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PHYSICAL PROPERTIES OF CONCENTRATED MILK AND ITSINFLUENCE ON POWDER MILK CHARACTERISTICS AND SPRAYDRYER DESIGN PARAMETERSjfpe_65687.94BLANCA E. ENRQUEZ-FERNNDEZ1, CARLOS R. CAMARILLO-ROJAS2and JORGE F. VLEZ-RUIZ1,31Department of Chemical, Food and Environmental Engineering, Universidad de las Amricas, Puebla. Ex-Hacienda. Sta. Catarina Mrtir, Cholula,Puebla. 72820, Mexico2Food Technology Department, Universidad Tecnolgica de Tecamachalco, Tecamachalco, Puebla, Mexico3Corresponding author. TEL: 222-2292648;FAX: 222-2292727; EMAIL:jorgef.velezudlap.mxAccepted for Publication May 31, 2011doi:10.1111/j.1745-4530.2011.00656.xABSTRACTThe present work analyzed the properties of two concentrated milks, as well as theinfluence of the reconstituted type on some properties of milk powder. Two sets ofmilk with high solids content (4360% w/w) were employed; one set was concen-tratedbyevaporationof liquidmilk,whiletheotherwaspreparedbyreconstitutionof milk powder. Both concentrated milks were characterized at the different solidscontents,measuringflowandphysicochemicalproperties;findinganon-Newtonianbehavior well fitted by the Power law model. The bh color parameter, densityand consistency coefficient increased, while luminosity, redness and flow indexdecreased as a function of solids concentration. Lately, the reconstituted milk withfour levels of concentration was spray dried, and their properties, such as apparentdensity, color, moisture, particle size and rehydration, were determined. Based onpropertiesofreconstitutedandpowdermilks,otherengineeringparameters,suchasdropdiameterandheattransfercoefficient,wereequated,inordertorelatephysicalpropertiesfordryerdesign.PRACTICAL APPLICATIONSThis work is not a sophisticated study. It covers the fundamentals and practicalaspects of a very important food process operation, drying of milk. Most of theworksonfoodpreservationmethodshavebeenconductedtoanalyzemicrobiologi-cal,physicochemical and processing aspects,and very few studies have been carriedout to analyze the transport phenomena in spray drying, passing by concentrationaspectsandproperties.Thus,thispracticalandusefulworkappliesmomentum,heatand mass transfer approaches to quantify the flow properties of two concentratesand how they influence some physical properties for milk powder and two designparametersforthedryerperformance.INTRODUCTIONPowderedfoodshavebeengaininggreaterandgreatersignifi-canceinthefoodindustry,forhumanfeedingandasaninter-mediate material. The manufacture of food powder includeseveral unit operations,being two of the most important,theconcentration by evaporation of water in which the heattransferistheoutstandingphenomenon,andtheairdehydra-tion by mean of spraying, in which the mass transfer is thetranscendental one. Spray drying is a well-established andwidelyutilizedindustrialtechniquetotransformliquidfoodsand/orverythermalsensitivematerialsintopowderpresenta-tion (Birchal and Passos 2005; Gadelha et al. 2009). Some ofthe most recognized commercial sprayed dairy powders arechocolate, skim milk, soluble coffee and whole milk, amongothers.Evaporation of milk is based on heat transfer betweensteam as the heating medium and fresh milk, as the liquidto be concentrated. Liquid foods are concentrated todecrease water content and activity, favoring some technicalbs_bs_bannerJournal of Food Process Engineering ISSN 1745-453087Journal of Food Process Engineering 36 (2013) 8794 2011 Wiley Periodicals, Inc.implications such as enhancing shelf life, inducing consis-tency and flavor changes, reduction of volume and weightand diminishing energy consumption during air drying.Concentration contributes to modify the Newtonian natureof rawmilk,producinganon-Newtonianfluidfoodproduct,which may show time dependency or not in its flow behavior(Vlez-Ruiz and Barbosa-Cnovas 1998, 2000; Vlez-Ruiz2009a).On the other hand, spray drying involves the atomizationoftheconcentratedliquidfeedintoadryingairstream,whichproduces moisture evaporation. The formation of dropletsduring spray drying is governed by the physical properties ofthe concentrated milk, the transport phenomena and theoperating conditions of the equipment (Masters 1991; Okoset al. 1992; Bienvenue et al. 2003; Baldwin and Pierce 2005).Considerable efforts have been conducted to develop experi-ments and models that contribute to the interpretation ofspray drying performance and to assist in dryer design,sincethecontrolandimprovementof spraydryingperformanceisof great importance (Kuts and Samsonyuk 1989; Onwulata2005; Chegini and Ghobadian 2007; Kelly 2008).Technically,the spray drying process is considered as part of the secondgenerationof dryers(Barbosa-Cnovas et al.2001),andcon-ceptually divided into three stages: the spraying phase, thedrying phase and the residual-collecting phase (Arnason andCrowe 1980;Vlez-Ruiz 2000;Bhandari 2008).For food pro-cesses through powder manufacture,it is very useful to knowthefundamentalsofmomentum,heatandmasstransferphe-nomena and how they are influenced by properties of theconcentratedmilk.The production of high-concentrated milk is difficult duetothelargeincreaseinapparentviscositywhentotalsolidsarearound or exceed 45% (Hayashi and Kudo 1990; Vlez-Ruizand Barbosa-Cnovas 1998,2000).Fluid milk with that con-centration is difficult to atomize, and in accordance withHayashiandKudo(1990),thelargedropletsresultingfromitdecreasethethermalefficiencyof thespraydryer.Thisdryingtechnique is very useful for thermo-sensitive foods, in whichthermaldamageislimited,thedehydrationisveryfast,takingafewseconds(Bimbenetet al.2002).Although the concentrated milk is a non-Newtonian fluid(Vlez-RuizandBarbosa-Cnovas1998),Filkov(1980)con-sidered the milk as a Newtonian fluid and stated the viscosityof sprayedliquidasnecessaryforpredictionof dropletdiam-eter. Weberschinke and Filkov (1982) developed a relation-ship for the milk drop diameter as a function of apparentviscosity. And in according to Keogh et al. (2004), if spraydriedmilkisusedforchocolateformulation,particlesizewillaffect its physical properties. Therefore, the design of anindustrial spray dryer requires accurate information of theconcentratemilkbehavior,toproduceafinalproductof highquality. The quality of milk powders based on a variety ofproperties, such as the color, density, final moisture content,particle size, solubility index (SI) and other physical proper-ties are of primary importance for engineering applicationsand design as well (Straatsma et al. 1999; Vlez-Ruiz 2000;Verdurmenet al.2002).This dehydration process is strongly influenced by thecharacteristics of concentrated milk, and although severalstudies have been completed (Filkov 1980; Hayashi andKudo 1990; Vlez-Ruiz and Barbosa-Cnovas 1998, 2000;Bienvenueet al.2003;IlariandMekkaoui2005),theinforma-tionontheeffectof milkonpowderpropertiesislimited,andpractical correlations of engineering parameters are scarce.Even for simulation purpose, predictive computer modelsand application of computational fluid dynamics (Straatsmaet al. 1999; Verdurmen et al. 2002; Lo 2005), several powderproperties are needed.According toVerdurmen et al.(2002),predictive mathematical and computer models have proventheir effectiveness in reducing process costs and improvingproductqualityinthefoodindustry.Thus, the objectives of this work were: to characterize theflow response of two types of concentrates, to analyze theinfluenceof flowpropertiesof reconstitutedmilkonthefinalproperties of milk powder and to find out some theoreticalcorrelationsfordesignof spraydryingequipment.MATERIALS AND METHODSMaterialsBothtypesof commercialwholemilks,liquid(Alpura,Gua-najuato, Mexico, 2.8% fat, 3.1% proteins and 4.8% carbohy-drates) for preparation of concentrated,and powder (Nido,Nestle, Veracruz, Mexico, 23.4% proteins, 26.3% fat and38.6% carbohydrates) for preparation of reconstituted milkwereacquiredatalocalsupermarket.Preparation of Concentrated andReconstituted MilksMilk samples were prepared by two ways: (1) concentrationof fluid milk (Alpura) by evaporation with a vacuum(50.82 kPa) lab rotavapor Bchi (R-111, BCHI Labortech-nikAG,Flawil,Switzerland),which was identified as concen-trated milk; and (2) by reconstitution of dried powder milk(Nido) inside a commercial shaker, which was identified asreconstitutedmilk.Inbothtypes,fourlevelsof concentrationwere reached (between 43 and 60% w/w). Brix degrees wereutilized as a rapid measure of sample solids, then lately weredeterminedastotalsolids.Characterization of MilksConcentrated and reconstituted milks were characterized byfollowingstandardmethods,makingsomedeterminationsinCONCENTRATED AND POWDER MILKSBLANCA E. ENRQUEZ-FERNNDEZ, CARLOS R. CAMARILLO-ROJAS and JORGE F. VLEZ-RUIZ88Journal of Food Process Engineering 36 (2013) 8794 2011 Wiley Periodicals, Inc.triplicate(coloranddensityforbothconcentrates,andmois-ture for reconstituted milk) and,the rest of the measures wascarried out only in duplicate (flow properties and moistureforevaporatedmilk).Moisture Content. By following the 990.20 methodology(AOAC 2000), 10 mL of sample was evaporated in a steambath for 30 min, and then dried in a vacuum oven at 105Cuntilconstantweight.Density. By mean of Grease pycnometers, the weight andvolumeof thesamplesweremeasured.ColorMeasurement. ByusingHunterparametersevalua-tion,with10 mLofmilkinreflectancemodewithaColorme-ter(GardnerColorgardSystem05,HunterLabs,Reston,VA),objective color was measured in terms of Lh (lightness), ah(redness and greenness) and bh (yellowness and blueness).The instrument sensor geometry utilizes two beams of light,90 in azimuth with 45 illumination and 0 viewing, it wascalibrated with a standard white plate (L = 92.89, a = -1.05,b = 0.82).Flow Behavior. Flow properties were determined instru-mentally with a Brookfield Viscometer (DV-I, BrookfieldEngineering Laboratories Inc., Middleboro, MA) using anupward sequence with 10.5 mL of milk, at a temperature of30C, for each concentration. Thus, a set of velocities on anupwardcurvewasprogrammedfrom0.5to100 rpm,andthecorresponding torque magnitudes were registered. Frompairs of the rotational velocitytorque values (maximumtorque of 0.0014374 N/m) and applying those constantsgiven by the manufacturer (Brookfield Engineering Labora-tories Inc.), the apparent shear rates and shear stresses weremathematically evaluated and graphically represented, byusingthenexttwoequations:?=()2222RRRccb(1)=TR L22b(2)where g is the shear rate (1/s),w is the angular velocity of thespindle (rad/s) = 2pN/60, N is the spindle speed (rpm), Rcistheradiusofthecup(m),Rbistheradiusofthespindle(m),sis the shear stress (Pa), T is the torque (N/m) and L is theeffectivelengthof thespindle(m).The flow parameters for both concentrated milks wereevaluated from the corresponding rheograms,by applicationof the Power law (PL, Eq. 3) and the Herschel and Bulkley(HB,Eq. 4)models.Theaccuracyofthefittingwasquantifiedbymeansof thesquarerootof meanerror:= K?n(3)=+0K?n(4)where K is the consistency coefficient (Pa sn), n is the flowbehaviorindex(dimensionless)ands0istheyieldstress(Pa).Spray Drying of MilkThedryingwasconductedinaverticalNirospraydryer(pilotplantmodel,GeaProcessEngineeringInc.,Soborg,Denmark). The reconstituted concentrates were suppliedinto the Niro spray dryer by a rotating atomizer (15,00024,000 rpm), with an air rate of 360 kg/h at 200C. Amaximum drying capacity of 35 kg/h may be reached,depending on the operating conditions. The drying conicchamber of 60 has a diameter of 1.2 m and a height of0.75 m.A hand anemometer (LCA-6000, Airflow Developments,Buckinghamshire,U.K.) was used at the air enter to quantifyair velocity. The milk powder was collected at the bottom ofthedryerandstoredinsealedbagsatconstanttemperatureof15C.Characterization of Dried MilkThecharacteristicsofthedriedmilkwerecompletedindupli-cateandfollowingthenextstandardmethods:Color Measurement. By using the same Hunter param-eters evaluation, with 10 g of powder, in reflectance mode(GardnerColorgardSystem05).Apparent or Bulk Density. This property was quantifiedintwoforms,nontapped(10times)andtapped(100times);itwas determined inside a test tube with 100 g of powder.Tapped density is often reported as bulk density at 100 taps(BaldwinandPierce2005).Moisture Content. Following the 997.05 methodology(AOAC 2000), 510 g of sample was dried in an oven at102 ? 2C.SI and Rehydration Degree. According to the AmericanDryMilkInstitute,thesolubilityindex(SI)maybemeasuredby reconstitution of 10 g of powder in 100 mL of water andwith a setting time of 15 min (Niro 2007). For rehydrationdegree (RD), 0.5 g of powder was diluted in 50 mL of waterBLANCA E. ENRQUEZ-FERNNDEZ, CARLOS R. CAMARILLO-ROJAS and JORGE F. VLEZ-RUIZCONCENTRATED AND POWDER MILKS89Journal of Food Process Engineering 36 (2013) 8794 2011 Wiley Periodicals, Inc.inside a glass tube, the tube was turned down and up eighttimes and then centrifuged for 5 min.After that,the quantityof sedimentwasmeasured.ParticleSize. ByusingdifferentTylersievesof 75,125,150,180, 300 and 500 mm, with 50 g of sample and utilizing aRo-Tap equipment (Ro-Tap,Test Sieve Shakers, W.S. Tyler,Mentor, OH), and following the indications of Masters(1991)tocomputetheaveragediameterof thesample.Prediction of Design Parameters forSpray DryingTwoimportantdesignparameters,thedropdiameterandtheconvectiveheattransfercoefficient,werepredictedfrommassbalance and heat transfer Eqs. (5) and (6), proper for thespray drying operation. Ideal mass balance was based onsolids content, while an ideal energy balance between theevaporation energy and the convective heat was utilized forthe convective coefficient (Masters 1991; Vlez-Ruiz 2000;BirchalandPassos2005):WWDsolidsPsolids(5a)1611161133DmDmDCDPPP+(5b)QdmdthA TwaterevapML(6a)where W is the weight of solids (kg),D is the diameter (m),risthedensity(kg/m3),misthemoisturecontent(kgwater/kgd.s.),Q is the required heat for water evaporation (kW), t is theprocess time (s), levapis the specific evaporation heat forwater (kJ/kg), h is the convective heat transfer coefficient(kW/m2C), A is the heat transfer surface (m2), DTMListhe logarithm mean of temperature difference (C), andsub-indexes D is for the drop,P for the particle and C for theconcentrate.From previous equations, the next final correspondingexpressionswereobtained:DDmmDPPPCC=+31 31111(5c)ht TDDCevMLDP=() 2 (6b)Statistical AnalysisThe statistical analysis was done by using a Minitab software(15th version, Minitab Inc., State College, PA), to establishsignificant differences among systems. Analysis of variance(ANOVA) was performed to determine the effects of boththe concentration and type of concentrated on the milk orpowderproperties.RESULTS AND DISCUSSIONInordertounderstandthepropertiesoftwoconcentrates,theeffect of reconstituted milk on powder milk, and the pre-dicted design parameters for drying performance,the resultsareanalyzedanddiscussedinthatorder.Characterization of Evaporated andReconstituted MilksBothtypesof milkwerecharacterizedatthedifferentlevelsofconcentration; the measured properties of both concentratesareincludedinTable 1.Allthesepropertiesreflectedtheeffectof the preparation process, as well as the effect of the solidsconcentration. Milk is white (combination of a and b) andTABLE 1. PROPERTIES OF CONCENTRATED MILK WITH DIFFERENT SOLIDS CONCENTRATIONSolids content (% w/w)Color parameters (dimensionless)Density(kg/m3)K(Pa sn)n(dimensionless)Evaporated:43.4 ? 0.6 (42.5 Brix)L: 87.5 ? 0.2, a: -2.7 ? 0.2, b: 15.1 ? 0.41,115 ? 160.1290.6947.7 ? 0.9 (45.0 Brix)L: 87.1 ? 0.1, a: -2.9 ? 0.1, b: 15.9 ? 0.11,124 ? 260.3840.6552.3 ? 0.6 (48.0 Brix)L: 86.6 ? 0.1, a: -2.9 ? 0.0, b: 16.2 ? 0.01,132 ? 2516.010.3060.1 ? 1.1 (49.5 Brix)L: 86.2 ? 0.1, a: -3.1 ? 0.1, b: 17.6 ? 0.01,181 ? 4459.980.21Reconstituted:44.9 ? 0.3 (42.5Brix)L: 90.0 ? 0.0, a: -4.9 ? 0.1, b: 17.5 ? 0.11,095 ? 480.7480.7349.9 ? 1.2 (45.0Brix)L: 89.6 ? 0.1, a: -5.0 ? 0.1, b: 17.9 ? 0.21,102 ? 503.4010.5751.1 ? 1.4 (48.0Brix)L: 89.4 ? 0.1, a: -5.1 ? 0.1, b: 18.3 ? 0.21,108 ? 416.0400.5956.1 ? 1.4 (49.5Brix)L: 89.2 ? 0.0, a: -5.3 ? 0.0, b: 19.2 ? 0.11,114 ? 2030.350.41CONCENTRATED AND POWDER MILKSBLANCA E. ENRQUEZ-FERNNDEZ, CARLOS R. CAMARILLO-ROJAS and JORGE F. VLEZ-RUIZ90Journal of Food Process Engineering 36 (2013) 8794 2011 Wiley Periodicals, Inc.luminous(highvaluesof L)asaconsequenceof milkcompo-nents; mainly, the large particles that scatter the light. Asexpected,densityandflowpropertieswerenotablyaffectedbythe concentration level, showing an increasing in the densityand consistency coefficient due to solids interaction,whereastheflowbehaviorindexdecreasedshowinganon-Newtoniannatureof pseudoplastictype.Colorparametersanddensitywererelatedtosolidscontentby a linear relationship (Table 2).For the flow response,bothconcentratedmilksweresatisfactorilyfittedbyPLmodel,andallthesamplesexhibitedashearthinningnature.Forconcen-tration above 43%, contrary to our results, Vlez-Ruiz andBarbosa-Cnovas(1998)reportedabetterfittingwiththeHBmodel for evaporated milk.Similarly,Bienvenue et al.(2003)fitted the flow response of concentrated skim milk to theBingham model in order to quantify the yield stress affectedby storage time. Both properties, flow (without yield stress)and color (high luminosity), may be related to a lower effectof heat treatment for evaporated and reconstituted milks;since the concentrates obtained by Vlez-Ruiz and Barbosa-Cnovas (1998) were exposed to a higher heat treatment,thus,thoseconcentratesexhibitedyieldstressandlowerlumi-nosity. Comparatively, reconstituted milk showed higher Lvalues that could indicate a less severe heat treatment due toan industrial application; thus, evaporated milk obtainedfrom the laboratory most likely received a longer heattreatment.Flow parameters of studied concentrates were similarlycorrelated to solids content, the consistency coefficient wasrelated to solids concentration by an exponential equation,whereastheflowindexwasrelatedtosolidsbyalinearone.Allthe obtained relations among the physical property andsolids content are included in Table 2, being all acceptable(R2 0.90) although better for some of them (R2 0.95); anadditional linear correlation was included for concentratedand reconstituted milks in which a fresh milk (13% w/w ofsolidscontent)withn = 1wasincluded,duetothefactthatitwastherawmaterialforpreparationforbothtypesof milk.ANOVA analysis indicated that there was a significant dif-ference (P 0.05) betweenevaporatedandreconstitutedmilks.Thus,thelevelofsolidsisnot different, but the correspondent properties are differentand may be attributed to the varied operational conditionsexperienced during the production and preparation treat-ments. Particularly, the reconstituted milk that has beenexposed to various treatments through the manufacturingprocess;whereasthattheevaporatedsamplethatreceivedtwoheat treatments,the concentration at the laboratory,in addi-tiontopreviouspasteurizationprocessgivenbytheindustry.Although there was significant difference between thephysical properties of both concentrates, reconstituted milkwasemployedforspraydryingexperimentsduetothefacilityandvelocityof preparationatlaboratoryscale.Spray Drying of Reconstituted MilkFour batches of reconstituted milk (40 L) at the correspon-dent levels of solids (42.5,45.0,48.0 and 49.5Brix) were pre-paredinordertobedehydratedinthespraydryerequipment.Flowpropertiesofthesesampleswereevaluatedat30and40C(Table 3),aspotentialtemperaturesfordryerfeeding.Milkpreviouslywarmedupto30Cwaspumpedbyaposi-tive displacement pump from a plastic tank, and the flowvolumetric rates varied as a function of the concentration,17.4, 32.4, 44.4 and 55.0 L/h, respectively; that was therequired flow to reach and maintain an air temperature of78C at the outlet of the equipment. The operational condi-tions for the dryer were: 20,600 rpm for the atomizer,227 ? 4.6C for air at the inlet,78 ? 8.1C for outlet tempera-ture and air velocity of 57.4 ? 10.3 m/s.Those milk powdersobtainedfromreconstitutedmilksweresubjectedtodifferenttechniques in order to be characterized; the results of thosedeterminationsareincludedinTable 4.TABLE 2. FITTING EQUATIONS FORDENSITY AND FLOW PROPERTIES OFCONCENTRATED MILKSPhysical propertyEvaporatedR2ReconstitutedR2Color parameters: (dimensionless)L = 90.830.078 SC0.97L = 93.260.073 SC0.97a = -1.620.025 SC0.95a = -3.050.040 SC0.93b = 8.84 + 0.144 SC0.98b = 10.7 + 0.149 SC0.94Density (kg/m3)r = 942.1 + 3.86 SC0.91r = 1,029 + 1.51 SC0.95Consistency coefficient (Pa sn)K = 9 10-9exp0.376C0.99K = 2 10-6exp0.293C0.99Flow index (dimensionless)n = 2.0840.032 SC0.93n = 1.8240.025 SC0.95(without inclusion of whole fresh milk, and mainly for concentrated milk with SC 43% w/w)Flow index (dimensionless)n = 1.2650.016 SC0.93n = 1.1860.012 SC0.95(with inclusion of whole fresh milk, n = 1, and mainly for concentrated milk with SC 43% w/w)Flow index (dimensionless)n = 1.0590.011 SC0.90n = 1.0240.009 SC0.95(with inclusion of water, n = 1, and mainly for concentrated milk with SC 43% w/w)SC, solids content (% w/w).BLANCA E. ENRQUEZ-FERNNDEZ, CARLOS R. CAMARILLO-ROJAS and JORGE F. VLEZ-RUIZCONCENTRATED AND POWDER MILKS91Journal of Food Process Engineering 36 (2013) 8794 2011 Wiley Periodicals, Inc.The four milk powders had moisture contents (MCP)below 5%, corresponding to this kind of dehydrated foods,although with an important variability in duplicated deter-minations. It was related to the solids concentration level ofthe concentrated; thus, an empirical relationship (Eq. 7)between the milk concentration and moisture content wasobtainedwithagoodfitting(R2= 0.96):MCXPC=21074 1946.(7)Further,consideringtherheologyofthereconstitutedmilkat30C,asimilarempiricalrelationship(Eq. 8)wasquantifiedforpowdermoistureandtheconsistencycoefficient(R2= 0.99);thatisnotcommonlyusedtoexpressmoistureasafunctionofaflowparameter,butitisapracticalrelationshipif the final moisture wants to be evaluated from the concen-tratedmilkconsistency:MCKPC=1 12540 4182.(8)whereMCPisthemoisturecontentformilkpowder(%w/w),XCis the moisture content of the reconstituted milk (% w/w)andKCistheconsistencycoefficientof thereconstitutedmilk(Pasn).Colorparametersdidnotshowsignificanteffect(P 0.05) of the solids content of milk. Both densities(tapped and nontapped) showed an increasing trend as afunction of milk concentration, with exception of concen-trate 45Brix. But curiously, the difference between thetapped and nontapped densities was related to the concen-tration, with values of 109, 88.7, 67.3 and 56.8 kg/m3,respectively. Tapped bulk densities for typical milk powder(Baldwin and Pierce 2005) have been reported among 380and 750 kg/m3, depending on the powder type and theircompactability degree.With respect to the particle size, the cumulative distribu-tionofsizesallowedtheevaluationofthemeansizeinarangeof 235 to 250 mm. These diameters in the range of 100400 mm are commonly reported for powder milks (Hall andHedrick 1971; Keogh et al. 2004; Ilari and Mekkaoui 2005;BaldwinandPierce2005;Lo2005).Both solubility tests (SI and RD; data not included) indi-cated that even though the utilized concentrate was fromreconstitutedmilk,noinsolublematerialwasformedafterthespray drying, the milk sample being thermally stable duringthedryingprocess.Modeling of Spray Drying Design ParametersBased on our results and considering ideal mass and energybalances, drop diameters and convective heat transfer coeffi-cients were predicted by Eqs. (5) and (6). These designparameters are not commonly reported in the literature,andtheobtainedmagnitudesarepresentedinTable 5.The predicted drop diameter (DD: 320340 mm) corre-spondstoarangeofdiametersthatisreportedorusedforcal-culationandsimulationpurposes(? 500 mm).Asafunctionofthediameterdecreasing,thedropshouldhavetheinconve-nience of a reduction in the area for heat and mass transferphenomena.Whereas the predicted convective coefficient (h) corre-sponds to intermediate values between 1,200 and 10,000W/m2K, cited by Vlez-Ruiz (2009b, 2009c) for evaporationof milk, boiling of corn syrup and water vaporization. Thesemagnitudes favor the heat transfer for water evaporation,among milk droplets and hot air at high flow rates.This heattransfer parameter is scarcely reported in powder milk pro-cesses; Hayashi and Kudo (1990) reported a volumetric coef-TABLE 3. PROPERTIES OF RECONSTITUTEDMILK AT TWO TEMPERATURESSolidscontent (Brix)30C40CK (Pa sn)n(dimensionless)K (Pa sn)n(dimensionless)42.50.45 ? 0.230.59 ? 0.070.34 ? 0.070.61 ? 0.0945.03.23 ? 0.190.58 ? 0.051.25 ? 0.160.68 ? 0.0148.09.68 ? 3.550.53 ? 0.304.16 ? 3.120.57 ? 0.0449.524.83 ? 2.190.55 ? 0.0112.48 ? 12.20.58 ? 0.07TABLE 4. PROPERTIES OF DRIED MILKSolids content ofreconstituted milk(% w/w)Moisture ofpowder milk(% w/w)Color parameters (dimensionless)DensityMeandiameter(mm)Nontapped(kg/m3)Tapped(kg/m3)44.7 ? 1.4 (42.5Brix)1.5 ? 1.0L: 92.6 ? 0.7, a: -4.6 ? 0.2, b: 16.8 ? 0.6485 ? 31594 ? 40235 ? 3548.1 ? 1.5 (45.0Brix)2.4 ? 1.0L: 90.7 ? 1.1, a: -4.6 ? 0.2, b: 18.0 ? 1.8468 ? 19556 ? 43248 ? 2653.3 ? 2.1 (48.0Brix)3.0 ? 1.3L: 91.5 ? 1.4, a: -4.2 ? 0.2, b: 16.1 ? 1.2539 ? 39606 ? 12250 ? 3558.2 ? 2.6 (49.5Brix)4.9 ? 1.0L: 90.9 ? 0.5, a: -4.8 ? 0.4, b: 18.2 ? 1.4564 ? 41621 ? 57245 ? 45CONCENTRATED AND POWDER MILKSBLANCA E. ENRQUEZ-FERNNDEZ, CARLOS R. CAMARILLO-ROJAS and JORGE F. VLEZ-RUIZ92Journal of Food Process Engineering 36 (2013) 8794 2011 Wiley Periodicals, Inc.ficient of 1120 for spray drying of milk and values of1922 W/m3Kforspraydryingof soyproteinmilk.Finally, an empirical correlation (R2= 0.98) was obtainedfor the predicted heat transfer coefficient (hp, W/m2K) as afunction of the consistency coefficient (KC, Pa sn) for thereconstituted milk at 30C, which allows to quantify thisdesign parameter with the knowledge of the flow propertiesof theconcentratedmilktobespraydried:hKp= 2810 90 2499.(9)CONCLUSIONSThe need for engineering data for process calculations andequipment design is augmenting day by day. Therefore,those studies dedicated to cover transport and engineeringaspects are very important. In this study, flow and physico-chemical properties of evaporated and reconstituted con-centrates were determined, and from them, some interestingand useful relationships were obtained: color, density andflow properties from both milk concentrates were correlatedto solids concentration. Similarly, properties such as color,density, mean diameter and moisture of dried milk weremeasured; furthermore, powder moisture content wasempirically related to solids concentration and consistencycoefficient of the milk concentrate. Additionally, other engi-neering parameters, such as drop diameter and heat transfercoefficient, were theoretically predicted from mass balanceand heat transfer analyses, giving acceptable values; and as afinal correlation, the predicted heat transfer coefficient wasexpressed as a function of the consistency coefficient. Mod-eling is very important because those predicting equationsallow a rapid estimation of engineering parameters duringthe manufacturing process of milk powders.REFERENCESAOAC.2000.OfficialMehodsofAnalysis,Associationof OfficialAnalyticalChemists,Washington,DC.ARNASON,G.andCROWE,C.T.1980.Assessmentofnumericalmodelsforspraydrying.InDrying80.Proceedingsof theSecondInternationalSymposium(A.S.Mujumdar,ed.)pp.410416,HemispherePublishingCorporation,NewYork,NJ.BALDWIN,A.andPIERCE,D.2005.Milkpowder.InEncapsulatedandPowderedFoods(C.H.Onwulata,ed.)pp.387433,CRCPress,BocaRaton,FL.BARBOSA-CNOVAS,G.V.,VEGA-MERCADO,H.andGNGORA-NIETO,M.M.2001.Dehydrationof foods:Past,presentandfuture.InProceedingsof theSecondInter-AmericanDryingConference,pp.4355,Ducere,Publishing,D.F.,Mexico.BHANDARI,B.2008.Spraydryingandpowderproperties.InFoodDryingScienceandTechnology:Microbiology,Chemistry,Applications(Y.H.Hui,C.Clary,M.M.Farid,O.O.Fasina,A.NoomhormandJ.Welti-Chanes,eds.)pp.215248,DEStechPublications,Inc.,Lancaster,CA.BIENVENUE,A.,JIMENEZ-FLORES,R.andSINGH,H.2003.Rheologicalpropertiesof concentratedskimmilk:Importanceof solublemineralsinthechangesinviscosityduringstorage.J.DairySci.86,38133821.BIMBENET,J.J.,SCHUCK,P.,ROIGNANT,M.,BRULE,G.andMEJEAN,S.2002.Heatbalanceof amultistagespraydryer:Principlesandexampleof application.Lait82,541551.BIRCHAL,V.S.andPASSOS,M.L.2005.Modelingandsimulationof milkemulsiondryinginspraydryers.BrazilianJ.Chem.Eng.22(2),293302.CHEGINI,G.R.andGHOBADIAN,B.2007.Spraydryerparametersforfruitjuicedrying.WorldJ.AgriculturalSci.3(2),230236.FILKOV,I.1980.Dropsizedistributionof non-Newtonianslurries.InDrying80.Proceedingsof theSecondInternationalSymposium(A.S.Mujumdar,ed.)pp.346350,HemispherePublishingCorporation,NewYork,NY.GADELHA,G.E.,GARCIA,M.,RODRIGUES,A.C.,SOUSA,E.,DANTAS,M.F.andDEAZEREDO,H.2009.Physicalpropertiesof spraydriedacerolapomaceextractasaffectedbytemperatureanddryingaids.LWT-FoodSci.Technol.42,621645.HALL,C.W.andHEDRICK,T.I.1971.Dryingof MilkandMilkProducts,AVIPublishingCompany,Inc.,Westport,CT.HAYASHI,H.andKUDO,N.1990.Effectof viscosityonspraydryingof milk.InDrying89(A.S.MujumdarandM.Roques,
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