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1 ShortCommunication Sonocrystallisationof
ShortCommunication Sonocrystallisationoflactoseinconcentratedwhey BogdanZisu ,VijayJayasena ,MikeWeeks ,MartinPalmer ,TunaD.Dincer DairyInnovationAustraliaLtd.,Werribee,Victoria,Australia CurtinUniversity,SchoolofPublicHealth,FoodScienceandTechnologyProgram,Perth,Australia articleinfoArticlehistory:Received9December2013Receivedinrevisedform25March2014Accepted25March2014Availableonline13April2014 Concentratedwhey Wheyconcentratedto32%lactosewassonicatedat30 1.Introduction Lactoseisthemostabundantcarbohydratefoundinmilk(4.4…5.2%)andamajorconstituentofmanyconcentratedanddriedmilk Theoverallcrystallisationprocessisslowandlactoserecoverycanbeimproved.Sonicationisknowntoreducecrystallisation Sonocrystallisationismosteffectivewhenultrasoundisdelivered atthenucleationphase Ultrasoniccavitationcanenhancetherateofreactionandfacil-itatemasstransferinliquid.Studieshaveshownthatsonocrystal-lisationgenerallyexhibitsfourcharacteristicswhicharenottypicalofcrystallisationwithoutsonication.Thesearefasterprimarynucleation,easeofnucleation,initiationofsecondarynucleationandproductionofsmallerandpurercrystalscrystals.Ultrasoundinthepresenceofananti-solventsuchasethanolwasusedtoincreasetheyieldoflactosecrystallisationon,inacetoneacetoneandinglycerinesolutionsolution.Morerecently,thesecharacteris-ticswerereportedinasimpleaqueoussystemwithoutanti-sol- Muchofthelaboratorydatareportedinliteratureisbasedondirectcontactsonication.Inthisapproach,atitaniumultrasonicprobewasimmerseddirectlyintotheproduct.Becausetheenergydensityisgreatestatthesurfaceofthesonotrodeitwillcausegradualpittinganddegradation.Althoughtheriskassociatedwithsuchpracticeisminimal,thereisconcernthaterosionofthesono-trodesmayresultinproductcontaminationion.Anon-contactalternativetodirectcontactsonicationexistsandthisdesignper-mitsmodularimplementationandin-lineoperation.Thesesonica-tioncellsaredesignedwithmultiplelowpowertransducersattachedtotheoutersurfaceofthemetalcell,eliminatingtheneedforsonotrodes.Soundwavespropagatethroughthemetalsurfaceovercomingsonotrodeerosionandimprovingenergydistribution.Thesegeneratelowerpowerdensitiesthansonotrodesbutef“-cientlyinitiatelactosenucleationandhavebeenimplementedindustriallyoutsidethefoodindustry Correspondingauthor.Address:180PrincesHighway,Werribee,Victoria3030,Australia.Tel.:+61399748948.E-mailaddress:(B.Zisu). UltrasonicsSonochemistry21(2014)2117…2121 ContentslistsavailableatScienceDirectUltrasonicsSonochemistryjournalhomepage:www.else Sonocrystallisationoflactoseisknowntooccurinthepresenceofanti-solventsandinaqueoussolutionsbuttheeffectofultra-soundonlactosecrystallisationinconcentratedwheyremainsunknown.Sincetheuseofanti-solventinthemanufactureoffoodgradelactoseisunlikelytobefeasibleatacommercialscale,theaqueouslactosestudystudyisprobablythemostrelevantreferencepublicationforindustry.Inthecurrentstudy,commerciallymanu-facturedwheyconcentratewassonicatedatpilotscaleusingnon-contactequipmenttostudytheeffectsonlactosecrystallisation. 2.Materialsandmethods Concentratedwheywassourceddirectlyfromacommercialdairyfactory(NorthernVictoria,Australia).Wheywasconcen-tratedto32±2%lactosebyevaporationat55C.Concentratedwheywasthen”ashcooledto30±1Ctoinitiatelactosecrystal-lisation.Twosonicationstudieswereconducted(Fig.1 Inthe“rst,sonicationwasperformedwitha20kHzSonolabSL250non-contactsonicator(ProsonixLtd.,Oxford,UK).Thepro-cessingchamberwas15.4cmindiameterwithacapacityof2.1L.Concentratedwheywastreatedwithhighintensitylowfre-quencyultrasoundat30±1Cdeliveringanappliedenergyden-sityof3…16J/mLinasinglepass.The

2 wheyconcentratewassampledimmediatelyfoll
wheyconcentratewassampledimmediatelyfollowingtheindustrial”ashcoolerandpumpedthroughtheSL250atvarious”owratesusingaperistalticpump(Master”exL/Smodel7554-95,Illinois,USA).Thecontrolsolution(T0)waspumpedthroughtheultrasonicrigattheappro-priate”owratewithoutsonication.Three”owrateswereexplored(0.75,1.2and2L/min;achievingresidencetimesof168,105and63s)attwopowersettings(100and200W).Theappliedenergydensity(J/mL)wascalculatedasdescribedbyZisuetal.al.andthecorrespondingenergydensitiesareshowninTable1Sonicatedwhey(400g)wastransferredto400mLglassbeakers(6.5cmdiameter)andallowedtocrystallizeatroomtemperatureC)for60min. Themagnitudeoftheexperimentwasscaledupinthesecondstudybasedonenergydensity.AProsonitronP500(ProsonixLtd.)non-contactsonicatorwasinstalledin-linewiththecommer-cialmanufacturingprocessimmediatelyfollowingthe”ashcooler.Theprocessingchamberwas15.4cmindiameterwithacapacityof6.4L.Concentratedwhey(30±1C)wasdivertedtothesonica-toratthedesired”owrate.Sonicationwasperformedinasinglepassat250…600Wand”owratesof4…12L/min(residencetimeof96…32s,respectively)toachieveappliedenergydensitiesof3…15J/mL.Controlsampleswerepassedthroughtheultrasonicrigattheappropriate”owratewithoutsonication.Sonicatedandcontrolwhey(400g)werethenplacedin400mLglassbeakers(6.5cmdiameter)andtransferredtoa30Cwaterbath.Sampleswerecooledto15Cbyloweringthetemperatureby2Cevery30min(4C/h)thenholdingattemperatureforupto24h.Wheywasstirredcontinuouslyduringthecoolingperiodandfortheentireholdingtimeusinganoverheadstirrer(RZR2020,Heidolph InstrumentsGmbH&Co.,Schwabach,Germany)“ttedwitha 30mmthreepaddleoperatingat650rpm. Whenasecondoff-linesonicationtreatmentwasrequired,a1kW(UIP100hd)200mmradialsonotrode(BS2d34SPEC)wasusedtodeliveranappliedenergydensityof4J/mL(HielscherUltrasonicsGmbH,TeltowGermany). Totaldissolvedsolid(Brix)weremeasuredat23Casanindica-torofcrystallisation(Refracto30GS,MettlerToledo,Schwerzen-bach,Switzerland).SampleswerefrozenimmediatelyandsenttotheDairyTechnicalServiceslaboratories(Kensington,Victoria,Australia)fortotalsolids(Testnumber:MOIS2110.00)andlactosebyenzymeanalysis(Testnumber:LACT0204.93)measurements. CrystallisationwascalculatedaccordingtoWestergaard %Crystallisation¼ ðS1 S2 100LTSS2 Þð1Þ whereS1 =%sugar(Ref.index)oftheconcentratedirectfromtheevaporator, =%sugar(Ref.index)ofthecrystallizedconcentrate,=%lactoseandTS=totalsolidscontentin%. Complementarytoabsorbance,wheysolutionswereviewedunderalightmicroscope(OlympusBH-2,Tokyo,Japan)“ttedwithandwithoutabluelight“lterat10magni“cationimmediatelyaftersonication(T0)and60min(T60)oftreatment.Wheywasalsoexaminedafter30min(T30)insomeexperiments.Imageswerecapturedwitha3.2megapixeldigitalcamera(Pro-MicroScanModelDCM310,OplenicCo.,Hangzhou,China)andwereusedtomeasurecrystalsizebyScopePhotoimageanalysissoftware(Ver-sion3.0,OplenicCo.,Hangzhou,China).Thesizeofcrystalwasreportedasthelengthofacrystalinthedirection(de“nedbyFriesetal.al.)andtheaveragecrystalsizewasmeasuredastheaveragesizeofalltheparticlesviewedunderthemicroscope.Theaveragegrowthrateofthe(010)face(de“nedbyMichaelsandVanKreveldKreveld)wascalculatedfromtheslopeoftheaveragecrystalsizeasafunctionoftime.Saturatedlactosesolutionwasusedtodilutethewheywhennecessarytoallowaccuratemea-surementofcrystalsize. 3.Resultsanddiscussion Crystallisationoflactoseincommerciallyconcentratedwheywassigni“cantlyincreasedbytheapplicationofultrasoundatalowenergydensityof3J/mLanda”owrateof2L/min(Fig.2).Asimilarobservationwasmadeforthevarious”owrates(0.75,1.2and2L/min)andpowerinputsexplored(3…16J/mL)(datanotshown).Regardlesso

3 fthesonicationintensityand”owrate,thelea
fthesonicationintensityand”owrate,theleastnumberoflactosecrystalswasobservedinthecontrolsolutionsatT0.Agreaternumberoflactosecrystalswerepresentinwheyimmediatelyaftersonication(T0)atallenergydensities(3…16J/mL).Althoughsomenucleationoccurredinthecontrolsolutionafter30and60minofcrystallisation,thenumberofcrys-talsobservedinsonicatedsolutionswasfargreateratanequiva-lenttime.Ultrasoundgeneratedalargenumberofnucleiresultinginthegrowthofmanysmallcrystals,differingtothegrowthoffewerbutlargercrystalswithouttreatment.Unlikeaqueoussolutionsofreconstitutedlactose,alowerenergydensity Fig.1.Process”owdiagramfortwoapproachestosonocrystallisation. Table1Appliedenergydensity(J/mL)deliveredbytheSL250atvarious”owratesandpowerFlowrate(mL/min)Electricalpower(W)100(J/mL)200(J/mL)7508161200510200036B.Zisuetal./UltrasonicsSonochemistry21(2014)2117…2121 wassuf“cienttoinitiatelactosecrystallisationinconcentratedwhey.Intheearlierstudyofreconstitutedlactose(37.5%solids),theminimumappliedenergydensityrequiredtoachievethedesiredleveloflactosecrystallisationinaqueoussolutionswas75J/gatafrequencyof20kHzkHz.Theef“ciencyofsonicationinthecurrentstudywaslikelycompoundedbythehigherlactoseconcentrationofconcentratedwhey.Thesamestudyalsoshowedthatsonicationreducedlactosecrystallisationinductiontimesatenergydensitiesofupto0.15Wg andthemetastablezonewidthalsoreducedbuttherewasnoeffectonindividualcrystalgrowthrateorcrystalmorphology. Subsequentscale-upstudiescon“rmedthatsonocrystallisationoflactoseinconcentratedwheywasscalableto”owratesofupto12L/minatappliedenergydensitiesof3J/mL.Scale-uppotentialwasonlylimitedbythepowerofthesonicator.LowerBrixread-ingsindicatingafasterrateofcrystallisationwereobtainedforwheysonicatedata”owrateof11L/minandanappliedenergydensityof3.3J/mLduringthe“rst150minofcrystallisation.Therateofcrystallisationslowedat150minandthedifferencebetweensonicationandstirringdiminishedat180minFig.3A).Althoughtherateofcrystallisationisincreasedbytheapplicationofultrasoundwhichinitiatestheformationofalargenumberofcrystals,theyieldofcrystallisationislimitedbythesol-ubilityoflactose.Asthelactoseconcentrationreducedduringthecrystallisationprocess,thedrivingforcefornucleationandgrowthdecreased.Consequentlythelactoseconcentrationreducesslowly tothesolubilityvaluegivensuf“cienttimetime.Incrystallisation studiesusinganti-solventtheyieldofcrystallisationissigni“-cantlyincreasedduetothereducedsolubilityoflactoseinthepresenceofalcohols Thewidedistributionofcrystalsizedepictsthevariousstagesofcrystalgrowth.Acousticcavitationappearedtogeneratealargernumberofsmallercrystalsandlesssecondarynucleationoccurred,comparedtothecontrol.Inunsonicatedwhey,largecrystalsformedearlyandtheformationofsecondarynucleiwidenedthecrystalsizedistribution.Ultimately,thecrystalsizepopulationinsonicatedwheywassmallerthanstirringanditsdistributionnar-rower(Fig.BandFig.).Theaveragecrystalsizeforsonicatedwheywas38.39±10.02mandforstirred57.9±17.71m.Therelativesizedistribution(SD/L )forsonicatedwheywasslightlylowerthanstirredat0.31and0.26,respectively.Initialnucleationwascausedby”ashcoolingwithsonicationresultinginasecondnucleationresponsewhichresultedintheformationofalargenumberofnucleiwhichreducedtheaveragecrystalsize.Measure-mentsaresupportedbymicroscopyinFig.5.Imagesalsocon“rmthetypicaltomahawkmorphologyoflactosecrystalsdescribedbyMichaelsandVanKreveld Theintensityofsonicationwasincreasedfrom3to15J/mLandcrystallisationwasfollowedfor24h(Fig.6).Atypicalresponsewasmeasured,thatis,theinitialrateofcrystallisationwassignif-icantlygreaterinsonicate

4 dwheyfollowedbyaslowerperiodofcrystalgro
dwheyfollowedbyaslowerperiodofcrystalgrowthbeyond150min.Althoughtheinitiallagtimeslo- Fig.2.Concentratedwheyviewedunderalightmicroscopeat10magni“cationimmediatelyafter”ashcoolingata”owrateof2L/minandafter60min(scalebarappliestoallimages). 050100150200 F2 Sonicated 050100150200 Time (min)BA Fig.3.ChangeinBrix(A)andcrystalsize(B)ata”owrateof11L/min.Sonicationwasappliedatanenergydensityof3.3J/mL. B.Zisuetal./UltrasonicsSonochemistry21(2014)2117…2121 wedtherateofcrystallisationearlyinstirredwhey,itacceleratedasthenumberofcrystalsincreased.Despiteapplying5energydensityduringsonication,therapidrateofcrystallisationcouldnotbemaintainedbeyond180minandthetwocrystallisa-tioncurvesbecamesimilarbeyond220min.Asimilarrateofcrys-tallisationwasmeasuredfor24htoyieldthesameamountofcrystallizedlactose. Tostimulatefurtherlactosenucleationandmaintaintherateof reaction,asecondtreatmentwithultrasoundat4J/mLwasappliedat120minintheregionwheretherateoflactosecrystallisationbeginstoslow(Fig.7).Inadditiontoinitialsonicationat6J/mL,secondaryultrasoniccavitationat120minmaintainedafasterrate 020406080100120 Sonicated Stirred Fig.4.Normalisedcrystalsizedistributionofstirredandsonicatedwheyattheendofcrystallisation. A Fig.5.Crystalmorphologyanddistributionviewedunderalightmicroscopeat10magni“cationfollowingstirring(A)andsonication(B). 0100200300400Crystallisaon (%)Time (min) Srring Sonicaon 250W 1000 mL/min (15 J/mL) 24 hrs Fig.6.Crystallisationofstirredandsonicatedwhey;sonicationwasdeliveredata”owrateof1L/minandanappliedenergydensityof15J/mL. 0100200300 Srring Sonicaon (6 J/mL) 2nd sonication 24 hrs Fig.7.Crystallisationofstirredandsonicatedwhey;initialsonicationwasdeliveredata”owrateof11L/minandanappliedenergydensityof6J/mL.Asecondtreatmentofultrasoundwasdeliveredduringcrystallisationat120minandanappliedenergydensityof4J/mL. B.Zisuetal./UltrasonicsSonochemistry21(2014)2117…2121 ofreactionfortwiceaslongasasingletreatmentextendingbeyond300minwhencomparedtostirring.Crystallisationslowsasitreachesthemetastablelimit(ML;wherespontaneousnucle-ationisimprobablebutcrystalswillgrow)andasecondsonicationtreatmentnearingthisconcentrationlimitseemstoimprovetherateofcrystallisation(Fig.8).Dincerandco-workershaveshownthattheimpactofultrasoundismoreprominentintheintermedi-atezonewhencomparedtostirringstirring.Thesolubility,labilezone,metastablezoneandforcedcrystallisationoflactoseconcentrationwereconvertedintototalsolidscontentofconcentratedwheyasdescribedinliteratureliterature.Brie”y,thesewerecalculatedasfollows;ReportedSolubility(=10.788e ),SecondaryNucle-ationThresholdSNT( ),MetastableLimit=17.446e ),ForcedCrystallisation(=17.152e andSuperSolubility(=22.308e )valueswereexpressedaslactoseconcentration(g/100gwater)asafunctionoftempera-ture.Usingthetotalsolidandlactosecontentsoftheconcentratedwhey,ateachtemperature,correspondingsolubility,SNTetc.,werecalculatedintermsoftotalsolidassumingonlylactosecrys-tallisedoutofsolution. Althoughtheamountoflactosecrystallisationwassimilarforbothtreatmentsatthesolubilitylimitafter24h(Fig.7),theresultindicatesthatmultipleultrasonictreatmentstocreateapulsingeffectmayyieldthemaximumamountofcrystallizedlactoseinashortertimethanconventionalstirring.Furtherworkisneces-sarytocon“rmthishypothesis. 4.Conclusion Sonicationinitiatesrapidlactosenucleationinconcentratedwheybuttherateofsonocrystallisationslowsaftertheinitialper-iodofacceleratedgrowth.Afastrateofreactioncanbemaintainedforlongerbyapplyingasecondultrasonictreatmentatthemeta-stablelimittostimulatefurthernucleiformation.Althoughtheyiel

5 dofcrystallizedlactoseislimitedbythesolu
dofcrystallizedlactoseislimitedbythesolubilityoflactose,theresultingcrystalsaresmallerthanconventionalstirringandtheprocessdeliversgreatercontrolofthecrystalsizedistribution. Acknowledgements TheauthorswouldliketoacknowledgeDairyAustraliafortech-nologytransferfundingandProsonixLtd.forsupplyingtheultra-sonicequipmentandtechnicalsupport. References GEANIRO(Ed.),MilkPowderTechnology…EvaporationandSprayDrying,“fthed.,GEAProcessEngineeringA/S,SoborgDenmark,2010,p.254 V.Westergaard,MilkPowderTechnologyEvaporationandSprayDrying,GEANiro,Copenhagen,Denmark,2004 H.Li,J.Wang,Y.Bao,Z.Guo,M.Zhang,Rapidsonocrystallisationinsaltingoutprocess,J.Cryst.Growth247(2003)192…198 R.Dhumal,S.Biradar,A.R.Paradkar,P.York,Ultrasoundassistedengineeringoflactosecrystals,Pharm.Res.25(2008)2835…2843 S.Ueno,R.I.Ristic,K.Higaki,K.Sato,Insitustudiesofultrasound-stimulatedfatcrystallizationusingsynchrotronradiation,J.Phys.Chem.107(2003) G.Ruecroft,D.Hipkiss,T.Ly,N.Maxted,P.W.Cains,Sonocrystallization:theuseofultrasoundforimprovedindustrialcrystallization,Org.ProcessRes.Dev.9(2005)923…932 R.Bund,A.Pandit,Sonocrystallisation:effectonlactoserecoveryandcrystalhabit,Ultrason.Sonochem.14(2007)143…152 M.D.LuquedeCastro,F.Prirgo-Capote,Ultrasoundassistedcrystallization(sonocrystallization),Ultrason.Sonochem.14(2007)717…724 R.K.Bund,A.B.Pandit,Rapidlactoserecoveryfrombuffalowheybyuseofanti-solvent,ethanol,J.FoodEng.82(2007)333…341 R.K.Bund,A.B.Pandit,Rapidlactoserecoveryfrompaneerwheyusingsonocrystallisation:aprocessoptimisation,Chem.Eng.Process.46(2007) E.Kougoulos,I.Marziano,P.R.Miller,Lactoseparticleengineering:in”uenceofultrasoundandanti-solventoncrystalgrowthandhabit,J.Cryst.Growth312(2010)3509…3520 S.Patel,Z.Murthy,Ultrasoundassistedcrystallisationfortherecoveryoflactoseinananti-solventacetone,Cryst.Res.Technol.44(2009)889…896 T.D.Dincer,B.Zisu,C.G.M.R.Vallet,V.Jayasena,M.Palmer,M.Weeks,Sonocrystallisationoflactoseinanaqueoussystem,Int.DairyJ.35(2013)43… S.Freitas,G.Hielscher,H.P.Merkle,B.Gander,Continuouscontact-andcontamination-freeultrasonicemulsi“cation-ausefultoolforpharmaceuticaldevelopmentandproduction,Ultrason.Sonochem.13(2006) [15]Prosonix,RevolutionizingRespiratoryMedicine(Websitevisited1December2013. B.Zisu,R.Bhaskaracharya,S.E.Kentish,M.Ashokkumar,Ultrasonicprocessingofdairysystemsinlargescalereactors,Ultrason.Sonochem.17(2010)1075… D.C.Fries,S.T.Rao,M.Sundaralingam,StructuralchemistryofcarbohydratesIII.Crystalandmolecularstructureof4-o-glucopyranosemonohydrate(-lactosemonohydrate),ActaCrystallogr.B27(1971)994…1005 A.S.Michaels,A.VanKreveld,In”uenceofadditivesongrowthratesinlactosecrystals,J.DairySci.20(1966)163…181 R.W.Hartel,CrystallisationinFoods,AspenFoodEngineeringSeries,2001.Chapter6,p.196 B.Butler,ModellingIndustrialLactoseCrystallisation,DepartmentofChemicalEngineering,UniversityofQueensland,Brisbane,Australia,1998 S.Y.Wong,R.K.Bund,R.K.Connelly,R.W.Hartel,Designingalactosecrystallizationprocessbasedondynamicmetastablelimit,J.FoodEng.111(2012)642…654 T.T.L.Vu,J.A.Hourigan,R.W.Sleigh,M.H.Ang,M.O.Tade,Metastablecontrolofcoolingcrystallisation,Comput.AidedChem.Eng.14(2003)527…532 1015202530Total solids (%)Temperature (°C) Control Force Cry 2nd sonicaon Sonicated Fig.8.Crystallisationpro“leofstirredandsonicatedwheyshowinglactosesolubility,forcedcrystallisationandthelabileandmetastablezones.Initialsonicationwasdeliveredata”owrateof11L/minandanappliedenergydensityof6J/mL.Thesecondbatchtreatmentofultrasoundwasdeliveredatanappliedenergydensityof4J/mL. B.Zisuetal./UltrasonicsSonochemistry21(2014)2117…