1 Introduction1 Introduction Whole milk, skim milk and infant formula emulsions are spray-dried to...
28
1 Introduction Whole milk, skim milk and infant formula emulsions are spray-dried to powder form at large industrial scale in order to accomplish better preservation, reduced bulk volume for economy of transportation and easier processing as food ingredients. However, during spray drying usually an unwanted layer of fat occurs on the particles' surface and this leads to detrimental effects on the powder properties, including reduced solubility in water (Fäldt & Bergenståhl, 1996; Millqvist-Fureby, Elofsson, & Bergenståhl, 2001), faster expiration due to lipid oxidation (Granelli, Fäldt, Appelqvist, & Bergenståhl, 1996; Hardas, Danviriyakul, Foley, Nawar, & Chinachoti, 2000; Keogh et al., 2001) and greater stickiness (Kim, Chen, & Pearce, 2005a; Nijdam & Langrish, 2006). This can mean a deteriorated product quality for the end user and a reduction in efficiency during manufacturing due to significant product loss and the necessity of additional processing steps, such as lecithination. For this reason, it is important to identify the driving forces that cause the formation of surface fat during spray drying of milk powder. A few studies previously speculated that the actual drying stage of the spray drying process might not be primarily responsible, but rather an atomization induced mechanism would already determine the eventual chemical surface composition (Fyfe, Kravchuk, Nguyen, Reduction of surface fat formation on spray-dried milk powders through emulsion stabilization with λ-carrageenan Martin Foerster a [email protected] Chang Liu a [email protected] Thomas Gengenbach b [email protected] Meng Wai Woo a [email protected] Cordelia Selomulya a, ∗ [email protected] a Department of Chemical Engineering, Monash University, Clayton, Victoria 3800, Australia b CSIRO Manufacturing, Bayview Avenue, Clayton, Victoria 3168, Australia ∗ Corresponding author. Monash University, Department of Chemical Engineering, 18 Alliance Lane, Clayton, Victoria 3800, Australia. Abstract The appearance of surface fat during the atomization process in spray drying of milk particles often impairs the functional powder properties. To investigate a possible approach that could minimise the surface fat formation, the interaction between a whole milk model emulsion and λ-carrageenan at various concentrations was studied, as well as how it influences the atomization behaviour and the resulting particle characteristics. Carrageenan can stabilize emulsions in the presence of milk protein by adsorption on the milk fat globule membranes. If too little or too much of the polysaccharide was added, bridging flocculation or depletion flocculation, respectively, occurred inside the emulsions. The best stability and minimal fat globule size were obtained for a carrageenan content of 0.3% w/w. Rheological investigation indicated that the extensional viscosity can be an important factor influencing the emulsion disintegration behaviour during atomization. The λ-carrageenan stabilized emulsions featured a significantly increased extensional viscosity and a better fat encapsulation in the corresponding spray-dried particles, promoting solubility and oxidative stability. Surface fat extraction showed that the most stable emulsion lead to particles with the least amount of surface fat. Though the surface of these particles was still covered by fat according to spectroscopic analysis, this surface fat layer was very thin in comparison to carrageenan-free powder as observed by confocal microscopy. Yet, the addition of carrageenan was also found to have one adverse effect on the intended powder properties, as the strengthened emulsion network translated into denser particles and thus a deterioration of the powder's reconstitution behaviour. Keywords: Milk powder;; Carrageenan; Spray drying; Surface fat; Atomization; Emulsion stabilization
Transcript of 1 Introduction1 Introduction Whole milk, skim milk and infant formula emulsions are spray-dried to...
1IntroductionWholemilk,skimmilkandinfantformulaemulsionsarespray-driedtopowderformatlargeindustrialscaleinordertoaccomplishbetterpreservation,reducedbulkvolumeforeconomyoftransportationandeasierprocessing
as food ingredients.However, during spray drying usually an unwanted layer of fat occurs on the particles' surface and this leads to detrimental effects on the powder properties, including reduced solubility inwater (Fäldt&
Bergenståhl,1996;Millqvist-Fureby,Elofsson,&Bergenståhl,2001),fasterexpirationduetolipidoxidation(Granelli,Fäldt,Appelqvist,&Bergenståhl,1996;Hardas,Danviriyakul,Foley,Nawar,&Chinachoti,2000;Keoghetal.,2001)
andgreaterstickiness(Kim,Chen,&Pearce,2005a;Nijdam&Langrish,2006).Thiscanmeanadeterioratedproductqualityfortheenduserandareductioninefficiencyduringmanufacturingduetosignificantproductlossandthe
necessityofadditionalprocessingsteps,suchaslecithination.Forthisreason,itisimportanttoidentifythedrivingforcesthatcausetheformationofsurfacefatduringspraydryingofmilkpowder.Afewstudiespreviouslyspeculated
thattheactualdryingstageofthespraydryingprocessmightnotbeprimarilyresponsible,butratheranatomizationinducedmechanismwouldalreadydeterminetheeventualchemicalsurfacecomposition(Fyfe,Kravchuk,Nguyen,
Reductionofsurfacefatformationonspray-driedmilkpowdersthroughemulsionstabilizationwithλ-carrageenan
MartinFoerstera
ChangLiua
ThomasGengenbachb
MengWaiWooa
CordeliaSelomulyaa,∗
aDepartmentofChemicalEngineering,MonashUniversity,Clayton,Victoria3800,Australia
bCSIROManufacturing,BayviewAvenue,Clayton,Victoria3168,Australia
∗Correspondingauthor.MonashUniversity,DepartmentofChemicalEngineering,18AllianceLane,Clayton,Victoria3800,Australia.
Abstract
Theappearanceofsurfacefatduringtheatomizationprocess inspraydryingofmilkparticlesoftenimpairsthefunctionalpowderproperties.To investigateapossibleapproachthatcouldminimisethesurfacefat
formation,theinteractionbetweenawholemilkmodelemulsionandλ-carrageenanatvariousconcentrationswasstudied,aswellashowitinfluencestheatomizationbehaviourandtheresultingparticlecharacteristics.
Carrageenancanstabilizeemulsionsinthepresenceofmilkproteinbyadsorptiononthemilkfatglobulemembranes.Iftoolittleortoomuchofthepolysaccharidewasadded,bridgingflocculationordepletionflocculation,
respectively,occurredinsidetheemulsions.Thebeststabilityandminimalfatglobulesizewereobtainedforacarrageenancontentof0.3%w/w.Rheologicalinvestigationindicatedthattheextensionalviscositycanbean
importantfactor influencingtheemulsiondisintegrationbehaviourduringatomization.Theλ-carrageenanstabilizedemulsionsfeaturedasignificantly increasedextensionalviscosityandabetterfatencapsulationinthe
correspondingspray-driedparticles,promotingsolubilityandoxidativestability.Surfacefatextractionshowedthatthemoststableemulsionleadtoparticleswiththeleastamountofsurfacefat.Thoughthesurfaceofthese
particleswasstillcoveredbyfataccordingtospectroscopicanalysis,thissurfacefatlayerwasverythinincomparisontocarrageenan-freepowderasobservedbyconfocalmicroscopy.Yet,theadditionofcarrageenanwas
alsofoundtohaveoneadverseeffectontheintendedpowderproperties,asthestrengthenedemulsionnetworktranslatedintodenserparticlesandthusadeteriorationofthepowder'sreconstitutionbehaviour.
Keywords:Milkpowder;;Carrageenan;Spraydrying;Surfacefat;Atomization;Emulsionstabilization
Deeth,&Bhandari,2011;Kim,Chen,&Pearce,2009;Xu,Howes,Adhikari,&Bhandari,2013).Thehypothesiswassupportedbyrecentstudiesdifferentiatingthe impactof theatomizationstagefromthedryingstage(Foerster,
Gengenbach,Woo,&Selomulya,2016a;Wuetal.,2014).Bycomparingthesurfacecompositionofthespray-driedparticleswiththeatomizeddroplets,whichwerecryogenicallyflash-frozenimmediatelyafterleavingthenozzle,itwas
learntthatthefreshlygenerateddropletswerealreadycoveredbyafatfilmandthatthissurfacefatcoverageremainedrelativelyunchangedthroughoutthefollowingdryingprocess.Itwasconcludedthatthesurfacefatcontentis
hencenotsignificantlyreduciblebymodifyingthespraydryingconditions.Also,fortherangeofatomizationnozzlesinvestigated,theatomizationtriggeredfataccumulationonthedropletsurfaceswasindependentoftheatomization
technique.Instead,apromisingwaytoreducetheamountofsurfacefatseemstomodifytheemulsionpriortospraydryinginordertomoderatethesegregationbetweenthelipidandtheaqueousphaseduringatomization.Further,it
iscrucialtounderstandtheactualmechanismthatcausestheemulsionstodisintegrateinawaythatresultsinthefatbeingpresentatthesurfaceassoonasindividualdropletsareformed.
Therefore,theobjectivesofthepresentstudywere,firstly,tocontributetowardsabetterinsightintothismechanismand,secondly,toinvestigateapotentialmethodtoimprovethepropertiesofmilkpowderbymodifyingthe
emulsiontobespray-dried.Towardsthefirstaim,milkmodelemulsionsofdifferentcompositionswereinvestigatedintermsoftheirbreak-upbehaviourundershearandextensionalstress.Therearevariouspossibleapproachesto
address thesecondaim.Asstudieshaveshown,addingasurfactant, suchaspolysorbate80or lecithin, tomilkemulsionsoroil/milkproteinemulsionsandsubsequentco-spraydryingenhanced theproductpowders'wettability
(Fonseca,Bento,Quintero,Gabas,&Oliveira,2011;Lallbeeharryetal.,2014;Millqvist-Fureby&Smith,2007).Yet,itwasalsoarguedthatsuccessivespraydryingandlecithincoating,astypicallydoneonindustrialscale,stillremains
moreefficient(Tianetal.,2014).Instead,milkemulsioncouldbemodifiedinawaythatstrengthenstheirstabilityinordertobringaboutagreaterfatencapsulationuponspraydrying,thusmakingsubsequentcoatingredundant.
Firstly,byemulsionstabilityanalysesofmilkproteincontainingoil/wateremulsions,heattreatmentattemperaturesabove60°C(Millqvist-Furebyetal.,2001),apHvaluereduction(Dalgleish,1997)andadditionofcalcium ions
(Agboola&Dalgleish,1996a,1996b)wereallshowntobenotsuccessfulinthisregard.However,throughthermalpre-treatmentat80°CWang,Liu,Chen,andSelomulya(2016)attainedacross-linkedemulsionofwheyproteinisolate
andfishoil,whosecorrespondingspray-driedpowdersfeaturedimprovedinhibitionoflipidoxidation.Secondly,thefatglobulesizeinsideoil/wateremulsionsalsoinfluencestheemulsionstabilityandthustheamountofsurfacefat,for
instancebymechanicaltreatmentduringhomogenizationviamicrofluidizationorultrasonication.Yet,theidealsizedependsonthetypeofoil,homogenizationtechniqueandspray-driedparticlediameter(Jafari,Assadpoor,Bhandari,
&He,2008;Munoz-Ibanezetal.,2016;Soottitantawat,Yoshii,Furuta,Ohkawara,&Linko,2003).Thirdly,ithasbeendemonstratedthattheadsorptionofcertainpolysaccharidesonthemembranesaroundthefatglobulesofvarious
emulsionscanenhancethestabilityagainstenvironmentalinfluences,suchasthermalandmechanicalstress(Drusch,Serfert,Scampicchio,Schmidt-Hansberg,&Schwarz,2007;Gharsallaouietal.,2010;Guzey,Kim,&McClements,
2004).Aprominentexampleispectin,whichwasforinstancefoundtoimprovethestoragestabilityofsunfloweroilemulsionwithwheyproteinisolateandsodiumcaseinateasemulsifiers(Einhorn-Stoll,Ulbrich,Sever,&Kunzek,
2005).Serfertetal.(2013)obtainedenhancedfishoilencapsulationandoxidativestabilityofpowdersfromanemulsionthatcomprisedofglucosesyrup,wheyproteinandpectinatpH4.However,whilethispolysaccharidewithits
negatively charged carboxylate groups can adsorb at casein below the latter's isoelectric point (pHof approximately 4.6) and is thus used in stabilization of acid dairy drinks, it is not effective at the pHofmilk itself (6.4–6.7)
(Kravtchenko,Parker,&Trespoey,1995;Surh,Decker,&McClements,2006).Incontrast,carrageenan,alinearsulphatedpolysaccharide,alsoundergoesattractiveelectrostaticinteractionwithκ-caseinatneutralmilieu(Dalgleish&
Morris,1988;Dickinson,1998)andthereforeisusedasstabilizerinpHneutraldairybeveragesthatarecommerciallyavailable(Bixler,Johndro,&Falshaw,2001;FAO,1987;Yanes,Durán,&Costell,2002).TheEuropeanFoodSafety
AuthorityandtheUSFood&DrugAssociation,forinstance,haveconcludedthatcarrageenanasafoodadditiveisconsideredassafe(FDA,2016;SCF,2003).
Carrageenanisanaturalhydrocolloidextractedfromredalgaeandiswidelyusedinfoodapplicationstoformgelsandstabilizebeverages.Itfeaturesone,twoorthreesulphategroupsperdisaccharideinitskappa(κ),iota(ι)
andlambda(λ)form,respectively.Singh,Tamehana,Hemar,andMunro(2003)observedanimprovementincreamingstabilityofasoyaoilemulsionthatcontained3%w/wsodiumcaseinatewithincreasingκ-carrageenancontentfrom
0to0.4%w/w.Foracaseinatecontentof0.5%w/w,however,additionofκ-carrageenanimpairedthestabilityduetoflocculation.Anemulsioncontainingflaxseedoilandwheyproteinreachedsubstantiallybetterstabilitywhenmixed
withanyofthethreemaincarrageenantypes,withthebestresultforλ-carrageenan(Stone&Nickerson,2012).Inskimmilkemulsions,ι-andκ-carrageenanwerefoundtoinducedepletionflocculationattemperaturesabovetheir
coil-helixtransitiontemperature(whichisbelow60°C),becauseonlythechargedensityoftheirhelixstructurewasgreatenoughtoallowadsorptionatthecaseinmembranes(Langendorff,Cuvelier,Michon,Launay,&Parker,2000).
Yet,λ-carrageenanremainsanactivestabilizeratelevatedtemperature,whichmightbeparticularlybeneficialforspray-dryingapplications.Furthermore,thehigherdensityofanionicsulphategroupsintheλ-formbringsalongthe
advantageofgelinhibitionandgoodwatersolubilityevenatlowertemperature(roomtemperature).
Afewreportshavebeenpublishedaboutthestabilizationofoil/wateremulsionsinthepresenceofcarrageenanandonetypeofmilkprotein.However,thereisalackofinvestigationhithertoontheimpactofcarrageenanfora
morecompletemodelsystemthatisrepresentativeofwholemilk,comprisingofallitsmaincomponents(lactose,wheyprotein,caseinandfat).Inaddition,carrageenan'ssubsequenteffectontheatomizationbehaviourduringspray
dryingandthusthepowderproperties,particularlyinrespecttosurfacefatformation,isstilltobestudied.Inthefirstpartofthepresentstudy,amilkmodelemulsionwasinvestigatedtofindtheoptimumλ-carrageenancontentin
termsof fatglobulesizeandemulsionstability. In thesecondpart, itwasstudiedwhether thestabilizationwithλ-carrageenan translated intooptimizedpowderpropertiesafter spraydrying.For thispurpose, thepowders (and
selectedatomizedemulsiondroplets)wereanalysedinrespecttotheircomponentdistributionviaX-rayphotoelectronspectroscopy(XPS),confocal laserscanningmicroscopy(CLSM)andsurfacefatextraction.Powderproperties
includingmorphology,porosity,solubility,wettabilityandoxidativestabilitywerecomparedfordifferentcarrageenanconcentrations.Animportantconnectinglinkbetweenmodifiedemulsionsandspray-driedparticlepropertieswas
theemulsions'behaviourduringatomization.Shearandextensionalviscosityanalysesgavenewinsightsintothedisintegrationprocessandhowitisinfluencedbyfatandhydrocolloidcontent.
2Materialandmethods2.1Emulsionpreparation
Amilkmodelemulsion,whichresembledthecompositionofbovinewholemilk,wasstabilizedwithλ-carrageenanatvariousconcentrations.Theemulsioncontained40.8%w/wlactose,31.1%w/wfatand27.0%w/wproteinin
drymatter(d.m.)andfeaturedasolidcontentof20%w/w.Itwaspreparedbydissolvinglecithinfree,commercialskimmilkpowder(homebrandfromColesSupermarketsAustraliaPtyLtd,Australia)inMilli-Qpurifiedwater(Merck
KGaA,Germany)withstirringat47°Cfor1h.Subsequently,sustainablysourcedrefinedElaeisguineensispalmfruitoil(AuromaPtyLtd,Australia),withaslipmeltingpointof37–39°Candafreefattyacidcontent(aspalmitic)ofless
than0.09%,wasadded.Followingprehomogenizationinahigh-speedcolloidmill(WiseMixHomogenizerHG-15D,DaihanScientific,SouthKorea)at1000rpmfor1min,differentamountsofλ-carrageenan(MelbourneFoodDepotPty
Ltd,Australia)wereaddedtoformcarrageenancontentsof0,0.1,0.2,0.3,0.4and0.5%w/winrespecttothetotalemulsionmass.Theemulsionswerestirredforfurther30minat47°Candthenwerehomogenizedinahighpressure
homogenizser(EmulsiFlex-C5,Avestin,Canada)withthreepassesat1350barandtwosubsequentpassesat650bar.Thehomogenizationtemperaturewasnotdirectlycontrolled,but thesampletemperaturewasmeasuredtobe
between45°Catthebeginningofthehomogenizationprocessand35°Cattheend.Theemulsionswerestoredatroomtemperatureandwerespray-driedandanalysedbythefollowingprocedureswithin3hafterpreparationifnot
statedotherwise.
2.2Emulsionanalysis2.2.1Turbiscanemulsionstability,emulsionmicrostructureandpHvalue
24hinstabilitytestsofeachemulsionwereconductedwithaTurbiscanClassicMA2000multiplelightscatteringinstrument(FormulactionSA,France)withapulsednearinfraredlightsource(wavelengthof850nm).Thebackscatteringfraction
asafunctionoftheemulsionheightinsideacylindricalglassmeasurementcellwasdeterminedevery30min.Theseresultswerecomparedwiththemicrostructureoforiginalemulsionsamplesthatwerestoredat6°Cforuptotendays.Imageswere
takenatvariouslocationsinsideemulsiondropsthatwerecontainedbetweenaglassmicroscopeslideandacoverslipunder10×magnificationwithaconventionalopticalmicroscope(B1-211A,Motic,P.R.China).ThepHvaluewasmeasuredwitha
benchtoppHmeter(H4212,HannaInstruments,USA)afterhomogenization.
2.2.2FatglobulesizedistributioninsideoriginalemulsionsandafteratomizationprocessTheemulsiondropletsize,henceforthdescribedasfatglobulesizeinordertodistinguishfromthedropletsizeofthespraysafteratomizationinthespraydryernozzle,wasanalysedbylaserlightscatteringusingaMastersizer2000apparatus
(MalvernInstruments,UK)equippedwithaHydro2000Gwetcell.Approximately250mlofthepre-dilutedemulsions(oilcontentof0.01%w/w)wereaddedtothewetcell,whichwasfilledwithabout1lofMilli-Qpurifiedwater,toestablishalaser
obscurationlevelof5.2–5.5%toavoidmultiplescatteringeffects.Theinstrumentoperatedatlaserwavelengthsof633and466nm.Thepumpandstirrerspeedsweresetto1000rpmand500rpm,respectively.Thephysicalpropertiesofthefatglobules
weredescribedwitharefractiveindexof1.462andanabsorbanceindexof0.1.Foursamplesweretakenfromeachemulsiontoconductindividualmeasurementsof20sduration,thestandarddeviationwasdeterminedfromthisandtheaveragewas
reportedasthemeandiameterovervolume :
where the particle diameter and number of particles in each size class are expressed by and , respectively. The size distribution and the corresponding volumetric mean diameters were determined for the original emulsions after
homogenization. In addition, theywere alsomeasured for the same emulsions after they had been passed through a spray drying atomization nozzle. The nozzlewas operated outside of the spray dryer and the atomized emulsionswere collected
immediatelyafterleavingthenozzle,andthusnocontactwithdryingairoccurred.Twodifferentatomizationtechniqueswereinvestigated:apressure-swirlsingle-fluidspraynozzle(MTBrassSeries,AmFogNozzleTechnologiesInc,USA)withanorificeof
0.2mmindiameteratafeedpressureof500kPa,andamicrofluidicjetnozzlethatisdescribedindetailinsection2.3.1.
2.2.3ShearviscosityandextensionalviscosityoftheemulsionsDynamic shear viscositiesweremeasuredat 25°Cwith a cone andplate rheometer (HaakeMars, ThermoFisherScientific,USA),whichwas equippedwith aMP60measuringplate and aC60/1 cone rotor.Each sample's viscositieswere
investigatedatsixdifferentshearratesintherangeof50–5001/s,andtheaverageofthreesamplestakenfromthesameemulsionwasdeterminedtogetherwiththerespectivestandarddeviation.
Theextensionalviscositywasofspecialinterestforinterpretationofthejetdisintegrationmechanismofthemicrofluidicjetnozzledescribedinsection2.3.1.ForafluidthatdoesnotfollowNewtonianbehaviour,suchastheemulsionsinvestigated
inthisstudy(seeFig.3b),noassumptioncanbemadeabouttherelationshipbetweenitsviscosityundershearstressanditsviscosityunderextensionalstress.Theviscosityofthemilkmodelemulsionwastoolowforstandardcapillary-breakupextensional
rheometry,however.Therefore,acoustically-drivenmicrofluidicextensionalrheometrywasemployed,whichisdesignedtocapturetheextensionalviscosityoflow-viscositysamples(McDonnell,Gopesh,etal.,2015;McDonnell,Jason,etal.,2015).These
measurementswereconductedatroomtemperature(25°C)at theSchoolofEngineering,RMITUniversity inMelbourne,Australia.Therheometerandthemathematicalanalysisprocedurehavebeendescribedelsewhere(Bhattacharjee,McDonnell,
(1)
Prabhakar,Yeo,&Friend,2011).Inbrief,asessiledropletof1μlinvolume(i.e.approximately1.2mmindiameter)wasplacedontothepiezoelectricsubstratesurfaceofasurfaceacousticwave(SAW)device.ApulseofSAWenergywasthenappliedtothe
droplet,causingittoelongateandtoformastableliquidbridgebetweenthesubstrateandaparallelopposingsurfaceatagaplengthof1.5mm.AtthispointtheSAWpulsewasterminated,allowingtheliquidbridgetothinundercapillaryforcesandthus
creatingauniaxialextensionalflow.Thediameter attheneckofthethinningemulsionfilamentwasrecordedwithahigh-speedcamerauntilithaddecreasedtohalfofitsinitialvalue( )(seeFig.1aaswellasVideo1,whichisavailableintheonline
versionof thesupplementary information).Theevolutionof the filamentdiameterwithrespect to timewasdeterminedwithstandard imageanalysis techniques.Fromthis, theOhnesorgenumberOhcouldbedetermined,allowingcalculationof the
extensionalviscosity bythefollowingexpression:
where was the emulsion density and the initial surface tension of the emulsion at 25 °C as taken fromBertsch (1983). Every samplewas analysed bymeasurement of three individual dropletswith ten runs per droplet, and from these the
averagevaluewastakenandthestandarddeviationwascalculated.Astheintentionofthisanalysiswastostudytheimpactofthefatglobulesonthefilmdisintegration,theemulsionpreparationwasslightlymodifiedforthepurposeoftheextensional
viscositymeasurements.Amixtureoflactose,calciumcaseinateandwheyproteinpowderwasusedinsteadofskimmilkpowder.Otherwiseitwouldnothavebeenpossibletoprepareemulsionswithverylowfatcontent,asskimmilkpowderitselfstill
containsasignificantamountoffat.Thus,alow-fatemulsionthatcontainedhardlyanyfat(0.3%w/wind.m.)couldbecomparedwithregular-fatemulsionsfeaturing31.1%w/wfatind.m.(and0or0.3%w/wcarrageenan).Alloftheseemulsionshada
solidcontentof20%w/w,andtheirratiooflactosetoproteinaswellastheirproportionbetweencaseinateandwheyproteinwereequivalenttotheearlierdescribedstandardemulsions.
(2)
Supplementaryvideorelatedtothisarticlecanbefoundathttp://dx.doi.org/10.1016/j.foodhyd.2017.04.005.
2.3Powderanalysis2.3.1Powderproductionwithmicrofluidicjetspraydryer
Amicrofluidicjetspraydryer,comprehensivelydescribedelsewhere(Foersteretal.,2016a),wasusedtodrytheemulsionsunderproductionofmonodisperseparticleswithuniformdryinghistory.Inshort,theutilizedatomizationnozzleconsisted
ofaglasstubewithanorificeof100μmindiameter.Apiezoelectricceramicjacketsurroundedthenozzletiptoimposeasinusoidalpulseof12kHz,causingdisintegrationofthefeedemulsionjetintoindividualdropletswithuniformsize(seeFig.1b).The
feedwaspushedthroughthenozzlebypneumaticpressureof34–53kPaforrespectivecarrageenancontentsof0–0.5%w/wtoaccountfortheincreasingviscosity.Thenozzlewaseitheroperateddetachedfromthespraydryingapparatusforcryogenic
flash-freezingoftheatomizeddroplets(describedinsection2.3.2)orwaspositionedontothedryingtowerforspraydrying.Thetowerwas3.2minheightandcontainedaconcurrentdryingairflow.Thetemperaturesofthedryingairatthetopandbottom
ofthedryingchamberwere200°Cand88°C,respectively.
2.3.2Cryogenicflash-freezingofatomizeddropletsTofacilitatethestudyofthechemicalsurfacecompositionandinternalcomponentdistributionofemulsiondropletsaspresent immediatelyafteratomization,amodifiedmethodologyofRogersetal. (2008)wasapplied.Milkmodelemulsion
dropletswith0.3%w/wcarrageenancontentwereflash-frozeninliquidnitrogenatadistanceof10cmfromthemicrofluidicjetnozzle,whichwasoperatedoutsideofthespraydryer.Afterwards,thedropletswerekeptinfrozenstatebycoolingwithdry
iceuntilfreeze-dryingwascarriedoutfor48hat0.1mbarandwithacollectortemperatureof−80°CinaFreeZone2.5lbenchtopfreeze-dryer(LabconcoCorp,USA).Asthemicrofluidicatomizationtechniquegeneratedmonodisperseparticles,themean
sizeoftheatomizeddropletsaswellofthecorrespondingspraydriedparticlescouldbedeterminedbysimpleimageanalysisofasmallpowdersample(100particles)withalightmicroscope(B1-211A,Motic,P.R.China)under4×magnification.
2.3.3SurfacefatextractionAmodifiedmethodofthegentlesurfacefatextractionmethodproposedbyWangetal.(2016)wasapplied.Thisapproachavoidedfatremovalfromtheinnerpartoftheparticlesbylimitingthetimeexposedtothesolventmedium.Whilethefree
fatonthesurfaceofapowderparticleisquicklydissolvedbyorganicsolvents,thefreefatintheinnerpartoftheparticlesisextractedconsiderablyslower(Kim,Chen,&Pearce,2005b).1gofpowderwasweighedoutonafilterpaperwithaporesizeof
2.5μm(Grade1803,FiltechPtyLtd,Australia),whichwassubsequentlytransferredintoaBüchnerfunnel.Thefunnelwasfilledwith30mlofpetroleumether(boilingpointof40–60°C,Sigma-AldrichPtyLtd,Australia),whereinthepowderrestedfor
2min.Afterwards,vacuumfiltrationwascommencedandthepowderwaswashedthreetimeswith20mlofpetroleumetherperpass.Thepowderfilledfilterpaperwasthenkeptinadryingovenat33°Cfor24hforevaporationofanyremainingether
residue,priortoasecondweighingtodeterminetheextractedamountofsurfacefat.Thestudywasconductedimmediatelyafterspraydryingandtheoriginalpowdersampleswerealsostoredat33°Caheadofthefatextractionprocesstoeliminateany
impactofadsorbedairhumidityonthemassmeasurements.Thesurfacefatcontentwasdeterminedforthreepowdersamplesthatwerecollectedforabout20mineachduringthesamespraydryingrunat40,60and80minaftera steadycolumn
temperatureprofilehadbeenreached,andthestandarddeviationwasdetermined.Theamountofextractedfreefatwaspresentedaspercentagerelativetotheparticles'originaltotalfatcontent.
2.3.4SpectroscopicsurfacecompositionmeasurementsThechemicalsurfacecompositionofselectedpowderswasestimatedbyXPSinvestigationwithanAXISNovaspectrometer(KratosAnalyticalInc.,UK).Thespray-driedparticlesofallcarrageenancontentswereanalysed,aswellastheatomized
dropletswith0.3%w/wcarrageenanaftercryogenicflash-freezing/freeze-dryingandthespray-driedpowdersfromemulsionswith0.1and0.3%w/wcarrageenanaftersurfacefatextraction.TheinstrumentwasequippedwithamonochromatedAlKαX-ray
sourceandahemisphericalanalyserthatwasoperatedinthefixedanalysertransmissionmodewiththestandardaperture(0.3mm×0.7mmanalysisarea).Thepressureinsidethemainvacuumchamberwasoftheorderof10−8mbar.Shallowwellsofa
custom-builtsampleholdercontainedthepowders,andtwodifferent locationswereanalysedforeachsampleatanominalphotoelectronemissionangleof0°withrespect to thesurfacenormal.Theactualemissionangle is ill-defined inthecaseof
particles(rangingfrom0°to90°),andhencethesamplingdepthrangedfrom0nmtoapproximately10nm.Alldetectedelementswereidentifiedfromsurveyspectra.Therespectiverelativeatomicconcentrationsweredeterminedfromtheintegralpeak
intensitiesandsensitivityfactorsprovidedbythemanufacturer.Theconcentrationsinlactose,proteinandfatcanbeinterpretedaslinearcombinationoftheatomicsurfacecomposition(PFäldt,Bergenstahl,&Carlsson,1993).Eachcomponent'sfraction
atthesurface,expressedinatomicconcentration,wasthusestimatedbylinearizationbasedontherepresentativestructuralformulasoflactose,milkproteinandmilkfat,aselaboratedbyChewetal.(2014).
2.3.5ConfocallaserscanningmicroscopyTheproteinandfatdistributionsinsideparticlesobtainedfromspraydryingofmilkmodelemulsionswith0,0.3and0.5%w/wcarrageenancontentwereinvestigatedbyCLSM.Themicroscopytechniqueandtheprecedinglabellingprocesswith
Fig.1Visualcomparisonofelongationaldisintegrationprocesses:(a)timesequenceofanemulsionbridgeduringextensionalviscometryfromcommencementofthinninguntilbreak-up,and(b)break-upofemulsionjetfrommicrofluidicjetnozzle.
alt-text:Fig.1
hydrophilicFastGreenFCF(bondedtoprotein)andhydrophobicNileRed(bondedtothefatphase)havebeenpreviouslydescribed(Foersteretal.,2016a).
2.3.6ScanningelectronmicroscopyThemorphologyofthespray-driedparticleswasimagedwithafield-emissionscanningelectronmicroscope(SEM)(FEINovaNanoSEM450FE-SEM,FEICorp,USA)usinga5kVelectronbeam.Theinternalfeaturesandporosityofparticlesthat
hadbeenintentionallycleavedasunderwithathinrazorbladewerestudiedaswellastheexteriormorphologybeforeandaftersurfacefatextraction.Thesampleswerecoatedwitha2nmthickIridiumlayertopreventthemfromelectricalcharging.
2.3.7PowderdissolutionandwettingbehaviourTwostudiestoevaluatethereconstitutionbehaviourofthespray-driedpowderswereundertaken.First, focusedbeamreflectancemeasurement(FBRM)wascarriedouttomonitorinsituthedissolutionasa functionof time.FBRMusesthe
measuredparticlechordlengthsandtheircorrespondingcountratestoquantifythedecreasingparticlesizeinthecourseofdissolution.TheworkingprincipleoftheFBRMdevice(LasentecD600L-C22-K,MettlerToledoLtd,Australia)andthedetailed
experimentalprocedurehavebeendescribedbyFang,Selomulya,andChen(2010).Inbrief,0.500gofsamplewereaddedonthesurfaceof25°Cwarmwaterthatwascontainedinaflat250mlbeaker.TheFBRMlaserprobewasimmersedintothewater
atawell-definedlocationandanangleof45°,andamagneticstirreroperatedat900rpm.Themeasurementshadbeenexecutedfor20minwithdatacollectionintervalsof2s.TheFBRMmeasurementswereconductedintriplicatewiththreepowder
samplesthatwerecollectedforabout10mineachduringthesamespraydryingrunat10,20and30minafterasteadycolumntemperatureprofilehadbeenobtained.
Second,amodifiedapproachoftheNiroAnalyticalMethodNo.A5a(GEA,2005)wasusedtodeterminethepowders'wettability.Thewettability,expressedintimeinseconds,definesadriedpowder'sabilitytopenetrateastillwatersurface.For
this,0.5gsamplewerepassedthroughafunnelontothequietsurfaceofMilli-Qpurifiedwater(25°C),whichhadbeenfilledintoa100mlmeasuringcylinderuptothe90mlmark.Acamera(DCR-HC36,SonyCorp,Japan)recordedthewettingprocess
fromthetimeofpowderadditionuntilthelastparticlehadovercomethewatersurfacetensionandconsequentlysunkdown.Thewettabilitystudywasruninduplicatewithtwopowdersamplesthatwerecollectedforabout10mineachduringthesame
spraydryingrunat100and110minafterasteadycolumntemperatureprofilehadbeenestablished.
2.3.8PeroxidevalueanalysisforoxidativestabilitystudyTheoxidativestabilityofthefatcontainedinthespray-driedparticlesofdifferentcarrageenanconcentrationswascomparedbymeansoftheirperoxidevaluesatintervalsofsevendays.Thepowderswerestoredfor35daysatacceleratedstorage
conditionsof33°Candambientairinadryingoven.TheperoxidevaluemeasurementswerecarriedoutfollowingtheguidelinesgivenintheOfficialMethodsofAnalysisbytheAssociationofOfficialAnalyticalChemists(AOAC,1990).Inshort,2gof
samplewereswirledfor30sin30mlofafreshlypreparedaceticacid(UnivarInc,USA)/chloroform(MerckKGaA,Germany)mixture(3:2byvolume)thatcontained1mlofasaturatedpotassiumiodate(Sigma-AldrichPtyLtd,Australia)solution.The
mixturewas thenkept indarkenvironment for5minprior toadditionof30mlofwater.Subsequently, titrationwitha0.002Msodium thiosulfate (Sigma-AldrichPtyLtd,Australia) solutionwasconductedunder stirringuntil theyellowcolourhad
disappeared.Lastly,1mlofanaqueousonepercentstarchindicatorsolutionwasaddedanditwasfurthertitratedunderstirringuntilthebluecolourhadvanished.Foreachsetofmeasurements,ablankcontrolwithoutpowderwasalsocarriedout.The
peroxidevalue in[milliequiv.peroxide/kgfat]wascalculatedbythefollowingexpression:
where wastheblankcorrectedtitrationvolumein[ml], thenormalityofthesodiumthiosulfatesolutionin[mol/l]and themassoffatcomprisedby2gofsamplein[g].Theanalysiswasruninduplicatewithsamplesthatwerecollected
forabout40mineachduringthesamespraydryingrunat120and160minafterasteadycolumntemperatureprofilehadbeenreached.
3Resultsanddiscussion3.1Impactofλ-carrageenancontentonemulsionproperties3.1.1Stabilityofthemodelemulsions
Thepreparationof themodelemulsions,asdescribed insection2.1, resulted incompletedissolutionofallcomponents.Thegoodwatersolubilityofλ-carrageenan incomparison to the lesschargedκand ι forms (Langendorff et al., 2000)
permitteditsdissolutionatarelativelylowtemperature,whichcanmeanbettercostefficiencyinindustrialapplicationsandtheavoidanceofproteindenaturationleadingtoreducedemulsionstability(Millqvist-Furebyetal.,2001).
Turbiscanemulsionstabilitymeasurements(Fig.2)wereperformedtoevaluatethecapabilityofλ-carrageenantoalterthestabilityofthemilkmodelemulsionsatdifferentconcentrationsasanindicatorforthenetworkstrengthbetweentheoil
andwaterphase.ThehomogeneityandstabilityorinstabilityoftheemulsionswasevaluatedbyanalysingtheTurbiscanbackscatteringdataoversampleheightasafunctionoftime.Themorepreciselythescansatdifferenttimesoverlapped,themore
stableweretheemulsions.Thelowbackscatteringvaluesatasampleheightoflessthan0.6cmandabove6cmforeventhemoststablesampleswereascribedtolightscatteringattheglassbottomofthemeasurementcellandmorelighttransmissionat
theverysampletopduetothemeniscuscurvature.
(3)
Theemulsionswithoutcarrageenanand0.1%w/wcarrageenanwereleaststable.Theyfeaturedanincreasingbackscatteringpercentageovertimethroughoutthesampleheightduetolargerfatglobulesasaresultofflocculation,anddisplayeda
Fig.2Modelemulsionstabilitiesdependingonλ-carrageenancontent:turbiscanbackscatteringmeasurementsovertime,andcorrespondingrepresentativemicroscopeimagesofthemicrostructuresinthefreshlypreparedemulsions.
alt-text:Fig.2
concomitantappearanceofcreamatthesurface,aswasobservedfromthemorepronouncedbackscatteringatthesampletop(height>6cm)incomparisontotheothersamples.
Theflocculationcouldbeinhibitedbytheadditionofmorepolysaccharide.Accordingtothewidthofthebackscatteringbands,thestabilityoftheemulsionwith0.2%w/wcarrageenanwasimprovedincomparisontolowerconcentrationsand
greateststabilitywasreachedfor0.3–0.4%w/wcarrageenan.Thisindicatedthattheλ-carrageenanbondedontotheproteinofthefatglobulemembranesandthusstabilizedtheoil/waterinterfacebypreventingcoalescenceofthefatglobulesduetotheir
increasedelectrostaticrepulsion.Theremighthavebeenanelectrostaticattractionbetweencarrageenanandwheyprotein,assuggestedbyStoneetal.(2012).Moreoften,though,thestabilizationofmilkemulsionshasbeenattributedtointeraction
betweencarrageenanandcasein(Dickinson,1998;Gu,Regnier,&McClements,2005;Langendorffetal.,2000),withthelatterrepresenting80%oftheproteincontainedinbovinemilk.ThepHvaluesofthemilkmodelemulsionsweremeasuredtobein
therangeof6.44±0.03,exceedingthecasein'sisoelectricpointof4.6.Whilethecaseinthuscarriedanegativenetcharge,theκ-caseinmoleculesstillfeaturedpositiveaminoacidresidueregions,asgenerallybelieved(Snoeren,Payens,Jeunink,&Both,
1975). This allowed absorbance of the negatively charged sulphate groups of the carrageenan at the positively charged patches of themembranes that surrounded the fat globules. The complexation increased the overall charge of the fat globule
membranestowardsmorenegativevalues.Dalgleishetal.(1988)foundfromζ-potentialmeasurementsusingmicro-electrophoresisthatthenegativechargedensityoncasein/λ-carrageenancomplexesinstronglydilutedskimmilkapproximatelydoubled
withverylowcarrageenancontentsfromabout0.001to0.01%w/w.Higherconcentrationsleadtoafurther,thoughlesssharpincreaseinchargedensitywithintherangeinvestigated(maximumofapproximately0.02%w/w).Theflatteningofthecharge
curveatgreatercarrageenanconcentrationswasascribedtothecationicproteinsurfacesreachingsaturationcoverage,anditwaspresumedthatthiswouldhaveledtocross-linkageanddepletionflocculationifthetotalsolidcontenthadbeenhigher.
InagreementwiththeworkbyDalgleishetal.(1988),inthepresentstudyfurthercarrageenanaddition(from0.4to0.5%w/w)resultedinphysicalemulsiondestabilization.Thebackscatteringprofileoftheemulsionwith0.5%w/wcarrageenan
resembledtheoneof0.2%w/w,beingmoreconstantovertimethanfor0and0.1%w/w.However,theemulsionwaslessstablethanfor0.3and0.4%w/w,whichpresumablywasasaresultofdepletionflocculationuponsaturationsurfacecoverageofthe
positivelychargedproteinareas(seeAppendixBforasupportingtheoreticalcalculationofthesaturationconcentration).Depletionflocculationisoftenobservedincolloidalsystemswhenthedropletsofthedispersedphasearesurroundedbyanadsorbed
layerofpolymer,whichsimultaneouslyexists inexcess inside thecontinuousphase.AsdiscussedbyLangendorffetal. (2000), if thecarrageenanconcentrationexceeds the saturation level toacertaindegree, the freecarrageenanwill repulse the
carrageenan-coveredsurfacesofthefatglobulesandproteinaggregatesandwillconsequentlyinducecoalescenceofthelipidphase.
TheTurbiscanstabilityresultswerecomparedwiththecorrespondingmicrostructuresofthefreshlypreparedemulsionsasvisualizedbythemicroscopicimagesinFig.2.Theemulsionwith0.5%w/wcarrageenanhadrelativelylargepatchesof
darkershade,suggestingphaseseparationthroughouttheemulsionwiththedarkpatchesbeinginterconnectedareasofflocculatedfatglobules.Thesepatcheswerenotobservedatconcentrationsof0.3–0.4%w/wcarrageenan,wherethemicrostructure
appearedmosthomogeneousamongstallsamples.Hereonlyafewdarkspotswereobserved,becausethemajorityoftheflatglobulesdidnotcoalesceandthusweresofinelydispersedinsidethecontinuousphase(thebrighter,greyregionsintheimages)
thattheywerenotvisibleunderthemicroscopeatthegivenmagnification.Incomparison,atlowerpolysaccharidecontentstheappearanceoftheemulsionmicrostructurewasmoreheterogeneouswithsubstantiallymoreandlargerdarkspots,probably
duetotheformationofmoreandlargerclustersbycoalescenceoffatglobules.Thesemostlikelyfurthercoalescedovertime, leadingtotheobservedcreaming.Itwasconfirmedthatthevisualhomogeneityofthemicrostructurecorrelatedwiththe
emulsionstabilitybytrackingthechangesoverseveraldaysinanemulsion(0.3%w/wcarrageenancontent),whichwasstoredat6°C(FigureA.1).Whilebeingrelativelyhomogeneousinitially,afterthefirst24hlargercoalescedlipidglobulesbecame
visibleandaftertendayssomegreypatcheshadeventuallyemerged,similarintheirappearancetowhatwasobservedforthefreshmodelemulsionof0.5%w/wcarrageenancontent.Itcanthusbeconcludedthatthemicrostructureimagessupportedthe
Turbiscanstabilityresults.
3.1.2FatglobulesizedistributionandshearviscosityofthemodelemulsionsFirstandforemost,Fig.3acomparestheimpactoftheλ-carrageenanconcentrationonthesizedistributionofthefatglobulestogetherwiththefreecaseinmicellesinsidetheoriginal,untreatedmodelemulsions.Atthelowestpolysaccharide
concentrationof0.1%w/w,thefatglobulesfeaturedmaximalsizewithameandiameterof1.09±0.0008μm,whichwasslightlylargerthanincaseofthecarrageenan-freemodelemulsion.Thisobservationwasexplainedbybridgingflocculation,where
thepolysaccharidechainsareonly looselyadsorbedon theproteinof the fatglobulemembranesandhencemaydevelopbridgesbetween the fatglobules, leading tophysical instability.Suchabridging flocculationhasalsobeenreported forother
emulsionsatlowpolysaccharideconcentration,suchasbySerfertetal.(2013)forafishoil/β-lactoglubinemulsionat0.05–0.15%w/wpectinconcentrationandbyDickinsonandPawlowsky(1997)foran-tetradecane/bovineserumalbuminemulsionat
0.001–0.04%w/wι-carrageenanconcentration.Inthepresentstudy,doublingtheλ-carrageenanconcentrationto0.2%w/wpreventedbridgingflocculationandthusresultedinasharpdeclineinfatglobulesize.Theglobulesizewasfurtherreducedby
addingmorecarrageenanofupto0.4%w/w,althoughthemeanvolumetricdiametersfor0.3and0.4%w/wonlydifferedslightly.Aminimalfatglobulesizeof0.66±0.0019μmindiameterwasthusachieved.Thisminimumcoincidedwiththepreviously
describedsaturationsurfacecoverageconcentrationandanestablishmentofoptimumemulsionstabilityat0.3–0.4%w/wcarrageenan(AppendixBandsection3.1.1).Thephysicalstabilizationwithcarrageenanpreventedcoalescenceofthefatglobules.
AscanbeseeninAppendixA(FigureA.2),thevolumetricsizedistributionoftheemulsionswasbimodal,consistingoftwomainpeaksatapproximately0.2and1.5μm.Thefirstpeakofthefatglobulesizedistributionoverlappedwiththepeakofthefree
caseinmicelleswiththeiraforementionedvolumetricmeandiameterof0.14μm.Thefirstpeakwasnotrepresentingthecaseinmicellesalone,becauseitsvolumewascloselyrelatedtothevolumeofthesecondpeakasinfluencedbythecarrageenan
content.From0.1to0.3%w/w,thevolumeofthesecondpeakdecreasedmoreandmore(decreaseinheightfromapproximately6.5%–to4.5%and3.5%).Themassofthefatphasewasconservedwithacorrespondingincreaseinvolumeofthefirstpeak
(increaseinheightfromapproximately5.5%–to8.7%and9.6%).Thisoccurredbecausecoalescenceofthesmallerfatglobuleswasinhibitedbygreaterelectrostaticrepulsionduetoλ-carrageenanadsorption.Comparingtheemulsionof0.1%w/wwiththe
carrageenan-freeemulsion,thesizedistributionshiftedtowardsthelargerfatglobulesofthesecondpeakduetobridgingflocculation.
Additionally,Fig.3aalsoillustratesthechangesinfatglobulesizeduringfilmdisintegrationinthetwoinvestigatedatomizationnozzles.Inbothcasesandindependentfromthecarrageenanconcentration,thefatglobulesdidnotcoalesceduring
atomization,butunderwentadecreaseinmeandiameterby6%inaverage.Themechanicalstress insidethenozzlescausedabreak-upofsomeofthelargerfatglobules,ascanbededucedfromaslightreductionofthesecondpeakinallatomized
emulsionsincomparisontothesizedistributionoftheoriginalemulsions(seeFigureA.2).
Asidefromtheobservedreductionindropletsizeofthedispersedphase,hydrocolloidscanprimarilyenhanceemulsionstabilitiesbymeansoftheirthickeningeffect.Despiteλ-carrageenanbeingnon-gelling,thedynamicshearviscosityofthe
modelemulsions increasedconsiderablywithcarrageenancontent,particularly in therangeof0.2–0.4%w/w(Fig.3b).An increase incarrageenanconcentration to0.5%w/w lackeda furtherappreciable rise in shearviscosity.The increasingshear
viscositywithhighercarrageenancontentpresumablywasaconsequenceoftheabsorbanceofcarrageenanonthemilkfatglobulemembranes.Thisleadtobridgingflocculationatlowcarrageenanconcentrationandtoelectrostaticemulsionstabilization
athigherconcentrationsuntilthesaturationleveloftheproteinsurfaceareasofthefatglobulemembranesandcaseinmicelleshadbeenreachedatabout0.4%w/wcarrageenancontent.Variationoftheshearraterevealednon-Newtonian,shearthinning
behaviour,beingmoredistinctatgreatercarrageenanconcentrations.Assuch,theviscosityunderextensionalstresswasnotcomputablefromtheshearviscosity,buthadtobedeterminedexperimentally.
3.1.3ImpactoffatandcarrageenancontentonshearandextensionalviscositiesItwashypothesizedthattheextensionalviscositycanbeacrucialfactorofinfluenceontheatomizationbehaviourofemulsionsduringspraydrying.Theatomizationtechniqueofthemicrofluidicnozzleemployedinthisstudywasnotbasedon
shearstress,butitimposedanormalstressontheemulsionjetviaasinusoidalcontractionoftheorifice.Fig.1visualizesthesimilaritiesbetweenthemicrofluidicjetatomizationandtheacoustically-drivenmicrofluidicextensionalviscometry.Ineither
case,theemulsionfilmwasformingafinethreadthatthinnedmoreandmorewithdistancefromthenozzleorificeorwithmeasurementtime,respectively.Atsomepoint,dependingontheviscousforces,excesssurfaceenergywasthenreached,causing
thethreadtobreakupintoanindividualdroplettoregainminimalsurfaceenergy.Tobetterunderstandtheimpactofadispersedfatphaseandtheemulsionstabilizationwithcarrageenan,theextensionalandshearviscositiesofselectedemulsionswere
compared(Table1).TheextensionalviscositiesweredeterminedaccordingtoEquation(2)fromthedataillustratedinAppendixC(FigureC.1).
Table1Rheologicalimpactoffatphaseandλ-carrageenan:composition,dynamicshearviscosity(atshearrateof199.1s−1)anduniaxialextensionalviscosityofalow-fatemulsionwithoutλ-carrageenan,aregular-
Fig.3Propertiesofthemodelemulsionsatdifferentλ-carrageenancontents:(a)meanvolumetricparticlesizesinoriginalemulsionandincollectedemulsionafterdisintegrationbyoneoftwoatomizationnozzlesasmeasuredwithlaserlightscattering,and(b)dynamicshear
viscositiesobtainedfromconeandplaterheometermeasurements(25°C).
alt-text:Fig.3
fatemulsionwithoutλ-carrageenanandsimilarfatcontenttothestandardmodelemulsions,andastandardmodelemulsionwith0.3%w/wλ-carrageenan.alt-text:Table1
Carrageenancontent[%w/w] Fatcontent[%w/wind.m.] Solidcontent[%w/w] Shearviscosity[mPa·s] Extensionalviscosity[mPa·s]
0 0.3 20 3.75±0.07 25.9±1.5
0 31.1 20 3.17±0.02 11.5±0.8
0.3 31.1 20 10.20±0.05 30.7±2.8
Thelow-fatemulsionwithalipidcontentofonly0.3%w/wind.m.andtheregular-fatemulsionwithafatcontentsimilartothestandardmodelemulsions(31.1%w/wind.m.)werecomparedtoevaluatetheimpactofthefatglobules.Their
presencecausedastrongdecreaseinextensionalviscositytolessthanhalfthevalueofthefat-freeemulsion(from25.9to11.5mPas).Therewasalsoadropindynamicshearviscosity,which,however,wasmarginalbycomparisonwith15%from3.75to
3.17mPas.Thesharpdecreaseinextensionalviscosityprovidesanexplanationforthereductioninmilkdropletsizewithhigherfatcontentuponatomizationwithamicrofluidicjetnozzleasobservedinapreviousstudy(Foersteretal.,2016a),where
similaremulsionswereinvestigated.Whiletheregular-fatemulsionhadasolidcontentof20%w/wintheaforementionedstudy,thelow-fatemulsioncontainedonly14%w/wsolidsandthusfeaturedalowershearviscosity(2.4mPas)thantheregular-fat
emulsion.Therefore,considerationoftheshearviscositiescouldnotexplainthemeasurementofsmallerdropletsizesinthepresenceoffat,asagreaterviscositytypicallyfavourstheformationofbiggerdroplets(Lefebvre,1989).InlightofTable1,not
onlytheshearviscositybutinparticulartheextensionalviscosityneedstobetakenintoaccounttodescribethedropletdisintegrationmechanismduringatomizationinspraydryingapplications.Aperforationmechanisminducedbythefatglobulesis
proposedtoexplaintheobservedsharpdropinextensionalviscositywiththeexistenceofasignificantlipidcontent.Theintrinsicmilkemulsionstabilitymightbelocallyreducedalongtheoil-waterinterfacesformedbythefatglobules.Withmorefat
globulesbeingdispersedthroughouttheregular-fatemulsion,theemulsionbecameperforatedbytheseareasoflowerstability.Duringatomizationunderelongationalstress,thefilmhencedisintegratedpreferablyalongthefatglobules,followingthe
lowest viscous resistance, figuratively speaking, like the ‘zipper of a jacket’. Such a perforation mechanism had already been briefly discussed several decades ago, when Dombrowski and Fraser (1954) and Zakarian and King (1982) undertook
photographicstudiesofthedisintegrationoffan-shaped,flatliquidsheetsthatweregeneratedwithasingle-holefan-spraynozzle.Thefilmsbrokeearlier,thatisatgreaterfilmthickness,inthepresenceofadispersedoilphase.Furthermore,recent
investigationsreportedthatduringthespraydryingofmilkemulsionssurfacelayersoffatexistedonthedropletsimmediatelyafteratomizationforvariouskindsofatomizationtechniques:microfluidicjetnozzlesofdifferentorificesize,pressureswirl
nozzlesofdifferentorificesizeandoperatedatdifferentfeedpressures,anddropletgenerationwithamicro-volumetricsyringe(Foersteretal.,2016a;Foerster,Gengenbach,Woo,&Selomulya,2016b;Wuetal.,2014).Afilmdisintegrationlocalizedalong
thedispersedfatphasewouldexplainwhythedropletsurfaceswerecoveredbyfatassoonasindividualdropletshadbeenformed.Iftheemulsionpreferablybreaksupalongtheinterfaceofthefatglobules,thefatglobuleswereimmediatelypresenton
thesurfaceoftheformeddroplets,presumablyinformofamoreorlessconsistentmonolayeroffatglobulesthatmighteitherruptureorstayintactuntilcompletionofthespraydryingprocess.Inviewofthat,itwasanticipatedthattheamountofsurface
fat on spray-driedmilk particles should be reducible by decreasing the size of the fat globules inside the emulsionswith the addition of λ-carrageenan. In addition, the emulsion stabilizationwith carrageenanwas hoped to shift the disintegration
mechanismawayfromthefatglobules.
Investigationoftheimpactofλ-carrageenan(0.3%w/w)ontheviscosityofthestandardregular-fatemulsionshowedthatthecarrageenanincreasedtheextensionalviscositysignificantly(Table1).Themilkmodelemulsionwith0.3%w/wλ-
carrageenanfeaturedanextensionalviscosityof30.7mPas,whichwasbyafactorof2.7greaterthantheoneofthepolysaccharide-freeemulsionofidenticalfatcontent.Thelossinextensionalviscosityduetoadditionofthelipidphasewasconsequently
overcomeandtheextensionalviscositywasevengreaterthantheoneofthelow-fatemulsion.Accordingly,thediameterofthemonodispersedroplets immediatelyafteratomizationwasslightlylargerfor0.3%w/w(122±2μm) incomparisontothe
carrageenan-freeemulsiondroplets(115±2μm).Thisindicatedthatthestabilizedemulsionsmighthavelesspreferablydisintegratedalongthedispersedfatphase.
3.2Impactofλ-carrageenancontentonthespray-driedparticles'properties3.2.1Chemicalsurfacecomposition
Theamountofsurfacefatonthespray-driedparticleswassignificantlyreducedatcertaincarrageenanconcentrations,asdeterminedbysurfacefatextraction(Fig.4a).Thesurfacefatamountedto4.7%for0.3%w/wcarrageenan,incontrastto
13.8%forthecarrageenan-freepowder.Theextentofsurfacefatformationduringspraydryingwasapproximatelyinverselyproportionaltotheemulsionstability,asthelowestamountwasobservedatintermediatecarrageenanconcentrations.Beingat
0.2–0.3%w/w,thiswasslightlyoffsetfromtheoptimumemulsionstabilityandfatglobulesizevaluesat0.3–0.4%(Fig.2andFigure3a).Inagreementwiththisfinding,amoreefficientfatencapsulationwithdecreasingfatglobulesizeinsidetheemulsions
tobespray-dried,indicatinggreateremulsionstability,wasalsoreportedinotherstudies(Jafarietal.,2008;Sarkar,Arfsten,Golay,Acquistapace,&Heinrich,2016).Astrengthenednetworkbetweenthelipidandaqueousphasesthroughstabilizationof
themilkfatglobulesbyadsorptionofλ-carrageenan,asalsoreflectedbythesubstantial increase inextensionalviscosity,possibly ledtoareductionofthe insection3.1.3discussedperforationmechanism.Asthenetworkalongthefatglobuleswas
reinforced,itisbelievedthattheemulsionfilmdisintegratedlesspreferablyalongthephaseinterfacesandthusasmalleramountoffatemergedonthesurfacesupondropletformation.Theemulsionstabilityseemedtoentailadecisiveinfluence,sincethe
fatproportionatthesurfacewentupagainto10.0%fortheemulsionwiththehighestcarrageenanconcentrationof0.5%w/w,whichpresumablywassubjecttodepletionflocculation.Otherthanthat,thereductioninfatglobulesize(discussedinsection
3.1.2)inthestabilizedemulsionspossiblycontributeddirectlytotheobservationoflesssurfacefat.Fromthefatextractiondata,thethicknessofthesurfacefatwasroughlyestimatedundertheassumptionofacontinuousfatlayerthathadthesame
compositionasmeasuredfortheverysurfacebyXPS(albeitthisisnotthecaseinreality).Surfacefatthicknessesof1.0,0.9,0.4,0.4,0.6and0.6μmwerecalculatedfortherespectivepowdersfromemulsionswith0–0.5%w/wcarrageenan.Interestingly,
theseestimationsapproximatelycorrespondedtotherespectivesizesofthefatglobulesasmeasuredinsidetheemulsions(Fig.3a).Thissuggestedthataboutamonolayeroffatglobules,albeitpresumablytosomeextentinrupturedform,mighthavebeen
presentonthespray-driedparticlesurfaces.Thisisinconformitywiththeproposedsurfacefatformationmechanisminconsequenceofpreferreddisintegrationalongthedispersedfatphaseduringatomization.Inviewofthis,asmallerfatglobulesizeled
tolessthicksurfacefatonthegenerateddropletsandthusonthespray-driedparticles.
XPSanalysisofthesurfaceconcentration(Fig.4b)onlyshowedminordifferencesbetweenthepowdersamples.AstheXPSsurfaceconcentrationinlactose,proteinandfatonthevariousspray-driedpowderswasalinearestimationderivedfrom
theatomicconcentrations, thesmalldifferencesbetweenthesampleswerenotstatisticallysignificant.Moregenerally, theXPSresultsshowedthat thepowderconsistedalmostcompletelyof fat (approximately88–94%v/v)at theirverysurfaceand
additionofcarrageenancouldnotinhibitthecreationofadominantfatcoveragealongtheoutmostparticlesurface.Assuch,XPSanalysisdidnotreflectthestronginfluenceofthecarrageenancontentontheextentofsurfacefatthatwasrevealedby
surface fatextraction.Proteintookuptheremainingvolumeof theanalysedsurface layer,whichwasdepleted in lactose.For0.3%w/wcarrageenan insidethemodelemulsion,Fig.4balsocompares thesurfaceconcentrationofspray-driedpowder
particleswiththeoneofthecorrespondingdropletsimmediatelyafteratomizationfor0.3%w/wcarrageenan.Apparently,asurfacefatlayerhadalreadybeenformedduringatomization(77%v/vfat)andtheXPSsurfaceconcentrationdidnotchange
Fig.4Impactofλ-carrageenancontentofthemodelemulsionsonthecorrespondingspray-driedparticles'surfacecomposition:(a)freesurfacefatfromextractionstudy,and(b)estimatedXPSsurfacecompositionofthespray-driedparticlesforallcarrageenanconcentrations,ofthe
dropletswith0.3%w/wdirectlyafteratomizationandofthespray-driedparticlesfromemulsionswith0.1and0.3%w/waftersurfacefatextraction.
alt-text:Fig.4
significantlythroughoutthesucceedingdryingstage.Furthermore,itwasconcludedthatatleastsomeofthefatglobulemembranesgotrupturedatthedropletsurfacesbymechanicalorthermalstressduringatomizationordrying,andthefreefatcould
spreadoverwideareasof thedroplet surface. If themajorityof themembraneswasstill intact, theXPSmeasurementwouldmost likelyhave indicatedgreaterproteinsurfaceconcentrations,because the thicknessof theadsorbedcasein layers in
homogenizedmilkmodelemulsionsaretypicallyintherangeofapproximately5–11nm(Dalgleish,Srinivasan,&Singh,1995;Fang&Dalgleish,1993),whichcoincideswiththeXPSmeasurementdepthoflessthanabout10nm.Instead,asaresultofthe
presumedmembraneruptureofatleastsomeofthefatglobulesatthesurface,primarilythelipidphasewasdetectedbyXPS.Thefatsurfaceconcentrationdidnotreach100%v/v,nevertheless,becausenotallglobulesgotrupturedatthesurface(see
section3.2.2)andsomeproteinoftheoriginalmembranesmighthaveremainednearthesurfaceorotherproteindiffusedtothesurfaceduringthedryingstageduetoitssurfaceactivity.Regardingtheextentofglobulerupture,theadsorbedcarrageenan
layerspresumablyhadanindirectinfluenceonthemembranestability:themembranesofthesmallerfatglobules,asforinstanceobtainedbyemulsionstabilizationwithcarrageenanatintermediateconcentrations,werelesssusceptibletorupturethan
theonesofthelargestglobules(Xuetal.,2013).
Theproteinandfatdistributionsobtainedfromconfocallaserscanningmicroscopyshowedthatthesurfacesofallspray-driedparticleswerecoveredbyafatlayer(Fig.5aandb).Moreover,thethicknessofthefatsurfacelayersstronglyvaried
withcarrageenancontent.For0%w/w,thesignalofthesurfacefatwasstrongerandreachedfurtherintotheinneroftheparticleincomparisonto0.3%w/w.Thecomponentdistributionintheatomizeddropletsof0.3%w/wcarrageenancontentappeared
toalreadyfeatureahardlyvisiblefatsurfacelayer(Fig.5c).ThelowvisibilityofthisthinsurfacelayerwasascribedtothelimitedresolutionoftheCLSMimageandtheporoussurfacestructureoftheatomizeddropletsafterfreeze-drying.Thevariationof
thethicknessofthesurfacefatobservedfromCLSMthusexplainedwhythesurfacefatextractiondemonstratedastrongdependenceoftheamountofsurfacefatonthecarrageenancontent.Additionally,asevenforlowsurfacefatcontentstheoutmost
surfacewascomprisedpredominantlybyfat,theCLSMimagesalsoexplainedwhytheXPSmeasurements,whichaccountedonlyforthecompositionattheveryparticlesurfaceduetotheshortsamplingdepth,detectedafatdominanceatthesurfaces
throughoutallspray-driedpowdersandontheatomizeddroplets.
Fig.5CLSMimagesofdistributionofprotein(signalfromFastGreenFCFvisualizedingreen)andfat(signalfromNileRedinred):(a,b)cross-sectionofspray-driedparticleswithλ-carrageenancontentsof0and0.3%w/w,and(c)cross-sectionofatomizeddroplet(afterflash-
freezingandfreeze-drying)with0.3%w/wλ-carrageenan.(Forinterpretationofthereferencestocolourinthisfigurelegend,thereaderisreferredtothewebversionofthisarticle.)
alt-text:Fig.5
3.2.2ParticlemorphologyandporosityInadditiontothechemicalsurfacecomposition,alsotheparticlemorphologyandporositycanaffectthefunctionalpropertiesofmilkpowder.SEMinvestigationshowedthattheparticlesurfacesobtainedfromemulsionswithoutcarrageenanor
withlowconcentrationthereoffeaturedconvexbumpsof2–4μmindiameter(Fig.6aandb).Withmorepolysaccharide,theparticlesurfacesbecamesmoother(Fig.6dande).Comparingtheparticlesurfacesat0.1%w/wbeforeandaftersurfacefat
extraction(Fig.6bandc),theconvexbumpshaddisappearedaftertheextractionprocessandinsteadconcavedimplesofapproximatelysimilarsizeanddistributiondensityremained.Itwashenceconcludedthatthebumpsconsistedoffatandwere
formedduringspray-dryingundercoalescenceoffatglobulesonthedryingparticles'surfaces.Accordingly,itappearsthatnotallofthefatglobulemembranesthatwerelocatedatthedropletsurfacesunderwentrupture(comparetosection3.2.1).With
theadditionofλ-carrageenan,thenegativechargeofthefatglobules'membranesroseandthuscoalescenceoffatglobulesonthesurfaceswasinhibitedandlesstonobumpswereobserved.Alternatively,thebumpsmighthavebeenformedbyprotein
aggregates.ComparingtheCLSMimagesbeforeandafterthedryingstage(Fig.5bandc),itappearsthatproteinclustershadbeenformedduringdryingorstorage,atleastintheprotein-richinneroftheparticles.Itiswellknownthatinspray-driedhigh-
caseinpowdersthecaseinhasatendencytoformnetworksofinterconnectedmicelleswithlowsolubilityinaqueousmedia(Crowley,Kelly,Schuck,Jeantet,&O'Mahony,2016;Schucketal.,2007).Also,ithasbeensuggestedinliteraturethat,atelevated
temperature of sufficient height and duration,whey protein exposes hydrophobic amino acid residues that then undergo linkagewith caseinmicelles, leading to hydrophobic aggregate formation (Corredig&Dalgleish, 1999). The reported protein
aggregateformationoccurredforparticlesthatwereveryhighinprotein,whereasinthepresentstudytheparticlesurfacesweredominatedbyfat.It ishencedoubtfulwhetherheresuchhydrophobicproteinaggregatescouldhavedevelopedatthe
particlesurfaces.
Although the external surfaces of all powder samples were non-porous, the internal cross-sections contained macro-porous structures, which were more pronounced at lower carrageenan content (Fig. 6f–i). It is hence believed that the
strengtheningoftheemulsionnetworkbyadditionofcarrageenantranslatedintodenserparticlesuponspray-drying.Thisalsoexplainswhythespraydriedparticlesfromemulsionswith0and0.3%w/wcarrageenanwereofsimilarsize(91±4and
90±3μmindiameter,respectively),despitetheatomizeddropletsbeingabout7μmlargerfor0.3%w/w(seesection3.1.3).Thus,boththeamountofsurfacefataswellastheparticleporosityaretobetakenintoaccountwhendiscussingtheimpactof
carrageenanonthefunctionalpowderproperties.
3.2.3FunctionalpowderpropertiesFig.7aillustratestheresultsofthedissolutionandwettabilitystudies.AttheendoftheFBRMdissolutiontest,theparticlesize,asrepresentedbythemedianchordlength,wasgenerallylargerforanyλ-carrageenanconcentrationincomparison
tothecarrageenan-freepowder.Intherangeof0.1–0.5%w/w,therewasalocalminimuminparticlesizeatanintermediatecarrageenancontentof0.3%w/w.Thecurvesofchordlengthoverfulldissolutiontimewereinagreementwiththisandare
providedinAppendixD(FigureD.1).Thewettabilitystudyrevealedthatthesamplescontaining0.3%w/wpolysaccharidecompletedthepenetrationofthewatersurfacethefastestinatimeofabout17min.Thewettingtimesoftheothersamples(0,0.1,
Fig.6Morphologyandporosityofspray-driedparticlesasinfluencedbyλ-carrageenancontent:(a–e)particlesurfaceswith(c)beingaftersurfacefatextraction,and(f–i)cross-sections.
alt-text:Fig.6
0.2and0.4%w/w),definedastotaltimerequiredforthelastparticleofeachsampletopenetratethewatersurface,didnotvarysignificantlyfromeachother,lyingbetween23and25min.Nowettingtimeforpowdersamplesobtainedfromspray-drying
ofanemulsionwith0.5%w/wcarrageenanaredisplayedinthechart,becausethemajorityofthoseparticleshadstillnotpenetratedthewatersurfaceafter1honehour.Theresultsofthewettingtimewereinlinewithphotographicmonitoringat20,60,
120and300s,whichalsoshowedasuperiorwettabilityfor0.3%w/wandaparticularlylimitedwettabilityfor0.5%w/w(FigureD.1inAppendixD).Forinterpretationoftheseresults,thedissolutionandwettabilitystudiesneedtobeinterpretedin
relationtoeachother.Thepowderwettabilityseemedtoinfluencethepowdersolubility,asthewettabilitycurveovercarrageenancontentwassimilarinshapetothedissolutioncurvewithaminimumat0.3%w/wcarrageenan.Theminimalvalueinchord
lengthandwettingtimeat0.3%w/wisbelievedtobeaconsequenceofthepowders'differentsurfacefatcontents.Astheamountofhydrophobicsurfacefatdecreasedfrom0to0.3%w/wofaddedcarrageenan,thetherebyimprovedwettabilityinaqueous
mediumcounteracted,tosomeextent,thedetrimentalimpactofthedecliningporositythatwasobservedfromSEMimaging.Presumablyasaresultoflowerparticleporositieswithgreatercarrageenancontent,thepowderdissolutionratewasloweredby
anycarrageenancontentincomparisontothepolysaccharide-freepowder.Therefore,anunwanteddeteriorationofthepowderrehydrationbehaviourwascausedbyemulsionstabilizationwithcarrageenan.
Furthermore,theinternalporosityofthepowdersalsoaffectedtheirperoxidevalues(Fig.7b).Thesewereusedasameasureoftheextenttowhichthelipid'sunsaturatedfattyacidchainshadundergoneprimaryoxidation.Directlyafterspray
drying(0days),nodifferenceinthedegreeofoxidationwasobservedbetweenanysample(colouroftheinitialanalytesolutionswasalreadysimilartotheblanktestspriortotitration).Apparently,thefattyacidshadnotbeenappreciablyoxidisedduring
emulsionpreparationorspraydryingforanypowdersample,andtheperoxidevalueshencewereapproximatedasbeing0milliequiv/kg.Themostsignificantchangesinperoxidevalueandthemostdistinctdifferencesbetweentheindividualpowder
sampleswerefoundtooccurduringthefirstsevendays.Thegreaterthecarrageenancontentofeachsamplewas,thelessstronglyincreasedthecorrespondingperoxidevalue,indicatinganimprovedoxidativestabilitybytheadditionofcarrageenan.This
was explained by the decreasing internal powder porosity at higher carrageenan concentration, which impeded oxygen diffusion inside the particles. Therefore, the peroxide values of the 0.5% w/w powder samples were by far the lowest (6–17
milliequiv/kg)overthewholestoragestudy.Itshouldbenotedthatthedifferenceinpowderdissolutionrateandwettabilitymighthavealsoaffectedtheperoxidevaluemeasurementitselfbyinfluencingtheaccessibilityofthetitrantandthesample
Fig.7Functionalpropertiesofspray-driedpowdersindependenceofλ-carrageenancontent:(a)wettingtimeonaquiescentwatersurfaceaswellasmedianofthefinalparticlechordlengthattheendoftheFBRMdissolutionanalysis,and(b)peroxidevalueforquantificationofthe
oxidativestabilityoverstoragetime.
alt-text:Fig.7
solutionintotheparticles.Inaddition,asmalleramountofsurfacefatmostlikelysupportedlowerperoxidevalues,too.Forinstance,therewasaconsiderabledifferenceintheperoxidevaluesattheendofthestoragestudy(35days)betweenpowders
withacarrageenancontentof0or0.1%w/w(approximately33milliequiv/kg)and0.2–0.4%w/w(27-22milliequiv/kg).Thiscorrespondedwellwiththesharpdropinextractedsurfacefatfrom0.1to0.2%w/w(Fig.4a).Thatthelipidcontainedinparticles
canbeprotectedfromahighrateofoxidationbyreducingtheamountofsurfacefatwaspreviouslydemonstratedbyGranellietal.(1996).
4ConclusionsThis studygave anunderstanding about the effect of λ-carrageenan, a linear sulphatedpolysaccharide, onmilkmodel emulsions in termsof stability anddisintegrationbehaviourduring spraydrying for thepurpose of
improvedmilkpowderpropertiesbyareductionofsurfacefat.Frominvestigationofemulsionsatdifferentcarrageenanconcentrations,itwaslearntthatcoalescenceofthedispersedlipidphasecanbeinhibitedbyadsorptionofλ-
carrageenan'ssulphategroupsonthemilkfatglobulemembranesandaconsequentincreaseinnegativechargeoftheseoil-waterinterfaces.Optimumelectrostaticemulsionstabilizationandminimumfatglobulesizewereobtained
withinacertainrangeofcarrageenanconcentrations(0.3–0.4%w/w)forthegivenmodelemulsions,whichagreedwithatheoreticalestimationofthesaturationcoverageofthecationiccaseinsurfacearea.Theemulsionstabilization
translatedintoaconsiderablythinnersurfacefatlayeronthespray-driedparticles.Thefatinpowdersobtainedfromacarrageenan-freeemulsionconsistedof13.8%freesurfacefat,incontrasttoonlyathirdofthis(4.7%)fora
carrageenan content of 0.3%w/w. These fat extraction results were confirmed by confocal laser scanningmicroscopic images. It was concluded that the emulsion stabilizationwith carrageenan possibly reduced the proposed
perforationmechanismalong the dispersed fat phase anddecreased the volumeof the fat globules that appeared at the droplet surface through this disintegration process, contributing to the observation of less surface fat at
intermediatecarrageenanconcentrations.Rheologicaldatasuggestedthatduringatomizationthemilkemulsionspreferablydisintegratedalongthedispersedfatglobules.Theextensionalviscositywasverysensitivetotheadditionof
oilandλ-carrageenan.Whiletheadditionofasignificantfatphaseatconstanttotalsolidcontentresultedinadecreasefrom25.9to11.5mPas,thepresenceofcarrageenan(0.3%w/w)avertedthistrendbyraisingtheextensional
viscosityup to30.7mPas.Thenew insights into the connectionbetweenemulsionproperties, atomizationbehaviour and resulting surface compositionof the correspondingparticles is of importance for industrial spraydrying
applications,sincesurfacefatcoverageaffectsthefunctionalpowderpropertiesdetrimentally.Inlightoftheseresults,andascarrageenanisalreadybeingusedincommerciallyavailabledairydrinks,theadditionofcarrageenaninto
milkemulsionsforreductionofthepowdersurfacefatcoverageuponspray-dryingseemstobefeasiblefromaneconomicalandconsumerpointofview.Besidesareductioninsurfacefat,theemulsionstabilizationwithλ-carrageenan
alsoinducedadecreaseininternalparticleporosity.Withregardtotherehydrationbehaviourinwater,atrade-offwasnotedbetweenthepositiveimpactofreducedsurfacefatandthenegativeinfluenceofagreaterparticledensity
withcarrageenan.Sincetheeffectof increaseddensitywasmoredominantonthewatersolubility,methodstoavoida loss inpowderporosityshouldbeexplored in futurestudies for thepurposeof ideal functionalmilkpowder
propertiesinindustrialapplications.Yet,thehigherpowderdensityappearedtoalsohaveafavourableeffect,asthepowder'soxidativerancidityafterstoragewasreducedwithgreatercarrageenancontent.Inafuturestudy,itcould
beinvestigatedhowtheimprovedemulsionstabilityandincreasedextensionalviscositybyadditionofcarrageenanimpactsthedisintegrationbehaviourandfatencapsulationefficiencyinspraydryingtechniquesthatarecommonly
applied in industrialmilk powder production. The charge density in emulsions containing skimmilk powder and different λ-carrageenan concentrations could be investigated by ζ-potentialmeasurements to also study how the
electrostaticcarrageenan/caseininteractionisinfluencedbyavariationinsodiumorcalciumcationconcentrations.
AcknowledgementsTheconfocallaserscanningmicroscopyworkwasperformedattheMelbourneCentreforNanofabrication(MCN)intheVictorianNodeoftheAustralianNationalFabricationFacility(ANFF).Theauthorsalso
wishtoacknowledgeuseoffacilitieswithintheMonashCentreforElectronMicroscopy.TheextensionalviscositymeasurementswereconductedbyDrAmarinMcDonnellandProfLeslieYeoatRMITUniversity,
SchoolofEngineering.SvenjaM.Beckisgratefullyacknowledgedforvaluablediscussions.Thisproject ispartofthedairyresearchactivitiesatMonashUniversity,supportedbytheAustralianResearchCouncil
(ARC)throughtheLinkageprogram(LP140100922).
AppendixE.SupplementarydataSupplementarydatarelatedtothisarticlecanbefoundathttp://dx.doi.org/10.1016/j.foodhyd.2017.04.005.
AppendixA.Fatglobulesizedistributionsandchangesinemulsionmicrostructureovertime
Fig.A1Emulsionhomogeneityasafunctionoftime:microscopeimagesofthemicrostructureofamodelemulsion(0.3%w/wcarrageenan)thatwasstoredat6°C.2
alt-text:Fig.A1
Fig.A2Volumetricsizedistributioninmodelemulsionsofdifferentcarrageenancontents:intheoriginalemulsions(firstcolumn)andafteratomizationinamicrofluidicjetnozzle(secondcolumn).3
alt-text:Fig.A2
AppendixB.EstimationofthesaturationcoverageoftheproteinsurfacesbycarrageenanThe emulsion stability investigation (section 3.1.1) indicated that saturation coverage of the cationic surface areas of the protein of the caseinmicelles and around the fat globules, and as such optimum stability that
deterioratesagainforhigherconcentrationspresumablyduetodepletionflocculation,occurredatapproximately0.4%w/wcarrageenan.Thisvaluewasabout30timesgreaterthanthevaluesreportedbyDalgleishetal.(1988).This
seemedreasonable,becausetheemulsionsinvestigatedinthepresentstudycontainedamuchhigherfatcontent,leadingtoagreaterproteinsurfaceareaaroundthelipidglobules,andasignificantlyhigherconcentrationinprotein
(5.4%w/w, in comparison to about0.025%w/w).Theoretical calculation, comparable to (Dalgleishet al., 1988),wasundertaken toprovide further supportingevidence that flocculationoccurreddue to excess carrageenanat a
carrageenanconcentrationabove0.4%w/w.Forthisconsideration,itwassupposedthatatsaturationlevelthepositivelychargedregionsoftheproteinatthesurfaceofthefatglobulesandthecaseinmicelleswerecompletelycovered
byamonolayerofcarrageen.Thefatglobulesfeaturedavolumetricmeandiameterofaround650nm(Fig.3a),andtheirsurfaceareawasthusabout0.64m2/gemulsionforthegivenlipidconcentrationinsidethemodelemulsions.
Estimatingasurfacecaseinconcentrationonthefatglobulesof1.50·10−3g/m2accordingtoanalysesbySrinivasan,Singh,andMunro(1996)ofasoyaoil/caseinateemulsionhomogenizedathighpressure,thenon-adsorbedamountof
caseinwas5.30·10−2g/gemulsion.Togetherwith thevolumetricmeandiameterof thecaseinmicellesbeingpreviouslymeasuredasapproximately140nm, thisamounted toa surfaceareaof caseinmicellesofabout1.82m2/g
emulsion.Hence,thecombinedsurfaceareaavailableforcarrageenanadsorptionwas2.46m2/gemulsion.Thecarrageenanmoleculeswereassumedtospananareaof6.0·102m2/gasadaptedfromDalgleishetal.(1988).Thismeant
anabsolutesurfaceareaof0.60,1.20,1.80,2.40or3.00m2/gemulsionheldbythepolysaccharidemoleculesforrespectiveconcentrationsof0.1,0.2,0.3,0.4or0.5%w/w.Consequently,thesurfaceareaofcaseinmicellesandfat
globuleswasapproximately commensuratewith thepresent carrageenan surfacearea fora carrageenancontentof0.4%w/w,andat0.5%w/w therewasmorecarrageenan inside theemulsion thancouldundergoelectrostatic
interactionwith the positively charged protein regions. The theoretical calculation thus agreedwellwith the observed emulsion stabilities (section 3.1.1) and the results about the fat globule sizes as a function of carrageenan
concentration(section3.1.2).Thecalculatedsaturationsurfacecoveragecorrespondedtoanadsorbedcarrageenanamountof1.62·10−3g/m2.
Annotations:
A1. PleaseremoveFig.B1(thereisnoFig.B1,thisgraphsisforFig.C1)
AppendixC.Timecurvesofneckdiameterduringextensionalviscosityanalysis
Fig.B14
alt-text:Fig.B1
A1
Fig.C1Extensionalviscositymeasurements:bridgeneckdiameterovertimeforlow-fatemulsion,regular-fatemulsion,regular-fatemulsionwithcarrageenan(0.3%w/w)andpurewaterforcomparison.5
alt-text:Fig.C1
Annotations:
A1. PleaseremoveFig.C2(thereisnoFig.C2,thisgraphisforFig.D2)
AppendixD.FullresultsofFBRMdissolutionstudyandimagestakenduringwettabilitystudy
Fig.C26
alt-text:Fig.C2
A1
Fig.D1Impactofλ-carrageenanconcentrationonpowderdissolutionrate:mediandiameteroftheparticles'chordlengthsasafunctionofdissolutiontime.7
alt-text:Fig.D1
ReferencesAgboolaS.O.andDalgleishD.G.,Enzymatichydrolysisofmilkproteinsusedforemulsionformation.2.Effectsofcalcium,pH,andethanolonthestabilityoftheemulsions,JournalofAgriculturalandFoodChemistry44(11),
1996a,3637–3642.
AgboolaS.O.andDalgleishD.G.,Kineticsofthecalcium-inducedinstabilityofoil-in-wateremulsions:Studiesunderquiescentandshearingconditions,LWT-foodScienceandTechnology29(5),1996b,425–432.
AOAC,OfficialmethodsofanalysisoftheassociationofofficialanalyticalChemistsVol.2,1990,AssociationofOfficialAnalyticalChemists;Arlington.
Fig.D2Impactofλ-carrageenanconcentrationonpowderwettability:photographstakenat20,60,120and300safteradditionofpowderontothewatersurface.8
alt-text:Fig.D2
BertschA.J.,Surfacetensionofwholeandskim-milkbetween18and135C,JournalofDairyResearch50(03),1983,259–267.
BhattacharjeeP.K.,McDonnellA.G.,PrabhakarR.,YeoL.Y.andFriendJ.,Extensionalflowoflow-viscosityfluidsincapillarybridgesformedbypulsedsurfaceacousticwavejetting,NewJournalofPhysics13(2),2011,
023005.
BixlerH.J.,JohndroK.andFalshawR.,Kappa-2carrageenan:Structureandperformanceofcommercialextracts:II.Performanceintwosimulateddairyapplications,FoodHydrocolloids15(4),2001,619–630.
ChewJ.H.,LiuW.,FuN.,GengenbachT.,ChenX.D.andSelomulyaC.,Exploringthedryingbehaviourandparticleformationofhighsolidsmilkproteinconcentrate,JournalofFoodEngineering2014.
CorredigM.andDalgleishD.G.,Themechanismsoftheheat-inducedinteractionofwheyproteinswithcaseinmicellesinmilk,InternationalDairyJournal9(3),1999,233–236.
CrowleyS.V.,KellyA.L.,SchuckP.,JeantetR.andO'MahonyJ.A.,Rehydrationandsolubilitycharacteristicsofhigh-proteindairypowders,In:McSweeneyP.L.H.andO'MahonyJ.A.,(Eds.),Advanceddairychemistry.Volume1B:
Proteins:Appliedaspects,4thed.,2016,Springer;Heidelberg,99–131.
DalgleishD.G.,Adsorptionofproteinandthestabilityofemulsions,TrendsinFoodScience&Technology8(1),1997,1–6.
DalgleishD.G.andMorrisE.R.,Interactionsbetweencarrageenansandcaseinmicelles:Electrophoreticandhydrodynamicpropertiesoftheparticles,FoodHydrocolloids2(4),1988,311–320.
DalgleishD.G.,SrinivasanM.andSinghH.,Surfacepropertiesofoil-in-wateremulsiondropletscontainingcaseinandTween60,JournalofAgriculturalandFoodChemistry43(9),1995,2351–2355.
DickinsonE.,Stabilityandrheologicalimplicationsofelectrostaticmilkprotein–polysaccharideinteractions,TrendsinFoodScience&Technology9(10),1998,347–354.
DickinsonE.andPawlowskyK.,Effectofι-carrageenanonflocculation,creaming,andrheologyofaprotein-stabilizedemulsion,JournalofAgriculturalandFoodChemistry45(10),1997,3799–3806.
DombrowskiN.andFraserR.P.,Aphotographicinvestigationintothedisintegrationofliquidsheets,PhilosophicalTransactionsoftheRoyalSocietyofLondon.SeriesA,MathematicalandPhysicalSciences1954,101–130.
DruschS.,SerfertY.,ScampicchioM.,Schmidt-HansbergB.andSchwarzK.,Impactofphysicochemicalcharacteristicsontheoxidativestabilityoffishoilmicroencapsulatedbyspray-drying,JournalofAgriculturalandFood
Chemistry55(26),2007,11044–11051.
Einhorn-StollU.,UlbrichM.,SeverS.andKunzekH.,Formationofmilkprotein–pectinconjugateswithimprovedemulsifyingpropertiesbycontrolleddryheating,FoodHydrocolloids19(2),2005,329–340.
FäldtP.andBergenståhlB.,Spray-driedwheyprotein/lactose/soybeanoilemulsions.2.Redispersability,wettabilityandparticlestructure,FoodHydrocolloids10(4),1996,431–439.
FäldtP.,BergenstahlB.andCarlssonG.,ThesurfacecoverageoffatonfoodpowdersanalyzedbyESCA(electronspectroscopyforchemicalanalysis),FoodStructure12,1993,225–234.
FangY.andDalgleishD.G.,Dimensionsoftheadsorbedlayersinoil-in-wateremulsionsstabilizedbycaseins,JournalofColloidandInterfaceScience156(2),1993,329–334.
FangY.,SelomulyaC.andChenX.D.,Characterizationofmilkproteinconcentratesolubilityusingfocusedbeamreflectancemeasurement,DairyScience&Technology90(2–3),2010,253–270.
FAO,Productionandutilizationofproductsfromcommercialseaweeds,In:McHughD.J.,(Ed),FoodandagricultureorganizationoftheUnitedNations,chapter3:Productionandutilizationofproductsfromcommercialseaweeds,
1987.
FDA,In:21CFR172.6202016,USFood&DrugAdministration,CodeofFederalRegulations,Title21.Volume3,Part172.
FoersterM.,GengenbachT.,WooM.W.andSelomulyaC.,TheImpactofatomizationonthesurfacecompositionofspray-driedmilkdroplets,ColloidsandSurfacesB:Biointerfaces2016a.
FoersterM.,GengenbachT.,WooM.W.andSelomulyaC.,Theinfluenceofthechemicalsurfacecompositiononthedryingprocessofmilkdroplets,AdvancedPowderTechnology2016b.
FonsecaC.R.,BentoM.S.G.,QuinteroE.S.M.,GabasA.L.andOliveiraC.A.F.,Physicalpropertiesofgoatmilkpowderwithsoylecithinaddedbeforespraydrying,InternationalJournalofFoodScience&Technology46(3),2011,
608–611.
FyfeK.,KravchukO.,NguyenA.V.,DeethH.andBhandariB.,Influenceofdryertypeonsurfacecharacteristicsofmilkpowders,DryingTechnology29(7),2011,758–769.
GEA,In:GEANiroanalyticalmethods.No.A5a-wettability,2005,GEAGroupAG;Germany.
GharsallaouiA.,SaurelR.,ChambinO.,CasesE.,VoilleyA.andCayotP.,Utilisationofpectincoatingtoenhancespray-drystabilityofpeaprotein-stabilisedoil-in-wateremulsions,FoodChemistry122(2),2010,447–454.
GranelliK.,FäldtP.,AppelqvistL.Å.andBergenståhlB.,Influenceofsurfacestructureoncholesteroloxidationinmodelfoodpowders,JournaloftheScienceofFoodandAgriculture71(1),1996,75–82.
GuY.S.,RegnierL.andMcClementsD.J.,Influenceofenvironmentalstressesonstabilityofoil-in-wateremulsionscontainingdropletsstabilizedbyβ-lactoglobulin–ι-carrageenanmembranes,JournalofColloidandInterface
Science286(2),2005,551–558.
GuzeyD.,KimH.andMcClementsD.J.,Factorsinfluencingtheproductionofo/wemulsionsstabilizedbyβ-lactoglobulin–pectinmembranes,FoodHydrocolloids18(6),2004,967–975.
HardasN.,DanviriyakulS.,FoleyJ.,NawarW.W.andChinachotiP.,Acceleratedstabilitystudiesofmicroencapsulatedanhydrousmilkfat,LWT-foodScienceandTechnology33(7),2000,506–513.
JafariS.M.,AssadpoorE.,BhandariB.andHeY.,Nano-particleencapsulationoffishoilbyspraydrying,FoodResearchInternational41(2),2008,172–183.
KeoghM.K.,O'KennedyB.T.,KellyJ.,AutyM.A.,KellyP.M.,FurebyA.,etal.,Stabilitytooxidationofspray-driedfishoilpowdermicroencapsulatedusingmilkingredients,JournalofFoodScience66(2),2001,217–224.
KimE.H.-J.,ChenX.D.andPearceD.,Effectofsurfacecompositionontheflowabilityofindustrialspray-drieddairypowders,ColloidsandSurfacesB:Biointerfaces46(3),2005a,182–187.
KimE.H.-J.,ChenX.D.andPearceD.,Meltingcharacteristicsoffatpresentonthesurfaceofindustrialspray-drieddairypowders,ColloidsandSurfacesB:Biointerfaces42(1),2005b,1–8.
KimE.H.-J.,ChenX.D.andPearceD.,Surfacecompositionofindustrialspray-driedmilkpowders.2.Effectsofspraydryingconditionsonthesurfacecomposition,JournalofFoodEngineering94(2),2009,169–181.
KravtchenkoT.P.,ParkerA.andTrespoeyA.,Colloidalstabilityandsedimentationofpectin-stabilizedacidmilkdrinks,1995.
LallbeeharryP.,TianY.,FuN.,WuW.D.,WooM.W.,SelomulyaC.,etal.,Effectsofionicandnonionicsurfactantsonmilkshellwettabilityduringco-spray-dryingofwholemilkparticles,JournalofDairyScience2014.
LangendorffV.,CuvelierG.,MichonC.,LaunayB.andParkerA.,Effectsofcarrageenantypeonthebehaviourofcarrageenan/milkmixtures,FoodHydrocolloids14(4),2000,273–280.
LefebvreA.H.,Atomizationandsprays,1989,Taylor&Francis;USA,11,.
McDonnellA.G.,GopeshT.C.,LoJ.,O'BryanM.,YeoL.Y.,FriendJ.R.,etal.,Motilityinducedchangesinviscosityofsuspensionsofswimmingmicrobesinextensionalflows,SoftMatter11(23),2015,4658–4668.
McDonnellA.G.,JasonN.N.,YeoL.Y.,FriendJ.R.,ChengW.andPrabhakarR.,Extensionalviscosityofcoppernanowiresuspensionsinanaqueouspolymersolution,SoftMatter11(41),2015,8076–8082.
Millqvist-FurebyA.,ElofssonU.andBergenståhlB.,Surfacecompositionofspray-driedmilkprotein-stabilisedemulsionsinrelationtopre-heattreatmentofproteins,ColloidsandSurfacesB:Biointerfaces21(1),2001,
47–58.
Millqvist-FurebyA.andSmithP.,In-situlecithinationofdairypowdersinspray-dryingforconfectioneryapplications,FoodHydrocolloids21(5),2007,920–927.
Munoz-IbanezM.,NuzzoM.,TurchiuliC.,BergenståhlB.,DumoulinE.andMillqvist-FurebyA.,Themicrostructureandcomponentdistributioninspray-driedemulsionparticles,FoodStructure2016.
NijdamJ.J.andLangrishT.A.G.,Theeffectofsurfacecompositiononthefunctionalpropertiesofmilkpowders,JournalofFoodEngineering77(4),2006,919–925.
SarkarA.,ArfstenJ.,GolayP.-A.,AcquistapaceS.andHeinrichE.,Microstructureandlong-termstabilityofspraydriedemulsionswithultra-highoilcontent,FoodHydrocolloids52,2016,857–867.
SCF,Opinionofthescientificcommitteeonfoodoncarrageenan,In:SCF/CS/ADD/EMU/199:Europeancommission-health&consumerprotectiondirectorate-scientificcommitteeonfood,2003.
SchuckP.,MejeanS.,DolivetA.,GaianiC.,BanonS.,ScherJ.,etal.,Watertransferduringrehydrationofmicellarcaseinpowders,LeLait87(4–5),2007,425–432.
SerfertY.,SchröderJ.,MescherA.,LaackmannJ.,RätzkeK.,ShaikhM.,etal.,Spraydryingbehaviourandfunctionalityofemulsionswithβ-lactoglobulin/pectininterfacialcomplexes,FoodHydrocolloids31(2),2013,438–445
SinghH.,TamehanaM.,HemarY.andMunroP.A.,Interfacialcompositions,microstucturesandpropertiesofoil-in-wateremulsionsformedwithmixturesofmilkproteinsandκ-carrageenan:1.Sodiumcaseinate,Food
Hydrocolloids17(4),2003,539–548.
SnoerenT.H.M.,PayensT.A.J.,JeuninkJ.andBothP.,Electrostaticinteractionbetweenkappa-carrageenanandkappa-casein,Milchwissenschaft1975.
SoottitantawatA.,YoshiiH.,FurutaT.,OhkawaraM.andLinkoP.,Microencapsulationbyspraydrying:Influenceofemulsionsizeontheretentionofvolatilecompounds,JournalofFoodScience68(7),2003,2256–2262.
SrinivasanM.,SinghH.andMunroP.A.,Sodiumcaseinate-stabilizedemulsions:Factorsaffectingcoverageandcompositionofsurfaceproteins,JournalofAgriculturalandFoodChemistry44(12),1996,3807–3811.
StoneA.K.andNickersonM.T.,Formationandfunctionalityofwheyproteinisolate–(kappa-,iota-,andlambda-type)carrageenanelectrostaticcomplexes,FoodHydrocolloids27(2),2012,271–277.
SurhJ.,DeckerE.A.andMcClementsD.J.,InfluenceofpHandpectintypeonpropertiesandstabilityofsodium-caseinatestabilizedoil-in-wateremulsions,FoodHydrocolloids20(5),2006,607–618.
TianY.,FuN.,WuW.D.,ZhuD.,HuangJ.,YunS.,etal.,Effectsofco-spraydryingofsurfactantswithhighsolidsmilkonmilkpowderwettability,FoodandBioprocessTechnology7(11),2014,3121–3135.
WangY.,LiuW.,ChenX.D.andSelomulyaC.,Micro-encapsulationandstabilizationofDHAcontainingfishoilinprotein-basedemulsionthroughmono-dispersedropletspraydryer,JournalofFoodEngineering175,2016,
74–84.
WuW.D.,LiuW.,GengenbachT.,WooM.W.,SelomulyaC.,ChenX.D.,etal.,Towardsspraydryingofhighsolidsdairyliquid:Effectsoffeedsolidcontentonparticlestructureandfunctionality,JournalofFood
Engineering123,2014,130–135.
XuY.Y.,HowesT.,AdhikariB.andBhandariB.,Effectsofemulsificationoffatonthesurfacetensionofproteinsolutionsandsurfacepropertiesoftheresultantspray-driedparticles,DryingTechnology31(16),2013,
1939–1950.
YanesM.,DuránL.andCostellE.,Effectofhydrocolloidtypeandconcentrationonflowbehaviourandsensorypropertiesofmilkbeveragesmodelsystems,FoodHydrocolloids16(6),2002,605–611.
ZakarianJ.A.andKingC.J.,Volatileslossinthenozzlezoneduringspraydryingofemulsions,Industrial&EngineeringChemistryProcessDesignandDevelopment21(1),1982,107–113.
Thefollowingisthesupplementarydatarelatedtothisarticle:
AppendixE.SupplementarydataThefollowingarethesupplementarydatarelatedtothisarticle:
MultimediaComponent1
Video1Thinningemulsionbridgeduringmicrofluidicextensionalviscometryofamilkmodelemulsionwith31.1%w/wfatind.m.andnocarrageenan.1
alt-text:Video1
MultimediaComponent2
Video2CLSMstackanimationofprotein(green)andfat(red)distributioninsideaspray-driedparticlefromacarrageenan-freemodelemulsionfromthetoptoaboutitsmiddlein1μmsteps.
alt-text:Video2
MultimediaComponent3
Video3CLSMstackanimationofprotein(green)andfat(red)distributioninsideaspray-driedparticlefromamodelemulsionwith0.3%w/wλ-carrageenanfromthetoptoaboutitsmiddlein1μmsteps.
alt-text:Video3
Graphicalabstract
QueriesandAnswersQuery:Pleasenotethatauthor’stelephone/faxnumbersarenotpublishedinJournalarticlesduetothefactthatarticlesareavailableonlineandinprintformanyyears,whereastelephone/faxnumbersarechangeableandthereforenotreliableinthelongterm.Answer:Ok
Query:Thecitation‘PiaFäldt&Bergenståhl,1996’hasbeenchangedtomatchtheauthorname/dateinthereferencelist.Pleasecheckhereandinsubsequentoccurrences,andcorrectifnecessary.Answer:Ok
Query:Refs.PiaFäldt&Bergenståhl,1996;Rogersetal.(2008);Dalgleishetal.,1988;Stoneetal.(2012)arecitedinthetextbutnotprovidedinthereferencelist.Pleaseprovidetheminthereferencelistordeletethesecitationsfromthetext.Answer:Rogers,S.,Wu,W.D.,Saunders,J.&Chen,X.D.2008.Characteristicsofmilkpowdersproducedbysprayfreezedrying.DryingTechnology,26,404-412.Theothercitationsarealreadyprovidedinthereferencelist.
Query:PleaseprovidecaptionforFig.B1andFig.C2.Answer:Thesefiguresdonotappearintheoriginalmanuscript.FigureC1andFigureD2seemtohavebeenduplicatedbymistakeduringthetypesettingprocess.Pleaseremove.
Query:PleaseprovidethevolumenumberorissuenumberorpagerangeorarticlenumberforthebibliographyinRefs.Chewetal.,2014,Foersteretal.,2016a,Foersteretal.,2016b,Lallbeeharryetal.,2014,Munoz-Ibanezetal.,2016,Snoerenetal.,1975.Answer:Chew,J.H.,Liu,W.,Fu,N.,Gengenbach,T.,Chen,X.D.&Selomulya,C.2014.Exploringthedryingbehaviourandparticleformationofhighsolidsmilkproteinconcentrate.JournalofFood
Highlights
• Stabilizsationofbilayermilkemulsionswithλ-carrageenan.
• Improvedstabilityandsmallestfatglobulesat0.3–0.4%w/wcarrageenan.
• Influenceoftheextensionalviscosityontheatomizationbehaviour.
• Significantreductionofsurfacefatat0.3%w/wcarrageenancontent.
• Enhancedoxidativestability,butlowersolubilityduetolessporouspowder.
alt-text:Image1
Engineering,143,186-194.Foerster,M.,Gengenbach,T.,Woo,M.W.,&Selomulya,C.(2016a).TheImpactofatomizationonthesurfacecompositionofspray-driedmilkdroplets.ColloidsandSurfacesB:Biointerfaces,140,60-471.Foerster,M.,Gengenbach,T.,Woo,M.W.,&Selomulya,C.(2016b).Theinfluenceofthechemicalsurfacecompositiononthedryingprocessofmilkdroplets.AdvancedPowderTechnology,27,324–2334.Lallbeeharry,P.,Tian,Y.,Fu,N.,Wu,W.D.,Woo,M.W.,Selomulya,C.,&Chen,X.D.(2014).Effectsofionicandnonionicsurfactantsonmilkshellwettabilityduringco-spray-dryingofwholemilkparticles.JournalofDairyScience,97(9),5303–5314.Munoz-Ibanez,M.,Nuzzo,M.,Turchiuli,C.,Bergenståhl,B.,Dumoulin,E.,&Millqvist-Fureby,A.(2016).Themicrostructureandcomponentdistributioninspray-driedemulsionparticles.Foodstructure,8,16-24.Snoeren,T.H.M.,Payens,T.A.J.,Jeunink,J.,&Both,P.(1975).Electrostaticinteractionbetweenkappa-carrageenanandkappa-casein.Milchwissenschaft,30,393-396.
Query:Pleaseconfirmthatgivennamesandsurnameshavebeenidentifiedcorrectly.Answer:Yes
Query:Yourarticleisregisteredasaregularitemandisbeingprocessedforinclusioninaregularissueofthejournal.IfthisisNOTcorrectandyourarticlebelongstoaSpecialIssue/Collectionpleasecontactshalini.kumar@elsevier.comimmediatelypriortoreturningyourcorrections.Answer:Yes
