khoa manufacture

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INTRODUCTIONhoa is partially dehydrated, heat desiccatedmilk product and it is widely used as a base

material for preparation of numerous indigenoussweets. The increasing demand of khoa basedindigenous sweets has created need for largescale industrial production, ensuring uniformproduct quality, product safety, energyconservation, etc. Development of an industrialscale khoa making plant has been a challengeto dairy scientists since several years. Manyefforts have been made in mechanization of khoamaking process to improve heat transfer andalso to overcome the drawbacks of traditionalmethods as well as to commercialize the processfor industrial requirements. Extensive studieswere also carried out on the hydrodynamics andheat transfer of thin film scraped surface heatexchanger (TFSSHE) for processing of liquid,concentrated liquids, and particulate viscousfoods. Studies were also undertaken on theapplicability of thin film scraped surface heatexchanger (SSHE) for the mechanization of khoa.

According to PFA rules, revised in 2002, khoais a product obtained from cow or buffalo milkor a combination thereof by rapid desiccationand having not less than 30% fat on dry matter

basis of the finished product. According to IndianStandards (IS: 4883-1980), khoa shall be heatcoagulated milk-product obtained by partialdehydration of milk of buffalo, cow, sheep, andgoat or their admixture. Milk solids suitablyprocessed may also be used. It shall not containany ingredient foreign to milk except citric acidin danedar khoa added to develop desirablecharacteristic.

A large variation in quality of market surplusindicates three major varieties of khoa viz. pindi,dhap and danedar. Chemical composition, sensorycharacteristics and end uses of such varietiesare found to be different. These varieties of khoaare received in Delhi market, which is thebiggest khoa marketing centre in the countrytoday. These types of khoa differ in quality andalso in price. All of these varieties are in demandand are required for specific types of sweets asshown below (De, 1980).

Gross composition and specific sweets preparedfrom different khoa is given in Table-1.

The work on continuous khoa making machinegained momentum in recent years as a resultof greater emphasis laid for the manufacture ofindigenous milk products in the organized sector.For handling high viscosity products with or

Mechanized Manufacture of DanedarMechanized Manufacture of DanedarMechanized Manufacture of DanedarMechanized Manufacture of DanedarMechanized Manufacture of DanedarKhoa using ThrKhoa using ThrKhoa using ThrKhoa using ThrKhoa using Three Stage See Stage See Stage See Stage See Stage SSHESHESHESHESHE

* Dairy Engineering Division, NDRI, Karnal 132001 Haryana

2012-045 Received:October 2011; Accepted:July 2012

A.K.Dodeja and Ankit Deep

National Dairy Research Institute, Karnal-132001 (Haryana)

The present investigation is undertaken to explore the feasibility of three stage SSHE formanufacture of danedar khoa. Trails were conducted to optimise the process parameters suchas initial acidity of milk, mass flow rate, steam pressure and scraper speed. Initial acidity ofmilk was varied from 0.16 to 0.19% LA. The mass flow rate was varied between 170 to 210 kg/h.Three levels of scraper speed were taken in first, four levels in second stage and three levels inthird stage i.e. 200, 175 150 rpm, 200, 175, 150, 125 and 25,20,15 rpm respectively. Thequality of danedar khoa so produced was evaluated in terms of sensory evaluation and texturalprofile analysis. The best quality of danedar khoa was prepared by using standardized milkwith 0.18% LA initial acidity and keeping scraper speed 175, 150, 15 rpm for first, second andthird stage SSHE and flow rate 190 kg/h and steam pressure 4, 2 and 1.5 kg/cm2.

Keywords: Scraped surface heat exchanger (SSHE), Danedar Khoa, heat transfer coefficient

Research Article

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275 Indian J. Dairy Sci. 65(4), 2012

without particulates, and for the products thattends to foul the heat transfer surface, the thinfilm scraped surface heat exchanger (SSHE) ismost suitable.

Khoa is the basic ingredient in most of milkbased sweets. However, no systematic attempthas been made in the development of scientificmethods for predicting equipment performance,suited to the formation of desirable texture ofIndigenous dairy products. Since there is scantyknowledge of basic research data pertaining tothe texture of the khoa, it has been difficult tomake ameliorative effort to mechanize theprocess of khoa production with desirable texture.The three stage SSHE developed for themanufacture of khoa was attempted for themechanized manufacture of danedar khoa

Hence the present dissertation work is envisagedto produce danedar khoa using thin film scrapedsurface heat exchanger..

MATERIALS AND METHODSSelection of Raw materialMilkFresh buffalo milk and Skimmed milk wereprocured from Experimental Dairy NDRI, Karnal.Standardization was done to 6% Fat and 9%SNF. Acidity was increased up to 0.18% LA.

Caustic Solution

Caustic solution of 0.75% strength was preparedby using sodium hydroxide flakes LR grade forCIP of TFSSHE.

WaterPotable water available at Dairy EngineeringDivision was used for washing and cleaning.

Experimental ProcedurePreparation of khoa in Three Stage ScrapedSurface Heat Exchanger.The operating features and performance ofoperation of three stage SSHE has been describedelsewhere (Sharma, 2007). The photograph ofexperimental set-up is given in Plate-1 and flow

diagram in Plate-2. Buffalo milk was poured intobalance tank through sieve to f i lter anyextraneous matter out. Then milk flow wasvaried between 170- 210 kg/hr with the help ofelectromagnetic flow meter by controlling therpm of feed pump from the control panel. Thescrapper blade assembly of all SSHEs were settheir pre-decided rpm by control panel. TheSteam pressure in first and second stage wasfixed at 4 kg/cm2 and 2 kg/cm2 (gauge)respectively. The steam pressure was adjustedbetween 1.5 kg/cm2 to 2.0 kg/cm2 in thirdstage according to observation of the body ofproduct coming to third stage, from second stage.The milk flow rate was so adjusted to get theconsistency required in the product. Homogenousmixture of final product was obtained from outletof third stage which was collected in trays andspread into layer of uniform thickness. Thenproduct was covered with aluminium foil andcooled at room temperature. When product gotcooled, it was cut into pieces and analysed asexplained below.

Measurement and AnalysisAnalysis of milkInitially the raw milk was tested for fat, SNFand total solids (TS) by Gerber method (IS: 1224,1977) using lactometer.

Total solid (%) = SNF + Fat

Titratable acidity was determined using themethod described in IS: 1479 (Part-I)-1960.

Analysis of khoaChemical analysisThe khoa manufactured using three stage SSHEby selecting process variables underconsideration was analysed for Moisture/TS bygravimetric method as per IS: 2785 (1964).

Sensory EvaluationThe khoa made from fresh standardized buffalomilk have typical sensory attributes, whichdepends on the process variables under study,viz. steam pressure, rotor speed and mass flow

Table-1 Gross composition of various types of khoa

Type Gross Composition Specific Sweets Prepared

Fat% Moisture %

Pindi 21-26 31-33 Burfi, PedaDhap 20-23 37-44 Gulabjamun, PantuaDanedar 20-25 35-40 Kalakand, Gourd Burfi, Milk Cakes

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rate. The khoa samples were subjected forsensory evaluation by a panel of 5-7 judgesselected from Dairy Technology and DairyEngineering Division. A 25-point descriptive scalewas used for sensory attributes like Flavour,Body & Texture and Colour & Appearance.

Texture Profile AnalysisAnalyser (Model TAXT2i, double cyclecompression) of Stable Micro Systems, U.

K., combined with Texture Expert ExceedSoftware, installed in Dairy Technology Division,NDRI, Karnal. Khoa was evaluated for variousrheological properties l ike hardness,adhesiveness, springiness, cohesiveness,gumminess and chewiness.

Process ParametersThere are various process variables of threestage scraped surface heat exchanger that wereselected for designed research project under studyfor manufacture of khoa:

Mass flow rate: 170 - 210 kg/hrFirst stage SSHEPressure: 4.0 kg/cm2RPM: 150, 175, 200Second Stage SSHEPressure: 2.0 kg/cm2RPM: 125, 150, 175, 200Third Stage SSHEPressure: 1.5 to 2.0 kg/cm2RPM: 15, 20, 25

The quality of khoa so produced was evaluatedin terms of sensory scores, textural profileanalysis and TS/Moisture

RESULTS AND DISCUSSIONSIn the present Investigation systematic attempthas been made to produce danedar khoa usingthin film scraped surface heat exchanger. Productobtained was subjected to sensory evaluationusing a panel of judges. Texture profile analysiswas done by using a texture analyser.Instrumental texture profile analysis was usedto compare the subjective sensory assessmentof the textural attributes of the product. Basedon these determinations, the operating parameterfor formation of desired texture of the producthas been optimized. The results obtained duringpresent investigation are discussed in theproceeding text hereunder following heads:

Preliminary StudiesInitially trials were conducted using standardisedmilk of 5.5% fat and 9.0% SNF with differentacidity levels (0.16, 0.17, 0.18, 0.19 %LA) by usingSSHE and it was found that size and type ofgrains formed in final product was most suitablein case of milk with 0.18% LA. Acidity of milkwas adjusted to predetermined value by usingeither natural souring by keeping it inunrefrigerated conditions for some time (if aciditywas to be slightly raised) or by addition of smallquantities of 10% citric acid solution in caseacidity was to be raised substantially andmeasuring acidity after addition of citric acidsolution. In no case milk was neutralised asmilk received never exceed 0.16% LA initialacidity. In case of milk with 0.16 % LA therewere no grains and product was pasty in textureand with loose body. As acidity was increasedto 0.17 % LA there was small grain formationbut in pasty texture. In case of 0.18 % LA therewas good amount of grain formation desired indanedar khoa and also product was not pasty intexture. As acidity was increased to 0.19 % LAgrains formed were much harder and of largesize. The product was having acidic off flavourand also definite wheying off was observed inthe product. Hence milk with 0.18 % LA waschosen for further studies for processoptimization.

Effect of Scraper speed on Sensory AttributesEffect of Scraper speed on FlavourFig.1 indicates the effect of scrapper speed onflavour. It is evident that as scrapper speedincreases flavour scores decreases. It can beobserved from graph that flavour scores are higherfor lower speed in previous stage. This may bedue to the fact that at the higher scraper speed,the residence time of the product in the SSHEis reduced which leads to less release offlavouring compounds at higher speeds.

Effect of Scraper speed on Body and TextureFig 2 indicates the effect of scrapper speed onbody and texture. It is evident that as third stagescrapper speed increases body and texture scoresdecreases. It can be observed from graph thatbody and texture scores are highest when previousstage scrapper speed is kept at 172.94 m/s anddecreases on either side of 172.94 m/scircumferential velocity (150 rpm). Also the bodyand texture scores are lowest at lowest or highest

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values of speed. This may be because at higherscrapper speeds the grains formed are brokenby blade at higher scrapper speed, which resultsin a poor body and texture of the final product.The best results were observed at 172.945 m/scircumferential velocity for first and second stagescrapper assembly.

Effect of Scraper speedon Colour and AppearanceAs third stage scraper speed increases colourand appearance scores decreases. As first orsecond stage speed increases colour andappearance scores increases. It can be observedfrom graph that colour and appearance scoresare higher for higher speed in previous stage.This may be because in third stage most ofcooking occurs due to less speed and moreresidence time causing more color developmentwhich provides better color and appearance score

with fall in third stage speed.

Effect of Scraper speed on Overall AcceptabilityFig 3 indicates the effect of scraper speed onoverall acceptability. It is evident that as scraperspeed increases overall acceptability scoresdecreases. It can be observed from graph thatoverall acceptability scores are highest whenscrapper speed is kept at 172.945 m/s anddecreases on either side of 172.945 m/s. Alsooverall acceptability scores are lowest at lowestor highest values of scrapper speed. This isobtained after summation of all three previoussensory scores hence it has all previous effectsadded l inearly to give overall ef fect onacceptability of the final product.

Effect of Scraper speed on Texture ProfileEffect of Scraper speed on HardnessIt is evident from Fig 4 that as third stage scraperspeed increases hardness decreases. As first



or second stage speed increases hardness alsoincreases. It can be observed from graph thathardness is higher for higher speed in previousstage. This may be because as third stagescrapper speed increases, the residence timeof the product within the system decreases,resulting in higher moisture which lowershardness of the final product. But in case ofincreasing scraper speed of first and secondstage hardness decreases.

Effect of Scraper speed on GumminessFig 5 indicates the effect of scraper speed ongumminess. It is evident that as third stagescrapper speed increases gumminess decreasesbut as first or second stage speed increasesgumminess also increases. It can be observedfrom graph that gumminess is higher for higherspeed in previous stage. This may be becausegumminess is product of hardness andcohesiveness hence gumminess varies directlyas hardness does.

Effect of Scrapper speed on ChewinessFig 6 indicates the effect of scrapper speed onchewiness. It is evident that as third stagescraper speed increases chewiness decreasesbut as first or second stage speed increaseschewiness also increases. It can be observedfrom graph that chewiness is higher for higherspeed in previous stage. This may be due tofact that chewiness is directly proportional tohardness so it shows nearly same trends ashardness does.

Effect of Scraper speed on AdhesivenessNo particular trend is observed between scraperspeed and adhesiveness. Hence we may assumeadhesiveness to be uncorrelated to scraper speed.

Adhesiveness of khoa mad e by SSHE is on higherside than that made by conventional method.This may be due to salt imbalance of the milkduring processing in SSHE. It supports theargument of earlier workers that conditionsshould be standardized during processing.

Effect of Scraper speed on SpringinessNo particular trend is observed between scraperspeed and springiness. Hence we may assumespringiness to be uncorrelated to scrapper speed.

Effect of Scraper speed on CohesivenessNo particular trend is observed between scraperspeed and cohesiveness. Hence we may assume

cohesiveness to be uncorrelated to scrapper speed.The cohesiveness of the product made by SSHEwas higher than that obtained from conventionalmethod. It indicates that the extent ofdeformation of the product before it ruptures ishigher in the case of SSHE than made byconventional method.

Effect of Scraper speed on Overall Heat TransferCoefficientFig 7 indicates the effect of scraper speed onoverall heat transfer coefficient. It is evidentthat as scraper speed increases overall heattransfer coefficient also increases. It can beobserved from graph that U value is higher forlower speed in previous stage. This is be becauseincreasing scrapper speed increases turbulenceand hence led to higher heat transfer rates.But increasing scraper speed in previous stagecauses most of heat transfer to take place thereonly and much more concentrated and viscousproduct is delivered to next stage from whichevaporation rate decreases due to highconcentration and viscosity hence reduces heattransfer leading to comparatively lower overallheat transfer coefficient.

Overall heat transfer co-efficient Value variedfor first stage from 1431 W/m2K to 1775 W/m2K and for second stage it varied from 758W/m2K to 1385 W/m2K and for third stage itvaried from 126 W/m2K to 567 W/m2K.

Effect of Scrapper speed on Electric PowerConsumptionFig 8 indicates the effect of scraper speed onelectric power consumption. It is evident thatas scraper speed increases electric powerconsumption also increases. It can be observedfrom graph that electric power consumption ishigher for higher speed in previous stage. Thisis because increasing scraper speed increaseswork load on scraper motor and hence led tohigher power consumption. But increasingscrapper speed in previous stage causes moreheat transfer to take place in that stage andmuch more concentrated and viscous product isdelivered to next stage hence increasing density(due to rise in TS) of product so it becomes moreheavy to be handled (scrapped and conveyed) andincreasing power consumption.

Electric power consumption for first stage variedfrom 360 to 480W and for second stage it varied


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Plate 1:- Three Stage Scraped Surface Heat Exchanger (SSHE)



Plate2:- Flow diagram of Three Stage Scraped Surface Heat Exchanger (SSHE)

from 348 to 876W and for third stage it variedfrom 60 to 144W and for feed pump it variedfrom 228 to 300W.

Energy consumption using SSHESteam consumption for processing milk intodanedar khoa using SSHE varied from 0.925 to1.131 with an average of 1.017 kg steam usedper kg of milk processed.

Comparison between market sample anddanedar khoa from SSHESelection of optimal operating parametercombinationThe optimal combination of operating

parameter for production of danedarkhoa with desirable textural attributes has beenselected on the basis of overall acceptability ofthe product including all the sensory attributesof khoa. Hence optimum operating parametersfor production of danedar khoa using SSHE are:

Initial Acidity of standardised milk : 0.18 % LA

Flow rate of milk through feed pump : 190 kg/hr

RPM of First Stage SSHE : 175 rpm(201.769 m/s)

RPM of Second Stage SSHE : 150 rpm(172.945 m/s)


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RPM of Third Stage SSHE : 15 rpm(17.294 m/s)

Steam Pressure in First Stage SSHE : 4 kg/cm2

Steam Pressure in Second Stage SSHE : 2 kg/cm2

Steam Pressure in Third Stage SSHE : 1.5 kg/cm2

Values in brackets represent circumferentialvelocity or velocity at tip of scraper blade.

Comparative studyComparative study was carried out with themarket sample and danedar khoa made by usingthree stage SSHE with processing parametersas mentioned above. Table 2 representscomparison between the instrumental texturalparameters of market sample and product madeby using TFSSHE with 69.01 ± 1.89 percent totalsolid contents. All the textural parameters excepthardness and adhesiveness of product made byusing SSHE and market sample having aroundsame total solid content were not significantlydifferent from each other. Hence it is concludedthat product manufactured from SSHE wascomparable with market samples with exceptionthat it was softer and more adhesive as comparedto market sample.

REFERENCESDe, S. 1980. Indian Dairy Products, Outlines of Dairy

Technology, pub. Oxford University Press, Delhi, pp.382-466

Prevention of Food Adulteration act amendment rules2002. Directorate of prevention of food adulteration,Union Ministry, Govt of India, New Delhi

Indian Standards: 10083 1982. Method of Test for thedetermination of SNF (Solids-not-fat) in Milk by theuse of the Lactometer. Bureau of Indian Standards,New Delhi

Indian Standards: 1479, Part I 1960. Methods of Test forDairy Industry. Rapid Examination of milk. Bureau ofIndian Standards, New Delhi

Indian Standards: 1479, Part II 1961. Methods of Testfor Dairy Industry. Rapid Examination of milk. Bureauof Indian Standards, New Delhi

Indian Standards: 4079 1967. Indian Standard methodsof testing dairy products.

Indian Standard Institution, New DelhiIndian Standards: 4883 1980. Specification for khoa.

First edition reaffirmed 1999. Indian StandardInstitution, New Delhi

Nand Kishore, 2007. Feasibility studies on manufactureof khoa from low fat milk using three stage scrapedsurface heat exchanger. MTech thesis, DeemedUniversity, NDRI, Karnal.

Table 2 : Comparison of market sample and product made from SSHE

Instrument Textural Parameter Danedar khoa from Market Samplethree stage TFSSHE (Danedar Khoa)

Hardnes s(N) 25.209 ± 6.801 33.553Adhesiveness(N.s) -0.901± 0.553 -0.311± 0.389Springiness 0.342 ± 0.115 0.349 ± 0.172Cohesiveness 0.295 ± 0.095 0.222 ± 0.055Gumminess(N) 7.451 ± 2.419 7.448 ± 3.304Chewiness(N) 2.55 ± 1.099 2.59 ± 2.184


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