Concentration_of_anthocyanins_by_the_membrane_filtration.1膜分离

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SeparationandPuri cationTechnology57(2007)

418–424

Concentrationofanthocyaninsbythemembrane ltration

BarbaraGilewicz- ukasik,Stanis awKoter ,JacekKurzawa1

FacultyofChemistry,N.CopernicusUniversity,7GagarinSt.,87-100Toru´n,Poland

Abstract

Nowadaystheuseofsyntheticdyesinthefoodindustryispopular.Asthesecompoundscancausethedevelopmentofvariousdiseases,including

thecancerorheartdisease,itisapressureonthetechnologiesofrecoveryofnaturaldiesfromthenaturalresources(fruits,vegetables,etc.).Oneofthevaluablenaturaldyesareanthocyanins,whicharepresentinthearoniafruitsavailableinabundantamountsinPoland.Inthisworktheinvestigationsontheconcentrationofanthocyaninsbynano ltrationhavebeenpresented.ThearoniasolutionscontainingNa2SO3–oneofthemostef cientextractantsofanthocyanins–havebeenused.Inordertodetermineitsin uenceontheretentionofanthocyanins,the ltrationofaroniasolutionwithandwithoutNa2SO4hasbeenalsoperformed.Theretentionsofanthocyanins,sodiumionsandionicspecieshavebeeninvestigated.Ithasbeenfoundthatinthepresenceofsodiumsulfate(IV)anthocyaninsarealmostcompletelyrejected(>99%).Inthecaseofpuresolutionorcontainingsulfate(VI)theretentionislower(91–95%).Thus,sodiumsulfate(IV)isnotonlyagoodextractantandpreservebutalsoitspresencehighlyincreasestheef ciencyofthe ltrationprocess.©2006ElsevierB.V.Allrightsreserved.

Keywords:Anthocyanins;Nano ltration;Membrane;Aronia

1.Introduction

IntheEuropeanCommunitytheinvestigationsonthesafetyoffoodregardingthetoxicologyoffunctionalingredientswerestartedin2002.Thefoodadditivesunderinvestigationincludealsothegroupofsyntheticdies.Theresultsofstudiesshowthatthesecompoundscancausethedevelopmentofvariousdiseases,includingthecancerorheartdisease.Thus,thereisapressureonthetechnologiesofrecoveryofnaturaldiesfromthenaturalresources(fruits,vegetables,etc.).

Aronia(blackchokeberry)isaviolet-blackfruit-berrynativetoNorthAmerica.Itcancontainupto800mgantho-cyanins/100gfreshweight[1]andhasalowtendencytobrown-ing[2].TheanthocyaninsofaroniaconsistsmainlyofCy3-galactoside(64.5%)andCy3-arabinoside(28.9%)[3];theothersareCy3-glucosideandCy3-xyloside.Thebasicantho-cyanidinstructure– avyniumcation–isshowninFig.1[4].Inneutralandbasicconditionstheanthocyaninsareunsta-ble.Theyundergostructuralconversionschangingthecolor.TheschemeofstructuralchangeofanthocyaninswithpHispresentedinFig.2[4].Inacidsolutions(pH<2),antho-cyaninsexistprimarilyintheformoftheredoryellow awyliumcation

1

(AH+).AthigherpHitlossesprotonandthebluequantoidalform(A)arises.The avyliumcationcanalsoeasilyundergoahydrationreactiongivingthecolorlesschromenol(B),beinginequilibriumwiththecolorlesschalconeform(C).

Manystudiesshowthepositiveeffectofanthocyaninsonhumanhealthbecauseofantioxidant,anti-in ammatoryandanticancerproperties(e.g.[5–7]andreferencestherein).Thesepropertiesbesidestheaestheticfunctionmaketheanthocyaninsaveryvaluablecomponentoffood.

Inthisworktheinvestigationsontherecoveryofantho-cyaninsfromthearoniafruits,availableinabundantamountsinPoland,arepresented.Theworkisfocusedonconcentrat-ingofanthocyaninsbynano ltration.Astheanthocyaninscanbeextractedusingdifferentchemicals,oneofthecomponentofaroniasolutionswassodiumsulfate(IV)Na2SO3,oneofthemostef cientextractants[8].Forcomparisontheconcentrationofaroniasolutionscontainingsodiumsulphate(VI)Na2SO4andpurearoniasolutionshavebeenalsoperformed.2.Experimental

2.1.Sourceofanthocyanins

Thearoniafruitshavebeenmixedusingajuicier,thedistilledwaterhasbeenadded3kgper1kgoffrozenfruits.Thenthesolidparticleshavebeenremovedbydecantationand ltration

Correspondingauthor.Tel.:+48566114318;fax:+48566542477.E-mailaddress:skoter@chem.uni.torun.pl(S.Koter).Presentaddress:“Agrohansa-Toru´n”Sp.zoo,Toru´n,Poland.

1383-5866/$–seefrontmatter©2006ElsevierB.V.Allrightsreserved.doi:10.1016/j.seppur.2006.03.026

B.Gilewicz- ukasiketal./SeparationandPuri cationTechnology57(2007)418–424

419

Fig.3.SchemeofUFprocess.

themembranearea—100cm2.Thepermeateofthatprocesshasbeenusedasafeedforthenano ltration.2.3.Nano ltration

IntheNFexperimentthedead-endcell(SEPASTOsmonics)hasbeenused(Fig.4).Themembraneareawas12cm2,thevol-umeofthefeedinthecellwas310cm3,theappliedpressure—upto20bar.ThemembraneBQ01fromOsmonicsInc.hasbeenused.Themembranecellwasthermostattedat25±1 C.Therotationspeedofmagneticstirrerwas700rpm.

Theretentioncoef cientofelectrolytesinthe ltrationofthepuresolutions(withoutaronia)wascalculatedfromtheformula:Robs=1

cpf

(1)

Fig.1.Flavyniumcation[4].

throughporousmaterial.Thechemicalcomponentsofaroniafruitsarenumerous(sugars,organicacids,VitaminC,B2,B6,E,PP,P,catechins,quercetin,tannins,pectins,etc.).Toincreasetheef ciencyofnano ltration,someofthem(ofhighmolecularweight)havebeenremovedbyultra ltration.2.2.Ultra ltration

TheUFexperimenthasbeenperformedusingthecross- owset-up(theBIO-2000TM,Bio-FloLtd.TM)(Fig.3).The atmembranecellhasbeenmadeinourworkshop.Thepoly-sulfonemembranehasbeenobtainedbythephase-inversionmethod(10wt.%solutionofpolysulfoneUdel1700inDMF,precipitatingagent–water).Theoperatingpressurewas1

bar,

wherecpandcfaretheconcentrationsofpermeateandfeed,respectively,determinedconductometricallyusingthecalibra-tioncurve.Theconductancewasmeasuredwiththeconduc-tometerELMETRONCX-731(Elmetron,Poland).

The ltrationofaroniasolutionswasperformedintwoways.Inthe ltrationBthefeedisapermeatefromtheUFprocess.Itwasperformedseveraltimes.InFigs.6–9eachrunofthe ltra-tionBisdenotedbyRomannumeral.Theprocesswas

conducted

Fig.2.Schemeofstructuralchangeofanthocyaninsinaqueoussolutions[4].

420B.Gilewicz- ukasiketal./SeparationandPuri cationTechnology57(2007)

418–424

whereApandAfaretheabsorbancesatλmax(=ca.510nm)ofpermeateandfeed,respectively,afterthecorrectionforthedilutionofsamples.

Todeterminetheretentionofsodiumcationstheirconcen-trationwasdeterminedbytheAASmethod.

Theconductanceofsolutions,containingaronia,havealsobeenmeasured.Fromthesemeasurementsthecoef cientRobs,Gindicatingtheretentionofionicsubstanceswasdetermined:Robs,G=1

Gpf

(3)

whereGpandGfaretheconductancesofpermeateandfeed,respectively.

2.4.ThemeasurementofapparenttransportnumberofNa+TheapparenttransportnumberofNa+,¯tNa+,app,hasbeendeterminedbytheemfmethod.Themembranepotential,Em,hasbeenmeasuredinthesystem:

Hg|Hg2Cl2(s)|KClsat.||Na2SO40.014m|membrane

Fig.4.SchemeofNFprocess.(1)N2cylinder,(2)magneticstirrer,(3)mem-branecell,(4)permeatevessel,(5)balance,(6)computer,and(7)thermostat.

|Na2SO40.027m||KClsat.|Hg2Cl2(s)|Hg

¯tNa+,apphasbeencalculatedaccordingtotheformula[9]:

2Em1

¯+t+,app=(4)

3i2

m /(γ m )),γdenotesthemeanwhereEi= (RT/F)ln(γ±±±

activitycoef cient,takenfrom[10].

untilca.64%ofpermeatewasobtained(ca.210gfrom310goffeedatthebeginningofprocess).Theretentateofthis ltra-tionwasgatheredandthen lteredagain( ltrationdenotedasC)—untilca.60–70goffeedwasleftinthecell.

Theretentioncoef cientofanthocyaninswasdeter-minedspectrophotometricallyusingthespectrophotometerSHI-MADZUUV-2101PC.Beforemeasurementsthesamplewasappropriatelydilutedandthenacidi edtopH1using1MHCl.Theretentioncoef cientofanthocyanins,Robs,A,wascalculatedfromtheformula:Robs,A

Ap

=1

f

(2)

3.Resultsanddiscussion

3.1.CharacteristicsofmembraneBQ01inpureelectrolytesolutions

At rstwaterandthepuresolutionsofNa2SO4andNa2SO3solutionshavebeen ltered.ThechangesofJv/ pandofRobsinthe ltrationareshowninFig.5

.

Fig.5.Dependenceof:(a)Jv/ pand(b)RobsonthefeedconcentrationforNa2SO3(hollowsymbols)andNa2SO4solutions( lledsymbols); p=10bar( )and20bar( );dottedlinesintheleft guredenoteLp=Jv,0/ pforthepurewaterdetermined:(1)before ltrationofelectrolytesand(2)2weekslater.

B.Gilewicz- ukasiketal./SeparationandPuri cationTechnology57(2007)418–424

421

Fig.6.TimechangesofJv/ pduringthe ltrationofaroniasolutionscontaining:(a)Na2SO3and(b)Na2SO4; ltrationofpurearoniasolutionisdenotedbysolidline,romannumeraldenotetherunof ltration“B”.

Inthe rst2weeksofexperimentsthehydrodynamicper-meabilityofthemembraneBQ01decreasedsubstantially.Thepermeabilitycoef cientofpurewaterLp=Jv,0/ p(markedinFig.5awithdottedline)decreasedfromca.4.3×10 11to2.6×10 11m3s 1N 1after2weeks.ThesameisobservedfortheNa2SO4solutions.Atthatinitialperiodthemembranewasmoreleaky,asitisindicatedbytheobservedretentioncoef- cientRobsofNa2SO4lowerthanthatofNa2SO3(Fig.5b),determined2weekslater.Therepeatedexperiments,performed“day-after-day”,showedthattheretentionofbothelectrolytesissimilar.

TheconcentrationandpressuredependenceofJv/ p(Fig.5a)canbeexplainedintermsoftheKedem–Katchalskyequations,accordingtowhichJv/ pisequal,whereLpishydro-dynamicpermeabilitycoef cient,σthere ectioncoef cient,and πistheosmoticpressuredifferenceofsolutionsseparatedbythemembrane.Thus,thedecreaseofJv/ pwithconcen-trationcanbeexplainedbytheincreased πwhichhampersthevolume ow.TheincreaseofJv/ pwith pmeansthat π(itisnotconstantbecausetheconcentrationsatthesur-faceofmembranechangeswith p)slowerincreasesthan p.Itisinaccordancewiththelowerretentionofelectrolytesathigher p(Fig.5b).Thisbehaviouroftheobservedreten-tioncoef cient,Robs,isincontradictiontothatexpectedfortherealretentioncoef cient,R.Accordingtotheexpression[11]:R=σ

1 F1 σF

(5)

wherekisthemasstransfercoef cient.Forsimplicityletusconsiderthecaseσ=1:

1

(6a)limRobs=exp(J1+Psσ→1vvFromthatformulaonecanconcludethatRobsdecreaseswith

Jv(or p),iftheconditionJv/k>1issatis ed.ThedecreaseofRobswiththefeedconcentrationisacommonfeatureandcanbeexplainedbytheincreasedsorptionofelectrolyteintothemembrane.

3.2.Nano ltrationofmixedaronia-electrolytesolutionsThe ltrationofsolutionscontainingaroniaandelectrolyte(Na2SO3orNa2SO4)wereperformedapplyingalwaysthesamesampleofmembraneunderthepressure p=20bar.Theelec-trolyteconcentrationwaschosentobe0.027mol/dm3—similarconcentrationsofNa2SO3areusedintheextractionofantho-cyanins.Theexperimentswereperformedintheorder:(1)aronia+Na2SO3solution,(2)aroniasolution,and(3)aro-nia+Na2SO4solution.

InFig.6thedependenceofJv/ pontimeofthe ltrationispresented.(thesymbolsof ltration“B”and“C”areexplainedintheexperimentalpart).Theexpectedfeatureofthat ltrationisthedecreaseofJv/ pwithtime,notmetwhenthepureelec-trolytesolutionswere ltered.ThisindicatesthatthefoulingofmembraneproceedscausedbytheparticlesofdyeorotherspeciesnotremovedintheUFpuri cationofaroniasolution.Aftereach ltrationBthesurfaceofmembranewasmechan-icallycleaned,thusthevaluesofJv/ paresimilar.ItistobenoticedthatinthepresenceofNa2SO3Jv/ pishigherthaninthepresenceofNa2SO4.Apartfromtheageingeffectofmembraneanotherreasoncanbealowerosmoticpressuredifferenceact-ingagainstthehydrodynamicpressure.Thedecreasedosmoticpressureresultsfromtwofacts:

(1)Na2SO3isasaltofweakacidH2SO3(pKa,1=1.9,

pKa,2=7.2[13])andasthepHofaroniasolution+0.027M

whereF=exp( jv(1 σ)/Ps),Psisthepermeabilitycoef cientofelectrolyte,RalwaysincreaseswithJvand,consequently,with p.OntheotherhandRobs,disturbedbythepolarizationlayeratthemembrane[12]isRobs=σ

1 F

(1 σ)exp(Jv(6)

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Fig.7.TimechangesofRobs,GandRobs,Na+duringthe ltrationofaroniasolutionscontaining:(a)Na2SO3and(b)Na2SO4; ltrationofpurearoniasolutionisdenotedbysolidline.

Na2SO3islow(ca.3.7),practicallyonlyHSO3 ionsexist;

(2)somefractionofHSO3 areboundwiththe avyliumcation

AH+[8].Boththeseeffectsreducethenumberofionsandthustheosmoticpressuredifferencebetweenthefeedandpermeate.Inthe ltrationofpreconcentratedsolution( ltrationC)Jv/ pispracticallynotin uencedbythepresenceofelectrolyte.OneshouldnoticethatinthecaseofNa2SO3thedecreaseofJv/ pcomparingtoBissubstantial(ca.50%).

3.2.1.Retentioncoef cients

Theretentionofanthocyanins(Robs,A),sodiumions(Robs,Na+)andofionicspecies(Robs,G)wasinvestigated.At rstletusdiscusstheionicretention.Itisimportanttoknowtowhatextenttheconcentratedsolutionofanthocyaninswillbepuri edofionicspecies.

Thearoniasolution(withoutelectrolyte)containssomeionicspecies—itsconductance(1.4mS)isonlyca.5timessmallerthanthatwithNa2SO4(7mS).Theconductanceofaroniasolu-tioncontainingNa2SO4isca.45%higherthanthatwithNa2SO3(4.8mS),whereastheconductanceofpureNa2SO4solution(5.8mS)isonly16%higherthanthatofNa2SO3(5.0mS).Thisdifferencecanbeexplainedby:

(1)theconcentrationofverymobileH+inthearonia+Na2SO3

solutiondecreases(pHchangesfrom2.9to3.7)becauseasitwasmentionedearlieratpH3.7onlyHSO3 ionsexist,(2)theHSO3 ionsformwith avyliumcationsanuncharged

species.Thus,itcanbealsoexplainedwhyRobs,G(Na2SO3)(ca.0.5–0.6,Fig.7a)islowerthanRobs,G(Na2SO4)(ca.0.8,Fig.7b):(1)theunivalentionsHSO3 easierpenetratethemembrane

thanthedivalentSO42 ,

(2)havinginmindthattheretentionofionicspeciesofpure

aroniasolutionislow(ca.0.4),thebindingofHSO3 withAH+increasesthenthecontentofmorepenetrableions,thusleadingtothedecreaseofRobs,G.Inthe ltrationBtheretentionofNa+(Na2SO4)ishigherthanthatinthecaseofNa2SO3.Itcon rmsthatSO42 aremorerejectedthanHSO3 .InviewofmodelcalculationsbyTsuruetal.[14],basedontheextendedNernst–PlanckequationandontheassumptionofDonnanequilibrium,thisobserva-tionsuggeststhatthemembraneischargednegatively.ItisinagreementwiththedeterminedvaluesoftheapparenttransportnumberofNa+(discussedfurtherinthetext).Inthe ltrationC(moreconcentratedfeed)Robs,Na+andRobs,GarepracticallythesamewhichmeansthatNa+andSO42 arerejectedtothesameextent—inthefeedofCthemolarratioofionscomingfromthearoniaisdecreasedbecauseinthe ltrationBtheywerelessrejectedthanSO42 .ThedecreaseofRobs,Ginthe ltrationCcomparingtoBiscausedbythehigherconcentrationofSO42 inthefeedbuttheretentionofNa+ispracticallythesame.Toshowhowthestateofthemembraneafterthe ltrationofsolutionscontainingaroniawaschanged,againthe ltra-tionofpureelectrolytesolutions(0.027MNa2SO3and0.027MNa2SO4)wasperformedonthesamesampleofmembrane,atthesamepressure20bar.Itwasfoundthat:

Jv/ pisca.7timessmallerthanthatbeforethearonia ltra-tion(Fig.5

a),

Fig.8.Reactionof avyliumcationwithHSO3 .