advances in fruit processing technologies.pdf
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Contemporary Food EngineeringSeries Editor
Professor Da-Wen Sun, DirectorFood Refrigeration & Computerized Food Technology
National University of Ireland, Dublin(University College Dublin)
Dublin, Ireland http://www.ucd.ie/sun/
Advances in Fruit Processing Technologies, edited by Sueli Rodrigues and Fabiano Andre Narciso Fernandes (2012)
Biopolymer Engineering in Food Processing, edited byVnia Regina Nicoletti Telis (2012)Operations in Food Refrigeration, edited by Rodolfo H. Mascheroni (2012)Thermal Food Processing: New Technologies and Quality Issues, Second Edition,
edited by Da-Wen Sun (2012)Physical Properties of Foods: Novel Measurement Techniques and Applications,
edited by Ignacio Arana (2012)Handbook of Frozen Food Processing and Packaging, Second Edition,
edited by Da-Wen Sun (2011)Advances in Food Extrusion Technology, edited by Medeni Maskan and Aylin Altan (2011)Enhancing Extraction Processes in the Food Industry, edited by Nikolai Lebovka, Eugene
Vorobiev, and Farid Chemat (2011)Emerging Technologies for Food Quality and Food Safety Evaluation,
edited by Yong-Jin Cho and Sukwon Kang (2011)Food Process Engineering Operations, edited by George D. Saravacos and
Zacharias B. Maroulis (2011)Biosensors in Food Processing, Safety, and Quality Control, edited by Mehmet Mutlu (2011)Physicochemical Aspects of Food Engineering and Processing, edited by
Sakamon Devahastin (2010)Infrared Heating for Food and Agricultural Processing, edited by Zhongli Pan and Griffiths
Gregory Atungulu (2010) Mathematical Modeling of Food Processing, edited by Mohammed M. Farid (2009)Engineering Aspects of Milk and Dairy Products, edited by Jane Slia dos Reis Coimbra
and Jos A. Teixeira (2009)Innovation in Food Engineering: New Techniques and Products, edited by Maria Laura Passos
and Claudio P. Ribeiro (2009) Processing Effects on Safety and Quality of Foods, edited by Enrique Ortega-Rivas (2009)Engineering Aspects of Thermal Food Processing, edited by Ricardo Simpson (2009)Ultraviolet Light in Food Technology: Principles and Applications, Tatiana N. Koutchma,
Larry J. Forney, and Carmen I. Moraru (2009)Advances in Deep-Fat Frying of Foods, edited by Serpil Sahin and Servet Glm Sumnu (2009) Extracting Bioactive Compounds for Food Products: Theory and Applications,
edited by M. Angela A. Meireles (2009)Advances in Food Dehydration, edited by Cristina Ratti (2009)Optimization in Food Engineering, edited by Ferruh Erdogdu (2009) Optical Monitoring of Fresh and Processed Agricultural Crops, edited by Manuela Zude (2009)Food Engineering Aspects of Baking Sweet Goods, edited by Servet Glm Sumnu
and Serpil Sahin (2008)Computational Fluid Dynamics in Food Processing, edited by Da-Wen Sun (2007)
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CRC PressTaylor & Francis Group6000 Broken Sound Parkway NW, Suite 300Boca Raton, FL 33487-2742
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ContentsSeries Preface ...........................................................................................................viiSeries Editor ..............................................................................................................ixPreface.......................................................................................................................xiEditors .................................................................................................................... xiiiContributors .............................................................................................................xv
Chapter 1 Ultraviolet Light for Processing Fruits and Fruit Products ..................1
Tatiana Koutchma and Marta Orlowska
Chapter 2 High-Pressure Processing .................................................................. 37
Fabiano A.N. Fernandes
Chapter 3 Ultrasound Applications in Fruit Processing ..................................... 51
Fabiano A.N. Fernandes and Sueli Rodrigues
Chapter 4 Membrane Applications in Fruit Processing Technologies ................87
Sunando DasGupta and Biswajit Sarkar
Chapter 5 High-Intensity Pulsed Electric Field Applications inFruitProcessing ........................................................................... 149
Ingrid Aguil-Aguayo, Pedro Elez-Martnez, RobertSoliva-Fortuny, and Olga Martn-Belloso
Chapter 6 Applications of Ozone in Fruit Processing ...................................... 185
Patrick J. Cullen and Brijesh K. Tiwari
Chapter 7 Irradiation Applications in Fruit and Other Fresh ProduceProcessing ..........................................................................203
Rosana G. Moreira and Elena M. Castell-Perez
Chapter 8 Minimal Processing ......................................................................... 217
Ebenzer de Oliveira Silva, Maria do Socorro Rocha Bastos, NdioJairWurlitzer, Zoraia de Jesus Barros, and Frank Mangan
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vi Contents
Chapter 9 Enzyme Maceration ......................................................................... 235
Sueli Rodrigues
Chapter 10 Fruit and Fruit Juices as Vehicles for Probiotic Microorganisms and Prebiotic Oligosaccharides ........................................................ 247
Sueli Rodrigues
Chapter 11 Freeze Concentration Applications in Fruit Processing ................... 263
Merc Ravents, Eduard Hernndez, and Josep Maria Auleda
Chapter 12 Refrigeration and Cold Chain Effect on Fruit Shelf Life .................287
Jos Maria Correia da Costa and Edmar Clemente
Chapter 13 Vacuum Frying of Fruits Applications in Fruit Processing ............. 331
Rosana G. Moreira
Chapter 14 Edible Coatings ................................................................................ 345
Henriette Monteiro Cordeiro de Azeredo
Chapter 15 Thermal Treatment Effects in Fruit Juices ....................................... 363
Ftima A. Miller and Cristina L.M. Silva
Chapter 16 Effect of Fruit Processing on Product Aroma .................................. 387
Narendra Narain and Jane de Jesus da Silveira Moreira
Chapter 17 Sensory Evaluation in Fruit Product Development .......................... 415
Deborah dos Santos Garruti, HeliofbiaVirginia de Vasconcelos Facundo, Janice RibeiroLima, and Andra Cardoso de Aquino
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Series PrefaceContemporary Food Engineering
Food engineering is the multidisciplinary field of applied physical sciences combined with the knowledge of product properties. Food engineers provide the technological knowledge transfer essential to the cost-effective production and commercialization of food products and services. In particular, food engineers develop and design pro-cesses and equipment to convert raw agricultural materials and ingredients into safe, convenient, and nutritious consumer food products. However, food engineering top-ics are continuously undergoing changes to meet diverse consumer demands, and the subject is being rapidly developed to reflect market needs.
In the development of food engineering, one of the many challenges is to employ modern tools and knowledge, such as computational materials science and nano-technology, to develop new products and processes. Simultaneously, improving food quality, safety, and security continues to be a critical issue in food engineering study. New packaging materials and techniques are being developed to provide more pro-tection to foods, and novel preservation technologies are emerging to enhance food security and defense. Additionally, process control and automation regularly appear among the top priorities identified in food engineering. Advanced monitoring and control systems are developed to facilitate automation and flexible food manufac-turing. Furthermore, energy saving and minimization of environmental problems continue to be important food engineering issues, and significant progress is being made in waste management, efficient utilization of energy, and reduction of effluents and emissions in food production.
The Contemporary Food Engineering Series, consisting of edited books, attempts to address some of the recent developments in food engineering. The series covers advances in classical unit operations in engineering applied to food manufacturing as well as such topics as progress in the transport and storage of liquid and solid foods; heating, chilling, and freezing of foods; mass transfer in foods; chemical and biochemical aspects of food engineering and the use of kinetic analysis; dehydration, thermal processing, nonthermal processing, extrusion, liquid food concentration, membrane processes, and applications of membranes in food processing; shelf-life and electronic indicators in inventory management; sustainable technologies in food processing; and packaging, cleaning, and sanitation. These books are aimed at pro-fessional food scientists, academics researching food engineering problems, and graduate-level students.
The editors of these books are leading engineers and scientists from many parts of the world. All the editors were asked to present their books to address the markets need and pinpoint the cutting-edge technologies in food engineering.
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viii Series Preface
All the contributions have been written by internationally renowned experts who have both academic and professional credentials. All the authors have attempted to provide critical, comprehensive, and readily accessible information on the art and science of a relevant topic in each chapter, with reference lists for further informa-tion. Therefore, each book can serve as an essential reference source to students and researchers in universities and research institutions.
Da-Wen SunSeries Editor
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Series EditorProfessor Da-Wen Sun, PhD, is a world author-ity on food engineering research and education; he is a member of the Royal Irish Academy, which is the highest academic honor in Ireland; he is also a member of Academia Europaea (The Academy of Europe). His main research activities include cooling, drying, and refrigeration processes and systems; quality andsafety of food products; bio-process simulation and optimization; and computer vision technology.
In particular, his innovative studies on vacuum cooling of cooked meat, pizza quality inspection using computer vision, and edible films for shelf-life extension of fruits and vegetables have been widely reported in the national and international media. Results of his work have been published in about 600 papers, including over 250 peer-reviewed journal papers (h-index = 36). Hehas also edited 13 authoritative books. According to Thomson Scientifics Essential Science IndicatorsSM updated as of July 1, 2010, based on data derived over a period of ten years and four months (January 1, 2000April 30, 2010) from the ISI Web of Science, a total of 2554 scientists are among the top 1% of the most cited scientists in the category of agriculture sciences, and Professor Sun is listed at the top with a ranking of 31.
Dr. Sun received his first class BSc honors and his MSc in mechanical engineer-ing, and his PhD in chemical engineering in China before working at various univer-sities in Europe. He became the first Chinese national to be permanently employed in an Irish university when he was appointed a college lecturer at the National University of Ireland, Dublin (University College Dublin [UCD]), in 1995. He was then continuously promoted in the shortest possible time to the position of senior lec-turer, associate professor, and full professor. Dr. Sun is now a professor of food and biosystems engineering and director of the Food Refrigeration and Computerized Food Technology Research Group at UCD.
As a leading educator in food engineering, Dr. Sun has contributed significantly to the field of food engineering. He has guided many PhD students who have made their own contributions to the industry and academia. He has also, on a regular basis, given lectures on the advances in food engineering at international academic institu-tions and delivered keynote speeches at international conferences. As a recognized authority in food engineering, Dr. Sun has been conferred adjunct/visiting/consulting professorships by over ten top universities in China, including Zhejiang University, Shanghai Jiaotong University, Harbin Institute of Technology, China Agricultural University, South China University of Technology, and Jiangnan University. In rec-ognition of his significant contribution to food engineering worldwide and for his outstanding leadership in the field, the International Commission of Agricultural and
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x Series Editor
Biosystems Engineering (CIGR) awarded him the CIGR Merit Award in 2000 and again in 2006; the U.K.-based Institution of Mechanical Engineers named him Food Engineer of the Year 2004; in 2008, he was awarded the CIGR Recognition Award in recognition of his distinguished achievements as the top 1% of agricultural engi-neering scientists around the world; in 2007, he was presented with the only AFST(I) Fellow Award in that year by the Association of Food Scientists and Technologists (India); and in 2010, he was presented with the CIGR Fellow Award (the title of Fellow is the highest honor in CIGR and is conferred upon individuals who have made sustained, outstanding contributions worldwide).
Dr. Sun is a fellow of the Institution of Agricultural Engineers and a fellow of Engineers Ireland (the Institution of Engineers of Ireland). He has also received numerous awards for teaching and research excellence, including the Presidents Research Fellowship, and has received the Presidents Research Award from UCD on two occasions. He is also the editor in chief of Food and Bioprocess TechnologyAn International Journal (Springer) (2010 Impact Factor = 3.576, ranked at the fourth position among 126 ISI-listed food science and technology journals); series editor of the Contemporary Food Engineering Series (CRC Press/Taylor & Francis Group); former editor of Journal of Food Engineering (Elsevier); and an editorial board member of Journal of Food Engineering (Elsevier), Journal of Food Process Engineering (Blackwell), Sensing and Instrumentation for Food Quality and Safety (Springer), and Czech Journal of Food Sciences. Dr. Sun is also a chartered engineer.
On May 28, 2010, he was awarded membership to the Royal Irish Academy (RIA), which is the highest honor that can be attained by scholars and scientists working in Ireland. At the 51st CIGR General Assembly held during the CIGR WorldCongress in Quebec City, Canada, in June 2010, he was elected as incom-ing president of CIGR and will become CIGR president in 20132014. The term of the presidency is six yearstwo years each for serving as incoming president, president, and past president. On September 20, 2011, he was elected to Academia Europaea (The Academy of Europe), which is functioning as European Academy of Humanities, Letters and Sciences and is one of the most prestigious academies in the world; election to the Academia Europaea represents the highest academic distinction.
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PrefaceFruits are major food products and key ingredients in many processed foods. They are a rich source of vital nutrients and constitute an important component of human nutrition. Consumers nowadays are more aware of the importance of healthy foods and require food products with high nutritional value along with high standards of sensory characteristics. Thus, fruit processing has to preserve the nutritional value of the fruit, while also preserving its natural color and flavor. This book reviews new advances in fruit-processing technologies.
Fruits are highly perishable, and about 20%40% of the fruits produced are wasted from the time of harvesting till they reach the consumers, either in natural form or in processed form. To reduce fruit loss and improve final sensory characteristics of processed fruits, new or improved technologies have been applied to fruit processing. This book reviews new technologies, such as ozone application, ultrasound process-ing, irradiation application, pulsed electric field, vacuum frying, and high-pressure processing, and improved technologies, such as ultraviolet and membrane processing, enzymatic maceration, freeze concentration, and refrigeration.
The effect of processing on sensory characteristics and nutritional value is addressed in each chapter. New trends in modified atmosphere packaging, effects of processing on aroma, and the use of fruit juices as a vehicle for probiotic microor-ganisms and prebiotic oligosaccharides as an alternative for dairy products are also covered in this book.
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EditorsSueli Rodrigues is currently a professor of food engineering at the Federal University of Cear, Fortaleza, Brazil, where she teaches and does research on pro-cess and product development. She graduated in chemical engineering from the State University of Campinas, Campinas, So Paulo, Brazil, and received her PhD in chemical engineering in 2003 from the same university.
Dr. Rodrigues has published more than 65 papers in scientific journals. Her research interests include bioprocess, ultrasound, and drying technology, especially with fruit and functional food processing.
Fabiano Andr Narciso Fernandes is currently a professor of chemical engineer-ing at the Federal University of Cear, Fortaleza, Brazil, where he teaches and does research on process and product development. He graduated in chemical engineering from the Federal University of So Carlos, So Carlos, So Paulo, Brazil. He received his PhD in chemical engineering in 2002 from the Sate University of Campinas, Campinas, So Paulo, Brazil.
Dr. Fernandes has published more than 90 papers in scientific journals. His research interests include drying technology, ultrasound technology, and the field of reaction engineering.
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xv
Contributors
Ingrid Aguil-AguayoDepartment of Food TechnologyUniversity of LleidaLleida, Spain
Andra Cardoso de AquinoDepartment of Chemical EngineeringFederal University of CearCear, Brazil
Josep Maria AuledaDepartment of Agri-Food Engineering
and BiotechnologyTechnical University of CataloniaBarcelona, Spain
Henriette Monteiro Cordeiro de AzeredoEmbrapa Tropical AgroindustryBrazilian Agricultural Research
CorporationFortaleza, Brazil
Zoraia de Jesus BarrosDepartment of Plant, Soil, and Insect
SciencesUniversity of MassachusettsAmherst, Massachusetts
Maria do Socorro Rocha BastosEmbrapa Tropical AgroindustryBrazilian Agricultural Research
CorporationFortaleza, Brazil
Elena M. Castell-PerezDepartment of Biological and
Agricultural EngineeringTexas A&M UniversityCollege Station, Texas
Edmar ClementeDepartment of ChemistryState University of MaringMaring, Brazil
Jos Maria Correia da CostaDepartment of Food TechnologyFederal University of CearFortaleza, Brazil
Patrick J. CullenSchool of Food Science and
Environmental HealthDublin Institute of TechnologyDublin, Ireland
Sunando DasGuptaDepartment of Chemical EngineeringIndian Institute of TechnologyKharagpur, India
Pedro Elez-MartnezDepartment of Food TechnologyUniversity of LleidaLleida, Spain
Heliofbia Virginia de Vasconcelos FacundoDepartment of Food and Experimental
NutritionUniversity of So PauloSo Paulo, Brazil
Fabiano Andr Narciso FernandesDepartment of Chemical EngineeringFederal University of Cear Fortaleza, Brazil
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xvi Contributors
Deborah dos Santos GarrutiEmbrapa Tropical AgroindustryBrazilian Agricultural Research
CorporationFortaleza, Brazil
Eduard HernndezDepartment of Agri-Food Engineering
and BiotechnologyTechnical University of CataloniaBarcelona, Spain
Tatiana KoutchmaGuelph Food Research CenterAgriculture and Agri-Food CanadaGuelph, Ontario, Canada
Janice Ribeiro LimaEmbrapa Tropical AgroindustryBrazilian Agricultural Research
CorporationFortaleza, Brazil
Frank ManganDepartment of Plant, Soil, and Insect
SciencesUniversity of MassachusettsAmherst, Massachusetts
Olga Martn-BellosoDepartment of Food TechnologyUniversity of LleidaLleida, Spain
Ftima A. MillerCenter of Biotechnology and Fine
ChemistryBiotechnology Higher SchoolCatholic University of PortugalPorto, Portugal
Jane de Jesus da Silveira MoreiraDepartment of Food TechnologyFederal University of SergipeSo Cristvo, Brazil
Rosana G. MoreiraDepartment of Biological and
Agricultural EngineeringTexas A&M UniversityCollege Station, Texas
Narendra NarainDepartment of Food TechnologyFederal University of SergipeSo Cristvo, Brazil
Marta OrlowskaGuelph Food Research CenterAgriculture and Agri-Food CanadaGuelph, Ontario, Canada
Merc RaventsDepartment of Agri-Food Engineering
and BiotechnologyTechnical University of CataloniaBarcelona, Spain
Sueli RodriguesDepartment of Food TechnologyFederal University of CearFortaleza, Brazil
Biswajit SarkarUniversity School of Chemical
TechnologyGuru Gobind Singh Indraprastha
UniversityNew Delhi, India
Cristina L.M. SilvaCenter of Biotechnology and Fine
ChemistryBiotechnology Higher SchoolCatholic University of PortugalPorto, Portugal
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xviiContributors
Ebenzer de Oliveira SilvaEmbrapa Tropical AgroindustryBrazilian Agricultural Research
CorporationFortaleza, Brazil
Robert Soliva-FortunyDepartment of Food TechnologyUniversity of LleidaLleida, Spain
Brijesh K. TiwariHollings FacultyManchester Food Research CentreManchester Metropolitan UniversityManchester, United Kingdom
Ndio Jair WurlitzerEmbrapa Tropical AgroindustryBrazilian Agricultural Research
CorporationFortaleza, Brazil
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1
1 Ultraviolet Light for Processing Fruits and Fruit Products
Tatiana Koutchma and Marta Orlowska
CONTENTS
1.1 Introduction......................................................................................................21.2 BasicsofUVProcessingofFoodsofPlantOrigin..........................................3
1.2.1 UVLightSources.................................................................................31.2.1.1 MercuryLamps......................................................................31.2.1.2 EnvironmentalImpact...........................................................51.2.1.3 PulsedLamps.........................................................................61.2.1.4 LightEmittingDiodes...........................................................7
1.2.2 UVLightPropagation..........................................................................71.2.3 BasicPrinciplesofPhotochemistry......................................................8
1.3 UVLightControlMeasuresinFruitProcessingFacilities..............................91.3.1 AirTreatment........................................................................................91.3.2 WaterTreatment...................................................................................91.3.3 NonfoodandFoodContactSurfaceDisinfection.............................. 101.3.4 Packaging............................................................................................ 101.3.5 FreshFruitandCutFruitSurfacesTreatment.................................... 11
1.4 UVTreatmentofWholeFreshFruits............................................................. 111.4.1 AntimicrobialEffect........................................................................... 111.4.2 PlantAntimicrobialDefenseMechanismTriggeredbyUV.............. 131.4.3 EffectsonBioactiveCompounds........................................................ 141.4.4 StorageofPost-UV-TreatedFruits...................................................... 161.4.5 FormationofVitaminD..................................................................... 161.4.6 EffectsonGeneralAppearance.......................................................... 18
1.5 UVTreatmentofFresh-CutProduce.............................................................. 181.6 UVPasteurizationofFreshJuices.................................................................. 21
1.6.1 UVAbsorptionofFreshJuices........................................................... 211.6.2 DesignofUVSystems........................................................................231.6.3 InactivationofPathogenic,Nonpathogenic,
andSpoilageOrganisms..................................................................241.6.4 InactivationofEnzymes.....................................................................241.6.5 EffectsonEssentialVitamins.............................................................27
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2 Advances in Fruit Processing Technologies
1.1 INTRODUCTION
Duringthelastdecade,therehasbeenanincreaseintheproductionoffreshfruitandfruitproductsduetothehealthpropertiesoffruits.Fruitproductscanbecon-sumedinraw,minimallyprocessedorprocessed,ready-to-eat/ready-to-drinkformsaswholefreshfruits,fresh-cutfruits,andfruitsasingredients,beverages,juices,andjams.Theprocessingoffruitsstartsafterharvestingandconsistsoffouractivities:stabilizationorpreservation,transformation,productionofingredients,andproduc-tionoffabricatedfoods.Theroleofprocessingtechnologyineachstageimpliesthecontrol ofmicrobiological, chemical, andbiochemical changes,whichoccur as aresultofmicrobialandenzymaticactivities,andoxidationreactions,whichcanleadtoproblemsofsafety,color,flavor,taste,andtexture.Processingtechnologiesthatdonotsignificantlyaltertheorganolepticornutritionalqualitiesoffruitsanddonotformanyundesirablechemicalcompoundsintheproducthaveobviousadvantagesinmodernfoodproduction.Theinterestinso-calledminimalprocessingtechnolo-giesledtothedevelopmentofnonthermalormildheathigh-techmethodsthathavethepotentialtoreplacetraditionalthermalpreservationtechniques.Theyresultnotonlyinbetterqualityandlongershelflifebutalso,potentially,inhighernutritionalvalueorproductswithhealthbenefits.A largenumberofstudieshaveassociatedconsumptionoffruitsandtheirproductswithdecreasedriskofdevelopmentofdis-easessuchascancerandcoronaryheartdisease(Hansenetal.,2003).Thismaybedue to thepresenceofhealth-promotingphytochemicals suchas carotenoids,fla-vonoids,phenoliccompounds,andvitamins(Gardneretal.,2000),whichhave,insomecases,beenshowntohavedisease-preventingproperties.Inthisrespect,itisofparamountimportancetodevelopprocessingmethodsthatpreservenotonlythesafetyoffruitsbutalsothesensorialandnutritionalqualityandbioactivityoftheconstituentspresentinfruitsandtheirproducts.
Ultraviolet(UV)lighttreatmentoffoodsisanonthermalphysicalmethodofpres-ervationthatisfreeofchemicalsandwasteeffluents,whichmakesitecologicallyfriendly.Itdoesnotproduceby-products.Itissafetouse,althoughprecautionsmustbetakentoavoidhumanexposuretoUVlightandtoevacuateozonegeneratedbyvacuumandfarUVwavelengths.Basedonrecentengineeringadvancesandnewscientificdata,UVlighttechnologyincontinuousandpulsedmodes(cUVandPL)offersthepromiseofenhancedmicrobiologicalsafetyoffreshfruitsandimprovedqualityoffruitproductsthathaveafreshnessofflavor,color,texture,andnutritionalvaluecloser to thoseofnontreatedproducts.ThediscoveryofUVinactivationofthechlorine-resistantparasitesCryptosporidium parvumandGiardiasp.hascata-lyzed the use of UV light in the water industry (Hijnen et al., 2006). UV hasbeenutilizedsimilarlyinthedisinfectionofair,nonfoodcontact,andfoodcontactsurfaces,andrecentlywasusedfortreatmentsofsurfacesofsolidfoodsandliquid
1.6.6 DestructionandFormationofFuran..................................................281.6.7 DestructionofPatulin.........................................................................29
1.7 ConclusionsandFutureTrends......................................................................29ListofAbbreviations................................................................................................ 31References................................................................................................................ 31
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3Ultraviolet Light for Processing Fruits and Fruit Products
foods,beverages,andingredients.ReportsareavailablethatindicatethatapplicationofUVlightcanalsoimprovethetoxicologicalsafetyoffoodsofplantoriginthroughitsabilitytoreducelevelsoftoxinssuchaspatulinmycotoxininfreshapplecider(Dongetal.,2010)andpossiblytocontrolbrowningthroughitseffectsonenzymes(Manzoccoetal.,2009).Regardingthepreservationoforganolepticandnutritionalattributes,recentresearchhasshownpromisingresultsintheexposureoffruitprod-uctstoUVirradiation.Inadditiontohighercost-efficiency,sustainability,andbroadantimicrobialeffects,UVlightnotonlyminimallyaffectsqualityattributesbutalsohasbeneficialeffectsonthecontentofbioactivecompounds.Ithasthepotentialforobtainingpremiumqualityproductsthatcanleadtofastercommercialization.
This chapter aims to provide detailed and critical information on the latestapplicationsofcontinuousandpulsedUVlightforprocessingfreshfruitsandfruitsproducts.ThefundamentalprinciplesandfeaturesofUVlightgeneration,propa-gation, and photochemistry are briefly reviewed, and the control measures to beadoptedwhereUVtechnologycanbeutilizedtoenhancesafetyduringfruitproduc-tionareanalyzed.ParticularfocusisgiventotheeffectsofUVlightonthesurvivalofpathogenicand spoilagemicroorganisms typical to fruits and theenvironmentessentialinfruitprocessingfollowedbyadiscussionofrecentresearchintoeffectsofUVlightonqualityandbioactivecompounds.
1.2 BASICSOFUVPROCESSINGOFFOODSOFPLANTORIGIN
1.2.1 UVLightSoUrceS
Lightisemittedfromgasdischargeatwavelengthsdependentonitselementalcom-position and the excitation, ionization, andkinetic energyof those elements.Gasdischarges are responsible for the light emitted from UV lamps. UV light trans-ferphenomenonisdefinedbytheemissioncharacteristicsoftheUVsourcealongwith considering long-term lamp aging and absorbance/scattering of the product.Consequently,theperformanceofaUVsystemdependsonthecorrectmatchingoftheUVsourceparameterstothedemandsoftheUVapplication.ThecommerciallyavailableUVsourcesincludelow-andmedium-pressuremercurylamps(LPMandMPM),excimer lamps(EL),pulsed lamps(PL),and light-emittingdiodes (LED).LPM and EL are monochromatic sources, whereas emission of MPM and PL ispolychromatic.TherearenoreportsontheapplicationofELinfruitprocessing,sothisUVsourceisnotdiscussedinthischapter.
1.2.1.1 MercuryLampsMercuryvaporUVlampsourceshavebeensuccessfullyusedinwatertreatmentfornearly50yearsandareconsideredas reliable sources forotherdisinfectiontreatments thatbenefit from theirperformance, lowcost, andquality.Typically,three general types of mercury UV lamps are used: low-pressure (LPM), low-pressurehigh-output(LPHO),andmedium-pressure(MPM).Thesetermsarebasedonthevaporpressureofmercurywhenthelampsareoperating.Theeffectsofmer-curyvaporpressureonspectradistributionisshowninFigure1.1.Vapordischargelamps consist of aUV-transmitting envelopemade froma tubeof vitreous silica
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it Processin
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FIGURE1.1 Effectsofvaporpressureofmercuryonoutputspectradistribution.
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5Ultraviolet Light for Processing Fruits and Fruit Products
glass sealed at both ends. The envelope is filled with mercury and an inert gas.Argon,themostcommonfiller,hasionizationenergyof15.8eV,whereasthelowestactivatedmetastablestateisat11.6eV(MasscheleinandRice,2002).
LPMlampsareoperatedatnominaltotalgaspressuresof102103Pa,whichcor-respondstothevaporpressureofmercuryatatemperatureof40C.TheemissionspectrumofLPMisconcentratedattheresonancelinesat253.7and185nm.The253.7nmlinerepresentsaround85%ofthetotalUVintensityemittedandisdirectlyrelatedtothegermicidaleffect.Thewavelengthof253.7nmismostefficientintermsofgermicidaleffectsincephotonsareabsorbedmostbytheDNAofmicroorganismsatthisspecificwavelength.Lightwithawavelengthbelow230nmismosteffectivefor the dissociation of chemical compounds. At wavelengths of 185nm, ozone isproduced fromoxygenandorganiccompoundscanbeoxidized(Voronov,2007).Thephotonswith thewavelengthof185nmareresponsibleforozoneproduction,andthecombinationofbothwavelengthsisaveryeffectivemeansforphotochemi-calairtreatment.Theratiooflightat185nmtolightat253.7nmvariesfrom12%to34%dependingontheoperatingcurrent,walltemperature,andinertgas.TheU.S.FDAregulationsapprovedtheuseofLPMlampsforjuiceprocessing,andtheyhavealreadybeensuccessfullycommercialized(U.S.FDA,CFRpart179,2000).
MPMlampsareoperatedatatotalgaspressureof104106Pa(MasscheleinandRice,2002).ComparedwiththeLPMlamps,thecoolestpossibletemperatureoftheMPMisabout400C,whereasitgoesupto600Candeven800Cinastableopera-tion.MPMlampsoperateinthepotentialgradientrangeof530W/cm.Theemis-sionspectrumofMPMcoverswavelengthsfromabout250nmtoalmost600nm,whichresultsfromaseriesofemissionsintheUVandinthevisiblerange.MPMlampsarenotconsideredtobeusefulfor targetedgermicidal treatment;however,theirstrongUVradiationfluxresultsinhighpenetrationdepth.Byvaryingthegasfilling,doping,andthequartzmaterial,thespectrumaswellastheradiationfluxoftheUVlampscanbevariedandmatchedtosuitspecificfoodprocessingapplica-tions,especiallyforoxidationorphotodegradation.
Recently,LPHOamalgamlampsthatcontainamercuryamalgamwasdevelopedand incorporated intodisinfection applications; however,LPMandMPMare thedominantsourcesforUVdisinfectiontreatment.
1.2.1.2 EnvironmentalImpactThe potential mercury exposure due to lamp sleeve breakage is a health concern.Breakageoflampscanoccurwhenlampsareinoperationandduringmaintenance.ThemercurycontainedwithinaUVlampisisolatedfromexposurebythelampenve-lopeandsurroundinglampsleeve.Forthemercurytobereleased,boththelampandlamp sleeve must break. The mercury content in a single UV lamp used for watertreatment typically ranges from 0.005 to 0.4g (5400mg). LPM lamps have lessmercury (550mg/lamp)comparedwithLPHO(26150mg/lamp)andMPMlamps(200400mg/lamp).TheEPAestablishedamaximumcontaminantlevel(MCL)formercuryat0.002mg/L.TheEPAhasfoundmercurytopotentiallycausekidneydam-agefromshort-termexposuresatlevelsabovethe0.002mg/LMCL(EPA,1995).Theconcernovertheimpactofmercuryreleaseintothefoodplantenvironmentstimulatedthedevelopmentandvalidationoflampswithmercury-freespecialtechnologies.
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6 Advances in Fruit Processing Technologies
1.2.1.3 PulsedLampsTheefficacyofpulsedflashlamps(PL)ispotentiallygreaterthancontinuoussourcesduetohighintensityandbroaderspectrum.PLtechnologiesarepromisingduetotheirinstantstart,highintensity,androbustpackagingwithnomercuryinthelamp,butmore research is needed to establish them for fruit treatment applications. Inthistechnology,alternatingcurrentisstoredinacapacitorandenergyisdischargedthroughahigh-speedswitchtoformapulseofintenseemissionoflightwithinabout100ms.Theemissionissimilar inwavelengthcompositiontothesolar light.TheUVpulseddevicescandeliverhigh-intensityUV,whichcanbothpenetrateopaqueliquidsbetterthanmercurylampsandprovideenhancedtreatmentrates.Figure1.2shows the normalized spectra of these three UV sourcesLPM, MPM, and PL.IndividualspectraarenotcomparableonaUVintensitybasisbutarecomparableon a spectral basis with reference to which wavelengths dominate the respectivewavelengthoutputs.
Table1.1providesasummaryofsomeof thebasiccharacteristicsofcommonUVsources incommercialuseandunderdevelopment thatcanbeusedforcom-parison purposes. It is evident that no single lamp technology will represent thebestsourceforallfoodapplications.However,situation-specificrequirementsmaydictateaclearadvantageforagivenprocesstechnology.ForUVreactorscontainingLPMorLPHOmercurylamps,UVabsorbanceandtransmittanceat253.7nmareimportantdesignparameters.However,forbroadbandUVlamps,suchasMPMorPLUVlamps, it is important tomeasurethefullscanofabsorbanceortransmit-tanceinthegermicidalregionfrom200to400nm.LampswithspecialtechnologiessuchasPLUVandELarepromisingduetothedifferentspectralbandsorspecificwavelengthsthattheycanprovidewithregardtoeffectsonqualityattributes.Theyalsohaveinstantstartandrobustpackagingwithnomercuryinthelamp.However,moreresearchisneededtoestablishtheirsuitabilityforfruitprocessingapplications.
2000.000
0.002
0.004
0.006
0.008
0.010
Nor
mal
ized
spec
trum
0.012
0.014
0.016
0.018
0.020
PL lamp
MPM lamp
LPM lamp210 220 230 240 250
Wavelength (nm)260 270 280 290 300
FIGURE1.2 Comparisonofspectrumsofcontinuous(LPMandMPM)lampsandPLUVsources.
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7Ultraviolet Light for Processing Fruits and Fruit Products
1.2.1.4 LightEmittingDiodesInrecentyears,UV-LEDshavebeendevelopedwiththefollowingadvantages:lowcost, energyefficiency, long life, easycontrolof emission, and no production ofmercury waste. The wavelength of the commercial UV-LED is around UV-Arange(315400nm)andenablesnewapplicationsinexistingmarketsaswellasopennewareas.AnLEDisasemiconductordevicethatemitslightwhencarriersofdif-ferentpolarities(electronandholes)combinegeneratingaphoton.Thewavelengthof thephotondependson theenergydifference thecarriersovercomeinorder tocombine.AnexampleofaUV-LEDsystemthatoperatesbetween210and365nmistheoneformedbyaluminumnitride(AIN),galliumnitride(GaN),andintermedi-atealloys.Currently,UV-LEDsarecommerciallyavailable inresearchgradeandlimitedquantitiesandtheirlifetimesreachtheorderof200h.Itisverylikelythatinthenearfuture,manyapplicationsthatmakeuseofmercurylampstodaywillbecarriedoutbyUV-LEDs.
1.2.2 UVLightProPagation
UVlightemittedfromtheatomsandionswithinthegasdischargeofaUVsourcewillpropagateawayfromthoseatomsandions.AsUVlightpropagates,itinteractswiththematerialsitencountersthroughabsorption,reflection,refraction,andscat-tering.EachofthesephenomenainfluencestheintensityandwavelengthoftheUVlightreachingthebacteriaorchemicalcompoundonthesurfaceorintheliquid.
Absorption(A)oflightisthetransformationofenergyoflightphotonstootherformsofenergyasittravelsthroughasubstance.Reflection(R)isthechangeinthedirectionofpropagationexperiencedbylightdeflectedbyaninterface.Scatteringis the phenomenon that includes any process that deflects electromagnetic radia-tionfromastraightpaththroughanabsorberwhenphotonsinteractwithaparticle.
TABLE1.1ComparisonofEfficiencyCharacteristicsofContinuousandPulsedUVSources
UVSource
ElectricalEfficiency
(%)
UVEfficiency
(%)
UVIntensity(W/cm2)
LampSurfaceT
(C)Lifetime,Month
OutputSpectrum
LPM 50 38 0.0010.01 40 1824 Monochromatic253.7nm
Excimer 1025 1030 0.050.5 Ambient 13 Monochromaticselectable
MPM 1530 12 12 4001,000 0.5 Polychromatic200400nm
Flashxenon 4550 9 600 1,00010,000
1 Polychromatic1001000nm
Surfacedischarge
1520 17 30,000 NA NA Polychromatic200800nm
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8 Advances in Fruit Processing Technologies
Thescatteringphenomenonplaysanimportantroleindisinfectingfoodliquidscon-tainingparticles.Experimentalmeasurementsareusuallymadeintermsoftrans-mittanceofasubstance(T)or(UVT),whichisdefinedastheratioofthetransmittedtotheincidentlightirradiance.AconvenientwayofpresentinginformationaboutUVTofmaterialsistogivethevaluesoftheirabsorptioncoefficientatvariouswave-lengths,overagivendepth(e.g.,1cm).Knowingthis,thetransmittanceforanypar-ticulardepthandthedepthoftheliquidthatwillabsorb90%oftheenergyat253.7nmcan be calculated. Other important terms to characterize UV light treatments infruitprocessingarefluence rateandfluence.Fluencerateisthetotalradiantpowerincidentfromalldirectionsontoaninfinitesimallysmallsphereofcross-sectionalareadA,dividedbydA(BoltonandLinden,2003).Fluenceisdefinedastheflu-enceratemultipliedbytheexposuretime.ThetermUV doseshouldbeavoidedasasynonymoffluencebecausedoserefersinothercontextstoabsorbedenergy,butonlyasmallfractionofallincidentUVlightisabsorbedbymicroorganisms(BoltonandLinden,2003).InthecaseofPL,fluenceisdeterminedasenergyperpulsemul-tipliedbythenumberofpulses.Theabsorbedfluenceindicatesthatradiantenergyisavailablefordrivingthesolutionreaction.However,whenUVlightisabsorbedbysolution,itisnolongeravailableforinactivatingthemicroorganisms.Theremaininginteractions,includingreflection,refraction,andscattering,changethedirectionofUVlight,butthelightisstillavailableforinactivation.TheradiantenergydeliveredtothemoleculeormicroorganismiscalledtheeffectiveordeliveredgermicidalUVdose.Microbialinactivationdependsprimarilyontheeffectivedose.TheformulasforcalculationsofthecriticalUVprocessparametersareavailableintheliterature(Koutchmaetal.,2008).
1.2.3 BaSicPrinciPLeSofPhotochemiStry
Photochemical reactions proceed as a direct result of radiation energy (photons)beingintroducedtoasystem.InviewofthewavelengthsusedinmostUV-lighttreatments, the molecules (A) are primarily affected by energy absorption thatresultsinphotochemicalreactions.Inthegeneralcase,theprocessmaybeviewedas
A h A Products+ ++v (1.1)
Thefirststepinthisreactionistheabsorbanceofaphotonbyareactantmolecule(A),leadingtotheproductionofanelectronicallyexcitedintermediate.Theexcitedstatecanbeforaperiodof1010108sinwhichtheenergyoftheelectronsisincreasedbytheamountofphotonenergy.Undersomeconditions,theintermediatemayundergoachemicalchangetoyieldproductsthatarerelativelystable.Foraphotochemicalreactiontoproceed,photonsmusthavesufficientenergytopromotethereactiontobreakorformabondandphotonenergymustbeabsorbedtopromotereactions.ThebondenergiesofinterestaregenerallycoincidentwithphotonenergiesintheUVportionofthespectrum.Inparticular,radiationwithwavelengthlessthanapproxi-mately320nmappearstobesufficientlyenergetictopromotephotochemicalreac-tionsinbiomolecules.Theextentofchemicalreactiondependsuponthequantumyieldandfluenceofincidentphotons.Aquantumyieldisaratioofabsorbedphotons
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9Ultraviolet Light for Processing Fruits and Fruit Products
thatcauseachemicalchangetothetotalabsorbedphotons.UVlightat253.7nmhasaradiantenergyof(472.27kJ/Einstein)112.8kcal/Einstein(oneEinsteinrepresentsonemoleofphotons).Itistheoreticallypossiblefor253.7nmlighttoaffecttheOH,CC,CH,CN,HN,andSSbondsifitsabsorbed.
1.3 UVLIGHTCONTROLMEASURESINFRUITPROCESSINGFACILITIES
Duringthemanufacturingprocess,fruitscanbeexposedtomicrobiologicalcross-contaminationfromsurfaces,water,andtheair,whichcancausetheirspoilageandraisesafetyissues.Thetraditionalapproachtocontrollingsuchcontaminationhasbeentotargetspecificsiteswithinthemanufacturingenvironmentwithcleaninganddis-infectionregimes.Sanitation,disinfection,andoxidationwithUVlightisaversatile,environmental-friendlytechnology,whichcanbeusedinfruitprocessingfacilitiesforthetreatmentofair,surfaces,andwatertoreducemicrobialcontaminationindifferentunitoperationsofplantfoodsproductionthatarebecomingmoreandmorepopular.
1.3.1 airtreatment
Clean,freshairisthebasisoftheindustrialproductionoffoodproductsofplantorigin.Microorganismsintheair,suchasviruses,bacteria,yeasts,andfungi,cancontami-naterawmaterialsandintermediateproductsandspoilfinishedproductsduringtheirprocessingandpackaging.LPMsourcesareusedverysuccessfullyintheseapplica-tions,fordisinfectioninairintakeductingandstoreroomsandtoensureairofverylowgermcontentinproductionareas.Short-waveUVradiationat185nmproducesozonefromtheoxygen in theambientairso that this isactivatedfor theoxidationprocess.UVoxidationbreaksdownpollutantsintheexhaustair.Forprovidingcleanairinsensitivemanufacturingfoodfacilities,acombinationoffiltersandUVlighthasbeenrecommended.Basically,twoapplicationsofUVarebecomingcommon.Inone,themovingairstreamisdisinfectedinmuchthesamemanneraswithawatersystem.Intheotherapplication,stationarycomponentsofthesystemsuchasairconditioningcoils,drainpans,andfilter surfacesareexposed tohelppreventmoldandbacteriagrowthortodisinfectthefiltertoaidinhandling.TheUVTinairishigherthanthatinwater,and,therefore,thenumberoflampsrequiredinalargeductisquitereason-able. Common airborne virus and bacteria are readily deactivated with UV. Fungi(moldsandspores)requiremuchhigherdoses.Inthemovingairstream,highwattagelampsareused,usuallywithoutaquartzsleeve.UVlampfixturesareplacedinsuchamannerastocompletelyirradiatesurfaceswherebacteriaandmoldmightcollectandgrow.Mathematicalmodelingsoftwareandbioassaytestinghavebeendevelopedtoallowefficientdesignandvalidationofthesesystems(KowalskiandBahnfleth,2002).LowoperatingcostsandreasonableequipmentcostscanmakeUVverycosteffective.
1.3.2 Watertreatment
Controlofmicroorganismsinindustrialprocesswatersisoftennecessarytomain-tainqualityoftheproductorprocess.Thefruitindustryisalarge-volumeconsumer
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10 Advances in Fruit Processing Technologies
ofwater,andthepotentialforreuseorrecyclingoffruitprocessingwaterrepresentsanattractiveeconomicbenefittotheindustry.AcombinationofUVlightandozonehasapowerfuloxidizingactiontoreducemicrobialloadandtheorganiccontentofwatertoverylowlevels.
1.3.3 nonfoodandfoodcontactSUrfacediSinfection
UVlight isaneconomicalsteptowardimprovedhygienecontrolmeasures in thefoodindustry.Moldandbiofilmscandeveloponnonfoodsurfaces(ceilings,walls,floors)andequipmentincludingtanksandvats,coolingcoils,andfoodcontactsur-facesofequipmentsuchascuttingequipmentandconveyorbelts(Kowalski,2006).Ingeneral,standardcleaninganddisinfectionproceduresareadequate tocontaintheseproblems,butalternativesareavailable,includingantimicrobialcoatingslikecopperandTiO2.UVirradiationoffoodprocessingequipmentandsurfaces,coolingcoildisinfectionsystems,wholeareaUVdisinfection,andafter-hoursirradiationofroomswhenpersonnelarenotpresentareallviablecontroloptionsformaintain-inghighlevelsofsanitationanddisinfectioninfoodindustryfacilities(KowalskiandDunn,2002).UVlightkillsupto99.9%oftotalgermsonconveyorbeltsfortransportingfruitsandvegetables.
1.3.4 Packaging
The packaging technologies play an important role in extending the shelf life offruits.UVlightmightbeappliedaspre-orpostpackagingtechnologytoreducethemicrobialspoilage.Asaprepackagingcontrolmeasure,UVtreatmentofpackagingin fruitfillingplants, for example, for lids, cups, sealing, andpackaging foils fordrinksandbeverages,helpstoextendtheshelflifeoffruitstuff.WhenusingcUVand PL as postpackaging treatment for packaged fruits, the considerations abouttransparencyarereferredtothepackagingmaterials.Forexample,materialssuchasglass,polystyrene,andPET,whichallowvisible light topenetrate through thecontainer,arenottransparenttotheUVwavelengthsthatareessentialformicrobialinactivation, and therefore, they are not suitable for cUV and PL treatments. Ontheotherhand,polymerssuchaspolyethylene,polypropylene,polybutylene,EVA,nylon, Aclar, and EVOH transmit UV light and hence meet the requirements forPLTverywell(Anonymous,2000).Inaddition,ink-printedlabelsordrawingscouldinterferewiththelightabsorptionofthetreateditemandshouldbeavoidedonthesurfaceofpackagingmaterials.Besidestheintrinsictransparencyofthematerial,forthesuccessofaUVprocessitisverycriticalthattheconditionoftheitemtobetreatedissuitableforthepenetrationofthelight.Thismeansthattheproductsurfaceshouldbesmooth,clear,andwithout roughness,pores,andgrooves,whichcouldshadowthemicrobialcells fromthe light,causing lesscomplete lightdiffusionandthusreducingprocesseffectiveness;forthesamereason,theitemtobetreatedshouldbecleanandfreeofcontaminatingparticulates.Inaddition,itemsthathaveacomplexgeometrycouldhaveareashiddenfromthelightandcouldrequireamoreaccuratedesignofthetreatmentchamberinorderforthelightpulsestoreacheachpointoftheproductsurface.
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11Ultraviolet Light for Processing Fruits and Fruit Products
1.3.5 freShfrUitandcUtfrUitSUrfaceStreatment
CUVandPLtreatmentsresultinvariouslevelsofinactivationofspoilageandpatho-genic microflora on the surface of a wide variety of solid foods. ComprehensivereviewsoftheliteratureinthisfieldhavebeencompiledbytheU.S.FDA(2000)andbyWoodlingandMoraru(2005).Thevariabilityoftheresults(a2-to8-logreductionwasgenerallyreported)ismostlikelyduetothedifferentchallengemicroorganismsusedinvariousstudies,theintensityofthetreatment,andthedifferentpropertiesofthetreatedsubstrates.WoodlingandMoraru(2005)demonstratedthattheefficacyof PL is affected by substrate properties such as topography and hydrophobicity,whichaffectboththedistributionofmicrobialcellsonthesubstratesurfaceandtheinteractionbetweenlightandthesubstrate(i.e.,reflectionandabsorptionoflight).Surfacedisinfectionoffreshandcutfruitproductsisabasisforlongershelflife.IndesigningaPLtreatmentforfruititems,bothsource(lightwavelength,energyden-sity,durationandnumberofthepulses,intervalbetweenpulses)andtarget(prod-ucttransparency,color,size,smoothness,andcleanlinessofsurface)parametersarecriticalforprocessoptimization,inordertomaximizetheeffectivenessofproductmicrobial inactivationand tominimizeproduct alteration.SuchalterationcanbemainlydeterminedbyanexcessiveincreaseintemperaturecausingthermaldamagetofruitsandalsobyanexcessivecontentofUV-Clight,whichcouldresultinsomeundesiredphotochemicaldamagetofruititselfortopackagingmaterials.Table1.2summarizescurrentandfutureapplicationsofcUVandPLavailablesourcesinfruitprocessingforair,surface,water,andlowUVTfruitdrinksandbeverages.
1.4 UVTREATMENTOFWHOLEFRESHFRUITS
1.4.1 antimicroBiaLeffect
Traditionally UV-light applications for treatments of whole fruits and vegetableswerefocusedonthedisinfectionrolewiththeobjectivetoextendtheshelflifeasnaturallyoccurringmicrofloramaypresentonthesurfaceofrawproducebothofnonpathogenicorspoilageandpathogenicnature(Table1.3).
TABLE1.2ApplicationofUVLightSourcesasaControlMeasureinFruitProcessing
UVSource
ReportedApplications
ProcessedWater Air Surfaces LowUVTJuices
LPM X X X X
MPM X X
Excimerlasers X X X
Pulsed X X
LED X X X
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12 Advances in Fruit Processing Technologies
Duringstorage, fruitsundergobiochemicalandphysiologicalchanges thatcanresult in loss of nutrients, color changes, and tissue disruption. Along with theseundesirable changes, crops become more susceptible to pathogenic decay, whichincreasesthepossibilityofillnessincidencesandalsocauseslargeeconomiclosses.
Enhancedshelf lifeofUV-treatedfruitscanbeassociatedwiththegermicidaleffectonpathogensthatmaybepresentonthesurfaceofthecrops.However,theUVtreatmentrequiresthatthewholesurfaceoftheobjectisexposedtotheUVlightforatimesufficientforanymicroorganismspresenttoaccumulatealethaldose.ThisalsomeansthatthetopographyofthesurfacedeterminestheefficacyofUVtreat-mentandpresentsitslimitationduetoshieldingeffects.TheimportanceofthefruitpositioningduringtheUV-CexposureofstrawberrieswasreportedbyStevensetal.(2005).TheauthorsfoundthatirradiationofthestemendsofthefruitsresultedinlowerdecayduringsubsequentstorageincomparisonwiththefruitsexposingonlyoneortwodifferentsidestoUV-Clight.
SeveralstudieshaveshownthatUVprocessingoffreshproduceiseffectiveinthereductionofpathogenicbacterialpopulation.Forinstance,Yaunetal.(2004)inocu-latedthesurfaceofRedDeliciousapples,leaflettuce,andtomatoeswithculturesofSalmonella spp.orEscherichia coli O157:H7.UV-C(253.7nm)appliedtoapplesinoculatedwithE. coli O157:H7 resulted in thehighest log reductionofapproxi-mately3.3 logsat240W/m2.Lower log reductionswereseenon tomatoes inocu-latedwithSalmonella spp.(2.19logs)andgreenleaf lettuceinoculatedwithbothSalmonella spp.andE. coli O157:H7(2.65and2.79logs,respectively).PLUVlight
TABLE1.3FreshProduceandTypicalMicrofloraPresentontheSurface
Commodity Microflora Reference
Fruits(ingeneral) Fungi:B. cinerea,Aspergillus niger; Martin-Bellosoetal.(2006)
Yeasts:Canidia,Cryptococcus,Fabospora,Kluyveromyces,Pichia,Saccharomyces,andZygosaccharomyces;
Bacteria:Shigellaspp.
Carrot B. cinerea Mercieretal.(1993)
Lettuce Enterobacter, Erwinia, Escherichia, Leuconostoc, Pantoea, Pseudomonas, Rahnela, Salmonella, Serratia,andYersinia
Allendeetal.(2006)
Tomato B. cinerea Charlesetal.(2008)
Apple E. coliO157:H7 Martin-Bellosoetal.(2006)
Raspberry Cyclospora cayetanensis Martin-Bellosoetal.(2006)
Strawberry Campylobacter jejuni Martin-Bellosoetal.(2006),Erkanetal.(2008),Pomboetal.(2011)
B. cinerea
Watermelon Salmonellaspp.,Shigellaspp. Martin-Bellosoetal.(2006)
Cantaloupe Campylobacter jejuni Martin-Bellosoetal.(2006)
Pineapple E. coli O157:H7,Salmonella StrawnandDanyluk(2010)
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13Ultraviolet Light for Processing Fruits and Fruit Products
wasalsoappliedtoreducethepopulationofpathogenicbacteriaonthesurfaceoffruits.Forinstance,BialkaandDemirci(2007,2008)exposedblueberriesinoculatedwithE. coliO157:H7andSalmonellatothePL(XenonCorp.)emittinginarangefrom100 to1100nm for 5, 10, 30, 45, and60s.The authors reported reductionsbetween1.1and4.3log10CFU/gofE. coliO157:H7and1.1and2.9log10CFU/gofSalmonella.Duetothehigh-intensitynatureofthePLsource,substantialincreaseinthetemperaturewasobservedduringfruitprocessingthatcouldcontributetothemicrobialreduction.TheimpactofthePLtreatmentonthenutrientsoftreatedcropshasnotbeenstudiedyet.
Thedeteriorationofmanyfreshfruitscanbecausedbyfungi,whichgiverisetovariousinfectionsonharvestedplantproduce.Forexample,Monilinia fructicolaisthemaincauseofbrownrotinpeaches,apricots,nectarines,andplums.Stevensetal.(1998)revealedthatUVtreatmentcanreducethefungalpopulationonpeaches.ThesurfacesofpeacheswereinoculatedwithsporesoftheM. fructicolaandthenfruitsweresubjectedtotheUVlight.AtUVfluenceof4.8kJ/m2,adecreaseingrowthofM. fructicolabyapproximatelyoneorderofmagnitudewasobserved.AnotherstudyperformedbyStevensetal.(2005)hasshownthatUV-C(253.7nm)treatmentat7.5and1.3kJ/m2resultedinhigherresistancetobitterrot(Colletotrichum gloeospori-oides),brownrot(M. fructicola),andgreenmold(Penicillium digitatum)inapples,peaches, and tangerines. Gonzlez-Aguilar et al. (2001, 2007) demonstrated thatexposure toUV-C light in the rangeof250280nmat4.93kJ/m2 lowered fungaldecayofmangofruitsstoredfor18daysat25Cby60%.Significantlylowerinci-denceofdecaywasalsoobservedafterUV-Ctreatmentinkumquatfruitandbitterorange(Citrus aurantium)inoculatedwithP. digitatum(Rodovetal.,1992;Arcasetal.,2000).InthecaseofpapayafruitsinoculatedwithColletotrichum gloeospori-oides,noneoftheUV-C(253.7nm)treatments(0.22.4kJ/m2)waseffectiveagainstanthracnosefungalsporulation(Ciaetal.,2007).Anotherfungus,Botrytis cinerea,isthemaincauseofgraymoldrotinmanycrops.ExposuretotheUV-Clightwiththepeak at thewavelengthof253.7nm reduced theB. cinerea growth in carrots(Mercier et al., 1993), tomatoes atUVfluenceof3.7kJ/m2 (Charles et al., 2008),pepperfruitsatUVfluenceof7kJ/m2(Vicenteetal.,2005),andstrawberries(Erkanet al., 2008; Pombo et al., 2011). Erkan et al. (2008) reported that in UV-treatedstrawberriesatfluencelevelsof0.43,2.15,and4.30kJ/m2,after20daysofstorageat10Cthepercentageoffungaldecaywas49.6,29.6,and27.98,respectively,whileincontrolfruitsthedecayreached89.98%.SimilarobservationshavebeenreportedbyPomboetal.(2011)whoinoculatedStrawberrieswithB. cinerea8hafterUV-Ctreatmentatthedoseof4.1kJ/m2.ThereductionoffungalgrowthwasfoundandcanbeattributedtotheplantdefensemechanismagainstpathogensinducedbyUVlight.
1.4.2 PLantantimicroBiaLdefenSemechaniSmtriggeredByUV
ExposuretoUVatverylowdosesoverhoursorevendaystriggersaseriesofbio-chemicaleventswithintheplanttissue.Thetermhormesishasbeenappliedtothistype of UV treatment. According to Shama (2007), hormesis involves the use ofsmalldosesofpotentiallyharmfulagentsdirectedagainstalivingorganismorliv-ing tissue to elicit a beneficial or protective response. Hormetic UV treatment is
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14 Advances in Fruit Processing Technologies
distinguishedfromconventionalUVtreatment.Inconventionaltreatment,theUVis directed toward microorganisms that are present on the surfaces of an object,whereas in thecaseofhormeticUVtreatment, theobject itself isexposed to theincidentUV.Thepurposeofthetreatmentistoelicitanantimicrobialresponseinthefruittissue.BothtypesofUVtreatmentemploythesamewavelengths;however,forhormetictreatmentsonlylowUVdosesareapplied(ShamaandAlderson,2005).TheplantdefensemechanismthatistriggeredbythehormeticUVdoseisnotyetfully known and understood. Figure 1.3 schematically presents some of the bio-chemicalresponsesofplantmembranethatwererecentlyreported.ItwasfoundthatUV-ChormetictreatmentatUVfluencesintherangeof0.44.3kJ/m2stimulatestheactivityofseveralgroupsofenzymesthatplaydifferentrolesinplantantimicro-bialdefenseactions.Thisincludes(1)enzymesofperoxidasesandreductasesthatareresponsiblefortheoxidativeburstandformationofligninpolymersgeneratingstructural barriers against invading pathogens; (2) glucanases and chitinases thatexhibitlyticactivitiestowardmajorfungalcellwallcomponents;and(3)l-phenyl-alanine ammonia lyase (PAL)involved in biosynthesis of phenolics, which arecharacterizedbyantioxidantandantimicrobialactivities(Erkanetal.,2008;Pomboetal.,2011).
ItwasfoundthatthehigheraccumulationofrishitininUV-C-treated(253.7nm,3.7kJ/m2)tomatofruitswaspositivelycorrelatedwithenhancedresistanceagainstgraymoldrot(Charlesetal.,2008).Inaddition,thehormeticUVtreatmentsresultin protective effects against microorganisms throughout the entire tissue ratherthanatitssurfaceonly.Stevensetal.(1999)showedthatsweetpotatoesinoculatedwithsporesofFusariumsolaniatadepthof12mmbelowthesurfacecouldbesuc-cessfullyprotectedfrominfectionfollowinghormeticUVtreatment.TheresearchattentionwasalsofocusedoncitrusfruitsandinfruitswheretheenhancementofresistancetophytopathogenssuchasP. digitatumhasbeenattributedtoaccumula-tionofthephytoalexinsscoparone.Asexample,Ben-Yehoshuaetal.(1992)reportedthat UV illumination of lemon reduced susceptibility to P. digitatu, which wasdirectlyrelatedtothelevelofscoparoneinthetreatedfruit.
1.4.3 effectSonBioactiVecomPoUndS
ThereportsrelatedtoUVhormesisinfreshproduceshowedthatduetotheinduc-tionofplantdefensemechanismsaccumulationofthephytochemicalsintheplantcellscanoccur.Theirantimicrobialandantioxidantpropertiesarehighlydesirableas they can contribute to delaying the onset of ripening and consequently reduc-ingeconomiclossesduetospoilage.Moreover, theformationofbioactivepheno-liccompoundssuchasphenolicacidsandflavonoidsincreasesthenutritionalvalueof UV-treated commodities. Phenolic acids and flavonoids are characterized byessentialhealthpromotingpropertiessuchasantiinflammatory,antihistaminic,andantitumoractivities.
Severalstudiesreportedincreaseinandbettermaintenanceofphenolicsandfla-vonoidcompoundsincropsprocessedwiththeUVlight.Thetypeofthepolyphe-nolsaswellastheiraccumulationandbettermaintenanceduringstoragewashighlydependenton thecropcommodityandappliedUVdose.Gonzlez-Aguilaret al.
-
15U
ltraviolet Ligh
t for Pro
cessing Fru
its and
Fruit Pro
du
cts
Cellmembrane
Accumulationof ROS (reactiveoxygen species)
Active species:ABACATCHSGSHJAMDARPALPMEPODSOD
Arabic acidCatalaseChalcone synthaseGlutathioneJasmonic acidMonodehydroascorbate reductasePhenylalanine ammonia lyasePectin methylesterasePolyphenol oxidaseSuperoxide dismutase
Eects
UVlight
O
O
H
O
OH
Presence of ROS induce activity of:- Antioxidant enzymes: SOD, CAT, POD, MDAR- GSH-Maintains cellular redox status
O2SOD
H2O2
H H
H OHO2
H2O2
Hydroxyl radicalSuperoxide radicalHydrogen peroxide
ABA Biosynthesis of JA
Activation of defensive gene expressions
Antioxidants
- Enzymatic antioxidant system - Phytoalexins
- Reduction of cell wall degrading enzymes (PME, cellulase, xylanase)
- Cell wall strengthening by formation of lignin polymers (peroxidases)
- Flavonoids- Chitinases and reductases (degrade fungal; cell walls)- Quinones (PPO)
- Phenolic compounds; phenolic acids, avonoids, anthocyanins (PAL, CHS)- Carotenoids- Lignans- Vitamin C
Hor
met
ic re
spon
se
Antimicrobialspecies
Cell wallreinforcement
H
H
FIGURE1.3 SchematicrepresentationofbiochemicalresponsesintheplanttissuemembranetriggeredbythehormeticUVtreatment.Enzymesthatplaycrucialrolesintheplantdefensivemechanismareshown.
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16 Advances in Fruit Processing Technologies
(2001, 2007) found higher levels of total phenols and polyamine compoundsinmangoesirradiatedwithUV-Cat4.93kJ/m2thaninfruitsexposedto2.46or9.86kJ/m2. In other studies, authors also observed induction of polyamine com-poundsinpeachesafterUV-Cexposure(Gonzlez-Aguilaretal.,2004).Theaccu-mulationofpolyaminesincropsmightbebeneficialinincreasingtheresistanceoffruittissuetodeteriorationandchillinginjury.Inparticular,exposureofcitrusfruitstoUVlightwasfoundtobeadvantageousin termsof theformationofflavonols.Forexample,Arcasetal.(2000)notedthatduetoUV-Cexposureat0.72kJ/m2,thecontentofnaringinandtangeretininthepeelofCitrus aurantiumfruitsincreasedby7%and55%,respectively.Table1.4summarizesresultsoftherecentstudiesofUVtreatmentsoffruitswhereUV-relatedenhancementinthecontentofthebioactivecompoundswasobserved.
1.4.4 StorageofPoSt-UV-treatedfrUitS
Thestorageconditions,suchastemperatureormodifiedatmosphere,canadverselyaffectthelevelsofUV-formedphytochemicals.Forinstance,Vicenteetal.(2005)observedincreaseintheantioxidantcapacityinpepperfruitsimmediatelyaftertheUV-Cexposure.Duringsubsequentstorageat10C,theantioxidantcapacityofpepperdecreased.However,after18daysofstorage,UV-treatedfruitsshowedmoreanti-oxidantsthancontrolfruit.Allendeetal.(2007)studiedtheeffectofthemodifiedatmosphere packaging on the quality of the UV-treated strawberries. The resultsrevealedthatstrawberriesstoredundersuperatmosphericO2andCO2-enrichedcon-centrationsat2Cshowedlowertotalphenoliccontentsafter5daysandavitaminCreductionafter12dayswhencomparedwiththefruitsthatwerekeptintheair.
1.4.5 formationofVitamind
MushroomsaretheonlyplantsourceofvitaminD2becausetheycontainahighamountofergosterol thatcanbeconvertedtovitaminD2afterexposuretoUVirradiation(Mauetal.,1998;JasingheandPerera,2005).Allthreec-UVbands(UV-A,UV-B,andUV-C)wereapplied for thepostharvest treatmentof ediblemushrooms.Mauetal.(1998)foundUV-B(310nm)lightmoreeffectivethanUV-C(253.7nm)incon-versionofergosterol tovitaminD2incommon(Agaricus bisporus)mushrooms.Itwasfoundthatduetoexposurefor2htoUV-B(9.86kJ/m2)andUV-C(14.71kJ/m2)light, the vitamin D2 content in common mushrooms increased from 2.20g/g ofdryweight to12.48and7.30g/g, respectively.UV-Birradiationalsoaffected thevitaminD2formationinShiitakeandStrawmushrooms,withtheincreaseratesof2.15and1.86g/h,respectively.However,Jasingheetal.(2006)reportedthatUV-Cexposure(23.0kJ/m2)for2hresultedinhigheryieldsofvitaminD2inalltreatedkindsofmushrooms,Shiitake,Oyster,Abalone,andButton,whencomparedwiththeUV-A(25.2kJ/m2).Itisknownthattheincreaseinphenolcontentmightbeaccompaniedbytissuebrowning.InthecaseoftreatmentsofShiitakeandStrawmushrooms(Mauetal.,1998;Jiangetal.,2010),thechangesincolorwerenotobserved.However,Mauetal.(1998)observedthatbothUV-BandUV-Ctreatmentsfor2hresultedindiscol-orationofcommonmushrooms.Therefore,theoptimalconditionsforUVprocessing
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17Ultraviolet Light for Processing Fruits and Fruit Products
TABLE1.4ExamplesofUVTreatmentsofFruitswiththeAccumulationofDifferentPhytochemicals
CommodityAffectedBioactive
CompoundsNumber/UVLamp/
PowerFluence Reference
Strawberries Increaseinantioxidantcapacityandtotalphenoliccontent
3/LPM/8W Erkanetal.(2008)
2.15kJ/m2
Blueberries Increaseinantioxidantcapacity,totalphenolicandanthocyaninscontent
15/LPM/8W, Wangetal.(2009)
2.15and4.30kJ/m2
Increasedtotalphenoliccontent 1UV-Bfluorescentlamp(305310nm)
Eichholzetal.(2011)
0.54kJ/m2
Grapeberries Increasedresveratrolderivativescontent
1/LPM/N/A Cantosetal.(2000)
0.01kJ/m2
3/UV-Blamp(340nm)/80W
Cantosetal.(2000)
N/A/LPM/510W Gonzlez-Barrioetal.(2009)
Apples Enhancedanthocyaninscontent UV-Blamp(320nm) Ubietal.(2006)
Peaches Enhancedcontentofpolyaminecompounds
N/A/LPM/15W Gonzalez-Aguilaretal.(2004)8.22W/m2
Mangoes Enhancedcontentsofphenolsandpolyaminecompounds(spermidine,putrescine,spermine)
N/A/LPM/15W Gonzlez-Aguilaretal.(2001,2007)8.22W/m2
Kumquat Enhancedphytoalexinscoparonecontent
LPM Rodovetal.(1992)
0.21.5kJ/m2
Orange Enhancedphytoalexinscoparonecontent
LPM Rodovetal.(1992)
1.59.0kJ/m2
Bitterorange Enhancedflavonolscontent(tangeretin)
1/LPM/N/A Arcasetal.(2000)
0.1W/m2
Limon Increasedtotalphenoliccontent 6/UV-Blamp(280400nm)/N/A
Interdonatoetal.(2011)
0.052and0.077kJ/m2
Pepperfruits Increasedantioxidantcapacity 4/LPM/30W Vicenteetal.(2005)
1,3,7and14kJ/m2
Greentomatoes
Increaseintotalphenoliccontent 2/UV-Blamp(311nm)/N/A
Liuetal.(2011)
20and40kJ/m2
Onions Enhancedquercetincontent UV-A(352nm) Higashioetal.(2005)
1.84W/m2
Shiitakemushrooms
EnhancedvitaminC,totalphenolic,andtotalflavonoidslevels
N/A/LPM/20W Jiangetal.(2010)
4kJ/m2
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18 Advances in Fruit Processing Technologies
stillneedtobedetermined.AsJasingheetal.(2006)concludedthattheirradiationof5goffreshShiitakemushroomsfor15minwithUV-AorUV-BissufficienttoobtaintherecommendedallowancesofvitaminDforadults(10g/day).
1.4.6 effectSongeneraLaPPearance
Nutritionalvalue,color,flavor,andtextureoffruitsarethemajorfactorsthatindi-cateproduct freshnessandhighly influence theconsumerschoice.Deteriorationandripeningduringstorageresultintissuedamage,discoloration,andformationofoff-flavor.UVtechnologycanbealsoprotectiveagainstthesesymptomsofsenes-cenceduetotheactivationoftheplantdefensivemechanismbythehormeticUVdoses.AccordingtoPomboetal. (2009),delayin thesofteningofplantproducecouldbeassociatedwithadecreaseintheexpressionofasetofgenesinvolvedincell-walldegradation,duringthefirsthoursafterUVtreatment.ItwasreportedthatoptimalUVtreatmentcanincreasetheshelflifeofstrawberries,apples,peaches,tomatoes,peppers,andbroccolibyreducingtherespirationrateandweight loss,retainingoverallvisualquality,delayingtheripeningandelectrolyteleakage,andmaintainingfirmness fora longer time,whencomparedwithcontrols (Luetal.,1991; Baka et al., 1999; Marquenie et al., 2002; Gonzalez-Aguilar et al., 2004;Lammertyn et al., 2004; Vicente et al., 2005; Costa et al., 2006; Allende et al.,2007;Lemoineetal.,2007;Pomboetal.,2009).Inordertoincreaseshelflife,theprocessingconditions,UVdose(kJ/m2),andemissionspectrumsshouldbeopti-mizedforagivencommodityofcrops.Lammertynetal.(2004)andAllendeetal.(2007) recommended 1.0kJ/m2 as optimal fluence for the UV-C processing ofstrawberriessinceathighertreatmentsauthorsobservedbrowninganddehydrationofthesepals.UV-Cfluencelevelsofabout45kJ/m2werefoundtohavethemostbeneficialeffectonshelflifeandqualityofmangofruits(Gonzlez-Aguilaretal.,2001,2007)andShiitakemushrooms(Jiangetal.,2010).ReportsareavailablethatapplicationofUVlightcanprotectthecolorofgreencommodities.Forinstance,Costaetal.(2006)andLemoineetal.(2007)reportedthatexposuretotheUV-Catpeakemissionof253.7nmandatfluencelevelsof78kJ/m2allowedretainingthehighestlevelsofchlorophyllandhencepreservesthegreencolorofbroccoliflorets.Similarly,UV-B(312nm)treatmentat8.8kJ/m2delayedthechlorophyllbreakdowninthebroccoliandlimepeel.Moreover,UVtreatmentresultedinreducedweightlossandshrivelingofthelimefruits(Aiamla-oretal.,2009;Srilaongetal.,2011).Aiamla-oretal.(2009)reportedthatattemptstodelaytheyellowingofbroccolibyUV-Alight(342nm)at4.5and9.0kJ/m2werenoteffective.
1.5 UVTREATMENTOFFRESH-CUTPRODUCE
Fresh-cutfruitsbecamepopularamongconsumersduetoincreasedpreferenceforminimallyprocessedfresh-likeandready-to-eatproducts.Mechanicaloperationsoffresh-cutfruitsproduction,suchaspeeling,slicing,shredding,etc.,oftenresultinenzymaticbrowning,off-flavors,texturebreakdown,andlowerresistanceoffresh-cutproducetomicrobialspoilageincomparisonwiththeunprocessedcommodities(Lemoineetal.,2007)becauseofpresenceofnaturalmicrofloraonthesurfaceof
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19Ultraviolet Light for Processing Fruits and Fruit Products
rawcommoditiesasshowninTable1.3.Therefore,duringoperationsofcuttingandshredding,cross-contaminationmayoccur,whichmightincreasetherisksoffood-borneoutbreaks.
To improvehygieneand safetyduringmechanicalprocessing, sanitizinganddripping treatments are commonly applied. During washing and dipping steps,raw or fresh-cut material is immersed into the tap water containing sanitizingagents(chlorine,sodiumhypochlorite)toremovespoilagemicroorganisms,pesti-cideresidues,andplantdebrisfromproductsurface(Martin-Bellosoetal.,2006).Toreducetheusageofsanitizingchemicals,UVlightaloneorincombinationwithozoneoranotherpreservativeagentwasexploredasnovelprocessingalternatives.FonsecaandRushing(2006)examinedtheeffectsofUV-Clight(1.413.7kJ/m2at253.7nm)onthequalityoffresh-cutwatermeloncomparedwiththecommonsani-tizingsolutions.Dippingcubesinchlorine(40L/L)andozone(0.4L/L)wasnoteffectiveinreducingmicrobialpopulations,andcubequalitywasloweraftertheseaqueous treatments compared with UV-irradiated cubes or control. In commer-cialtrials,exposureofpackagedwatermeloncubestoUV-Cat4.1kJ/m2producedmore than 1-log reduction in microbial populations by the end of the productsshelflifewithoutaffectingjuiceleakage,color,andoverallvisualquality.HigherUVdosesneithershoweddifferencesinmicrobialpopulationsnorresultedinqual-ity deterioration (13.7kJ/m2). Spray applications of hydrogen peroxide (2%) andchlorine (40L/L)without subsequent removalofexcesswater failed to furtherdecreasemicrobialloadofcubesexposedtoUV-Clightat4.1kJ/m2.Itwascon-cludedthatwhenproperlyused,UV-Clightistheonlymethodtestedthatcouldbepotentiallyusedforsanitizingfresh-cutwatermelon.Similarly,exposureofslicedapplestoUV-Cresultedinhigher(1log)reductionofListeria innocuaATCC33090,E. coliATCC11229,andSaccharomyces cerevisiaeKE162incomparisonwithapplespretreatedwithantibrowningandsanitizingagents(1%w/vascorbicacid0.1%w/vcalciumchloride).ThecombinationofUV-Cwithantibrowningpretreatmentbetterpreservedthecolorofslicedapplesduringstorageat5Cfor7days(Gmezetal.,2010).OtherstudieshaveshownthatUV-Ctreatmentappliedalonewasefficient in thereductionof thenumberofmicrobiologicalorganismspresentonthesurfaceoffresh-cutcrops.TheexamplesofsuccessfulapplicationsofUV-ClightaregiveninTable1.5.
Similarlytorawcrops,theeffectivenessofUVtreatmentonreductionofmicro-bialdeteriorationandqualityretentionwasdefinedbythedeliveredUVdoseandoverallcharacteristicsofthesurfaceexposedtotheUVlight.Allendeetal.(2006)foundabetterpreservationofRedOakLeaflettuceirradiatedbyUV-Clightonbothsidesoftheleaves.AsoptimalconditionfortheincreasingoftheshelflifeofRedOakLeaf lettuce, theauthors recommended theUVfluenceof2.37kJ/m2.Undesirablequalitychangesoccurringathigherfluencesincludedtissuesofteningand browning. Lamikanra et al. (2005) stressed that the moment of the applica-tionofUVlightduringthefruitprocessingisanimportantfactor.Intheirstudies,theauthorsexposed thecantaloupemelon toUV-Cat254nmduringcuttingandaftercuttingofthefruits.CuttingofcantaloupemelonundertheUV-Clightwasaseffectiveaspostcuttreatmentinreductionofyeast,molds,andPseudomonasspp.populations.However,fruitcuttingduringsimultaneousexposuretoUV-Cresulted
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20 Advances in Fruit Processing Technologies
inimprovedproductquality,thatis,reducedrancidityandrespirationrate,andalsoincreased firmness retention, when compared with postcut and control samples.BetterpreservationoffruitsprocessedduringtheUVexposurecanberelatedtothedefenseresponseofthewoundedplantenhancedbytheUV.Mechanicalinjuryoftheplanttissuesactivatestheexpressionofwound-induciblegenes.UVradiationis
TABLE1.5SummaryofStudiesoftheEffectofUV-CLightonReductionofMicroorganismsinFresh-CutProduce
Fresh-CutCommodity MicrobiologicalOrganism
Number/UVLamp/PowerFluence Reference
Watermelon Mesophilic,psychrophilic,andenterobacteria
15/LPM/36W Arts-Hernndezetal.(2010)1.6,2.8,4.8,7.2kJ/m2
Cantaloupemelon
Yeast,mold,Pseudomonasspp.,mesophilicaerobes,lacticacidbacteria
1/LPM/N/A Lamikanraetal.(2005)
0.0118kJ/m2
Apple L. innocuaATCC33090;E. coliATCC11229andSaccharomyces cerevisiaeKE162
2/LPM/15W Gmezetal.(2010)
5.60.3;8.40.5and14.10.9kJ/m2
Pear L. innocuaATCC33090,Listeria monocytogenesATCC19114D,E. coliATCC11229,andZygosaccharomyces bailiiNRRL7256
2/LPM/15W Schenketal.(2007)
15,31,35,44,56,66,79,and87kJ/m2
RedOakLeaflettuce
Enterobacter cloacae,Enterobacter asburiae,Erwinia carotovoraECC71,E. coliRecA_HB101andRecA+MC4100,Escherichia vulneris,Escherichia hermannii,Leuconostoc carnosum,Pantoea agglomerans,Pseudomonas fluorescensBiotypeGandA,Pseudomonas corrugata,Pseudomonas putidaC552,Pseudomonas tolaasii,Rahnela aquatilis,Salmonella typhimurium,Serratia ficaria,Serratia plymuthica,Serratia liquefaciens,Yersinia aldovae
15/LPM/15W Allendeetal.(2006)
1.18,2.37,7.11kJ/m2
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21Ultraviolet Light for Processing Fruits and Fruit Products
capableofinducingtheexpressionofplantdefense-relatedproteinsthatarenormallyactivatedduringwounding.Forexample,Lamikanraetal.(2005)reportedsignifi-cantincreaseinascorbateperoxidaseenzymeactivityduringstorageofcantaloupemelonprocessedunderUV-Clight.Peroxidasesprotectplantcellsagainstoxidation.Higherlevelsofterpenoids(-cyclocitral,cis-andtrans--ionone,terpinylacetate,geranylacetone,anddihydroactinidiolide)werefoundincantaloupetissues,whichcanplayimportantrolesasphytoalexinsinthediseaseresistanceofavarietyofplantfamilies(Lamikanraetal.,2005;Beaulieu,2007).Significantincreaseinantioxida-tivecompounds,suchasphenolicsandflavonoids,wasalsoobservedbyAlothmanetal.(2009)inUV-treatedfresh-cutbanana,pineapple,andguavafruits.However,decreaseinvitaminCwasobservedinallfruits.
In termsofUVeffectsonfruitsflavor,Beaulieu(2007)andLamikanraetal.(2005) reported that fruits processedwithUV light preserved their aroma to thesameextentasnontreatedcontrolsamples.Detailedstudiesofvolatilecompoundsinthin-slicedcantaloupetissuesrevealedthatUVtreatment isnotresponsibleforthechemicaltransformationstoesterbonds,esterase,andlipasedecrease.However,Beaulieu(2007)indicatedthatimpropercutting,handling,sanitationtreatment,andstoragecanradicallyalterthedesirablevolatilearomaprofileincutcantaloupeandpotentiallyleadstodecreasedconsumeracceptance.
1.6 UVPASTEURIZATIONOFFRESHJUICES
Fresh juices are popular beverages in the worlds market. They are perceived aswholesome,nutritious, alldaybeverages.For itemssuchas juicesor juicebever-ages,minimalprocessingtechniquesareexpectedtobeusedtoretainfreshphysical,chemical,andnutritionalcharacteristicswithextendedrefrigeratedshelf life.TheU.S.FDAapprovalofUVlightasanalternativetreatmenttothermalpasteurizationoffreshjuiceproducts(U.S.FDA,2000)ledtothegrowinginterestandresearchinUVtechnology.KeyfactorsthatinfluencetheefficacyofUVtreatmentoffruitjuicesincludeopticalproperties,designofUVreactors,andUVeffectsoninactiva-tionofpathogenicandspoilageorganisms.ThereareanumberofstudiesrecentlypublishedthatexaminedUVlightnotonlyasapotentialmeansofalternativepas-teurizationbystudyingeffectsonmicroflorabutalsoitseffectsonflavor,color,andnutrientcontentoffreshjuicesandnectars(Koutchma,2009).
1.6.1 UVaBSorPtionoffreShJUiceS
Fruitjuicesarecharacterizedbyadiverserangeofchemical,physical,andopticalproperties.Chemicalcomposition,pH,dissolvedsolids(Brix),andwateractivityhavetobeconsideredashurdlesthatcanmodifytheefficacyofUVmicrobialinac-tivation.Opticalproperties(absorbanceandscattering)arethemajorfactorsimpact-ingUVlighttransmissionandconsequentlymicrobialinactivation.UVabsorbanceandtransmittanceat253.7nmareimportantparameterstodesignUVpreservationprocessusinganLPMorLPHOsource. In thecaseof thebroadbandcontinuousUVandPL,itisimportanttomeasurethespectraoftheabsorbanceortransmittanceintheUVgermicidalregionfrom200to400nm.Thejuicescanbetransparentif
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22 Advances in Fruit Processing Technologies
10%3.5J/cm2)inthefreshlypreparedciderthaninthecommercialone.Inthecommercialfreshapplecider,UVCinducedlittlefuranatdoseslessthan3.5J/cm2.WhenfreshappleciderswereUVtreatedtoachievethe5-logreductionofE. coli,asrequiredbytheU.S.FDA,lessthan1ppbfuranwasfound. Itwasconcluded that a significant amountof furancouldbeaccumulatedif apple ciderwasovertreated.Overall, these results suggested that little furan isinduced inapplecider ifUV-Cprocessing isused for thepurposeof appleciderpasteurization.Thedestructionofd4-furanbyUV-Cindifferentsolutionsandappleciderwasalsoanalyzedinthisstudy.Therewaslittledestructionofd4-furanatadoseof0.9J/cm2whend4-furaninwater,glucose,sucrose,ascorbicacid,orappleciderwasUVtreated,butinfructosesolutions,88%ofd4-furanwasdestroyed.Inwater, lessthan10%ofd4-furanwasdestroyedevenatadoseof9J/cm2.Infruc-tosesolution,alld4-furanwasdestroyedat9J/cm2.Inadoseresponsestudy,itwasdemonstratedthatmostd4-furanwasdegradedeveninthelowdose(
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30 Advances in Fruit Processing Technologies
ofundesirablepathogenic,nonpathogenic,andspoilagemicroorganismsonthesurfacesoffreshfruitsandfruitproductsandinjuices.Inordertoachievetherequiredmicrobialreductionalongwithcolor,texture,andflavorpreservation,optimalUVprocessingconditionsandproperUVsourcehastobefoundforagivenproduct.RecentstudiesreportedapotentialofUVlightforenhancementofhealthpromotingcompoundssuchasantioxidants,polyphenols,andflavo-noids.Moreover,UVlightcanberecommendedaseffectivemeanstocontrolmicrobial loads in theair,water,nonfood,and foodcontact surfaces in fruit-processing facilities. A variety of UV sources are commercially available orcurrently under development that can be applied for specific fruit processingpurposes,whereasLPMlampsandxenonPLarecurrentlythedominantsourcesforUVtreatmentoffruitssincetheywereapprovedbytheU.S.FDAandHealthCanada.AnumberofUV-lightcontinuousflowsystemsthatincludedannularlaminarandturbulentflowreactors,thin-filmdevices,andstaticanddynamicmixersweredevelopedandvalidatedforavarietyoffruitjuicesforpasteuriza-tionpurposes.ThecorrectUVdesigncanreducetheinterferenceoflowUVTandviscosityassociatedwithsomejuicesandthereforeimprovestheUVinac-tivationefficiency.MoreworkisneededinregardtothedesignofUVsystemscapableofdeliveringsufficientUVdosestoallpartsofthetreatedliquidwithlowUVRsuchasfruitjuices.
NumerousstudiescitedherehaveshownthebeneficialeffectsoftheUVtreatmentonthepreservationofmanyfruits,bothrawandfreshcut.However,onthebasisoftheavailableliterature,themechanismthatunderliesthehormeticresponseinfreshproduceisstillopentodebate.InresponsetotheexposureofUVlight,plantsacti-vatedifferentenzymesperoxidases,reductases,andchitinases,whichdifferintheirchemical structure and absorptive properties in UV-A, UV-B, and UV-C ranges.Therefore,plantresponsevariesdependingonappliedUVemissionspectrumandUVdose.ToimprovethestateoftheexistingknowledgeonUVprocessingoffreshproduce,furtherstudiesarenecessarythatwillmeasureandreportconditionsandparametersoftheUVtreatment,suchaslampcharacteristics,emittedwavelength,andUVfluencelevels.
TheeffectofUVlightonthequalityoffruitsrequiresfurtherstudies.DespitethefactthatUVispurelyanonthermaltreatment,thepossibleundesirableeffectsmay include damage to vitamins and proteins, destruction of the antioxidants,changesincolor,andformationofoff-flavorsandaromasdependingonUVspectraandapplieddose. Inaddition, theeffectsofUV lighton thepotential formationofchemicalcompoundsinfoodsthatmaypresentahealththreatshouldbeevalu-atedtodeterminewhether thereisanytoxicologicalorchemicalsafetyconcernsassociatedwithproducts thathaveundergoneUVtreatment.CloserexaminationofUV-lightpotentialtodestroyundesirablecompoundsorpollutantsalsodeservesmoreattention.Due to lowpenetrationofUVlight, thecombinationswithotherpostharvesttechnologies(ozone,ultrasound,modifiedpackagingatmosphere,sani-tizing,andantibrowningagents)mightbeattractiveforprocessorsandmoreeffi-cient.LimiteddataareavailableonUVprocessingcombinedwithothertreatments,andfurtherstudiesarenecessary.
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31Ultraviolet Light for Processing Fruits and Fruit Products
LISTOFABBREVIATIONS
A AbsorptionAIN AluminumnitrideEL ExcimerlampEPA U.S.EnvironmentalProtectionAgencyEVA EthylenevinylacetateEVOH EthylvinylalcoholcopolymerFDA U.S.FoodandDrugAdministrationLED LightemittingdiodesLPHO Low-pressurehigh-outputlampLPM Low-pressuremercurylampMCL MaximumcontaminantlevelMPM MediumpressuremercurylampPBS Phosphate-bufferedsalinePL PulsedlampPME PectinmethylesterasePPO PolyphenoloxidaseR ReflectionRDA RecommendeddailyallowanceTorUVT TransmittanceortransmittanceofmaterialintheultravioletrangeUV UltravioletUV-A Ultravioletlightrange:315400nmUV-B Ultravioletlightrange:280315nmUV-C Ultravioletlightrange:200280nmcUV ContinuousultravioletmodeVUV Vacuumultravioletradiation(100200nm)
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