantolerate two cups of milk spread over a day or withmeals. In case of lactose malabsorption, the symp-toms are ameliorated by using lactase tablets or byconsuming yogurt. Yogurt and some fermented milkscontaining live and active cultures furnish the enzymelactase to assist in digesting lactose. Lactose-reducedmilk and ice cream products are also available.

Heated milk contains up to 0.2% lactulose, a lac-tose derivative. Since lactulose is not a digestible in-gredient, it acts somewhat like a soluble fiber. Lac-tulose is generally used for treatment of constipationand chronic encephalopathy. Some recent data indi-cates that lactulose may enhance calcium absorptionin the intestine.

Milk Fat

Several positive findings have emerged for the con-sumption of milk fat. Milk fat exists in an emulsionform in milk making it highly digestible. Also, milkfat contains 10% short and medium chain fatty acids.Their 1:3 positions in the glyceride molecule allowgastric lipase with specificity for these positions topredigest them in the stomach itself. Butyric acid, acharacteristic fatty acid of milk fat, is absorbed inthe stomach and small intestine and provides energysimilar to carbohydrates. Medium chain fatty acidsare transported to the liver for rapid source of en-ergy. The fatty acids lower the pH for facilitating


protein digestion. At the same time, acid barrier forpathogenic activity is enhanced. Free fatty acids andmonoglycerides are surface tension lowering agents,thereby exerting an antiinfective effect.

The flavor of milk fat is unique and it adds tomouth-feel of foods comprised of milk and dairyfoods. Milk fat is a concentrated form of energy. Fatprotects organs and insulates body from environmen-tal temperature effects. It carries vitamins A, D, E,and K and supplies essential fatty acids includingarachidonic acid, linolenic acid, omega 3-linoleic,eicosopentaenoic acid, and docosahexaenoic acid.The essential fatty acids cannot be synthesized by thebody and must be supplied by our diet. The omega-3fatty acids have a role in memory development andmaintenance.

Conjugated linoleic acids (CLA) are a class of fattyacids found in animal products such as milk and yo-gurt. Rumen flora synthesizes CLA, which has beendemonstrated to exhibit potent physiological prop-erties. CLA is a strong antioxidant constituent ofmilk fat, and may prevent colon cancer and breastcancer. CLA has been shown to enhance immuneresponse. Prostaglandin PGE-2 promotes inflamma-tion, artery constriction, and blood clotting. CLA mayreduce the risk of heart disease by reducing the lev-els of prostaglandin PGE-2. Studies have indicatedthat CLA may increase bone density, reduce chronicinflammation, and normalize blood glucose levels byincreasing insulin sensitivity.

Another constituent of milk fat is sphingolipids.They occur at a level of only 160 �g/kg. Recentstudies show that they are hydrolyzed in the gas-trointestinal tract to ceramides and sphingoid bases,which help in cell regulation and function. Studies onexperimental animal show that sphingolipids inhibitcolon cancer, reduce serum cholesterol, and elevatethe good cholesterol HDL. They could protect againstbacterial toxins and infections as well.

Butyric acid is liberated from milk fat by lipase inthe stomach and small intestine. It may exert benefi-cial effect on the gastric and intestinal mucosa cells.In the colon, butyric acid is formed by fermentationof carbohydrates by the resident microbiota. Butyricacid in that location works as a substrate for coloncells and confers anticancer properties.

Minerals and Vitamins

Milk and dairy products are, in general, an excellentsource of calcium, phosphorus, and magnesium indiet. High levels of these minerals are in optimum

ratio for bone growth and maintenance. As a foodsource, milk offers good bioavailability of miner-als and vitamins. To prevent osteoporosis, continuedconsumption of milk is cited as important by leadingexperts in nutrition and medical science. Other func-tions of calcium involve regulation of blood pressureand prevention of colon cancer.

The fat-soluble vitamins A, D, E, K and water-soluble vitamins are well known for their beneficialrole in human nutrition. Milk is a good source ofB-vitamins.

PROBIOTICSDetailed discussion on probiotics is given in Chap-ter 22. Probiotics may be defined as a food or supple-ment containing concentrates of defined strains of liv-ing microorganisms that on ingestion in certain dosesexert health benefits beyond inherent basic nutrition.They are believed to contribute to the well-beingof the consumer by improving the host’s microbialbalance in the gastrointestinal tract. This definitionstresses upon the importance of ingestion of severalhundred millions of live and active microbial culture.Recent advances in probiotic research show muchpromise in new product development of functionalfoods based on milk (Sanders, 1994, Chandan, 1999,Shah, 2001). There has been marked proliferationin the number of probiotic products in the market.Probiotics and associated ingredients might add anattractive dimension to cultured dairy foods for ef-fecting special functional attributes.

Milk is an excellent medium to carry or gener-ate live and active cultured dairy products. They addan attractive dimension to cultured dairy productsfor augmenting current demand for functional foods.The buffering action of the milk proteins keeps theprobiotics active during their transit through the gas-trointestinal tract. Other potential carriers are fruitjuices, candies, ice cream, and cheese. In general,worldwide consumption of fermented milk prod-ucts has increased due to their high nutritional pro-file, unique flavor, desirable texture, and remarkablesafety against food-borne illness. Concomitantly, ittranslates to a sizeable enhancement in milk utiliza-tion and the intake of valuable nutrients containedtherein. Addition of fruit preparations including fruitflavors and fruit purees has enhanced the versatilityof flavor, texture, color, and variety of yogurt con-taining probiotics. Incorporation of nuts, grains, andchocolate syrups gives the fermented milk novel andmultiple textures and flavors to attract its use as a


snack, breakfast food, or as a dessert item. Probioticmixtures are also exclusively sold either in the formof powders, capsules, or tablets and labeled in themarket as natural organic foods/supplements.

Beneficial Microflora

Cultures associated with health benefits are yogurtbacteria (Streptococcus thermophilus and Lacto-bacillus delbrueckii spp. bulgaricus), other lacto-bacilli, and bifidobacteria (Nakazawa and Hosono,1992; Salminen et al., 1998). Table 20.7 gives a listof various probiotics being used in commercial fer-mented milks.

Yogurt organisms possess a distinctly high lac-tase activity, making it easily digestible by individu-als with a lactose-maldigestion condition. To bolsterprobiotic function, most commercial yogurt is nowsupplemented with Lactobacillus acidophilus andBifidobacterium spp.

The probiotic preparations are also available in theform of tablets, powder, or capsules. They contain

Table 20.7. Probiotic and BeneficialMicroorganisms in Commercial Products

Lactobacillus acidophilus group:Lactobacillus acidophilusLactobacillus johnsoni LA1Lactobacillus gasseri ADHLactobacillus crispatus

Lactobacillus casei/paracaseiLactobacillus casei subsp. RhamnosusLactobacillus reuteriLactobacillus brevisLactobacillus delbrueckii subsp. bulgaricusLactobacillus fermentumLactobacillus helveticusLactobacillus plantarum

Bifidobacterium adolescentisBifidobacterium animalisBifidobacterium bifidumBifidobacterium breveBifidobacterium infantisBifidobacterium longum

Streptococcust thermophilusEnterococcus faeciumPediococcus acidilacticiSaccharomyces boulardiiAdapted from: Chandan, 2004; Shah, 2001, 2004; Saxelinet al., 2003.

organisms from the genera Lactobacillus, Enterobac-ter, Streptococcus, and Bifidobacterium. These gen-era are important members of the gastrointestinal mi-croflora and are all relatively beneficial. The strainsof lactic acid bacteria used in probiotics are mostlyintestinal isolates such as Lb. acidophilus, Lb. ca-sei, Enterococcus faecium, and Bifidobacteriumbifidum.

Yogurt starter bacteria, Lb. delbrueckii ssp. bul-garicus and Streptococcus thermophilus, are also in-cluded as probiotics in this table because yogurt hasbeen associated with several health benefits in thepast. They are now reported to persist and remain vi-able throughout the gastrointestinal tract of rats andhumans. For sustained benefit, it is necessary to ingestthem on continuous basis. Even with intestinal iso-lates such as Lb. acidophilus, it is necessary to doseregularly rather than to assume that a few doses willallow the organisms to colonize the gut permanently.Currently even Bacillus laterosporus and Bacillussphaericus and other little-known probiotics are for-tified with enzymes, antiinflammatory compounds,specific amino acids, colostrum, and chelated min-erals in probiotic preparations. Lb. acidophiulus andBifidobacterium bifidum strains are known to differwidely in their ability to grow in the presence of bilesalts (Gilliland, 2003). Both are reported to be stableat various concentrations of bile salts.

Health Benefits of ProbioticProducts

Health benefits of probiotics are enumerated inTable 20.8.

The belief in the beneficial effects of the probioticapproach is based on the knowledge that the intestinalmicroflora provides protection against various dis-eases. Probiotics have been with us for as long aspeople have eaten fermented milks but their associ-ation with health benefits dates only from the turnof the century when Metchnikoff drew attention tothe adverse effects of the gut microflora on the hostand suggested that ingestion of fermented milks ame-liorated the so-called autointoxication (Metchnikoff,1908). It has been shown that germ-free animals aremore susceptible to disease than their conventionalcounterparts who carry a complete gut flora. Thisdifference has been shown for infections caused bySalmonella enteritidis and Clostrodium botulinum.Another source of evidence that supports the protec-tive effect of the gut flora is the finding that antibi-otic treated animals, including humans can become


Table 20.8. Health Effects of Probiotics

Effects Corroborated by Scientific Evidence Effects of Potential Nature

Assisting lactose digestion Controlling candida and bacterialinfections (vaginitis)

Treatment of rotaviral diarrhea Alleviating constipationTreatment of infant gastroenteritis Antimutagenic/anticarcinogenic effectsTreatment of antibiotic related diarrhea Lowering cholesterol and blood pressureModulating intestinal (microbiota) ecology Alleviation of microbial overpopulation in

small intestineReducing harmful fecal enzymes, biomarkers

of cancer initiationAlleviation of dermatitis and skin allergies

Enhancing/modulating immune system Prevention and treatment of Crohn diseasePositive effects on cervical and bladder cancer Treatment of Clostridium difficile diarrheaAdapted from: Fonden et al., 2003; Shah, 2001, 2004.

more susceptible to disease (Saavedra, 1995). In hu-mans pseudomembranous colitis, a disease caused byClostridium difficile, is almost always a consequenceof antibiotic treatment (Shah, 2004).

The third source of the supporting evidence comesfrom experiments in which dosing with fecal suspen-sions has been shown to prevent infection (Schwanand Sjolin, 1984). In humans it has been shown thatC. difficile infection can be reversed by adminis-tering fecal enemas derived from a healthy humanadult. Probiotics also deplete the essential nutrientsfor the pathogenic organisms thus eliminating theirgrowth.

Figure 20.2 illustrates how yogurt and cultureddairy products might exert functional benefits to theconsumer (Chandan, 1999).

Requirements for EffectiveProbiotics

Criteria for live and active cultures have been estab-lished by the industry with a view to maintain theintegrity of refrigerated and frozen yogurts. In addi-tion, the probiotics must implant and multiply rapidlyin the gut to avoid them from being expunged en-tirely. They must not only be able to tolerate and passthrough the high acidity (low pH) of stomach, butalso be able to grow and proliferate at physiologicallevels of bile salts and adhere to the intestinal ep-ithelial cells. Bile salts produced by the gall bladderare essential in helping to emulsify fat before it canbe digested in the intestine. Probiotics that can colo-nize should also be resistant to several antibiotics andproducer of bacteriocin as natural antimicrobial sub-stances. A Bifidobacterium strain should be negative

for the production of catalase, nitrate reductase, ure-ase, and for the formation of indole. In addition,liquefaction of gelatin, gas formation from glucose,response to rhamnose, sorbose, glycerol, erythritol,adinotol, and dulcitol should be negative. Commer-cial probiotic strains must have verified safety of usein human diet. They should possess stability to acidand bile, and exhibit colonization and adherence inthe GI tract.

Production of Enzymes, Vitamins,and Bacteriocins

Other beneficial effect of probiotics includes the im-provement of lactose utilization in large proportionof the world’s population who are unable to effec-tively digest lactose. The enzyme lactase responsiblefor lactose digestion, although present in the suck-ling infant, disappears after weaning. In areas of theworld where milk is not a staple food, lack of enzymecauses no problems. However, if people from theseregions migrate to Europe or North America, prob-lems arise because ingestion of lactose in some formis difficult to avoid. Lactose malabsorption refers toincomplete digestion of lactose resulting in a flat orlow rise in blood sugar following ingestion of lactosein a clinical lactose intolerance test. The disaccha-ride lactose is hydrolyzed to glucose and galactoseby lactase and subsequently absorbed in the smallintestine. Lactase is a constitutive, membrane-boundenzyme located in the brush borders of the epithe-lial cells of the small intestine. The intact residuallactose left over following impaired lactase activityenters the colon where it is fermented by inherentmicroflora to generate organic acids, carbon dioxide,


Proteins/Bioactive peptides

Fats/energy

Minerals

Vitamins

Suppression of foodborne pathogens

Reduction incarcinogeniccompounds

Cholesterol reduction

Improved lactosedigestion

Restore ecologicalbalance in colon

Immune modulation

Fermented milk withbeneficial bacteria

Physiologicalbenefits

Cell mass:probiotic and

beneficial bacteria

Nutritionalattributes

Figure 20.2. Potential mode of healthattributes of yogurt and fermented milks.

methane, and hydrogen. The fermentation productstogether with the osmotically driven excessive wa-ter drawn into the colon are primarily responsiblefor abdominal pain, bloating, cramps, diarrhea, andflatulence. These symptoms are associated with lac-tose maldigestion when lactose is not fully digestedin the small intestine. It has been known for sometime that lactose deficient subjects tolerate lactosein yogurt better than the same amount of lactose inmilk. It is possible to show increased lactase activityin the small intestine of humans that have been fedyogurt.

Probiotics also produce some of the B-vitamins in-cluding niacin, pyridoxine, folic acid, and biotin. Pro-biotics produce antibacterial substances, which haveantimicrobial properties against disease-causing bac-teria. Acidophilin produced by Lb. acidiophilus isreported to inactivate 50% of 27 different disease-causing bacteria. Children with Salmonella poi-soning and Shigella infections were cleared of all

symptoms using Lb acidophilus. Bifidobacterium bi-fidum effectively kills or controls Escherichia coli,Staph. aureus and Shigella. Acidophilus is also re-ported to control viruses such as herpes.

Bioavailability of Calcium

One of the primary functions of calcium is to providestrength and structural properties to bone and teeth.The major source of dietary calcium is dairy products,supplying 75% of the intake. Milk and dairy productsare excellent sources of bioavailable calcium. Addi-tion of lactic acid to unfermented yogurt, as well asregular fermented yogurt displays an improved bonemineralization as compared to the unfermented yo-gurt. It is postulated that the acidic pH due to addedlactic acid or naturally contained in fermented yo-gurt converts colloidal calcium to its ionic form andallows its transport to the mucosal cells of the intes-tine. (Fernandes et al., 1992).


Reduction in Serum Cholesterol

Probiotics effectively help to reduce cholesterol lev-els circulating in blood. Some studies have indicateda modest lowering of serum cholesterol in subjectsconsuming milk fermented with Lb. acidophilus, Lb.rhamnosus GG and yogurt cultures.

Prevention of Diarrhea, Vaginitisand Dermatitis

Probiotics improve the efficiency of the digestivetract especially when bowel function is poor. Es-tablishment of probiotics in the GI tract may pro-vide prophylactic and therapeutic benefits againstintestinal infections. Probiotics may have a role incircumventing traveler’s diarrhea (Fernandes et al.,1992; Elmer et al., 1996). Yogurt supplemented withprobiotic organisms reduces the duration of cer-tain types of diarrhea. Fermented milk with probi-otics has been recommended to replace milk dur-ing the treatment of diarrhea because it is toleratedwell than milk. A double blind study has shownthat only 7% of infants receiving probiotic formulacontaining Bifidobacterium bifidum and Streptococ-cus thermophilus develop diarrhea against 31% inci-dence in placebo group (Saavedra et al., 1994). Thevaginal microflora changes drastically during bacte-rial infection. Bacteria of genera Escherichia, Pro-teus, Klebsiella, and Pseudomonas along with yeast,Candida albican are recognized as etiological agentsin urinary tract infection among adult women. It hasbeen shown that the normal urethral, vaginal, and cer-vical flora of healthy females can competitively blockthe attachment of uropathogenic bacteria to the sur-faces of uroepithelial cells. Lactobacilli strains sup-plemented in the diet or directly applied are reportedto coat the uroepithelial wall and prevent the adher-ence of uropathogens. Milk fermented with yogurtcultures and Lactobacillus casei influences the in-testinal microflora of infants (Guerrin-Danan et al.,1998).

Anticarcigoenesis

Bifidobacteria and lactobacilli, especially Lb. aci-dophilus have been shown to have powerful anticar-cinogenic features, which are active against certaintumors (Goldin and Gorbach, 1992). An epidemio-logical study reported a positive correlation betweenconsumption of probiotic and prevention of coloncancer. Several reports suggest prevention of cancer

initiation by various probiotics by reducing fecal pro-carconogenic enzymes nitroreductase and azoreduc-tase (Lee et al., 1996).

Immunomodulatory role

An interesting development in recent years has beenthe finding that lactobacili administered by mouth canstimulate macrophage activity against several differ-ent species of bacteria (Brassart and Schiffrin, 1997,Rangavajhyala et al. 1997. For example, Lb. caseigiven to mice increased phagocytic activity. Lacto-bacilli injected intravenously are reported to survivein the liver, spleen, and lungs and enhance the naturalkiller cell activity.

Probiotics have been reported to be useful in thetreatment of acne, psoriasis, eczema, allergies, mi-graine, gout, rheumatic and arthritic conditions, cys-titis, candiadiasis, colitis and irritable bowl syn-drome, and some forms of cancer. Recent reportssuggest that Lb. acidophilus may be able to inhibitHIV, the virus that causes AIDS. It is reported thatcertain strains of Lb. acidophilus (and certain speciesof Enterococcus) produce large amounts of hydro-gen peroxide. Hydrogen peroxide alone, or in com-bination with certain minerals or dietary components,can arrest the growth of HIV. More research in thisarea is needed to make a definitive validation of theseclaims.

Potential mechanisms by which probiotics may ex-ert their beneficial effects are (a), competition withother microflora for nutrients, (b) production of acidsinhibitory to certain enteropathogens, (c) produc-tion of bacteriocins or inhibitory metabolites, (d) im-munomodulation, and (e) competition for adhesionto intestinal mucosa.

Since efficacy of a probiotic is directly related tothe number of live and active cells consumed, it isimportant to specify potency or colony forming units(cfu) of the culture per unit weight or volume of theproduct. In addition, the culture should be active interms of growth potential (Chandan, 1999).

Manufacture of Probiotics for Useas Food Supplements

Various probiotic strains are screened for their ef-fectiveness and formulated for stability during shelflife of the product. In general, the process of probi-otic manufacture involves growing of probiotic cul-tures by a process involving growth in a well-definednutrient medium. In the manufacturing process, the


microorganisms are concentrated first by removingunspent liquid medium by sedimentation, ultrafil-tration, reverse osmosis, and/or centrifugation. Cry-oprotectant is added before freezing to prevent“freezer damage” to the bacteria. Following freezing,the mass is freeze-dried. The final product is then sub-jected to fine screening and quality control involvingseveral tests. When the product passes all the rig-orous tests, it is then mixed with excipient to stan-dardize the specific desired count (most commonly>10 billion CFU/gram). Following that a natural sta-bilizer is added to prevent the loss of its viabilityduring packaging, shipping, storage, marketing, andconsumption. The viability of the cells should notbe damaged during the manufacturing and freeze-drying process. The cultures that can be used aloneor in combination include Lactobacillus acidophilus,Lb. brevis, Lb. delbrueckii ssp. bulgaricus, Lb. casei,Lb. casei ssp. rhanmosus, Lb. helveticus, Lb. lactis,Lb. plantarum, Lb. reuteri, Lb. salivarius, Bifidobac-terium bifidum, B. breve, B. infantis, B. longum, Ente-rococcus faecium, Str. thermophilus, and Pedicoccuscerevesiae.

Supplementation of probiotics with prebiotics canbe a very effective functional food (Shah, 2001).For example, prebiotic fructooligosaccharide (FOS)is exclusively used by a few strains of Bifidobac-terium bifidum and Lb. acidophilus. Thus a combina-tion of FOS along with these cultures will induce theproliferation of these cultures in preference to othermicroflora in the gastrointestinal tract. This combina-tion is termed as synbiotics. Prebiotic consumption isreported to increase the levels of bifidobacteria in hu-man volunteers at the expense of less desirable bacte-rial species. Additionally, prebiotic supplements havebeen shown to improve the absorption of calcium and

magnesium in animal models, and this may be of im-portance for humans as well.

FORTIFICATIONTraditionally, milk has been fortified with vitamins Aand D. Now, popular ingredients of functional signif-icance are being incorporated to enhance the marketvalue of dairy foods and dairy-based foods. Someof these ingredients designed to enhance consumerappeal are: (a) calcium, claimed to prevent osteo-porosis and cancer, and control hypertension; (b) an-tioxidants (vitamins C and E), claimed to preventcancer, cardiovascular disease, and cataracts. In ad-dition, dietary fiber (psyllium, guar gum, gum acacia,oat fiber, soy components) as well as multivitamin-mineral mixes are being incorporated in fat-free milkto provide targeted niche consumers meal replace-ments. Such products supply a substantial proportionof daily essential nutrients. In addition to infant for-mula line of products based on fat-free milk, there isa proliferation of energy and weight-reduction shakedrinks for consumer segments ranging from adults togeriatric populations. More recently, the food indus-try has leveraged this area to develop and market anumber of drinks and powders targeted to consumersinterested in weight reduction, meal replacement, andsupplementing their diet with wellness foods (Table20.9). Antioxidants have shown promise, but forti-fication strategy must include an understanding oftheir impact on flavor, texture, mouth feel, and shelflife of the product. Also, it is imperative to know ameaningful dose-benefit relationship associated withthe specific fortified dairy food.

Another ingredient of interest is docosahexaenoicacid (DHA). They are long chain polyunsaturated

Table 20.9. Various Milk-Based Product Categories Containing Milk Fractions

Category Food or Supplement

Clinical nutrition Total enteral formulas containing casein, milk proteins and theirhydrolyzates for tube or oral administration in hospitalized patients

Health foods or Sports nutrition Drinks, tablets, energy bars or cookies can deliver easily absorbableprotein hydrolyzates, bioactive peptides and bioavailable milkminerals; Glutamine peptide supports immune system and facilitatesiron absorption

Infant nutrition Demineralized whey, lactose, caseinates, milk protein concentrate, anddairy minerals are constituents of hypoantigenic and hypoallergenichumanized infant formulas

Weight-reduction drinks Meal replacement milk shakes fortified with such supplements as milkproteins, vitamins and minerals, prebiotics


fatty acids from fish oils and marine algae. They areclaimed to exert cancer inhibition, antiallergy effects,and improvement in learning ability. DHA-fortifieddrinks are targeted at school children in some coun-tries.

PHYSIOLOGICALLY ACTIVEINGREDIENTSAnother possible opportunity to develop functionalfoods is to leverage the use of inherent milk con-stituents of known physiological attributes. Commer-cially available milk fractions are being used in avariety of milk-based products (Table 20.9).

Besides milk fractions inherently present in nor-mal milk, a new class of oral therapeutic prepara-tions is being developed. They constitute a new classof bovine antibodies or immunoglobulins. They com-prise of antibodies from colostrum of cows. They aredesigned to attack infections in the GI tract of hu-mans. They are consumed orally to provide passiveimmunotherapy. Regular bovine colostrum containsantibodies against many human pathogens such asEscherichia coli, Staphylococcus aureus, Staphylo-coccus epidermidis, Streptococcus pyogenes, Strep-tococcus faecalis, Streptococcus viridans, Candidaalbicans, Salmonella typhimurium, Proteus vulgaris,Klebsiella pneumoniae, and Pseudomonas aerugi-nosa. Cows are cost effective bioreactors producingabout 500 g of antibodies in the first 4 days of par-turition. During the dry period, pregnant cows areimmunized against specific antigens derived fromhuman pathogens. Postpartum milk is collected for4 days and harvested for immunoglobulins, followedby formulation for site-specific delivery. Polyclonalantibodies contained in the immunoglobulin formu-lations may bind multiple target sites.

Application of engineered immunoglobulins(Gregory, 1997) to milk as such or in associationwith cultures may be another innovative approachto design a product with a distinctive appeal to cer-tain segment of consumers. Certain preparation maycontain specific immunoglobulins to combat someconditions.

REFERENCESAimutis WR. 2004. Bioactive properties of milk

proteins with particular focus on anticarcinogenisis.J. Nutr. 134:4S, 989S–995S.

Brassart D, Schiffrin EJ. 1997. The uses of probioticsto reinforce mucosal defence mechanisms. TrendsFood Sci. Technol. 8:321–326.


Chandan RC. 2004. Yogurt. In: JS Smith, YH Hui(Eds), Food Processing, Blackwell Publishing,Ames, IA, pp. 297–318.

Elmer GW, Surawicz CM, McFarland LV. 1996.Biotherapeutic agents—A neglected modality forthe treatment and prevention of selected intestinaland vaginal infections. JAMA, 275:870–876.


Fonden R, Saarela M, Matto J, Mattila-Sandholm T.2003. Lactic acid bacteria in functional dairyproducts. In: T Mattils-Sandholm, M Saarela (Eds),Functional Dairy Products. CRC Press, Boca Raton,FL, p. 251.

Gilliland SE. 2003. Probiotics. Encyclopedia of FoodSciences and Nutrition, Vol. 8, Academic Press,London, pp. 4792–4798.

Goldberg I (Ed). 1994. Functional Foods, DesignerFoods, Pharmafoods, Nutraceuticals. Chapman &Hall, New York.

Goldin BR, Gorbach SL. 1992. Probiotics for humans.In: R Fuller (Ed). Probiotics—The Scientific Basis.Chapman and Hall, New York, pp. 355–376.

Gregory AG. 1997. Method for microfiltration of milkor colostum whey. US Patent no. 5,670,196.

Guerrin-Danan C, Chabanet C, Pedone C, Popot F,Vaissade P, Bouley C, Szylit O, Andrieux C. 1998.Milk fermented with yogurt cultures andLactobacillus casei compared with yogurt andgelled milk: Influence on intestinal microflora inhealthy infants. Am. J. Clin. Nutr. 67:111–117.

Hoolihan L. 2004. Beyond Calcium. The protectiveattributes of dairy products and their constituents.Nutrition Today 39(2, March–April): 69—77.

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Lee H, Rangavajhyala N, Gradjean G, Shahani KM.1996. Anticarcinogenic effect of Lactobacillusacidophilus on N-nitrosobis(2-oxopropyl) amineinduced colon tumor in rats. J. App. Nutr. 48:59–66.

Mattila-Sandholm T, Saarela M. 2003. FunctionalDairy Products. CRC Press, Boca Raton, FL.

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Rangavajhyala N, Shahani KM, Sridevi G, SrikumaranS. 1997. Nonlipopolysaccharide component(s) ofLactobacillus acidophilus stimulates the productionof interlukin-1� and tumor necrosis factor-� bymurine macrophages. Nutrition and Cancer28:130–134.

Saavedra JM. 1995. Microbes to fight Microbes: A notso novel approach to controlling diarrheal disease.J. Pediatr. Gastroenterol. 21:125–129.

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(Designer Foods, Pharmafoods, Neutraceuticals).Chapman and Hall, New York, pp. 295–322.

Saxelin M, Korpela R, Mayra-Makinen A. 2003.Introduction: classifying functional dairy products.In: T Mattils-Sandholm, M Saarela (Eds), FunctionalDairy Products. CRC Press, Boca Raton, FL, p. 6.

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21Health Benefits of Yogurt and

Fermented MilksNagendra P. Shah

IntroductionYogurt and Other Fermented MilksCultured ButtermilkCultured CreamFermented Milks of Eastern EuropeFermented Milks of AsiaNordic (Scandinavian) Fermented MilksFermented Milks from the Middle EastHealth Benefits of Fermented Milks

Nutritional Value of Fermented MilksNutritional Function

Physiological EffectsAntimicrobial Activity and Gastrointestinal InfectionsAnticancer EffectsReduction in Serum CholesterolImmune System Stimulation

Health Benefits of Nordic Fermented MilksHealth Effects of KefirHealth Benefits of Bio-Yogurt

References

INTRODUCTIONAlthough there are no records available to trace theorigin of yogurt and other fermented milks, it isbelieved that fermentation was the first techniqueemployed by humans for preservation of milk. Fer-mented milks are reported to have originated in theMiddle East before the Phoenician era. The tradi-tional Egyptian fermented milks, Laban Rayeb, andLaban Khad, were consumed in Egypt as early as7000 bc. Ancient Turkish people in Asia, wherethey lived as nomads, are believed to have madeyogurt first. The first Turkish name appeared in theeighth century as ‘yoghurut.’ According to the Per-sian tradition, Abraham owed his longevity to yogurtconsumption (Prajapati and Nair, 2003). Emperor

Francis I of France was cured of debilitating illnessby yogurt. Another legend tells that yogurt originatedfrom the Balkans. Peasants of Thrace made souredmilks, known as ‘Prokish’ from sheep milk. Asia con-tributed to the early spread of fermented milks bythe Tartars, Huns, and Mongols in their invasions ofRussia and European areas. South East Asia includ-ing Persia (or Iran), Iraq, Syria, and Turkey still re-mains a key area for production and consumption offermented milk. Fermented milk is also a traditionalfood in the Balkans. Its popularity has now spread toEurope and many other parts of the world. The word‘yogurt’ was derived from the Turkish word ‘Jugurt’and Table 21.1 shows the synonyms for yogurt oryogurt-related fermented milks known in differentcountries.

A major factor in the evolution of fermented prod-uct is that the Middle East area has a subtropi-cal climate and the temperature may reach around40◦C. This is the ideal temperature for the growthof starter bacteria and milk turned sour and coag-ulated rapidly. However, the souring of milk wasnot a uniform process as there was no controlover the starter bacteria in fermentation of milk.This gave rise to insipid product, with irregularcoagulum filled with air (Kosikowski and Mistry,1997).

Fermented milk plays an important role in the di-ets of some European communities, particularly inBulgaria. Today, fermented milk is manufactured inmany countries around the world.

Yogurt has played an important role in human nu-trition. The fermented milk products vary consider-ably in composition, flavor and texture, depending onthe nature of fermenting organisms, the type of milk,and the manufacturing process used.

327




Table 21.1. Yogurt and Yogurt-Like Products as Known in Various Countries of the World

Traditional Name Country Traditional Name Country

Jugurt/Eyran Turkey Tiaourti GreeceBusa Turkestan Cieddu ItalyKissel Mleka Balkans Mezzoradu SicilyUrgotnic Balkan mountains Gioddu SardiniaLeben/Leban Lebanon and some

Arab countriesFilmjolk/Fillbunke/

Filbunk/Surmelk/Taettem-jolk/Tettemelk

Scandinavia

Zabady Egypt and Sudan Tarho HungaryMast/Dough Iran and Afghanistan Viili FinlandRoba Iraq Skyr IcelandDahi/Dadhi/ Dahee India, Bangladesh, Nepal Yogurt/Yogurt/ Yaort Rest of the worldMazun/Matzoon Armenia Yourt/Yaourti/ Yahourth/

Yogur/Yaghourt(“Y” is replaced by “J”

in some instances)Katyk TranscaucasiaSource: Tamime and Deeth, 1980; Kosikowski and Mistry, 1997.

Although yogurt has many desirable properties,it is still prone to deterioration. The containerstraditionally used by nomads were made from ani-mal skins. Because of whey evaporation through theskin, the solids content and lactic acid concentrationrose. This gave rise to concentrated or condensedyogurt. Such type of product was manufactured inArmenia, where mazun (Armenian yogurt) is pro-cessed to yield concentrated yogurt. Another methodof concentration of yogurt was by placing the productin an earthenware vessel. Evaporation through poresof earthenware vessels helped increase solids contentand lactic acid concentration. This practice also keptthe product cool and is still practiced in some parts ofIndia and Nepal. Nevertheless, the condensed yogurthad a limited keeping quality and salting was car-ried out to extend the keeping quality. Different typesof concentrated yogurt containing various quantitiesof salt are made in Turkey. Sun drying of saltedproduct was another means of extending the keep-ing quality further. Dried yogurt balls are stored inglass jars and covered in olive oil. In some countriesincluding Turkey, Lebanon, Iraq, and Iran, rubbingof wheat flour to dried yogurt is carried out to in-crease the keeping quality to almost indefinite period.This product is known as “kishk.” As refrigerationbecame widespread, a variety of new generation ofyogurts emerged and the interest in traditionalproducts declined.

At the beginning of this century, Nobel LaureateElie Metchnikoff at the Pasteur Institute in Paris wasthe first to propose a scientific rationale for the bene-ficial effects of bacteria in yogurt. In his treatise ‘The

Prolongation of Life’, he hypothesized that yogurtbacteria, Lactobacillus delbrueckii ssp. bulgaricusand Streptoccocus thermophilus, control infectionscaused by enteric pathogens and regulate toxemia,both of which play a major role in ageing and mor-tality. He linked health and longevity of Bulgarianpeasants to their high consumption of fermentedmilks, particularly yogurt. Later, it was found thatyogurt starter is unable to implant in the intestine.Moro in 1900 isolated Lb. acidophilus from feces ofinfants. Hence, focus was given to Lb. acidophilus asa more suitable organism for therapeutic properties.This observation provided a major boost to manu-facture and consumption of yogurt (Prajapati andNair, 2003).

The first commercial production of yogurt inEurope was undertaken by Danone in 1922 in Madrid,Spain. There was a rapid advancement in the tech-nology of yogurt and understanding of its propertiessince 1950.

YOGURT AND OTHERFERMENTED MILKSYogurt is defined as “a product resulting from milk byfermentation with a mixed starter culture consistingof Str. thermophilus and Lb. delbrueckii ssp. bulgari-cus.” However, in some countries including Australiaother suitable lactic acid bacteria in addition to yo-gurt starter (Str. thermophilus and Lb. delbrueckii ssp.bulgaricus) are permitted for use as starter cultures.As a result, some yogurt manufacturers use Lac-tobacillus helveticus and Lactobacillus jugurti for

21 Health Benefits of Yogurt and Fermented Milks 329

manufacturing yogurt. Similarly, yogurt in Australiacan be made with ABT starter cultures, which in-clude Str. thermophilus, Lactobacillus acidophilus,and Bifidobacterium spp. In ABT starter cultures, Str.thermophilus is the main fermenting organism. Thefirst US Federal Standards of Identity for yogurt werepublished in 1981. The US standard allows the useof other culture organisms as long as Lb. delbrueckiissp. bulgaricus and Str. thermophilus are used formaking yogurt and the titratable acidity, expressedas lactic acid, and must be at least 0.9%. The titrat-able acidity requirement and some other provisionsof the standard have been stayed and are in limbo formany years. Manufacture of yogurt is discussed indetails in Chapter 13.

Recent advances have been supplementation ofyogurt starter with probiotic organisms such as Lb.acidophilus and Bifidobacterium spp. to increase thetherapeutic value of the product and use of exo-polysaccharide producing starter cultures to improvetextural characteristics of yogurt.

Bulgarian buttermilk is a high acid product madeby fermenting pasteurized (85◦C/30 minutes) milkwith Lb. delbrueckii ssp. bulgaricus at 42◦C for 10–12 hours. The product is very tart as it contains about

1.4% titratable acidity. This fermented milk is popu-lar in Bulgaria.

CULTURED BUTTERMILKCultured buttermilk is low-acid fermented milk fer-mented primarily by mesophilic cultures includingLactococcus lactis ssp. lactis and Lc. lactis ssp. cre-moris as well diacetyl-producing organisms as shownin Table 21.2.

Lc. lactis ssp. lactis and Lc. lactis ssp. cremorisare acid producers, while Lc. lactis ssp. lactis bio-var diacetylactis and Leuconostoc mesenteroides ssp.cremoris produce flavor and aroma compounds suchas diacetyl. For production of cultured buttermilk,pasteurized milk (85◦C for 30 minutes) is fermentedat 22◦C with starter microorganisms until a titrat-able acidity of 0.9% is reached. Incubation at highertemperatures favors the growth of Lc. lactis ssp. cre-moris and Lc. lactis ssp. lactis leading to high acidproduct, which limit the aroma production by Lc.lactis ssp. lactis biovar diacetylactis and Leu. mesen-teroides ssp. cremoris. The product has a shelf life of10 days at 5◦C.

Table 21.2. Some Fermented Milks and Their Starter Cultures

Product Starter Organisms

Butter milk (Bulgarian) Lactobacillus delbrueckii ssp. bulgaricusButter milk (cultured) Lactococcus lactis ssp. lactis biovar diacetylactis, Leuconostoc mesenteroides

ssp. cremorisCultured cream Lc. lactis ssp. lactis, Lc. lactis ssp. cremoris, Lc. lactis ssp. lactis biovar

diacetylactis, and Leu. mesenteroides ssp. cremorisDahi Lb. delbrueckii ssp. bulgaricus, Streptococcus thermophilus or Lc. lactis ssp.

lactis, Lc. lactis ssp. cremoris, Lc. lactis ssp. lactis biovar diacetylactis, andLeu. mesenteroides ssp. cremoris

Filjolk Lc. lactis ssp. lactis, Lc. lactis ssp. cremoris, Lc. lactis ssp. lactis biovardiacetylactis

Kefir Lc. lactis ssp. lactis, Lc. lactis ssp. cremoris, Lc. lactis ssp. lactis biovardiacetylactis, and Leu. mesenteroides ssp. dextranicum, Str. thermophilus,Lb. delbrueckii ssp. bulgaricus, Lb. acidophilus, Lb. helveticus, Lb. kefir,Lb. kefiranofaciens, Kluyveromyces marxianus, Sacchamyces spp.

Kumys Lb. acidophilus, Lb. delbrueckii ssp. bulgaricus, Sacchamyces lactis, Torulakoumiss

Tatmjolk Lc. lactis ssp. lactis, Lc. lactis ssp. cremoris, Lc. lactis ssp. lactis biovardiacetylactis

Viilli Lc. lactis ssp. lactis, Lc. lactis ssp. cremoris, Lc. lactis ssp. lactis biovardiacetylactis, Geotrichum candidum

Yakult Lb. paracasei ssp. caseiYogurt Lb. delbrueckii ssp. bulgaricus, Str. thermophilusSource: Lee and Wong, 1993.


CULTURED CREAMCultured cream, also known as sour cream, is low-acid fermented milk with similar flavor as buttermilk.The product contains 18% fat. The same starter cul-ture and incubation temperature are used as culturedbuttermilk.

FERMENTED MILKS OFEASTERN EUROPEKefir is a refreshing drink of northern slope ofCaucasian mountains of China. Since early times,people who lived in the mountains learnt to makekefir. Kefir grains are used as starter cultures. Legendtells that kefir was given to orthodox people byProphet Mohammad. Prophet Mohammad kept thesecret of kefir to himself from the outside world; oth-erwise the so-called magic strength could be lost.Kefir was traditionally made in skin bags. Naturalfermentation took place in skin bags under sunlight.The finished product contained substantial amountof lactic acid, alcohol, and carbon dioxide. The sackswere filled with fresh milk and the process repeated(IDF, 1984; Koroleva, 1988). Russian doctors recom-mended kefir for treatment of intestinal and stomachdiseases. The first scientific literature about kefir ap-peared at the end of eighteenth century.

Kefir is a product made by fermenting milk withacid and alcohol-fermenting organisms. Kefir grainsare complex consortium of about 30 species of bac-teria and yeasts. The microorganisms are embeddedin the matrices made up of polysaccharides. Thepolysaccharide, known as kefiran, is produced byLactobacillus kefiranofaciens. The product contains0.9–1.1% lactic acid, 0.3 to 1% alcohol and 1% car-bon dioxide. The product is very popular in EasternEurope (IDF, 1984). The microorganisms associatedwith kefir grains, which are equivalent to starter cul-tures in other fermented milks, are shown in Table21.2. Incubation is carried out at 18–22◦C for ap-proximately 20 hours.

Kumys is another fermented milk of EasternEurope. The product is described in the section below.

FERMENTED MILKS OF ASIADahi is a popular fermented milk in India, Africa,Central Europe, analogous to the western yogurt. InIndia, Nepal, and other Asian countries, dahi is stillmade in every household in villages as well as inurban areas using traditional method (Prajapati andNair, 2003). The product is typically made from pas-

teurized or boiled milk, inoculated with dahi as starterleft over from the previous day. Incubation is carriedout in a warm place usually overnight. The organismsused as starter cultures are shown in Table 21.2.

The product is claimed to have good nutritional andhealth properties, which make the product very pop-ular. Dahi has been used in India since Vedic times.Lord Krishna (c 5000 bc) had been depicted with eat-ing dahi, buttermilk, and ghee. Ayurveda, the tradi-tional Indian medicine, mentions health properties ofdahi including its role in controlling gastrointestinaldisorders. Dahi is used as a part of daily diet in Indiaand is eaten along with rice and other main meals.

Kumys (also known as kumiss) is traditionallyprepared from mare milk and is popular in EasternEurope and Asiatic regions. The name kumiss is re-ported to be named after a tribe called Kumanes in theAsiatic Steppes. Scythian tribes, which roamed fromplace to place in South East Asia and Middle Asia,were reported to drink kumiss made from mare’s milksome 2500 years ago (Koroleva, 1988). Kumys hasbeen mentioned by Marco Polo as being a pleasantdrink. The finished product had high acidity and vary-ing amount of alcohol and carbon dioxide. It wasconsumed as a food as well as weak alcoholic drink.

Kumys is fermented milk that contains lactic acid(0.6–1.0%) and alcohol (0.7–2.5%). The main or-ganisms involved in fermentation are Lb. delbrueckiissp. bulgaricus and Lb. lactis ssp. lactis and lactose-fermenting yeasts, e.g., Saccharomyces lactis orTorula spp. Carbon dioxide is produced by the yeast.The milk is not heat treated, hence a high level ofstarter culture (30%) is used. The incubation is car-ried out at 26–28◦C and depending on the fermenta-tion time the product may contain 0.6% lactic acidand 0.2% alcohol, 0.8% lactic acid and 1.5% alcohol,or 1.0% lactic acid and 2.5% alcohol.

Yakult is a popular fermented milk in Japan. Theproduct is made with Lb. paracasei ssp. paracaseistrain Shirota. The product contains low milk solids(3.7%) and high levels of sugar (14%).

Dadih is a popular fermented milk of Indonesia.The product is equivalent to Indian Dahi and ismade by natural fermentation of raw buffalo milk at28–30◦C. Lb. casei ssp. casei, Leuconostoc mesen-teroides and Lc. lactis ssp. lactis biovar diacetylactisare usually involved in the fermentation.

NORDIC (SCANDINAVIAN)FERMENTED MILKSNordic fermented milks are made from encapsulatedEPS producing lactococci, primarily L. lactis ssp.


cremoris. The products are characterized by high vis-cosity and ropiness and if one lifts the product with aspoon, long strings will appear. An example of suchtype of product is “langfil” also known as “tatmjolk,”a popular product in Sweden. Similar fermented milkmarketed in Norway is “tettemelk.” Filmjolk is sourmilk popular in Sweden.

Viili is popular fermented milk of Finland. Theproduct is made primarily with the help of Lc. lac-tis ssp. lactis biovar diacetylactis and Leuconostocmesenteroides ssp. cremoris and lactose fermentingmold Geotrichum candidum. The cream layer is usu-ally covered with the mold and the product is eatenwith a spoon. Pasteurized milk is fermented at ap-proximately 20◦C until a final acidity of 0.9% isreached.

Ymer is Danish fermented milk made from fer-mentation of ultrafiltered milk retentate (usually 15%solids). The starter cultures used for cultured butter-milk are also used for ymer. Lactofil is a similar prod-uct as ymer and is popular in Sweden. Starter cultureused for ymer is similar to cultured buttermilk.

Skyr is produced from skim milk and is popular inIceland. Lb. delbrueckii ssp. bulgaricus and Lb. caseiare used as a starter culture. The product is concen-trated by separating the whey using a cheese-cloth.

Probiotic fermented milks contain various speciesof probiotic organisms, particularly Lb. acidophilus,Bifidobacterium spp. and Lb. casei. Lb. delbrueckiissp. bulgaricus and Str. thermophilus do not survivein the gastrointestinal tract. Since probiotic organ-isms grow slowly in milk, the trend is to use Lb.delbrueckii ssp. bulgaricus and Str. thermophilus asthe primary starter culture and probiotic organisms asadjunct organisms. With this approach, the fermenta-tion time could be short. Some examples of fermentedmilks containing probiotics include “Bioghurt,”“Biogarde,” and “Bifighurt.” These products arepopular in Germany. A similar product popular inDenmark is known as “Cultura.” This product con-tains Lb. acidophilus and Bifidobacterium bifidum.

FERMENTED MILKS FROM THEMIDDLE EASTFermented milks in the Middle East are classifiedbased on the total solids content of the product.Fermented milks with similar solids content as milkinclude zabady, laban rayeb, and laban kad. Concen-trated fermented milks containing 20–40% solidsinclude labneh and laban zeer. Dried fermentedmilks include kishk (Kurmann, and Rasic, 1988).

Zabady is traditionally made by boiling buffalomilk followed by inoculation with previous day’sproduct as a starter culture. The product is made inuncovered containers and postprocessing contami-nation with yeasts and molds is very common. As aresult, the product has a limited shelf life. Organismscommonly found in zabady include Str. thermophilus,and Lb. delbrueckii ssp. bulgaricus. However,Bacillus subtilis, Alcaligenes spp. and Micrococcusspp. are also found as contaminants.

Laban rayeb is an indigenous product of Egypt.This product is made in households by milking an-imals in earthenware pots and keeping undisturbeduntil fermented by natural microflora of milk.

Laban kad is traditionally made in goatskin bagsby fermentation with natural flora of milk. The or-ganisms isolated from this product include Lc. lactisssp. lactis, Leu. mesenteroides ssp. dextranicum, Leu.mesenteroides ssp. cremoris and Lb. casei.

Gariss is an indigenous fermented milk of Sudan.The product is made from camel’s milk by naturalfermentation of milk in leather bags. Lactobacillushelveticus, Lb. delbrueckii ssp. lactis and yeasts suchas Candida spp. and Kluveromyces spp. are usuallyinvolved in fermentation.

Labneh is a popular product of Lebanon and Syria.The product is made as full cream zabady (equiva-lent to yogurt) followed by draining of whey usinga cheese-cloth. Laban zeer is a traditional productof Egypt. Fermented buttermilk (laban kad) obtainedfrom churning of naturally fermented cream is storedin earthenware jar (known as “zeer”). The increasein solids is due to evaporation of moisture throughporous pot. Organisms isolated from the product in-clude Bacillus spp. and Lactobacillus spp. Saccha-romyces and yeast is also found.

Table 21.2 shows the important fermented milksand starter cultures used in production of these prod-ucts. Table 21.3 shows the origins of some importantfermented milks.

HEALTH BENEFITS OFFERMENTED MILKSNutritional Value ofFermented Milks

Health effects are divided into two groups: nutritionalfunction and physiological function. The nutritionalattribute is expressed as the function of supplying nu-trition sufficiently. The physiological function refersto prophylactic and therapeutic functions beyond


Table 21.3. Origins of Some Important Fermented Milk Products

Country ofProduct Origin Period Characteristics

Airan Central Asia,Bulgaria

1253–1255 AD Milk soured by Lb. bulagricus and usedas refreshing beverages

Bulgarian milk Bulgaria 500 AD Very sour milk fermented by Lact.bulgaricus

Dahi India 800–300 BC Milk soured by using previous day souredmilk as starter

Kefir CaucasusianChina

– Milk fermented with kefir grainscontaining lactobacilli and yeast. Lacticacid, alcohol, and CO2 give sparklingcharacteristics

Kishk Egypt, Arabworld

Fermented milk mixed with par boiledwheat and dried

Kumys or Kumiss Central AsiaMongol,Russia

400 BC Mare milk is fermented by lactobacilliand yeast. Lactic acid, alcohol, andCO2 give sparkling characteristics

Laban Egypt 5000–3000 BC Soured milk coagulated in earthenwareutensils

Langfil orTattemjolk

Sweden Milk fermented with slime producinglactococci

Leben Iraq 3000 BC Milk soured with yogurt bacteria andwhey is partially drained by hangingthe curd in clothes

Mast Iran Natural yogurt with firm consistency andcooked flavor

Skyr Iceland 870 AD Fermented milk made from ewe milk withthe help of rennet and starter

Taette Norway – Viscous fermented milkTrahana Greece – Fermented milk made by mixing wheat

flour followed by dryingViili Finland – Viscous milk fermented with lactic acid

bacteria and moldYakult Japan 1935 AD Highly heat-treated milk fermented by L.

casei Shirota strainYmer Denmark – Protein fortified milk fermented with

leuconostocs and lactococciYogurt or yoghurt Turkey 800 AD Custard-like sour fermented milkSource: Prajapati and Nair, 2003.

nutritional function. Potential nutritional and healthbenefits of fermented foods are listed in Table 21.4.

Nutritional Function

Milk is a complete food for newborn mammals. Itis the sole food during the early stages of rapid de-velopment. Milk contains well-balanced macronutri-ents including carbohydrate, fat, and protein. Milkcontains approximately 5% lactose, 3% protein, 4%fat, and 0.7% minerals used for mammalian growth

and development. Milk is also a good source ofmicronutrients including calcium, phosphorus, mag-nesium, and zinc. Milk proteins have high nutri-tive value due to the favorable balance of essentialamino acids (Buttriss, 1997). Milk proteins are defi-cient only in sulfur-containing amino acids such ascysteine and methionine. Milk also contains antimi-crobial substances, which provide protection againstinfection in neonates. The most important character-istics of human milk as compared with cow’s milk areits low protein, low ash, and high lactose contents.


Table 21.4. Potential Nutritional and Health Benefits of Fermented Foods

Beneficial Effect Possible Causes and Mechanisms

Improved digestibility Partial breakdown of proteins, fats and carbohydratesImproved nutritional value Higher levels of B-vitamins and certain free amino acids, viz.

methionine, lysine and tryptophanImproved lactose utilization Reduced lactose in product and further availability of lactaseAntagonistic action toward

enteric pathogensDisorders such as diarrhoea, mucous colitis, ulcerated colitis; prevention

of adhesion of pathogensAnticarcinogenic effect Reduction of carcinogen-promoting enzymes; inhibitory action toward

cancers of the gastrointestinal tract by degradation of precarcinogens;stimulation of the immune system

Hypocholesterolemic action Production of inhibitors of cholesterol synthesis; use of cholesterol byassimilation and precipitation with deconjugated bile salts

Immune modulation Enhancement of macrophage formation; stimulation of production ofsuppressor cells and � -interferon

Source: Gomes and Malcata, 1999.

Nutritionally fermented milks have a similar com-position to that of the unfermented counterpart fromwhich it is made. However, the composition can bemodified by addition of other ingredients such as non-fat dry milk, whey powder, fruit, and sugar. Bacterialfermentation results in lowering of lactose and in-creased level of lactic acid. Fortification with milksolids also results in increased protein and lactosecontents, although, some lactose is converted to lac-tic acid.

Lactose

Lactose is considered as an excellent food for babiesand has a favorable effect in the intestinal tract. Lac-tose requires longer time for digestion; this providesa suitable medium for beneficial probiotic bacteriaincluding Lb. acidophilus and bifidobacteria, whichin effect dominate the putrefactive bacteria and min-imize the production of gas by them. The beneficialeffect of lactose on the absorption of calcium is wellestablished.

Lactose stimulates gastrointestinal activity. Lac-tose increases the capacity of the body to utilize phos-phorus and calcium. Polysaccharides such as cellu-lose (e.g., carboxy methyl cellulose) are generallyadded to yogurt mix as a stabilizer and many of thesepolysaccharides are considered as “bifidus factor”and may prevent constipation by providing bulk.

Lactic acid acts as a preservative by reducing pH,which inhibits the growth of potentially spoilage andharmful bacteria. Lactic acid also influences physicalproperties of casein curd to induce a finer suspension,which appears to promote digestibility.

During fermentation, lactic acid bacteria convert20–30% of lactose into lactic acid. Consequently, thelactose levels in fermented milks can be lower thanmilk. Fermented milks with lower lactose contentare better tolerated by lactose intolerant individuals.Yogurt in general is supplemented with 2–4% skimmilk powder, so the protein and sugar contents areusually higher than cow’s milk. Even after fermen-tation, the product may contain 4–5 g of lactose per100 g of the product (Deeth and Tamime, 1981). Nev-ertheless, yogurts fortified with skim milk powderand containing higher levels of lactose also appear tobe tolerated by lactose malabsorbers (Gurr, 1987).

Milk Proteins

Milk protein is considered to be of high nutritionalvalue in terms of its biological value, net protein uti-lization, and protein efficiency ratio. The proteins inmilk are of excellent quality as caseins and wheyproteins (�-lactalbumin and �-lactoglobulin) containhigh levels of essential amino acids. Protein contentof fermented milks such as yogurt is often increaseddue to supplementation with skim milk solids (typi-cally, 2–3%). This means that it is an even more at-tractive source of protein than its liquid counterpart.The levels of soluble proteins, nonprotein nitrogenand free amino acids are higher in yogurt as a resultof heat treatment to milk and breakdown of caseinby starter bacteria. Lactic acid bacteria require aminoacids for their growth; they break down milk proteinsdue to their proteolytic activity.

Protein in fermented milks is reported to be to-tally digestible. Fermented milks are more digestible


than milk due to proteolytic activity of starter bacte-ria resulting in higher levels of peptides and aminoacids (IDF, 1991). Feeding of yogurt resulted in in-creased weight gains and increased feed efficiency inrats compared to that of milk from which it is pre-pared. The substance promoting body weight gainwas found to be of MW ≥ 20,000, possibly related tothe cells of Str. thermophilus. Thus, it can be assumedthat yogurt made with Str. thermophilus will have agrowth promoting effect, possibly due to enhancedbio-availability of minerals, in particular iron. Thisindicates a higher protein value of fermented prod-ucts compared to unfermented milk. Consumption of250 g of fermented milks per day can serve an indi-vidual with the minimum daily requirement of animalprotein, which is reported to be 15 g (IDF, 1991).

Milk is heat treated (typically 85◦C for 30 min)for making most fermented milks. This results insoft curd when milk proteins are coagulated by theacid produced by yogurt starter bacteria. Milks withsofter curds resulting from such high heat treatmentshow more human milk like characteristics and aremore digestible as a substitute for mother’s milk thanharder curds. Further, the more open nature of thecasein aggregates allows the proteolytic enzymes ofgastrointestinal tract freer access during digestion.The soft curd does not give rise to any feeling of dis-comfort; this is very important in children. The curdformed from milk in the stomach of the young by theaction of chymosin and pepsin is less accessible tosubsequent enzymatic digestion.

The digestibility of milk protein is the highest(>90%) among proteins. This may be due to decreasein protein particle size and an increase in soluble ni-trogen, nonprotein nitrogen and free amino acids dur-ing heat processing of milk and proteolysis by starterbacteria. In general, yogurt has been found to be moredigestible than milk.

Milk Fat

Milk fat is highly digestible. Lactic acid in fermentedmilks has been found to promote peristaltic move-ment, which improves overall digestion and absorp-tion of food. Traditional yogurt contains 3–4% fat.Concentrated yogurt (labneh) or yogurt from sheepmilk may contain 7–8% fat. The recent trend is toproduce yogurt from skim milk. The overall energy(calorie) content of yogurt reflects both the fat contentof the milk from which it was made and the supple-mentation of ingredients such as cream or sugar. Milk

fat improves consistency and mouthfeel of the prod-uct. Milk fat has highest value as an energy sourcewith each gram of fat providing 9 kcal. Milk fatsupplies essential fatty acid including linoleic andlinolenic acid and fat-soluble vitamins such as vita-min A, carotene, vitamin D, E, and K. Choline, aconstituent of phospholipid, promotes the oxidationof lipids in the liver and acts to maintain an equilib-rium cholesterol concentration (Deeth and Tamime,1981). Yogurt is reported to produce hypocholestero-laemic effects.

Enhancement in Absorption of Vitamins andMinerals. Milk contains more calcium than otherfoods. Similarly, absorption of calcium is better frommilks than from other forms. The mineral content ishardly altered during fermentation; however, reportssuggest that the utilization of Ca, P, and iron in thebody is better for fermented milks than that of milk.One possible reason could be phospho-peptides re-leased by the hydrolysis of casein that accelerate ab-sorption. Animal studies on the amount of calciumin bone and bone weight and strength suggested thatlactic acid was involved. These observations suggestthat calcium absorption from fermented milk is betterthan unfermented counterpart. The utilization of Caand P in the body is known to improve in the pres-ence of lactose and vitamin D. Calcium is requiredfor bone metabolism and prevention of osteoporosis.Yogurts contain appreciable quantity of sodium andpotassium and thus may not be suitable for feedingbabies less than 6 months, unless these minerals arereduced prior to yogurt manufacturing.

Fermented milks are an excellent source of vitaminB2 and also a good source of vitamin A, vitamins B1,B6, B12, and pantothenic acid. The level of fat-solublevitamins, particularly vitamin A, is dependent on thefat content of the product. Some lactic bacteria areable to synthesize the B vitamin folic acid (Reddyet al., 1976). Vitamin content of yogurt in general ishigher as starter bacteria synthesize certain B groupvitamins during fermentation. Levels of some B vi-tamins, particularly vitamin B12, are reduced dueto requirement of some lactic acid bacteria for thisvitamin.

The fortification of fermented milks with vitaminsA and C is possible and losses over 2 weeks in stor-age are likely to exceed 50%. However, the major-ity of vitamin C is lost by heat treatment (Bourliouxand Pochart, 1988). Similarly, vitamin B12 is reportedto be undetectable after storage for 5 days. Low-fat


yogurt is popular in many developed countries; hencefortification with vitamin A should be encouraged.

Alleviation of Lactose Malabsorption. The aver-age lactose content in yogurt mix is 8.5%, which de-creases in yogurt to approximately 5.75% after fer-mentation. About 25–30% of lactose is converted tolactic acid during fermentation. Lactose content inother fermented milks varies depending on fortifica-tion and breakdown of lactose by starter bacteria.

Lactose malabsorbers often complain of “gastricdistress” after consuming fresh, unfermented milkor milk products. Lactose malabsorption is a condi-tion in which lactose, the principal carbohydrate ofmilk, is not completely hydrolyzed into its compo-nent monosaccharides, glucose, and galactose. Sincelactose is cleaved into its constituent monosaccha-rides with the help of lactase or �-D-galactosidaseenzyme, lactose malabsorption results from a defi-ciency of this enzyme. Lactase deficiency is a com-mon problem in many parts of the world. The preva-lence of lactose malabsorption varies depending onthe ethnic origin of the population. Infants in generalhave higher lactase activity than adults. Prevalence oflactose malabsorption is common in China, Thailand,Japan, and Africa and Australian aborigines, but lesscommon among Caucasians. Temporary deficiencyof �-galactosidase occurs in people suffering from di-arrhea. The unabsorbed lactose reaches colon, whereit is fermented by colonic flora to volatile fatty acids,lactic acid, CO2, H2, and CH4. The unhydrolyzedlactose withdraws water and electrolytes from duo-denum and jejunum. The lactase deficient people cansuffer from bloat, flatulence, abdominal pain, and di-arrhea (Shah, 1993).

Fermented milks, in particular yogurt appears tobe well tolerated by lactose malabsorbers and lac-tose malabsorbers suffer fewer symptoms with fer-mented dairy foods. Reduced levels of lactose infermented products are due to partial hydrolysis oflactose during fermentation and is partly responsiblefor greater tolerance of yogurt. Factors other than thepresence of yogurt starter are responsible for bettertolerance of lactose in lactose maldigesters from fer-mented dairy foods. At least three factors appear tobe responsible for better tolerance of lactose fromyogurt including (a) yogurt bacteria, (b) lactase en-zyme or �-galactosidase elaborated by these bacte-ria, and most importantly (c) oro-caecal transit time.The traditional cultures used in making yogurt (i.e.,Lb. delbrueckii ssp. bulgaricus and Str. thermophilus)

contain substantial quantities of �-D-galactosidase,and it has been suggested that the consumption ofyogurt containing cultures with high levels of lac-tase may assist in alleviating the symptoms of lac-tose malabsorption. Bacterial enzyme is reported toauto-digest lactose intracellularly before reaching theintestine (Savaiano et al., 1984). Auto-digestion oflactose intracellularly by bacterial �-galactosidasebefore reaching the intestine is an important factorthat improves digestibility of lactose. The organismsare lysed in the presence of bile salts and the re-leased lactase causes hydrolysis of ingested lactose.The action of bile increases the cellular permeabilityof yogurt bacteria allowing the release of intracel-lular �-galactosidase activity. Hence, the amount oflactose reaching the colon is too small to cause lac-tose malabsorption. Yogurt also has buffering effectand due to this the organisms reach the duodenumand the �-galactosidase activity is not inactivated. �-Galactosidase is destroyed in vitro at pH below 3.0,but buffering capacity of yogurt is able to keep thepH above 3.0 (Onwulata et al., 1989).

Slower gastric emptying of semisolid fermentedmilk products such as yogurt is another factor respon-sible for better absorption of lactose. Delayed gastricemptying is responsible for hydrolysis of lactose byindigenous �-galactosidase located in the sides andtips of the viili of the jejunum and by bacterial �-galactosidase. Viscous foods such as yogurt or foodswith higher solids are reported to delay gastric emp-tying and are effective in alleviating lactose intolerantsymptoms (Shah et al., 1992) As a result, fermentedmilk containing live culture and �-galactosidase isbetter tolerated than unfermented milk. As coagu-lated milk, because of its viscous nature, passes moreslowly through the gut than unfermented milk. Reg-ular yogurt appears to be more effective than eitherpasteurized yogurt or buttermilk. Pasteurized yogurt,in which starter bacteria and enzyme activity are de-stroyed due to heat treatment, is also tolerated welldue to slower gastric emptying (Shah et al., 1992).

Yogurt bacteria hydrolyze lactose into glucose andgalactose with the help of �-galactosidase. Glucoseis used directly as a source of energy by the organ-isms. There is often accumulation of free galactose inyogurts. A part of the galactose is converted to glu-cose in the liver. Some of the galactose is used for syn-thesis of brain cerebrosides and nerve tissues. Galac-tose was reported to cause cataracts of eyes in rats(Goodenough and Kleyn, 1976). However, the diet inrats was composed entirely of yogurt. No such effect


has been reported in humans possibly due to: (i) bet-ter metabolism of galactose, (ii) lack of the enzymeresponsible for metabolism of galactose in rats, and(iii) yogurt is only a small part of the human diet.

Two types of lactic acid, L (+) and D (−), are pro-duced during fermentation. Lb. delbrueckii ssp. bul-garicus produces only D (−) lactic acid, whereas Str.thermophilus produces L (+) lactic acid. D (−) lacticacid is not metabolised to pyruvic acid in the body be-cause of lack of D2-hydroxy acid dehydrogenase andthis results in metabolic acidosis in neonatal infants.The concentration of L (+) will vary with the ratioof Str. thermophilus, and Lb. delbrueckii ssp. bulgar-icus and is usually approximately 50% of the totalamount as the ratio of the two organisms in the prod-uct is usually 1 : 1. L (+) isomer is easily digestedand is completely harmless. Both isomers are foundto improve the digestibility of the casein and aid inretention of calcium in the intestine (Shah, 1999).

PHYSIOLOGICAL EFFECTSMany health benefits have been attributed to fer-mented milk products as listed in Tables 21.3. A con-siderable amount of evidence has been accumulatedfor some benefits such as improved lactose tolerance.Physiological benefits include antimicrobial activityand gastrointestinal infections, anticancer effects, re-duction in serum cholesterol, and immune systemstimulation (Holm, 2003).

Antimicrobial Activity andGastrointestinal Infections

The gastrointestinal tract has a large number of in-digenous microflora. There is a balance between use-ful microorganisms and harmful microflora. This bal-ance is affected by gastrointestinal illnesses, stress,and use of antibiotics leading to disturbances of itsfunction. Fermented milks have been used to improveintestinal health since ancient times. This includes di-arrhea caused by infection due to pathogenic bacteria.Fermented foods are reported to improve the compo-sition and metabolic activity of intestinal microflora.

Starter bacteria used in fermented milks producelactic acid, and bacteriocins as antimicrobial sub-stances. These antimicrobial substances are producedto suppress the multiplication of pathogenic and pu-trefying bacteria. Lowering of pH due to lactic acidproduced by starter bacteria during fermentation andin the gut has bactericidal or bacteriostatic effect.Many species of lactic acid bacteria also produce

H2O2 as an antimicrobial substance. However, it isbelieved that lactic acid is the only antimicrobialagent of any importance. The low pH resulting fromthe production of lactic acid during the fermentationcreates an undesirable environment for the growth ofspoilage microorganisms (Shah, 2000).

Controversies have surrounded the efficacy ofyogurt as a therapeutic agent. Reports suggest thatLb. delbrueckii ssp. bulgaricus do not survive gastric(acid) and intestine (bile salt) conditions. Str. ther-mophilus is susceptible to acidic conditions. How-ever, Lb. delbrueckii ssp. bulgaricus is acid tolerant.Some reports suggest that yogurt bacteria can survivepassage through the gastrointestinal tract. However, itis agreed that Lb. delbrueckii ssp. bulgaricus is unableto implant. Hence, it is unlikely that Lb. delbrueckiissp. bulgaricus can be used for treating gastrointesti-nal disorders. Nonetheless, yogurt has been used intreating infantile diarrhea and normalization of gas-trointestinal flora. The organism is also reported toincrease the population of Bifidobacterium spp.

Lb. delbrueckii ssp. bulgaricus has been shown toproduce several bacteriocin including “bulgarican,”which has shown broad spectrum antibacterial ac-tivity. Antimicrobial compounds isolated from skimmilk cultures of Lb. delbrueckii ssp. bulgaricus andStr. thermophilus have shown activity against a rangeof organisms including Salmonella, Shigella, E. coli,and Pseudomonas (Dave and Shah, 1997).

Fermented milks have shown beneficial effects onintestinal health. Alleviation of infant diarrhea andantibiotic associated diarrhea due to consumption offermented milks has been reported (Saavedra et al.,1994). Consumption of fermented milks has shownto increase the counts of bifidobacteria and decreasethe levels of putrefactive compounds in feces. This isbecause of enhancement of intestinal immune func-tion by lactic acid bacteria in fermented milks andantimicrobial substances produced during fermenta-tion, which have shown improvement in intestinalmicroflora.

Anticancer Effects

Cancer is one of the main causes of death in westerncountries. Epidemiological studies suggest thatcancer is caused by environmental factors, partic-ularly diet. The consumption of cooked red meatespecially barbequed meat and low consumption offiber are reported to play a major role. Several factorsresponsible for causes of colorectal cancer includingbacteria and metabolic products such as genotoxic


compounds (nitrosamine, heterocyclic amines,phenolic compounds, and ammonia). Many bacterialenzymes such as �-glucuronidase generate thesecarcinogenic products, except lactic acid bacteria andprobiotics, such as Lactobacilli and bifidobacteria.Lactic acid bacteria and fermented products havepotential anticarcinogenic activity. An inverse rela-tionship between consumption of fermented dairyfoods and the risk of colorectal cancer has been found.Lactic acid bacteria suppress bacterial enzymes, andreduce intestinal pH (Orrhage et al., 1994).

Several studies have shown that fermented dairyproducts or preparation containing lactic acid bacte-ria inhibit the growth of tumor cells in experimentalanimals. Animal studies using chemical carcinogen1, 2-dimethyl hydrazine (DMH) have been carriedout. Rats were given DMH to induce colon cancerand fed with fermented milks. DMH is activated inthe large intestine by �-glucuronidase. Addition ofLactobacillus to the diet has been reported to de-lay tumor formation. The inhibitory effects of fer-mented milks on colon cancer are either becauseof the decrease of mutagenic activity or modifica-tion of intestinal microflora. Antimutagenic effects ofmilk fermented with Lb. delbrueckii ssp. bugaricusand Str. thermophilus have been reported. Yogurthas been found to reduce the levels of bacterialenzymes, �-glucuronidase, azoreductase, and ni-troreductase. These enzymes are believed to con-tribute to pathogenicity of bowel cancer as they cat-alyze conversion of procarcinogens to carcinogens(Lankaputhra and Shah, 1998; Goldin and Gorbach,1977, 1984, Cenci et al., 2002).

Several types of fermented milks including yo-gurt, colostrum fermented with Lb. delbrueckii ssp.bulgaricus, Str. thermophilus, and Lb. acidophilusor milk fermented with Lb. helveticus are reportedto suppress cancer cell growth. Studies have shownseveral compounds including supernatants of milkfermented by Lb. delbrueckii ssp. bulgaricus, cellsof Lb. delbrueckii ssp. bulgaricus, Str. thermophilus,and Lb. helveticus ssp. jugurti in yogurt, exopolysac-charide in kefir have inhibitory effects on cancer cellgrowth.

Reddy et al. (1973) were the first to report the an-ticancer effect of yogurt in mice. Since then severalstudies have demonstrated that Lb. delbrueckii ssp.bulgaricus, and Str. thermophilus strains are able toslow down the evolution of tumors in mice. Antipro-liferative effect of fermented milk on the growth ofhuman breast cancer line has also been demonstrated.Only live bacteria appear to have anticancer effect.

Antitumor actions of yogurt are claimed to be dueto the stimulation of the immune functions of thebody, as well as improvement in intestinal microflorapopulation. The anticarcinogenic effect of lactic acidbacteria is due to the result of removal of sources ofprocarcinogens or the enzymes, which lead to theirformation. Short-chain fatty acids produced by lacticacid bacteria are reported to inhibit the generationof carcinogenic products by reducing enzyme activ-ities. The other mechanism includes improvement inthe balance of intestinal microflora, normalized in-testinal permeability (prevention or delaying of toxinabsorption), and strengthening of intestinal barriermechanisms.


There is a high correlation between dietary satu-rated fat or cholesterol intake and serum cholesterollevel. Elevated levels of serum cholesterol, partic-ularly LDL-cholesterol have been linked to an in-creased risk of cardiovascular disease, which is oneof the main causes of death in developed countries.Cholesterol lowering properties of fermented milkswere observed as early as 1960s among Masai tribesof East Africa. Mann and Spoerry (1974) observed adecrease in serum cholesterol levels in men fed largequantities (8.33 L/man/day) of milk fermented withLactobacillus. Those people had low-blood choles-terol levels although they consumed a large quantityof meat. Consumption of high quantity of yogurt wasfound to be responsible for lowering of serum choles-terol. Rabbits fed on a high cholesterol diet supple-mented with yogurt showed lower cholesterol levelsas compared to the diet supplemented with nonfer-mented milk. Cholesterol-lowering effects of yogurthave been reported in human volunteers. The subjectsconsumed 240 mL of yogurt three times per day.

The role of fermented milks in reducing theserum cholesterol is not completely understood.Cholesterol is an essential component of cell mem-brane and is required to produce certain hormonesand bile acids. It is synthesized by the liver andfrom absorbed foods. The mechanism of control-ling blood cholesterol level is complex. Metaboliteof starter cultures in fermented milks is reportedto produce hydroxymethyl-glutarate, which in-hibits hydroxymethylglutaryl-CoA reductase, an en-zyme required for the synthesis of cholesterol inthe body. This could limit cholesterol synthesis.Calcium, orotic acid, lactose, and casein have beensuggested as possible hypocholesterolemic factors.


Lactobacillus in fermented milks is reported tocause deconjugation of bile acid in the small intestinewith consequent fecal excretion of bile acids and alowering of the body sterol pool (Klaver and Meer,1993).

Conjugate bile acids are reported to enhance ab-sorption of cholesterol. Microorganisms also assimi-late or absorb cholesterol. EPS produced by Lc. lactisssp. cremoris in fermented milks are reported to in-terfere with absorption of cholesterol similar to thatwith dietary fiber.

Despite several studies, this effect is still notconsidered an established effect and double-blindedplacebo-controlled human clinical trials are neededto substantiate this claim. Similarly, mechanisms in-volved in reducing cholesterol level should be clari-fied. Additional research is needed to substantiate thepossible hypocholesterolaemic effect of yogurt.

Immune System Stimulation

The health benefits of fermented milks are primar-ily because of the ability of starter bacteria to sur-vive in the gastrointestinal tract. Yogurt starter bac-teria are reported to survive in the stomach and arealso found in feces. The intestinal system defendsthe body against bacterial and viral infection andcancer and allergies. The intestine is body’s largestimmune organ and the intestinal microflora and themetabolic activity of intestine is equivalent to that ofthe liver. The intestinal tract works as a peripheral or-gan to protect against intestinal infections and affectssystemic immunological function. Its function is af-fected by intestinal microflora. The mechanism forimmunomodulation is not clearly understood. Lacticacid bacteria (LAB) are likely to, directly or indi-rectly (by changing the composition or activity of theintestinal microflora), influence the body’s immunefunction, but the mechanism is not fully understood.LAB can affect function of immune cells and activa-tion of macrophages and “natural killer” (NK) cellsby LAB have been reported. Yogurt cultures are re-ported to produce � -interferon by T-cells. LAB alsostimulate cytokines as represented by TNF-� (tumornecrosis factor) and IL-6 and IL-10 (interleukines 6or 10). Translocation of small number of ingestedbacteria via M cells to the Peyer’s patches of the gutassociated lymphoid tissue in the small intestine isclaimed to be responsible for enhancing immunity.Ingestion of yogurt has been reported to stimulatecytokine production in blood cells, and activation ofmacrophages and NK cells has been observed.

Fermented milks have been reported to inhibitinfections in mice caused by Klebsiella pneumo-niae. Mice fed with fermented milks were healthierand lived longer. In a human clinical study, feedingyogurt starter bacteria in yogurt increased the serumlevel of � -interferon and NK cell count.

Another potential mechanism of immune systemstimulation involves the changes in fecal enzymessuch as �-glucuronidase thought to be involved incolon carcinogenesis. Nitrate is metabolized by ni-trate reductase. Yogurt bacteria are reported to havenitrate reductase activity. Nitrate is an intermediateproduct in the formation of N-nitroso compounds,which are highly carcinogenic (Goldin and Gorbach,1984).

HEALTH BENEFITS OF NORDICFERMENTED MILKSNordic fermented milks are suggested to play im-munomodulating role. This is primarily due to anti-genic structures of the surface of lactococci. The pri-mary starter culture, Lc. lactis ssp. cremoris in viiliis reported to stimulate secretion of immunoglobu-lins, mainly IgM. Proliferation of T lymphocytes wasalso observed with this strain. This organism has alsoshown induction of cytotoxicity of peritoneal murinemacrophages against sarcoma cells. Intraperitonealinjection (at a dose of 10 mg/kg) of freeze-dried cellpreparation was reported to retard the growth of as-citic and solid sarcomas in mice. This effect has alsobeen reported for freeze-dried preparations of langfil(at a dose of 50 mg/kg) and ropy yogurt (at a dose of100 mg/kg). Lc. lactis ssp. cremoris is also reportedto reduce mutagenic effect of nitrosated beef extractby 40% as determined by Ames test using Salmonellatyphimurium. Lc. lactis ssp. cemoris, which is also re-ported to lower serum cholesterol in rats. Lactococciisolated from Nordic fermented milks are reported toinhibit common pathogens such as Staphylococcusaureus and Escherichia coli (Kitazawa et al., 1991)

Health Effects of Kefir

Kefir is reported to inhibit the growth of pathogenicand spoilage microflora including Escherichia coliO-157, Salmonella and Listeria by bacteriocin pro-duced by LAB isolated from kefir grains. Oral ad-ministration of water-soluble fraction of kefir grainssimulated antibody production and reduced tumorsize in mice. Reduction in lactose-malabsorption re-lated symptoms is also reported in mini-pigs. The


organisms in kefir grains are reported to assimilatecholesterol (Kitazawa et al., 1991).

Health Benefits of Bio-Yogurt

A number of health benefits are claimed in favor ofproducts containing probiotic organisms such as Lb.acidophilus and Bifidobacterium spp. It is recom-mended that the probiotic products contain at least106 viable cells of Lb. acidophilus and Bifidobac-terium spp. per gram of product. It is also recom-mended that the products must be consumed on a reg-ular basis. The dosage level should be at least 100 gso that the level of organisms consumed would be108 or 109 (Shah, 2000). Health benefits of probioticbacteria include antimicrobial properties, improve-ment in lactose metabolism, antimutagenic proper-ties, anticarcinogenic properties, reduction in serumcholesterol, antidiarrhoeal properties, immune sys-tem stimulation, improvement in inflammatory boweldisease, and suppression of Helicobacter pylori in-fection. There is sufficient evidence to support theview that oral administration of Lactobacilli and bi-fidobacteria is able to restore the normal balance ofmicrobial populations in the intestine (Armuzzi et al.,2001; Cats et al., 2003).

REFERENCESArmuzzi A, Cremonini F, Bartolozzi F, Canducci F,

Candelli M, Ojetti V, Cammarota G, Anti M, DeLorenzo A, Pola P, Gasbarrini G, Gasbarrini A.2001. The effect of oral administration ofLactobacillus GG on antibiotic-associatedgastrointestinal side-effects during Helicobacterpylori eradication therapy. Aliment Pharmacol.Therapy 15(2):163–169.

Bourlioux P, Pochart P. 1988. Nutritional and healthproperties of yogurt. World Reviews of Nutritionand Dietetics 56:217–258.

Buttriss J. 1997. Nutritional properties of fermentedmilk products Int. J. Dairy Technol. 50(1):21–27.

Cats A, Kulpers EJ, Bosschaert MA, Pot RG,Vandenbroucke-Gauls CM, Kusters JG. 2003. Effectof frequent consumption of Lactobacillus casei—containing milk drink in Helicobacter pylori—colonised subjects. Aliment. Pharmacol. Therapy17(3):429–35.

Cenci G, Rossi J, Throtta F, Caldini G. 2002. Lacticacid bacteria isolated from dairy products inhibitgenotoxic effect of 4-nitroquinoline—1—oxide inSOS-chromotest. Syst. Appl. Microbiol. 25(4):483–90.

Dave R, Shah NP. 1997. Characteristics of bacteriocinproduced by L . acidophilus LA-1. Intern. Dairy J.7:707–715.

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Goldin BR, Gorbach SL. 1977. Alterations in faecalmicroflora enzymes related to diet, age, lactobacillussupplement and dimethyl hydrazine. Cancer 40:2421–2426.

Goldin BR, Gorbach SL. 1984. The effect of milk andLactobacillus feeding on human intestinal bacterialenzyme activity. Amer. J. Clin. Nutr. 39:756–761.

Gomes AMP, Malcata FX. 1999. Bifidobacterium spp.and Lactobacillus acidophilus: biological,biochemical, technological and therapeuticalproperties relevant for use as probiotics. Trends inFood Sci. Technol. 10:139–157.

Goodenough ER, Kleyn DH. 1976. Influence of viableyogurt microflora on digestion of lactose by the rat.J. Dairy Sci. 59:601.

Gurr MI. 1987. Nutritional aspects of fermented milkproducts. FEMS Microbiology Reviews46:337–342.

Holm F. 2003. Gut health and diet: the benefits ofprobiotic and prebiotics on human health. TheWorld of Ingredients. 2:52–55.

IDF. 1984. Fermented milks. International DairyFederation Bulletin No. 179:16–32.

IDF. 1991. Cultured dairy products in human nutrition.Int. Dairy Fed..Bulletin No. 225:1–32.

Kitazawa H, Toba T, Itoh T, Kumono N, Adachi S,Yamaguchi T. 1991. Antitumoral activity ofslime-forming, ecapsulated Lactococcus lactisssp. cremoris islolated from Scandinavian ropysour milk, ‘viili’. Animal Sci. Technol. 62(3):277–283.

Klaver FAM, Meer RVD. 1993. The assumedassimilation of cholesterol by lactobacilli andBifidobacterium bifidum is due to their bile saltdeconjugating activity. Appl. Environ. Microbiol.59:1120–1124.

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Mann GV, Spoerry A. 1974. Studies of a surfactant andcholesterolemia in the Massai. Amer. J. Clin. Nutr.27:464–469.

Onwulata CI, Ramkishan Rao D, Vankineni P. 1989.Relative efficiency of yogurt, sweet acidophilusmilk, hydrolysed-lactose milk, and a commerciallactase tablet in alleviating lactose maldigestion.Amer. J. Clin. Nutr. 49:1233–1237.

Orrhage K, Sillerstrom E, Gustafsson JA, Nord CE,Rafter J. 1994. Binding of mutagenic heterocyclicamines by intestinal and lactic acid bacteria.Mutation Research 311:239–248.

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Streptococcus thermophilus to infants in hospital forprevention of diarrhoea and shedding of rotavirus.Lancet 344:1046–1049.

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22Probiotics and Fermented Milks

Nagendra P. Shah

IntroductionTaxonomy of Lactic Acid BacteriaProbiotic BacteriaSelection Criteria for Probiotics

Genus LactobacillusGenus BifidobacteriumHealth Benefits of Lactobacillus acidophilus and Bifi-

dobacteriaAntimicrobial Activity and Gastrointestinal InfectionsEffectiveness Against DiarrhoeaImprovement in Lactose MetabolismAntimutagenic PropertiesAnticarcinogenic PropertiesReduction in Serum Cholesterol

Helicobacter pylori InfectionInflammatory Bowel DiseaseImmune System Stimulation

ConclusionsReferences

INTRODUCTIONLactic acid bacteria are widely used as starter cul-tures in fermentation of milk, vegetables, meats, bev-erages, and bakery products. Fermentation with lacticacid bacteria results in altered composition, improvedflavor, and prolonged shelf life. Lactic acid bacteriaare widespread in nature, and are found primarilyin the environment with high concentration of car-bohydrates, peptides and amino acids, and vitamins.Many lactic acid bacteria are normal inhabitants ofthe human body. The use of probiotic organisms suchas Lactobacillus acidophilus and Bifidobacteriumspp. in fermented milks became popular by the endof 1970s as a result of increased knowledge aboutthese organisms. New fermented products containingLb. acidophilus, Bifidobacterium spp., Lactobacillus

casei Shirota, Lactobacillus rhamnosus GG, and Lac-tobacillus reuteri have been developed in Europe.However, Lb. acidophilus and Bifidobacterium spp.are most commonly used as probiotics. It is estimatedthat over 70 products containing Lb. acidophilus andBifidobacterium spp. including yogurt, buttermilk,frozen desserts, and milk powder are produced world-wide. Probiotic organisms are also available as pow-ders, capsules, and tablets (Mittal and Garg, 1992). Anumber of health benefits are claimed in favor of pro-biotic organisms including antimicrobial properties,control of gastrointestinal disorders, improvement inlactose metabolism, anticarcinogenic properties, andreduction in serum cholesterol.

TAXONOMY OF LACTICACID BACTERIALactic acid bacteria are divided in several generabased on their ability to ferment specific sugars, tem-perature for growth, nutrient needs, sensitivity tosalt, and the presence of specific enzymes. Methodsfor classifying lactic acid bacteria in various gen-era, species, or strains have evolved from overallmorphology of the organisms and growth conditionsto physiological behavior and metabolic pathways.More accurate techniques for the classification of lac-tic acid bacteria involve molecular structure and ge-netic information such as DNA-DNA and DNA-RNAhomology analyses and sequencing of 16S rRNA(Klein et al., 1998; Stiles and Holzapfel, 1997).

Lactic acid bacteria can be divided into two gen-eral categories, according to their metabolic end-products. Homofermentative lactic acid bacteria pro-duce lactic acid as their principal end-product,whereas heterofermentative lactic acid bacteria

341




produce acetic acid, CO2, and ethanol in additionto lactic acid. Mesophilic lactic acid bacteria growbest at a temperature range of 25–30◦C, whereasthermophilic lactic acid bacteria prefer a temperaturerange of 40–44◦C.

Lactic acid bacteria are Gram-positive, usuallycatalase-negative and grow under microaerophilic tostrictly anaerobic conditions. The most importantgenera are: Lactobacillus, Lactococcus, Enteroco-coccus, Streptococcus, Pediococcus, Leuconostoc,and Bifidobacterium. Phylogenetically, Gram-positive bacteria are divided into two major branches.With the exception of bifidobacteria, all the above-mentioned genera of lactic acid bacteria have low(<50) %G + C (guanine plus cytosine) content. Nev-ertheless, Bifidobacterium shares similar physiologi-cal and biochemical properties as lactic acid bacteriaand some common ecological niches such as thegastro-intestinal tract. Species of these genera can befound in the gastrointestinal tract of man and animalas well as in fermented foods. Some physiologicalcharacteristics are of interest for their function as pro-biotics including survival in the gastrointestinal tract.This is based on their resistance to low pH and bile.

PROBIOTIC BACTERIAThe word “probiotic” originated from Greek mean-ing “for life”. Probiotics are defined as “live microbialfeed supplement, which beneficially affects the hostby improving its intestinal microbial balance”. Pro-biotics have been consumed in foods such as yogurtfor perhaps thousands of years, and while the “cul-tures” were thought to have beneficial effects, it wasnot until the 1900s that scientists began to investigatethe reasons for those benefits.

A number of genera of bacteria (and yeast) are usedas probiotics including Lactobacillus, Streptococcus,Leuconostoc, Pediococcus, Bifidobacterium, and En-terococcus; however, the main species believed tohave probiotic characteristics are L. acidophilus, Bifi-dobacterium spp., and Lb. casei. Members of the gen-era Lactobacillus and Bifidobacterium have a longand safe history in the manufacture of dairy prod-ucts and are also found as a part of gastrointestinalmicroflora. Probiotic bacteria with desirable proper-ties and well-documented clinical effects include Lb.johnsonii La1, L. rhamnosus GG (ATCC 53103), Lb.casei Shirota, Lb. acidophilus NCFB 1478, B. ani-malis Bb12 and Lb. reuteri.

Traditionally, probiotic organisms have beenadded to yogurt and other fermented foods; however,

recently, these organisms are incorporated in drinksand marketed as supplements including tablets, cap-sules, and freeze dried preparations. Today, there areover 70 bifidus- and acidophilus-containing productsproduced worldwide including sour cream, butter-milk, yogurt, powdered milk, and frozen desserts.More than 53 different types of milk products thatcontain probiotic organisms are marketed in Japanalone. The probiotics in Europe are very popular, buttheir use is largely restricted to the yogurt sector.

A probiotic yogurt may contain Lb. acidophilusonly or Lb. acidophilus and Bifidobacterium spp.(known as AB culture) or Lb. acidophilus, Bifidobac-terium spp. and Lb. casei (known as ABC culture)as probiotic organism in addition to the two yogurtstarters (Lactobacillus delbrueckii ssp. bulgaricusand Streptococcus thermophilus). The combined useof two (e.g., AB culture) or three (e.g., ABC culture)probiotic strains is common in commercial probioticfoods, as these strains are believed to act synergisti-cally on each other.

Thus, probiotic yogurts may contain up to five dif-ferent groups of bacteria. Unlike yogurt starter bacte-ria, probiotic organisms grow slowly in milk. The fer-mentation time for making yogurt is approximately4 hours with yogurt starter bacteria, whereas the fer-mentation time could be as long as 24 hours withprobiotic bacteria only. Thus the trend is to use yo-gurt bacteria as the main starter culture and probioticbacteria as an adjunct starter (Shah, 2000a).

SELECTION CRITERIA FORPROBIOTICSThere is increasing evidence that probiotics can ben-efit the human host by acting as a first line of defenceagainst disease-causing pathogens by improving theintestinal microflora.

The parameters for screening microorganisms forpotential valuable probiotic strains should include thefact that there is a necessity for the strain to be viableand metabolically active within the gastrointestinaltract. In addition, it is important that viability of theorganisms and stability of the desirable characteris-tics of the strain can be maintained during commer-cial production as well as throughout the shelf lifeof the product (Gilliland, 2003). To have probioticstrains with predictable and measurable health bene-fits, a concerted effort for strain selection is required.Common criteria used for selecting probiotic bacteriaare shown in Table 22.1.

22 Probiotics and Fermented Milks 343

Table 22.1. Criteria Used for Selecting Probiotic Bacteria

Genera of human originNontoxic and nonpathogenicResistant to acid, bile, and oxygenProduction of antimicrobial substances and antagonistic toward pathogenic bacteriaAbility to adhere to intestinal mucosaColonization potential in the human gastrointestinal tractDemonstrable efficacyImmunomodulatoryAble to withstand technological processes and remain viable throughout the shelf lifeViability at high populations, preferably at 106−108

Source: Adapted from Salminen and Ouwehand, 2003; Gilliland, 2003.

Genus Lactobacillus

In 1909, Moro was the first scientist to isolate fac-ultative anaerobic rods from the faeces of breast-fed infants, which he called as Bacillus acidophilus.The name of Lb. acidophilus has been derived from“acidus” meaning “acid” and “philus” meaning “lov-ing”. Lb. acidophilus contains mainly obligately ho-mofermenters whose major end-product is lacticacid, but a few are facultative heterofermenters. Theyoccur naturally in the gastrointestinal tract of humansand animals, in the human mouth and vagina, and insome traditional fermented milks, such as kefir. TheG + C content of their DNA is usually between 32and 53 mol%. They are either microaerophilic, aero-tolerant, or anaerobic and strictly fermentative. Glu-cose is fermented predominantly to lactic acid in ho-mofermenters, or to equimolar amounts of lactic acid,CO2 and ethanol in the case of heterofermenters. On

the basis of DNA-DNA homology, six major specieshave been identified: Lb. acidophilus, Lb. crispatus,Lb. amylovorus, Lb. gallinarum, Lb. gasseri, and Lb.johnsonii (Gopal, 2003).

At present, 56 species of the genus Lactobacillushave been recognized (Table 22.2).

Lb. acidophilus is the most commonly suggestedorganism for dietary use. Lb. acidophilus is a Gram-positive rod with rounded ends that occurs as singlecells, as well as in pairs or in short chains. The typicalsize is 0.6–0.9 �m in width and 1.5–6.0 �m in length.Lb. acidophilus is nonmotile and nonspore formingorganism. Most strains are microaerophilic or aner-obic, so the surface growth on solid media is gen-erally enhanced by anaerobiosis or reduced oxygenpressure and providing 5–10% CO2 in anaerobic jarsduring growth. The organisms require carbohydrates

Table 22.2. List of Species (by Alphabetical Order) of the Genera Lactobacillusa

Lactobacillus Species

L. acetotolerans L. curvatus L. intestinalis L. plantaruma

L. acidophilusa L. delbrueckii L. jenseniia L. reuteria

L. alimentarius L. farciminis L. johnsonii L. rhamnosusa

L. amylophilus L. fermentuma L. kefir L. ruminisL. amylovorus L. fructivorans L. kefiranofaciens L. sakeL. avarius L. fructosus L. malefermentans L. salivarusa

L. bifermentans L. gallinarum L. mali L. sanfranciscoL. brevisa L. gasseria L. minor L. sharpeaeL. buchneria L. graminis L. murinus L. suebicusL. casei ssp. caseia L. halotolerans L. orisa L. vaccinostercusL. collinoides L. hamsteri L. parabuchneria L. vaginalisa

L. confuses L. helveticus L. paracaseia L. viridescensL. coryniformis L. hilgardii L. pentosusL. crispatusa L. homohiochii L. pontis

aSpecies isolated from human sourcesSource: Adapted from Sgorbati et al., 1995; Gomes and Malcata, 1999.


as energy and carbon source as well as nucleotides,amino acids, and vitamins. Most strains can fermentcellobiose, fructose, galactose, glucose, lactose, mal-tose, mannose, salicin, sucrose, and aesculine. Lb.acidophilus utilizes sucrose more effectively thanlactose. The glucose moiety is metabolized via theEmbden-Meyerhof-Parnas pathway with lactic acidas essentially the sole end product in homolactics.Supplementation with manganese, oleic acid, estersespecially Tween 80, are stimulatory or essential formost species. Therefore, these compounds are in-cluded in MRS medium. Acetaldehyde, a carbonylflavoring molecule, also results from metabolism oflactose. Growth of Lb. acidophilus occurs at as highas 45◦C; however, the optimum growth temperatureis between 35◦C and 40◦C. The organisms grow inslightly acidic media at pH of 6.4–4.5. Growth ceaseswhen pH of 4.0–3.6 is reached. Acid tolerance of or-ganisms varies from 0.3% to 1.9% titratable acidity,with an optimum pH at 5.5–6.0 (Curry and Crow,2003; Shah, 1997).

Lb. acidophilus tends to grow slowly in milk, lead-ing to the risk of overgrowth of undesirable microor-ganisms. Ironically, most strains of Lb. acidophilusdo not survive well in fermented milk due to the lowpH, and it is difficult to maintain large numbers in theproduct. Lb. acidophilus grows poorly in milk evenas they show a high level of �-galactosidase activity.This is partly related to low concentration of smallpeptides and free amino acids in milk, which wouldbe insufficient to support the bacterial growth.

Isolation and Enumeration

MRS agar can be used as a nonselective medium forisolation of Lb. acidophilus from pure cultures. How-ever, for selection of Lb. acidophilus from a mixedpopulation of different genera of microorganisms, aselective medium must be employed. MRS mediumsupplemented with bile will assist growth of Lb. aci-dophilus. MRS agar at pH 5.2 can also be used to sup-port the growth of Lb. acidophilus. Most media thatsupport the growth of Lb. acidophilus also support thegrowth of Lb. casei and Lb. rhamnosus. Basal agar(BA; 10 g trypton, 10 g Lablemco powder, 5 g yeastextract, 1 g Tween 80, 2.6 g K2HPO4, 5 g sodiumacetate, 2 g tri-ammonium citrate, 2 g MgSO4.7H2O,0.05 g MnSO4.4H2O, 12 g bacteriological agar, and 1liter of distilled water)—sorbitol agar, BA-mannitolagar and BA-esculin agar can be used for selectiveenumeration of Lb. acidophilus in presence of Lb.casei and Lb. rhamnosus. Similarly, MRS-maltose

agar can be used as a selective medium in presenceof these organisms. Lb. acidophilus prefers anaero-bic conditions and growth is stimulated in agar un-der a standard anaerobic environment of 5% oxygen,85% nitrogen, and 10% carbon dioxide. BA-sorbitolagar can be used for enumerating L. acidophilusfrom dairy foods containing Lb. delbrueckii ssp.bulgaricus, Str. thermophilus, and Bifidobacteriumspp. For further details on isolation and enumerationof Lb. acidophilus, see Dave and Shah (1996) andTharmaraj and Shah (2003).

Genus BIFIDOBACTERIUM

Bifidobacteria are normal inhabitants of the humangastrointestinal tract. Recent in vivo scientific studiesusing animals or human volunteers have shown thatconsumption of live bifidobacteria have an effect onthe gut microflora. Selected strains survive stomachand intestinal transit and reach the colon in abundantnumbers. Newborns are colonized with bifidobacte-ria within days after birth and the population appearsto be relatively stable until advanced age, then thepopulation declines. However, diet, antibiotics, andstress are reported to influence the population of bi-fidobacteria in the intestines.

Bifidobacteria were first isolated from feces ofbreast fed infants by Tissier in 1899–1900. He de-scribed it as rod-shaped, nongas-producing anaero-bic microorganisms with bifid morphology, which hetermed Bacillus bifidus. Bifidobacteria are generallycharacterized as Gram-positive, nonspore forming,nonmotile, and catalase-negative anaerobes. Theyhave various shapes including short curved rods,club-shaped rods, and bifurcated Y-shaped rods. Bi-fidobacteria are anaerobes with a special metabolicpathway, which allows them to produce acetic acidin addition to lactic acid. Acetic acid and lactic acidare formed primarily in the molar ratio of 3:2. Theyare fastidious organisms and have special nutritionalrequirements, thus often these bacteria are difficultto isolate and grow in the laboratory (Shah, 1997;2002).

The taxonomy of bifidobacteria has changed con-tinuously since they were first isolated. They havebeen assigned to the genera Bacillus, Bacteroides,Nocardia, Lactobacillus, and Corynebacterium, be-fore being recognized as separate genera in 1974.All members of genus Bifidobacterium contain>50 mol% G + C, whereas Lactobacilli contain<50 mol% G + C in DNA. Based on the mol%G + C contents, all lactic acid producers have been


Table 22.3. List of Species (by Alphabetical Order) of the Genera Bifidobacteriuma and theirmol% G + C contents

Bifidobacterium sp. Mol% G + C Bifidobacterium sp. Mol% G + C

B. adolescentisq 58.9 B. indicum 60.0B. angulatuma 59.0 B. infantisa 60.5B. animalis 60.0 B. longuma 60.8B. asteroides 59.0 B. magnum 60.0B. bifiduma 60.8 B. mericicum 59.0B. boum 60.0 B. minimum 61.6B. brevea 58.4 B. pseudocatenulatuma 57.5B. catenulatuma 54.0 B. pseudolongum 59.5B. choerinum 66.3 B. pullorum 67.5B. coryneformes – B. ruminatium 57.0B. cuniculi 64.1 B. saeculare 63.0B. dentiuma 61.2 B. subtile 61.5B. gallicum 61.0 B. suis 62.0B. gallinarum 65.7 B. thermophilum 60.0B. globosuma 63.8

aSpecies isolated from human speciesSource: Adapted from Sgorbati et al., 1995; Gomes & Malcata, 1999.

allocated into two divisions: Clostridium and Acti-nomycetes. The Actinomycetaceae family consistsof five genera: Bifidobacterium, Propionibacterium,Microbacterium, Corynebacterium, and Brevibac-terium. Presently, there are 29 species in the genus Bi-fidobacterium (Table 22.3), 14 of which are isolatedfrom human sources (i.e., dental caries, faeces, andvagina), 12 from animal intestinal tracts or rumen,and three from honeybees. Bifidobacterium speciesfound in humans are: B. adolescentis, B. angulatum,B. bifidum, B. breve, B. catenulatum, B. dentium,B. infantis, B. longum, and B. pseudocatenulatum.B. breve, B. infantis, and B. longum are found in hu-man infants. B. adolescentis, and B. longum are foundin human adults (Shah and Lankaputhra, 2002).

Bifidobacteria are saccharolytic organisms andproduce acetic acid and lactic acid without generationof CO2. All bifidobacteria from human origin are ableto utilize glucose as well as galactose, lactose and,usually, fructose as carbon sources. Bifidobacteriumspp. are also able to ferment complex carbohydrates.The substrates fermented by the largest number ofspecies are: D-galactosamine, D-glucosamine, amy-lose and amylopectin. Fructose-6-phosphate phos-phoketolase is the characteristic key enzyme, whichis the most direct and reliable test for assigning anorganism to the genus Bifidobacterium.

The optimum pH for the growth of bifidobacteriais 6.0–7.0, with virtually no growth at pH 4.5–5.0

or below or at pH 8.0–8.5. Optimum growth occursat a temperature of 37–41◦C, maximum growth isat 43–45◦C, while minimum growth temperature is25–28◦C.

The main probiotic organisms that are currentlyused worldwide belong to the genera Lactobacillusand Bifidobacterium and are shown in Tables 22.4 and22.5, whereas the leading commercial probiotic lac-tobacilli and bifidobacteria are shown in Table 22.6.

Strains with peer reviewed published evidencefrom human clinical trials are shown in Table 22. 7.

A limited number of investigations have also beencarried out into the potential properties of genera in-cluding Pediococcus, Leuconostocs, and Propioni-bacterium and Enterococcus faecium. E. faecium ismore pH stable than L. acidophilus and produces bac-teriocins against some enteropathogens. These prop-erties make this organism attractive as a probiotic.

It is obvious from published reviews that fourstrains with the most published clinical data are Lb.rhamnosus GG, Lb. casei Shirota, B. animalis Bb-12,and Saccharomyces cerevisiae Boulardii.

Isolation and Enumeration

Bifidobacteria are fastidious organisms. MRS agarcan be used as a nonselective medium for isola-tion of Bifidobacterium spp. MRS-NNLP (nalidixicacid, neomycin sulfate, lithium chloride, and


Table 22.4. Lactobacilli Used as Probiotic Cultures

Species Strains

L. acidophilus LA-1/LA-5 (Chr. Hansen)L. acidophilus NCFM (Rhodia)L. acidophilus Johsonii La1 (Nestle)L. acidophilus DDS-1 (Nebraska Cultures)L. acidophilus SBT-2062 (Snow Brand Milk Products)L. bulgaricus Lb12L. lactis L1A (Essum AB)L. casei Immunitas (Danone)L. plantarum 299v, Lp01L. rhamnosus GG (Valio)L. rhamnosus GR-1 (Urex Biotech)L. rhamnosus LB21 (Essum AB)L. reuteri SD2112/MM2) (Biogaia)L. rhamnosus 271 (Probi AB)L. plantarum (Probi AB)L. reuteri (also known as MM2) SD2112L. casei Shirota (Yakult)L. paracasei CRL 431 (Chr. Hansen)L. fermentum RC-14 (Urex Biotech)L. helveticus B02Source: Adapted from Krishnakumar and Gordon, 2001; Holm, 2003.

paramomycin sulfate) agar is selective medium forcounting bifidobacteria. Bifidobacteria can be selec-tively enumerated from dairy foods containing Lb.delbrueckii ssp. bulgaricus, Str. Thermophilus, andLb. acidophilus using MRS-NNLP agar. Cysteine(0.05%) must be added to the medium. Cysteine pro-

vides essential nutrient and lowers redox-potential.Incubation conditions are anaerobic environment at37◦C for 72 hours. When L-cysteine is not present inthe media, bifidobacteria either do not grow or formpin-point colonies. Bifidobacteria do not grow underaerobic conditions. For further details on isolation

Table 22.5. Bifidobacteria Cultures Used as Probiotic Cultures

Species Strains

B. adolescentisB. longum BB536 (Morinaga Milk Industry)B. longum SBT-2928 Snow Brand Milk Products)B. breve YakultB. bifidus Bb-11B. lactis (reclassified as B. animalis) Bb-12 (Chr. Hansen)B. essensis Danone (Bioactivia)B. lactis Bb-02B. infantis ShirotaB. infantis Immunitas (Danone)B. infantis 744B. infantis 01B. laterosporus CRL 431B. lactis LaftiTM, B94 (DSM)B. longum UCC 35624 (UCCork)B. lactis DR10/HOWARU DaniscoSource: Adapted from Krishnakumar and Gordon, 2001; Holm, 2003; Playne et al., 2003.


Table 22.6. Leading Commercial Probiotic Lactobacilli and Bifidobacteria.

Lactobacillus Strain Manufacturer

L. acidophilus La-5 (Chr. Hansen, Denmark)L. acidophilus NCFM (Rhodia, USA)L. casei Shirota (Yakult, Japan)L. acidophilus Johsonii La1 (Nestle, Switzerland)L. plantarum 299v (Probi, Sweden)L. reuteri MM2 (Biogaia, Sweden and USA)L. rhamnosus GG (Valio, Finland)BifidobacteriumB. lactis (reclassified as Bb-12 (Chr. Hansen, Denmark)

B. animalis)B. longum BB536 (Morinaga Milk Industry, Japan)B. longum SBT-2928 (Snow Brand Milk Products, Japan)B. breve (Yakult, Japan)B. lactis LaftiTM, B94 (DSM, Australia)B. longum UCC 35624 (UCCork, Ireland)B. lactis DR10/HOWARU (Danisco, Denmark)Source: Adapted from Krishnakumar and Gordon, 2001; Holm, 2003; Playne et al., 2003.

and enumeration of bifidobacteria, see Dave and Shah(1996) and Tharmaraj and Shah (2003).

Health Benefits of LACTOBACILLUSACIDOPHILUS and Bifidobacteria

A number of health benefits are claimed in favorof products containing probiotic organisms. Someof the health benefits are well established, whileother benefits have shown promising results in animalmodels. However, additional studies are required inhumans to substantiate these claims. Health bene-fits imparted by probiotic bacteria are strain specific,and not species- or genus-specific. It is important tounderstand that no strain will provide all proposed

benefits, not even strains of the same species. Not allstrains of the same species will be effective againstdefined health conditions. The strains Lb. rhamnosusGG (Valio), Sacch. cerevisiae Boulardii (Biocodex),Lb. casei Shirota (Yakult), and B. animalis Bb-12(Chr. Hansen) have the strongest human healthefficacy data against management of lactose malab-sorption, rotaviral diarrhoea, antibiotic-associated di-arrhoea, and Clostridium difficile diarrhoea (Playneet al., 2003) (Table 22.8).

Health benefits of probiotic bacteria include an-timicrobial activity and gastrointestinal infections,improvement in lactose metabolism, antimutagenicproperties, anticarcinogenic properties, reduction inserum cholesterol, antidiarrhoeal properties, immune

Table 22.7. Strains with Peer Review Published Evidence from Human Clinical Trials.

Lactobacillus rhamnosus GG (Valio)Lactobacillus casei Shirota (Yakult)Lactobacillus acidophilus NCFM (Rhodia)Lactobacillus plantarum 299v (ProViva)Lactobacillus reuteri (Biogaia)Lactobacillus acidophilus Johnsonii La1 (Nestle)Lactobacillus acidophilus La5 (Chr. Hansen)Bifidobacterium animalis Bb 12 (Chr. Hansen)Bifidobacterium longum BB536 (Morinaga)Bifidobacterium breve (Yakult)Enterococcus faecium SF68 (Cemelle)Saccharaomyces cerevisiae Boulardii (Biocodex)Source: Adapted from Krishnakumar and Gordon, 2001; Holm, 2003; Playne et al., 2003.


Table 22.8. Reported Studies and Proven Effects of Some Currently Available Probiotics

Strains Reported Effects in Clinical Studies Scientifically Established Effects

L. johnsonii LJ1 Adherence to human intestinal cells,balances intestinal flora

Mucosal adherence, immune enhancement

L. acidophilusNCFM

Lowering of fecal enzyme activity,improvement in lactose absorption,production of bacteriocin

Alleviation of lactose malabsorption

L. rhamnosus GG Prevention of antibiotic associateddiarrhea and rotavirus diarrhea,Shortening of duration of rotavirus

Management of Clostridium difficilediarrhea, prevention of acute diarrhea,prevention of antibiotic diarrhea, reductionin fecal enzyme associated diarrhea

L. casei Shirota Prevention of intestinal disturbance;balancing intestinal flora; loweringof fecal enzyme activity

B. animalis Bb12 Treatment of rotavirus diarrhea;balancing intestinal flora

Shortening of duration of rotavirus

L. reuteri Colonizing the intestinal tract inanimal studies Shortening ofduration of rotavirus diarrhoea,immune enhancement

Shortening of duration of rotavirus

S. cerevisiae(boulardii)

Prevention of antibiotic associateddiarrhoea; treatment of C. difficilecolitis

Prevention of antibiotic associateddiarrhoea

E. faecium (Gaio) Reduction in cholesterol Reduction in cholesterolSource: Adapted from Fonden et al., 2000; Salminen and Ouwehand, 2003; Plyne et al., 2003.

system stimulation, improvement in inflammatorybowel disease, and suppression of Helicobacter py-lori infection (Kurmann and Rasic, 1991). Thereis sufficient evidence to support the view that oraladministration of Lactobacilli and bifidobacteriais able to restore the normal balance of micro-bial populations in the intestine (Ouwehand et al.,1999).

Antimicrobial Activity andGastrointestinal Infections

Probiotic bacteria produce lactic acid and acetic acid,hydrogen peroxide, and bacteriocins as antimicrobialsubstances. The antimicrobial substances are pro-duced to suppress the multiplication of pathogenicand putrefying bacteria. Lactic acid and acetic acidare the main organic acid produced. Other acids pro-duced in small quantities include citric acid, hippuricacid, orotic acid, and uric acid. Lactic and aceticacids account for over 90% of the acids produced.Lowering of pH due to lactic acid or acetic acidproduced by these bacteria in the gut has a bacte-riocidal or bacteriostatic effect. Both bifidobacteriaand Lb. acidophilus show antagonistic effects to-

ward enteropathogenic Escherichia coli, Salmonellatyphimurium, Staphylococcus aureus, and Clostrid-ium perfringens. Lb. acidophilus produces variousbacteriocins and antibacterial substances such as Lac-tocidin, Acidolin, Acidophilin, Lactacium-B, and in-hibitory protein (known as bacteriocin-like inhibitorysubstances; BLIS). Similarly, Bifidobacterium pro-duces Bifidolin and Bifilong, which inhibit severalpathogenic bacteria. Hydrogen peroxide producedby Lb. acidophilus is inhibitory to many pathogens.Preparations containing Enterococcus faecium havebeen used for treatment of acute enteritis and othergut disorders. Ent. faecium is found in the feces ofhealthy adults.

Two types of lactic acid, L(+) and D(−), are pro-duced during fermentation by lactic acid bacteria.Some species of bacteria including Lb. delbrueckiissp. bulgaricus and Lactococcus lactis produce onlyD(−) lactic acid, whereas some lactic streptococciand Lb. casei produce L(+) lactic acid. Lb. helveti-cus and Lb. acidophilus produce a racemic mixtureof L(+) and D(−) lactic acid. D(−) lactic acid isnot metabolised to pyruvic acid in the body due toa lack of D2-hydroxy acid dehydrogenase and thisresults in acidosis in neonatal infants. L(+) isomer


is completely harmless. Bifidobacteria and Lb. ca-sei produce L(+) lactic acid. Thus the lactic acidproduced by bifidobacteria and Lb. casei is easilymetabolised, while providing antimicrobial proper-ties (Shah, 1999).

Effectiveness Against Diarrhoea

One of the main applications of probiotics has beentreatment and prevention of diarrhoea. A major prob-lem associated with antibiotic treatment is appear-ance of diarrhoea, often caused by Clostridium dif-ficile. This organism is found in small numbers inthe healthy intestine; however, disruption of indige-nous microflora due to antibiotic treatment leads toan increase in their number and toxin production,which causes symptoms of diarrhoea. Treatment withmetonidazole or vancomycin is usually effective butrecurrences are common. Administration of exoge-nous probiotic is required to restore the balance offlora. Probiotics have proved to be useful as a prophy-lactic regimen with antibiotic-associated diarrhea, aswell as for treatment after onset of antibiotic induceddiarrhea. A daily dose of Lactobacillus GG has beenfound to be effective in termination of diarrhea. Stud-ies with a yeast preparation containing Sacch. cere-visiae Boulardii has also been effective in treatmentof Clost. difficile related colitis.

Rotavirus is one of the most common causes ofacute diarrhea in children worldwide. During diar-rheal stage of infection, the permeability of gut ep-ithelial cells is increased to intact proteins. Probioticsare claimed to shorten duration of rotavirus diarrheain children (Saavedra et al., 1994). The strongestevidence of a beneficial effect of defined strains ofprobiotics has been established using Lb. rhamno-sus GG and B. lactis Bb-12 (now reclassified as B.animalis Bb-12) for prevention and treatment of di-arrhea and acute diarrhea in children mainly causedby rotaviruses. Selected probiotic strains are also ef-fective against antibiotic-associated diarrhea. Certainprobiotic strains can inhibit the growth and adhe-sion of a range of enteropathogens. Studies haveindicated beneficial effects against pathogens suchas Salmonella enteriditis and Salm. typhimurium. B.longum SBT-2828 has shown inhibition of entero-toxigenic Escherichia coli. Mix of pediatric bev-erage containing B. animalis, Lb. acidophilus, andLb. reuteri has been found to be useful in the pre-vention of rotavirus diarrhoea (Guandalini et al.,2000).

Lb. rhamnosus GG has been reported to be more ef-fective in the treatment of rotavirus diarrhea as com-pared with preparations containing Str. thermophilusand Lb. delbrueckii ssp. bulgaricus. Lb. reuteri hasalso been effective in shortening the duration ofrotavirus diarrhea. It reduces the duration of diarrheain children suffering from rotavirus diarrhea. Treat-ment with Lactobacillus GG was associated with en-hancement of IgA- specific antibody-secreting cellsto rotavirus and serum IgA antibody level.

The mechanisms by which fermented dairy foodscontaining probiotics or culture containing milks re-duce the duration of diarrhea are unclear. One possi-ble mechanism is that probiotic bacteria may preventthe growth of pathogens by competing for the attach-ment sites by producing specific binding inhibitor orby production of antimicrobial substances. Probioticbacteria can also potentiate the immune response tointestinal pathogens.

There is also strong evidence that probiotic strainscan prevent traveller’s diarrhea (Hilton et al., 1997).Traveller’s diarrhea is caused by bacteria, particularlyenterotoxigenic E. coli. Several studies have beencarried out to assess the effects of probiotic prepa-rations as prophylaxis for traveller’s diarrhea; how-ever, the results have been conflicting. In one study,Danish tourists on a 2-week trip to Egypt, were givena mixture of live freeze-dried preparation of Lb. aci-dophilus, B. animalis, Lb. delbrueckii ssp. bulgari-cus and Str. thermophilus at a daily dose of 109 cfu.The administration of probiotic preparation reducedthe frequency of diarrhea. A similar study conductedwith Finnish tourists using lyophilized preparationof Lactobacillus GG has shown to reduce the occur-rence of traveler’s diarrhea.

Yogurt containing B. longum was found to be effec-tive in reducing the course of erythromycin induceddiarrhea. Antibiotic treatment disturbs the balance ofgastrointestinal flora leading to diarrhea. Fecal countsof Lactobacillus GG indicated that the organisms col-onized the intestine despite erythromycin treatment.Probiotic reparations containing 4 × 109 B. animalisBb-12 and Lb. acidophilus La-5 has shown similarresults when volunteers received ampicillin alongwith probiotic preparation. Recolonization with bi-fidobacteria as shown by an increase in their countsis reported with treatment with Lb. acidophilus La-5 and B. animalis Bb-12. A lower degree of colo-nization by Clost. difficile was also observed. Severalstudies have shown reduction in diarrhea in subjectstaking Sacch. cerevisiae Boulardii during the periodof antibiotic treatment.


Improvement in Lactose Metabolism

Relief of lactose maldigestion symptoms by probi-otics is probably the most widely accepted healthbenefits of probiotic organisms. Lactose malabsorp-tion is a condition in which lactose, the principalcarbohydrate of milk, is not completely hydrolysedinto its component monosaccharides, glucose andgalactose. Since lactose is cleaved into its constituentmonosaccharides by the enzyme �-D-galactosidase,lactose malabsorption results from a deficiency ofthis enzyme. Lactose malabsorbers often complain of“gastric distress” after consuming fresh, unfermentedmilk or milk products due to the formation of hydro-gen gas by microbial action on undigested lactosein the gut. The prevalence of lactose malabsorptionvaries depending on the ethnic origin of the popu-lation. It is common in China, Thailand, Japan, andAfrican and Australian aborigines, but less commonamong Caucasians. Temporary deficiency of �-D-galactosidase occurs in people suffering from diar-rhea (Shah, 1993; Shah et al., 1992).

The traditional cultures used in making yogurt (i.e.,Lb. delbrueckii ssp. bulgaricus and Str. thermophilus)contain substantial quantities of �-D-galactosidaseas compared with probiotic organisms, and the con-sumption of yogurt has been found to assist in allevi-ating the symptoms of lactose malabsorption (Shah,2000b). �-D-galactosidase is affected by bile. Be-cause bifidobacteria are resistant to bile, they mayhave a better chance of colonizing the gut and deliv-ering this enzyme to its site of action over an extendedperiod of time.

There is convincing evidence that lactose malab-sorbers suffer fewer symptoms with fermented dairyproducts. Yogurt or probiotic yogurt is tolerated wellby lactose malabsorbers. Factors other than the pres-ence of yogurt starter or probiotic bacteria are re-sponsible for better tolerance of lactose in lactosemaldigesters from fermented dairy foods. Reducedlevels of lactose in fermented products due to partialhydrolysis of lactose during fermentation is partlyresponsible for greater tolerance of yogurt. Auto-digestion of lactose intracellularly by bacterial �-D-galactosidase before reaching the intestine is an im-portant factor that improves digestibility of lactose(Onwulata et al., 1989). Slower gastric emptying ofsemisolid milk products such as yogurt is anotherfactor responsible for better absorption of lactose.Because of slower gastric emptying, small quantityof lactose is reached in the jejunum at a time and thereis more effective hydrolysis of lactose by indigenous

�-galactosidase located in the sides and tips of the vi-ili of the jejunum. Regular yogurt appears to be moreeffective than either pasteurized yogurt or buttermilk.Pasteurized yogurt is also tolerated well due to slowergastric emptying as the enzyme activity and starterbacteria are destroyed due to heat treatment (Shahet al., 1992).

McDonough et al. (1987) reported that the pres-ence of bacterial-derived �-galactosidase in yogurtcontributes to the in vivo degradation of lactose. Sig-nificantly lower breath hydrogen levels were reportedto produce following consumption of yogurt com-pared with milk or heated yogurt (Savaiano et al.,1984). A French group confirmed that viable cul-tures reached the duodenum and contained active �-galactosidase. The group confirmed the role of slowgastric emptying of semisolid milk foods in digestionof lactose in milk (Vesa et al., 1996).

Although, there are limited studies conducted onthe efficacy of bifidus products in management of lac-tose malabsorption, the effects of acidophilus milk inalleviation of lactose malabsorption have been thor-oughly researched (Gilliland, 1989; 1991).

Antimutagenic Properties

Antimutagenic effect of fermented milks hasbeen detected against a range of mutagens andpromutagens including 4-nitroquinoline-N’-oxide,2-nitrofluorene, and benzopyrene in various testsystems based on microbial and mammalian cells.However, antimutagenic effect might depend on aninteraction between milk components and the lac-tic acid bacteria. The mechanism of antimutagenic-ity of probiotic bacteria has not been clearly under-stood. It has been suggested that microbial bindingof mutagens to the cell surface could be a possi-ble mechanism of antimutagenicity (Orrhage et al.,1994). Probiotic strains have been associated with areduction in fecal enzymatic activities. A decreasein fecal and urinary mutagenicity as a result of con-sumption of Lb. acidophilus NCFB 1748 has been re-ported. Lactococcus spp. was ineffective. Similarly,reduction in fecal enzymatic activities including �-glucuronidase, azoreductase, and nitroreductase in-volved in mutagens activation with strains of probi-otics has been reported (Goldin and Gorbach, 1977;1984).

Lankaputhra and Shah (1998) studied the an-timutagenic activity of organic acids producedby probiotic bacteria against eight mutagensand promutagens including 2-nitroflourene (NF),


Aflatoxin-B (AFTB), and 2-amino-3-methyl-3H-imidazoquinoline (AMIQ). AFTB is a diet-relatedpotent mutagen produced by a fungal strain of As-pergillus flavus, which is a major food contaminantspecies prevalent in most Asian countries. AMIQ is aheterocyclic amine mutagen. This is a major mutagenformed in heat-processed beef in Western diets. TheTA-100 mutant of Salmonella typhimurium (His−)strain is used as a mutagenicity indicator organism.The mutagenicity test is carried out using the AmesSalmonella test. Among the organic acids, butyricacid showed a broad-spectrum antimutagenic activ-ity against all mutagens or promutagens studied. Livebacterial cells showed higher antimutagenicity thankilled cells against the mutagens studied. This sug-gests that live bacterial cells are likely to metabolisemutagens. Inhibition of mutagens and promutagensby probiotic bacteria appeared to be permanent forlive cells and temporary for killed cells. Killed cellsreleased mutagens and promutagens when extractedwith dimethyl-sulfoxide suggesting binding of mu-tagens to bacterial cells. The results emphasized theimportance of consuming live probiotic bacteria andof maintaining their viability in the intestine to pro-vide efficient inhibition of mutagens.

Anticarcinogenic Properties

There are several factors responsible for causes ofcolorectal cancer including bacteria and metabolicproducts such as genotoxic compounds (nitrosamine,heterocyclic amines, phenolic compounds, and am-monia). The consumption of cooked red meat espe-cially barbequed meat and low consumption of fiberare reported to play a major role in causing colorec-tal cancer. The colonic flora has been shown to be in-volved in colonic carcinogenesis. This effect is medi-ated by microbial enzymes such as �-glucuronidase,azoreductase, and nitroreductase, which convert pro-carcinogens into carcinogens. Lactic acid bacteriaand fermented products have potential anticarcino-genic activity and an inverse relationship betweenconsumption of fermented dairy foods and the riskof colorectal cancer has been found. Lactic acidbacteria suppress bacterial enzymes such as beta-glucuronidase, azoreductase, and nitroreductase, andreduce intestinal pH.

Experiments carried out in animal models showedthat certain strains of Lb. acidophilus and Bifidobc-terium spp. are able to decrease the levels of en-zymes such as �-glucuronidase, azoreductase, andnitroreductase responsible for activation of procar-

cinogens and consequently decrease the risk of tu-mor development. Several studies have shown thatpreparation containing lactic acid bacteria inhibitthe growth of tumor cells in experimental animalsor indirectly lower carcinogenicity by decreasingbacterial enzymes that activate carcinogenesis (Yoonet al., 2000). Animal studies using chemical car-cinogen 1,2-dimethyl hydrazine (DMH) have beencarried out. DMH is activated in the large intestineby �-glucuronidase. Addition of Lactobacillus to thediet has been reported to delay tumor formation. Inhuman studies indirect evidence of potential benefitsof probiotics have been obtained by monitoring muta-genic activity of human intestinal contents and feces.Lb. acidophilus 1748 and Lb. casei are reported todecrease mutagenic activity in feces caused by friedbeef (Lidbeck et al., 1991).

Short chain fatty acids produced by Lb. aci-dophilus and bifidobacteria are reported to inhibitthe generation of carcinogenic products by reduc-ing enzyme activities. When incubated in vitro with4-nitroquinoline-1-oxide (4NQO), some probioticstrains inhibited the genotoxic activity of 4NQO. Lb.casei was most effective, followed by Lb. plantarumand Lb. rhamnosus. Some strains of Lb. acidophilusand Lb. delbrueckii ssp.bulgaricus were not as effec-tive (Cenci et al., 2002).

The anticarcinogenic effect of probiotic bacteriais reported to be due to the result of removal ofsources of procarcinogens or the enzymes, whichlead to their formation. The proposed mechanismsinclude improvement in the balance of intestinal mi-croflora, normalized intestinal permeability (lead-ing to prevention or delaying of toxin absorption),and strengthening of intestinal barrier mechanisms.Mechanism of anticarcinogenicity also involves ac-tivation of nonspecific cellular factors such asmacrophages and natural killer cells via regulationof � -interferon production. Orally administered bi-fidobacteria are also reported to play a role in theincreasing of production of IgA antibodies and func-tions of Peyer’s patch cells (Singh et al., 1997).


There is a high correlation between dietary saturatedfat or cholesterol intake and serum cholesterol level.The level of serum cholesterol is a major factor forcoronary heart diseases. Elevated levels of serumcholesterol, particularly LDL-cholesterol have beenlinked to an increased risk for cardiovascular disease.Feeding of fermented milks containing very large


numbers of probiotic bacteria (∼109 bacteria/g) tohypercholesterolemic human subjects has resulted inlowering cholesterol from 3.0 to 1.5 g/liter. The roleof probiotic bacteria in reducing the serum choles-terol is not completely understood. Mann and Spoerry(1974) observed a decrease in serum cholesterol lev-els in men fed large quantities (8.33 liter/man/day)of milk fermented with Lactobacillus, possibly be-cause of the production of hydroxymethyl-glutarateby probiotic bacteria, which is reported to inhibithydroxymethylglutaryl-CoA reductases required forthe synthesis of cholesterol.

Probiotic bacteria are reported to deconjugate bilesalts. The deconjugated bile acid does not absorblipid as readily as conjugated counterpart, leadingto a reduction in cholesterol level. Lb. acidophilusis also reported to take up cholesterol during growthand this makes it unavailable for absorption into theblood stream (Klaver and Meer, 1993). A lower serumcholesterol concentration in rats fed with fermentedmilk containing Lb. acidophilus and bifidobacteriahas been observed.

Despite several studies, the reduction in serumcholesterol effect is still not considered an establishedeffect and double-blinded placebo-controlled humanclinical trials are needed to substantiate this claim.Similarly, mechanisms involved in reducing choles-terol level need to be clarified.

HELICOBACTER PYLORI INFECTIONHelicobacter pylori is a pathogenic bacterium, whichcauses peptic ulcers, type B gastritis, and chronicgastritis. H. pylori is present in the stomach as an op-portunistic pathogen without causing any symptoms(Armuzzi et al., 2001; Sakamato et al., 2001).

Antibiotic treatments can successfully eradicateH. pylori. However, antibiotics often cause side ef-fects and make the bacteria more antibiotic resis-tant. Probiotic organisms do not appear to eradicateH. pylori, but they are able to reduce the bacterialload in patients infected with H. pylori. Lb. john-sonii La1 and Lb. gasseri OLL2716 have been foundto reduce H. pylori colonization and inflammation(Felley et al., 2001). Similarly, Lb. casei Shirota, andLb. acidophilus are able to inhibit the growth of H.pylori. In an intervention study, 14 patients infectedwith H. pylori received Lb. casei Shirota (2 × 1010

cfu/day) fermented milk for 6 weeks. H. pylori bac-terial load was assessed by the breath urea test. Ure-olytic activity was reduced in 64% of the patients that

consumed fermented products containing probiotics,compared to 33% of the control group (Cats et al.,2003).

Inflammatory Bowel Disease

Inflammatory bowel disease (ulcerative colitis andCrohn’s disease) is related to the intestinal microflora.Inflammatory bowel disease affects up to 2 millionpeople worldwide. Symptoms of inflammatory boweldisease include a disturbance in bowel habits and mu-cosal inflammation. In the intestine of people withinflammatory bowel disease, the number of Lacto-bacillus and Bifidobacterium is lower, and that ofcoccoids and anaerobes are higher. Probiotics do notcure the disease. However, once patients are in re-mission through treatment with corticosteroids, someprobiotics can prolong the remission, thus reducingthe relapses and the use of corticosteroids. This im-proves the quality of life of patients.

Immune System Stimulation

The intestine is body’s largest immune organ and theintestinal microflora and the metabolic activity of in-testine is equivalent to that of the liver. Probioticsmay directly or indirectly (by changing the composi-tion or activity of the intestinal microflora) influencethe body’s immune function (Marteau et al., 1997).Yogurt and probiotic cultures produce � -interferonby T-cells. Probiotics also stimulate cytokines as rep-resented by TNF-� (tumor necrosis factor), and IL-6and IL-10 (interleukines 6 or 10). Immunomodula-tion by L. acidophilus and bifidobacteria, in particularIgA levels and the nonspecific immunity has been ob-served. It is important to note that probiotics may notnecessarily provide changes to immune system ofhealthy subjects. The mechanism for immunomod-ulation is not clearly understood. Translocation ofsmall number of ingested bacteria via M cells to thePeyer’s patches of the gut associated lymphoid tis-sue in the small intestine is claimed to be responsi-ble for enhancing immunity. Ingestion of probioticyogurt has been reported to stimulate cytokine pro-duction in blood cells and enhance the activities ofmacrophages.

CONCLUSIONSProbiotic products containing Lb. acidophilus, Bifi-dobacterium spp. and Lb. casei are becoming increas-ingly popular. Other probiotic organisms including


Ent. faecium, Sacch. cerevisiae Boulardii and Pro-pionibacterium have a potential to be used in pro-biotic products. Several health benefits have beenclaimed for probiotic bacteria; however, not all probi-otic bacteria are effective in providing health benefits.Proper strain selection and assessment of health ben-efits should be carried out before incorporating thesestrains for providing health benefits.

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Index

acceptance testing, 126“just right” scaling, 126hedonic scale, 126

Acetobacter spp. 301acidity, 121. See also pH

apparent, 121developed, 121real, 121titratable, 121, 182, 198,total, 121

acidophilus milk, 295, 296, 303, 304history, 303microbiology, 305production of sweet acidophilus milk,

304acidulants for fruit preparations, 159adulteration, 14affective test, 268, 269

focus group, 269, 270just right intensity, 274nine-point hedonic scale, 270

agitation, 15agitation of mix, 288analysis, 117

antimicrobial substances, 125brilliant black reduction test, 125delvotest, 125immunoassays, 125reference method, 125

analytical tests, 268anticarcinogenesis, 322antimicrobial substances, 125aseptic packaging, 146–147

Bacillus stearothermophilus, 125bactofugation, 9, 10bacteriophages, 90

characteristics, 96control of, 96–98effect on cultured product, 90

resistance mechanisms, 97–98starters, 90, 95types of, 96

balance tank, 20basic dairy processing principles, 73–88batch blending system, 8batch pasteurization, 8batch processes, 19beneficial microflora, 319bifidobacerium, 203, 344

isolation and enumeration, 344Bifidobacterium spp. 296, 305bioactive dairy ingredients, 312bioactive peptides, 316, 317boiling point, 38booster pump, 21brix, 159, 160, 165buffering capacity, 32bulgarian milk/buttermilk, 296, 306buttermilk, 329buttermilk, cultured, 279–284buttermilk powder, 172buttermilk sales trend, 11

Candida spp. 301casein fractions, 23, 314caseinates, 174catalase, 89category scale, 270cavitation, 3centrifugal, 4chakka, 14chemical tests, 122

flavorful substances, 122free fatty acids, 122

cholesterol, 20cirtate-fermenting bacteria, 125

clarification, 9cleaning, 43, 45code dating, 68

355



356 Index

Code of Federal Regulations, 57State preemption, 62

Codex standards, 68fermented milks, 68

additives, 70composition, 69cultures, 69

cold separation, 18coliform bacteria, 124colligative properties, 38

boiling point, 38freezing point, 38osmotic pressure, 38

color, milk, 31colors, 158, 165Committee on Sensory Evaluation of Dairy Products of

ADSA, 127composition and specifications of dairy ingredients,

167–168compositional, 117

acidity, titratable, 121fat, 118lactose, 120moisture, 119protein, 120solids, 119

concurrent, 7condensed milk, 172, 181contents, vcontinuous mixing systems, 9continuous pasteurization, 19contributors, viicooling, 6, 43, 44, 46, 286countercurrent, 7cream, 170cream separation, 9culture bacteria, 125culture containing milks, 295–310cultured buttermilk, 279–284, 329

key steps in manufacture, 280breaking, cooling and distribution, 282buttermilk starter culture, 281flavor, body and texture, 283milk supply, 280processing of milk, 281sensory evaluation, 283

cultured cream sales trend, 11cultured/sour cream, 285–294, 330

body and texture, 289early history, 285filled sour cream, 291flavor defects, 290manufacturing procedure, 288present standards, 287problems and corrections, 289sour cream products, 290

curd tension, 37

dahi, 7, 14, 90, 99, 295, 329history, 297microbiology, 299–300production, 298quality, 299

dairy foods production, United States, 5dairy ingredients, 167, 179

composition, 167, 180origin, 179performance in yogurt formulation, 168

dairy processing principles, 73–87overview of dairy processing equipment, 73

centrifugal operations, 81centrifugal pump, 74from farm to factory, 78heat transfer operations, 75homogenization, 84–86membrane technology, 86–87microbial transformation, 78mixing operations, 76positive displacement pump, 74–75separation, 77storage, raw milk, 79–80thermal processing systems, 82–84

density, 36, 122dermatitis, 322descriptive, 269

flavor profile, 269panelist selection, 269quantitative, 269scale usage, 269spectrum technique, 269texture profiling, 274training, 269

descriptive analysis, 126quantitative, 127

diacetyl, 92, 103–105diarrhea, prevention, 322difference, 269

attribute, 269paired comparison, 269ranking, 269

direct acidification, 287discrimination tests, 268

duo-trio, 268triangle, 268

drinkable yogurt, 270dual-stage, 23dye-binding, 120

electrical conductivity, 34electrochemical properties, 33Elliker’s lactic agar, 125Enterobacteriaceae, 124equipment, 51

3A sanitary standards, 52exoplysaccharide, 96, 106

Index 357

farm requirements, 43barns, 43milking, 43milking equipment, 43

fat free sour cream, 291fat globule size, 24fat globules, 170fat, tests for,

Babcock, 118ether extraction, 118Gerber, 118Mojonnier, 118

Roese-Gottlieb, 118fermentation, 10, 89fermentation vessels, 285–288fermented dairy packaging materials, 129–150fermented milks, 68, 271, 327, 295–310, 328

additives, 70composition, 69consumption, 8culture containing milks, 295–310cultures, 7, 9, 69, 329forms, 7middle east, 1, 331origin, 332packaging, 143–145Russia/eastern europe, 13, 330Scandinavia, 12, 330South Asia, 13, 330world production, 6, 7

filled sour cream, 291flavor defects, 290flavor, milk, 31flavor profile, 127flavorful substances, 122flavoring, 58, 59, 60, 63, 68flavors

fruit, 158preparation, 158vanilla, 158

flow controller, 20flow diversion valve, 21foaming, 37food additives, 62, 70Food and Drug Administration, 155, 159–160, 162, 190,

229, 230, 235, 247–248fortification, 323free-choice profile, 127free fatty acids, 122freezing point, 14, 38fruit preparation, 151–166

acidulants, 159banana, 154blueberries, 153cherry, 154flavors, 161formulation, 154

high intensity sweeteners, 155organic, 154, 160packaging, 164peaches, 153pectin, 157preservatives, 159processing, 160

aseptic process, 163hot kettle process, 162

quality checks, 165raspberries, 153raw materials, 152specifications, 155stabilizers, 156strawberries, 153sweeteners, 155

functional foods/disease prevention, 311–326beneficial microflora, 319bioactive dairy ingredients, 312, 316bioactive peptides, 317casein fractions, 314lactose, 317, 333lactose malabsorption, 335milk fat, 317, 334milk proteins, 313, 333

nutritional value, 315nutritional profile of yogurt, 314physiological effects, 316, 336probiotics, 318

anticarcinogenesis, 322, 336calcium, 321fortification, 323health benefits, 319immunomodulatory role, 322, 338manufacture, 322mode of action, 321physiological effects, 336physiologically active ingredients, 324prevention of diarrhea, vaginitis, dermatitis,

322production of enzymes and vitamins, 320reduction in serum cholesterol, 337

whey proteins, 314functional properties of milk constituents, 316

gelatin, 190Geotrichum candidum, 92, 301, 306Grade “A” PMO, 42, 57

labeling, 48standards, 49, 50, 51

grading, 265USDA quality approval rating, 265, 266

HACCP, 47prerequisite program, 47

Health Attributes of Yogurt and Fermented Milks,327–340. See also health benefits

358 Index

health benefits, 309, 319, 331, 347, 311–354anticarcinogenic, 351antimutagenic, 350beneficial effects, 333bioyogurt, 339Heliobacter pylori infection, 352immune system stimulation, 352irritable bowel disease, 352kefir, 338lactose metabolism, 333, 350nordic fermented milks, 338nutritional value, 331reduction in serum cholesterol, 351

heat effects/stability, 34, 35heat exchanger, 7heating, 6heterofermentative, 11High Temperature Short Time Pasteurization (HTST),

19history and consumption trends, 3holding tube, 21homofermentative, 11homogenization, 16, 171, 221, 287–289homogenizer, 23homogenizer valve, 24HPLC method, 121

imitation sour cream, 290immunomodulatory role, 322index, 355infrared method, 118ingredients, 179

acesulfame-K, 189aspartame, 156, 188condensed skim milk, 181dairy, 167, 179

composition, 180gelatin, 190gums and pectins, 192milk protein concentrate/ultrafiltered milk, 183neotame, 189nonfat dry milk, 181saccharin, 189stabilizers, 190, 191starch, 191sucralose, 189sweeteners

corn, 184high intensity, 156, 188nutritive, 184

whey solids, 182yogurt manufacture, 179–194

in-line standardization, 18international dairy federation, 119, 125international standards, 68interstate commerce, 62

judging, 265, 266

kefir, 9, 13, 92, 113, 295–296, 330description, 301grains, 296, 301–302history, 300microbiology, 301, 302production, 298–300quality, 301

keldermilk, 12kishk, 13kosher, 67koumiss, 9, 13, 92, 93, 295–296, 330

description, 303history, 302microbiology, 303production, 303quality, 305

laban, 331laban rayeb, 13labeling, 62, 249

flavors, 63information panel, 63ingredients, 64nomenclature, 58–61nutrient claims, 251nutrition, 65

daily reference values, 65, 250format, 67

principal display panel, 62serving size, 65standard of identity, 63

labneh, 7, 13, 270, 271laboratory analysis of fermented milks, 117–128lactic acid bacteria, 10

lactic acid bacteria, 125lactic acid bacteria, taxonomy, 341Lactobacillus, 108, 125, 296, 301, 305, 344

acidophilus, 109, 110, 296, 303, 304, 305brevis, 301casei subsp. casei, 99delbrueckii subsp. bulgaricus, 94, 99, 108,

109subsp. lactis, 99

helveticus, 99, 306kefir, 301kefiranfaciens, 301

Lactococcus, 99, 121, 125, 301lactis, 92

subsp. cremoris, 94, 99, 307subsp. lactis, 94, 99subsp. lactis (Cit+), 92, 93, 99, 106

lactose, 27, 28, 29, 317, 333�-lactose, 28�-lactose, 28

Index 359

lactose, tests for, 120HPLC method, 121polarimetric method, 12

langfil, 12lassi, 14Leuconostoc, 106, 125, 301line scale, 270lipolysis, 15Listeria monocytogenes, 94Long Time Low Temperature (LTLT), 19low fat sour cream, 290

MacConkey glucose agar, 124manufacture of various types of yogurt, 211–236. See also

yogurt, manufacturemastitis, 14membrane fouling, 26membrane technology, 25mesophilic microorganisms, 12microbiological tests, 124, 165. See also analysismicrofiltration (MF), 25microorganisms, 10microscope view of cultures, 108, 109, 110,

bifidobacteria, 203Lactobacillus acidophilus, 110, 202Lactobacillus delbrueckii spp. bulgaricus, 109,

201Streptococcus thermophilus, 108, 200yogurt culture, 109, 197

milk, 2, 167composition, 8, 18, 168, 170

breed, 170camel, 8constituents, 19donkey, 8genetic variant, 17goat, 8mare, 8season, 170sheep, 8species, 168yak, 8

composition, physical and processing characteristics,17

definition, 17functional properties, 316minor constituents, 30nutritional composition, 313physical characteristics, 31physical structure, 18–19

milk and milk based dairy ingredients, 167–178milk enzymes, 26

alkaline phosphates, 26lactoperoxidase, 26lipoprotein lipase, 26lysozyme, 26

plasmin, 26protease, 26

milk fat, 19, 317fatty acid profile, 20

milk fat globule, 20, 21membrane, 21, 22size distribution, 21

milk powder, 167composition, 167high heat, 168low heat, 168medium heat, 168whey protein nitrogen index, 167

milk pricing, 52classification, 54component, 52producer, 53

milk production, 3United States, 3, 4world, 3, 4, 8

milk protein concentrates, 172, 183milk proteins, 22, 23, 313, 314, 333, 334

biologically active, 26caseins, 23, 313composition, 23, 313functional aspects, 27isoelectric point, 24nutritional value, 315

milk safety, 41history, 41imports, 48inspections, 42

check rating, 43compliance ratings, 43

milk transportation, 43, 47delivery, 46hauler, 43shipping information, 43trucks, 43

minerals, 29, 318partition in milk, 30

mishti doi (dahi), 14mixing, 7Mycoderma spp. 303

nanofiltration (NF), 25National Conference on Interstate Milk Shipments, 42, 47,

49National Yogurt Association, 61, 67Newtonian fluids, 123nonfat dry milk, 181

composition, grade a, 182heat treatment classification, 183standards, 169, 182

nonfat milk solids, 120nuclear magnetic resonance (NMR), 119

360 Index

nutritional function, 332nutritional profile of yogurt, 314nutritional value, 331, 333

official methods of analysis, 119optical properties, 31organic, 160organoleptic, 165osmotic pressure, 38oxidation-reduction potential, 33

package in product distribution, 139–140packaging, 45, 47, 62, 129–150

biodegradability, 143definition, 130distribution, 130economics, 140environment, 142fundamentals, 130future trends, 147–148graphic design assessment, 140graphics, 130interactions with product, 137–139primary, 130recycling, 143regulation, 141secondary, 130structural design, 130technology, 130

packaging for yogurt and fermented milks, 143packaging levels, 133

converters, 133distributors, 134equipment, 134packagers, 134packaging developments, 134–136raw material suppliers, 133resources available, 136–137

packaging materials, 130glass, 131metal, 131oxygen-barrier materials, 133paper and paperboard, 131plastic, 132, 212polyester, 132polyethylene, 132

packaging sour cream, 286, 292containers, 286, 288hot packaging, 286

paring disc, 17pasteurization, 19, 46, 59, 61Petrifilm®, 124pH, 32, 121, 196, 204–206, 222, 227, 228, 223, 231, 233,

234indicator, 121

phage infection protein, 97

phage inhibitory media, 97phosphatase, 20phospholipids, 20physical properties of milk, 31, 122

acidity, titratable, 32buffering capacity, 32color, 31density, 36, 122electrical conductivity, 34electrochemical, 33flavor/off flavor, 31, 32, 33oxidation-reduction potential, 33refractivity, 31rheological, 123specific gravity, 122tests, 122–124thermal, 34water-holding capacity, 123

physiological effects, 309, 316, 336, 338, 351anticancer effects, 336, 351antimutagenic, 350diarrhea, 320, 349Heliobacter pylori infection, 352immune system stimulation, 338, 352irritable bowel disease, 352lactose metabolism, 350reduction in serum cholesterol, 337, 351

physiologically active ingredients, 324plasmids, 93–94plate heat exchangers, 12, 20Podoviridae, 96polarimetric method, 121positive displacement, 4positive lobe, 5precipitation, 24

alcohol, 24heat, 24polyvalent ion, 24

preface, ixpreference mapping, 270preference testing, 126preservatives, 60, 62, 70, 159pressure differential meter, 22principles of yogurt processing, 195–210probiotic milks, 295, 305, 318, 341

history, 305production, 305quality, 305

probiotics, 318, 319, 341, 343health benefits, 319, 320, 347manufacture, 322mode of health benefits, 321requirements for effective, 320

probiotics and fermented milks, 341–354beneficial effects of probiotics, 348. See also probiotics,

health benefits

Index 361

anticarcinogenic, 351antimicrobial activity, 348antimutagenic, 350diarrhea, effective against, 349

commercial probiotic strains, 347genus bifidobacterium, 344–346

isolation and enumeration, 345genus lactobacillus, 343, 346

isolation and enumeration, 344immune system stimulation, 352inflammatory bowel disease, 352lactose intolerance, 350Heliobacter pylori infection, 352physiological effects, 336probiotic bacteria, 342reduction in serum cholesterol, 351selection criteria, 342–343strains with peer reviewed clinical trials, 347

processing plants, 44construction, 44equipment, 45

processing principles, 2protein adsorption, 24protein tests, 120

dye-binding, 120infrared analyzer, 120

Kjeldahl, 120proteins, minimum requirements, 315

nutritional values, 315Pseudomonas spp. 93pumps, 3

quality assurance, yogurt plant, 247analytical tests, 254daily reference values, 250defects in yogurt and causes, 262–263Food and Drug Administration, 247food labeling, 249nutrient claims, 251–253nutrition facts label, 254quality control programs, 255–256

compositional analysis, 258criteria for live and active yogurt, NYA,

258–260microbiological, 258overrun, 258quality tests, 257sensory, 258shelf life test, 258viscosity, 258

regulatory obligations, 247specification program, 260

process and product specification, 261raw milk quality, 260

trouble shooting, 262–263weight control, 263

quality-based method, 267quality control, sensory tests for, 127

raw milk, 6reagents

ammonium hydroxide, 118ethanol, 118isoamyl alcohol, 118phenolphthalein, 121sulfuric acid, 118

Real Seal, 67reference method, 118reference samples/standards, 118, 120, 121, 127refractivity, 31refrigeration, 7, 21regulations for product standards and labeling,

57regulatory requirements for milk production, transportation

and processing, 41rennet coagulation, 24rennet (use in sour cream), 285, 288representative sample, 13restriction-modification, 97reverse osmosis (RO), 25rheological tests, 123

apparent viscosity, 123rupture stress, 123stress/strain curve, 123thixotrophic fluids, 123viscometer, 123

sampling, 49sediment, 14sensory analysis of yogurt, 270

attributes and references, 272judging criteria, 267quality terms, 268sensory analysis techniques, 265sensory descriptors, 271USDA quality guidelines, 266

sensory evaluation, 265, 273appearance, 267, 274consistency, 267flavor, 267, 273odor, 273taste, 273texture, 274

sensory tests, 126acceptance testing, 126basker’s tables, 126descriptive analysis, 126flavor thresholds, 127free-choice profiling, 127in quality control, 127preference testing, 126procrustes analysis, 127

362 Index

separation, 9serum cholesterol reduction, 322shelf stable packaging, 145–146

aseptic packaging, 146post-fill retorting, 145

shrikhand, 7, 14silo, 15single service containers, 45, 48single-stage, 23Siphoviridae, 96skyr, 7, 12, 297, 306, 331smoothing screen, 289solids, total, 119

forced-draft oven, 119hot air oven, 119infrared instrument, 119microwave oven, 119sand pan method, 119

sour cream, 285–294sour cream cultures, 285, 287, 288sour cream history, 285, 286, 287soy milk yogurt, 273specific gravity, 36, 122spiral wound, 26stabilizers, 58, 60, 70, 190, 286, 287, 289

in yogurt, 191pectin, 192

Standard Methods for the Examination of Dairy Products,118, 119, 120, 124, 125

standardization, 16standards, 287, 290standards of identity, 57

cream, 58cultured milk, 58milk, 58sour cream, 59stayed provisions, 59yogurt, 59

starch, native/modified, 191starter culture

characteristics, 101, 102definition of, 89factors affecting, 90, 93–98functions of, 90, 93, 100miscellaneous, 113production of, 112–113types of, 96yogurt and fermented milks, 89–116

Stokes law, 21Streptococcus, 106, 125

thermophilus, 94, 95, 106, 108surface activity, 37surface concentration of protein, 24sweet acidophilus milk

history, 303microbiology, 305

production, 304quality, 304

sweeteners, 58, 59, 60, 184high intensity, 188

acesulfame-K, 189alitame, 190aspartame, 188cyclamates, 190neotame, 189saccharin, 189stevia, 190sucralose, 189thaumatin, 190

nutritive, 184–188corn sweeteners, 186–187liquid sugar, 185maltodextrins, 186sucrose, 184

tanker, 13temperature, 43, 44, 46, 50, 51testing body, 286tests, 118–127. See also analysistexture attributes, 271

nonoral viscosity, 271, 272oral viscosity, 271, 273

thermal processing, 19thermal properties, 34threshold, 269titratable acidity, 58, 59, 61, 121tubular, 26turbulence, 23

ultrafiltered milk, 183ultrafiltration (UF), 25Universal Product Code, 68

vaginitis, 322viili, 7, 12, 92, 93, 297, 331

history, 306microbiology, 307

violet red bile agar, 124viscometer, 123viscosity, 36, 123vitamins, 30, 318volumetric flow, 5volumetric flow meter, 15

warm separation, 18water, 19water-holding capacity, 123whey, 51

solids, 182whey products, 173

microparticularted whey protein, 174

Index 363

whey powders, 173whey protein concentrates, 173

whey proteins, 25, 314bovine serum albumin, 25, 26, 314denaturation, heat, 220immunoglobulins, 25, 26, 314�-lactalbumin, 25, 314�-lactoglobulin, 25, 314proteose peptones, 25

yakult, 330yeast and mold counts, 124

ymer, 7, 12, 331yogurt, 90, 270, 271, 274, 328

acidification, 167bulk starter, 215effect of processing on starter, 91flavor, 167formulation, 224lactic agar, 125manufacture, 149, 211–236

blended/swiss-style, 223concentrated, greek, 232custard, 226drink/smoothies, 230, 231french style, 226frozen, 233fruit-flavored, 223heat-treated, 234, 235light, 226natural, 229nutritional profile, 314organic, 229, 230plain, 223plant cleaning and sanitizing, 237–246sundae style/fruit on the bottom, 226, 227,

228vanillawhips/mousse, 231

yogurt: fruit preparations and flavoring materials, 151–166.See also fruit preparations

yogurt, manufacture of various types, 211–236blended, 224

flow sheet diagram, 225classification, 216coagulation, 222concentrated/strained yogurt, 232–233cooling, 222custard style, 226french style, 226frozen, 233–234

flow sheet diagram, 234fruit flavored, 223fruit on the bottom style, 228general procedure for all yogurt types, 211greek style, 232

light, 226market, 214–219natural yogurt, 229organic, 229230plain, 223

flow sheet diagram, 224post culturing heat treatment, 234–235processes, 220pumping, 223smoothies, drinks, 230–231

flow sheet diagram, 232starter production, 212, 214stirring, 223styles and definitions, 214–217sundae style, 226–227vanilla flavored, 227whips, mousse, 231

yogurt market, 10, 11sales trends, 10, 218, 219segmentation, 11

yogurt microstructure, 170, 176fat globules, 170

yogurt packaging, 143–145, 212yogurt: plant cleaning and sanitizing,

237–246bacteriophage control, 244CIP cleaning, 242cleaning, 237COP cleaning, 241foam cleaning, 240manual cleaning, 239normal soils, 238

complex carbohydrates, 238fat, 238minerals, 239proteins, 238sugars, 238

phage control, 244sanitizing, 243special soils, 239

bacteriophage, 239biofilms, 239

yogurt processing, principles of,195–210

changes during processing, 206carbohydrates, 206cell mass, 207flavor compounds, 206lipids, 206post-fermentation, 208proteins, 206vitamins, 207

coagulation, 222cooling, 222heat treatment, 195, 220homogenization, 197, 221

364 Index

yogurt processing, principles of (continued )mix preparation, 195processing steps, 196, 220starters for yogurt, 197–198

characteristics, 199collaborative growth, 201factors for growth, 198–199inhibiting factors, 203strain selection, 204

yogurt properties, effect of milkbreed and genetic variants, 170mammalian species, 168

milk powders, 171seasonal variations in milk, 170

yogurt: sensory analysis, 265packaging, 211statistics, 214, 215styles and definition, 214, 216, 217types of, 91, 13

yogurt starters, production, 212yogurt texture, 167

homogenization, 171

zabady, 13, 331

manufacturing yogurt and fermented milks 2006 chandan

Food

fermented milks editor

dairy science

department of food science

blackwell publishing

white arun kilara

manufacture of yogurt

dairy foods

dairy packagi