www.elsevier.com/locate/procbio
Effectsofprocessingonthecontentandcompositionofisoflavonesduringmanufacturingofsoybeverageandtofu
C.-J.C.Jacksona,*,J.P.Dinia,C.Lavandiera,H.P.V.Rupasinghea,H.Faulknera,
V.Poysab,D.Buzzellb,S.DeGrandiscaGuelphCenterforFunctionalFoods,LaboratorySer6icesDi6ision,Uni6ersityofGuelph,95StoneRoadWest,Guelph,Ont.,CanadaN1H8J7bGreenhouseandProcessingCropsResearchCenter,AgricultureandAgri-FoodCanada,Harrow,Ont.,CanadaN0R1G0cBioLaunchInc,Box242,Rockwood,Ont.,CanadaN032K0Received16August2001;receivedinrevisedform22October2001;accepted24October2001
Abstract
Isoflavonespresentinsoybean(Glycinemax)havebeencreditedwithperformingseveralhealth-promotingfunctions,suchas,preventionofcardiovasculardiseases,cancers,andmenopausalsymptoms.Inthisstudy,theeffectoftheprocessingofsoybeanonthetotalcontentofisoflavones(includingaglyconesandglucosides)andtherelativeconcentrationsof12isoflavonecompoundsduringthepreparationofsoybeverageandtofuwereinvestigated.Themeanrecoveriesofisoflavonesinsoybeverageandtofuinrelationtotheirinitialconcentrationintherawsoybeanswere54and36%,respectively.Theestimatedpercentageoftotalisoflavoneslostinthewaterusedtosoakrawsoybeans,theokara(wastefromheat-treatedslurry),andwheywere4,31,and18%,respectively.Theisoflavoneprofileofrawsoybeanswasalteredasaresultofprocessing.Duringprocessing,thedetectablelevelsofaglycones,glucosides,andacetylglycosidegroupsincreased,whilstthecorrespondingmalonylglucosidesdecreased.Thelossofisoflavonesthroughtheby-products,suchas,okaraandwhey,wasconsiderable.Appropriatetechniquesshouldbedevelopedtorecoverandutilizethesefunctionalconstituentsfromsoybeanby-products.Inaddition,processingtechniqueshavetobeoptimized,sothatthefinalproductscontainthenutrientandnutraceuticalcontentofthestartingmaterialasmuchaspossible.©2002ElsevierScienceLtd.Allrightsreserved.
Keywords:Isoflavones;Daidzein;Genistein;Glycitein;Soybeans;Okara;Whey;Value-addedproducts
1.Introduction
Isoflavonesareagroupofnaturallyoccurringhetero-cyclicphenolsfoundmainlyinsoybean(Glycinemax)andhavebeencreditedwithperformingseveralhealth-promotingfunctions.Twelveisoflavonecomponentshavebeenisolatedfromsoybeans;threeaglycones(daidzein,genisteinandglycitein)andtheirrespectivenineglucosidicconjugates(Fig.1).Theglucosidesin-cludethree7-O-glucosides(daidzin,genistinandglycitin),three6¦-O-acetylglucosides(6¦-O-acetyl-daidzin,6¦-O-acetyl-genistinand6¦-O-acetyl-glycitin)andthree6¦-O-malonyl-glucosides(6¦-O-malonyl-*Correspondingauthor.Tel.:+1-519-767-6246;fax:+1-519-767-6240.
E-mailaddress:cjackson@lsd.uoguelph.ca(C.-J.C.Jackson).
daidzin,6¦-O-malonyl-genistinand6¦-O-malonyl-glycitin).
Severalinvestigatorshavesuggestedthatsoyfoodconsumptionmaycontributetolowerratesofcertainchronicdiseasessuchashormone-dependentcancers,certaincardiovasculardiseases,andosteoporosis.ThelowerincidenceofcertaindiseaseshasbeenreportedinAsiancountrieswheresoybeanconsumptionishigh(averageintakeofisoflavonesis40–80mgperday)[1–3].Soyfoodsaresuggestedtoprovideaprotectiveeffectonthebreast,intestine,liver,bladder,prostate,skinandstomachfromcancerdevelopment[4,5].Genistein,whichpossessesweakestrogenicactivity,hasbeenshowntoactinanimalmodelsasananti-estrogenand,therefore,mayplayaprotectiveroleinhormon-ally-influencedcancers,suchasbreastcancer[6,7].Experimentsonbothanimalsandhumanshaveshownthatsoybeanproteinhashypocholesterolemic
0032-9592/02/$-seefrontmatter©2002ElsevierScienceLtd.Allrightsreserved.PII:S0032-9592(01)00323-5
1118C.-J.C.Jacksonetal./ProcessBiochemistry37(2002)1117–1123andanti-atherogenicproperty[8].Recently,inametaanalysisoftheeffectsofsoyproteinintakeonserumlipids,soyproteinsignificantlydecreasedserumconcen-trationsoftotalcholesterol,lowdensitylipoproteins(LDL)cholesterolandtriglycerideswhencomparedwithproteinofanimalorigin[9,10].Studiesinprimatesindicatethatsoyproteinmayexertitsanti-atherogeniceffectsviaassociatedisoflavones[11].Soyisoflavonesalsohaveantioxidantproperties,whichmayprotectLDLfromoxidation[12].Consumptionof25gofsoybeanproteinperdaycancontributetotheloweringofserumcholesterollevelsandthepreventionofheartdisease[13].Thishealthclaimplacessoyfoodsamongaselectedcategoryof‘functionalfoods’possessinguniquemedicinal,aswellas,nutritionalvalue.
Epidemiologicalstudieshaveshownthatwomenwhohavehigherintakeofsoyfoodshavelowerratesofosteoporosis[5].Genisteinadministrationintwoovariectamizedratmodels,reducedratesofboneloss[9],andisoflavonesmaydirectlyinhibitboneresorption[14].Asisoflavonesareweakestrogens,ingestionofsoybeanfoodshasbeenproposedasanalternativeto
Fig.1.Structuresofthe12isoflavonesinsoybean.
hormonereplacementtherapyforpost-menopausalwomen[15].
Theprocessingofsoybeansaffectsthenutritionalcontentofthesoyfoodproductssignificantly[16,17].Therehavebeenreportsontheisoflavonecontentofsomesoybeanvarietiesandsoyfoodsaswellastheeffectsofprocessingonthesecompounds[18–20].Dis-tributionofisoflavonesincommercialsoyfoodprod-uctsisdeterminedbythevarietyofthesoybeans,theprocessingconditions,andbydilutionwithnon-soyingredient[16].Heatprocessing,enzymichydrolysisandfermentationsignificantlyalterthedistributionoftheisoflavonecomponentsinsoyfoods[16].Certainprocessingmethods,suchasboiling,milling,andproteincoagulationintofuproductiondonotdestroydaidzeinorgenisteinsignificantly,whileothermethodssuchasroasting(highheattreatment)resultina15–21%lossofdaidzeinandgenistein,respectively[21].Defoamingduringtheheatingprocessofsoybeverageproductionmayalsoremoveisoflavones[22].Theob-jectiveofthisinvestigationwastoanalyzetheisoflavonelevelsaftereachprocessingstep,fromOn-tariogrownsoybeantosoybeverageandtofuprepara-tion,inordertodeterminetheeffectofprocessingondistribution,retentionandtransformationofisoflavones.
2.Materialsandmethods
2.1.Materials
RCATAngora,asoybeancultivarwithhighlevelsofisoflavones[20]wasgrownandsoyproductswereprocessedattheGreenhouseandProcessingCrops,ResearchCenter,AgricultureandAgri-FoodCanada,(GPCRC-AAFC),Harrow,Ont.,Canada.Soybever-ageandmomentofuwaspreparedasdescribedbyMullinetal.[23](Fig.1).HPLCgradeacetonitrileandmethanolwerepurchasedfromCaledon(Mississauga,Ont.).
2.2.Isofla6onestandards
Sixisoflavonestandardswereusedinquantificationoftotalisoflavones;daidzein(SigmaChemicalCo,St.Louis,MO),genistein(FlukaBiochemika,Ronkonkonma,NY),glyciteinandglycitin(Plantech,UK),anddaidzinandgenistin(IndofineChemicalCompany,BelleMead,NJ)andtheirextinctioncoeffi-cientsweremeasured(Table1).Theglucosides6¦-O-malonyldaidzin,6¦-O-malonylgenistin,6¦-O-malonyl-glycitin,6¦-O-acetyldaidzin,6¦-O-acetylgenistinand6¦-O-acetylglycitinwereisolatedinourlaboratoryandusedforpeakconfirmationonly.Theidentityofallstandardswasconfirmedbymassspectra.
C.-J.C.Jacksonetal./ProcessBiochemistry37(2002)1117–11231119
Table1
Extinctioncoefficientsofisoflavonestandardsusedinthequantifica-tionofunknownsStandard
umax(nm)
matumaxMolecularWorking
weightrange(mg/ml)Daidzein250260002540.2–110Genistein262373002700.5–120Glycitein262223872840.1–20Daidzin258290004160.3–90Genistin262417004320.3–80Glycitin26226303
446
0.1–35
Thequantitiesofmalonyl-andacetyl-glucosideswereestimatedbyusingthestandardcurvesoftheirrespec-tiveaglyconeorglucosidesandcorrectingfortheirmolecularweight.Biochanin-A,anisomerofglycitein,whichwasnotfoundinsoybeans,wasusedtoestimateanalyterecovery.
2.3.Soybe6erageandtofupreparation
Soybeverageandsoft(silken)tofuwaspreparedbasedontraditionalmethods[26]asdescribedindetailbyMullinetal.,[23](Fig.2)Whiletherearemanyvariationsoftofuprocessingmethodsusedinindustrialfacilities,themethod[23]usedinthisstudyisalabora-toryscaleproceduredevelopedfollowingmanyAsianendusersanddesignedtoemphasizedifferencesinproteinqualityamongcultivarsbyusingaconstantwater:proteinratioof18:1.Ithasgoodreproducibilitywithinandacrosslaboratoriesforevaluatingcultivarsforsoymilkandtofuyieldandquality[23].
Proteinandmoisturecontentsofsoybeanswerede-terminedusingaGrainspecnearinfra-redwholegrainanalyzer(FossElectricMultispecDivision,York,UK).Astandardamountofwaterpergramprotein(18:1)wasusedtopreparesoybeverage.Halfoftherequired
Fig.2.Themajorstepsinvolvedinsoybeverageandtofuprepara-tion.
amountofwater(ca.400ml)wasaddedtothesoy-beans,andthemixturewasblendedusingacommercialWaringblenderathighspeedfor4min.Theremainingwaterwasboiledandaddedtotheheavyslurryandblendedathighspeedfor1mintoformlightslurry.Acommercialjuiceextractorwasusedtoextractthesoybeveragefromtheslurry.Theslurrywaspouredintotheextractor,thesoybeveragewascollected,andtheokara(grit)wasre-centrifugedtoextracttheremainingsoybeverage.Thevolumeofsoybeveragewasmea-suredtodeterminethebeverageyieldperkgsoybeanseedprotein.
Soybeveragewasheatedupto98°C(withstirring)andheldatthesametemperaturefortwominutes.Coagulantsolution(1.5ggluconodeltalactone(GDL)in20mldistilledwater)wascombinedwiththeheatedsoybeverageinabeaker,andthismixturewasallowedtostandfor30mintosolidifytotofu.Thetofuwasremovedfromthebeakerandwrappedinfine-meshpolyestercloth.Thewheywascollected,andthetofuwasplacedintherunningcoldwaterforatleastonehour.Theweightofthetofuwasthenrecordedtodeterminetheyieldoftofuperkgsoybeanseedprotein.
2.4.Isofla6oneextraction
Allsampleswerefreeze-dried,andthesedriedsam-pleswereusedintheisoflavoneanalyses.Approxi-mately,0.3goffinelygroundrawsoybean,0.15gofsoakedsoybean,0.05gofslurry,0.5gofdriedbever-ageofokara,0.5goftofu,and0.2gofwheywereweighedinto125mlflatbottomflasks,and12mlofextractionsolution(acetonitrile:0.1NHClin5:1ratio)wasaddedtoeachflask.Thesolutionwasmixedusingarotaryshaker(120rpm)overnightatroomtempera-ture.Extractsweresuctionfilteredinto250mlroundbottomflasksthroughWhatmanNo.42filterpaperandwashedtwicewith12mlvolumesofextractionsolu-tion.Sampleswerecondensedtoapproximately1mlusingavacuumrotaryevaporator(Bu¨chi,Brinkmann,Switzerland)withawaterbathat30°C.Thedriedmaterialwasre-dissolvedinamixtureofmethanol:water(80:20,v:v)toafinalvolumeof10mlandfilteredthrougha0.22mmPTFEsyringefilter(MSI,Westboro,MA)priortoHPLCanalysis(modifi-cationofWangandMurphy,[16]).Allstepswereperformedinreducedlightconditionstominimizelight-inducedisoflavonedegradation.
2.5.HPLCanalysisofisofla6ones
Analysisofisoflavoneswasperformedbyamodifica-tionofamethoddescribedbyWangandMurphy[16].HighPerformanceLiquidChromatograph(HPLC)ap-paratusconsistedofWaters(Marlborough,MA)600Emultisolventdeliverysystem,717plusautosampler,
1120C.-J.C.Jacksonetal./ProcessBiochemistry37(2002)1117–1123996photodiodearray(PDA)detectormonitoringat200–350nmoraWaters486tunableabsorbanceUVdetectorsetat254nm,andanNECcomputerwithMILLENNIUM(version2.10)chromatographysoftware.ThecolumnusedwasaYMC-packODS-AM-303column(5mm,250×4.6mmi.d.)(YMCInc,Wilming-ton,NC)equippedwithanAMdirectconnectC-18guardcolumn.AllHPLCanalyseswereperformedatambienttemperature.AHewlett–Packard8452Adiodearrayspectrophotometerwasusedtoverifytheconcen-trationsofstockstandardspriortouse.
ThemobilephasesforHPLCconsistedofsolvent(A)0.1%(v/v)aceticacidinfilteredMilliQwater,and(B)0.1%(v/v)aceticacidinacetonitrile.Thesolventgradi-entwasasfollows:SolventBwasincreasedfrom15to25%over35min,thenincreasedto26.5%withinnext12min,andfinallyto50%within50sandheldatthatpercentagefornext14.50min.Theflowratewas1ml/minupto48minandincreasedto1.3ml/minfrom48.50mintill63min.AWater996seriesphotodiodearraydetector(MilliporeCorp,Marborough,MA)monitoredfrom200to350nm.Theminimumde-tectableconcentrationsforgenisteinanddaidzeinwere100and185ng/ml,respectively.UVspectrawererecordedandarearesponseswereintegratedbyWaterssoftware(MILLENNIUM,version2.10).
2.6.Calibrationcur6esandreco6ery
Crystallinestandardsweredissolvedin80%methanoltogiveaconcentrationofabout1000mg/ml.Theconcentrationsofthestocksolutionswerecalcu-latedusingtheabsorbancevalueatthewavelengthofmaximumabsorption(umax)ofdilutedstandardsolu-tions,themolecularweightoftheisoflavoneandtheextinctioncoefficient[24].ThepurityofeachstandardwasdeterminedbythepercentageofthepeakareaintheHPLC/PDAchromatograph.Standardcurveswereobtainedbyplottingstandardconcentration(atnineconcentrations)asafunctionofpeakareainHPLCchromatograms.Highlinearity(R\\0.99)wasobtainedforeachcurve.Quantitiesof6¦-O-acetyl-daidzin,6¦-O-acetyl-genistin,6¦-O-acetyl-glycitin,6¦-O-malonyl-daidzin,6¦-O-malonyl-genistinand6¦-O-malonyl-glycitinweredeterminedbyusingstandardcurvesfordaidzin,genistin,andglycitin,respectively,andadjust-ingforthemolecularweightdifferences.
Recoverywasestimatedusingaddedbiochanin-A.Allsampleswerespikedwithapproximately100mlofbiochanin-Asolution(1000mg/ml)in80%methanol.Thesolventwasallowedtodrypriortotheadditionofextractionsolventbettertoimitateendogenousisoflavones.Recoveryvaluesrangedfrom80to100%.TheHPLCchromatographyofthetwelveisoflavonesareillustratedinFig.3.
Fig.3.Reverse-phaseHPLCchromatogramofthetwelveisoflavonesinsoybean.
2.7.Statisticalanalyses
Theprocessingtreatmentwasreplicatedthreetimes.Allexperimentalunitswereanalyzedinduplicate.Val-ueswerepresentedastheaverageofsixreplicatemean9S.D..One-wayANOVAwasperformedtode-terminesignificantdifferencesinisoflavonespresentinthesoyproductduringthedifferentprocessingsteps(h=0.05).
3.Resultsanddiscussion
Thisinvestigationshowedthatthetotalrecoveryofisoflavonesintofuwasaslowas36%(basedondrymatter)whencomparedwiththeamountpresentinrawsoybeancv.RCATAngola(Table2).However,therecoveryofisoflavonesinthesoybeveragewas54%.Itisapparentthateachprocessingstepintofumanufac-turingcontributestothelossofisoflavones,resultinginaconsiderableamountofisoflavonesbeinglostintheresultantby-products.Similartothepresentresults,WangandMurphy[17]observedrecoveryoftotalisoflavonesintraditionalmomemtofuas33%.How-ever,recoveryofisoflavonesfromsoybeveragewashigher(67%)inthepresentstudycomparedwiththatinWangandMurphy’[17]studywhereitwasonly36%.Thedifferenceseemstoresultfromthetypeofcoagu-lantusedintofupreparation.Itisapparentfromthisstudythatuseofglucanodeltalactone(GDL)asthecoagulantmightbebetterandmoreefficientthanCaCO4thatwasusedinthepreviousstudy[17]intermsofrecoveringisoflavonesintofufromsoybeverage.Thelossofisoflavoneswiththesoakingwaterasestimatedbythedifferencesintheamountdetectedinrawsoybeansandsoakedsoybeanswas4%.Thetotal
C.-J.C.Jacksonetal./ProcessBiochemistry37(2002)1117–11231121
isoflavonecontentoftheslurry(550mg)waslowerthanthatoftherawsoakedsoybeans(690mg)(Table2)andachangeindistributionofisoflavonecompo-nentswasobserved(Table3).Grindingofsoaked-soy-beaninboilingwaterseemstoresultinthemajorlossofisoflavonesduringprocessing.
Thepresentstudyalsoshowedthatthecompositionoftheisoflavonescouldvaryfromonesteptoanotherduringprocessing.Themalonylconjugateswereespe-ciallyunstablewhenexposedtoheat.Thelevelsofisoflavoneaglycones,daidzeinandgenistein,increasedby12-and23-fold,respectively,duetothesoaking,heating,andgrindingprocesses.Levelsofmalonyldaidzinandmalonylgenistindecreased,duetothecleavageofmalonylestergroupstoformdaidzinandgenistinuponheatingandgrinding.Itiswelldocu-mentedthattheprofileofisoflavoneschangesduetotemperatureduringprocessing[25–27].Itisalsore-portedthatmalonylglucosidesareeasilydecarboxy-latedtotheircorrespondingacetylderivatives,asweobserved[2,27].
Whentheslurrywasfilteredtoextractthesoybever-age,approximatelytwo-thirdsoftheisoflavonesparti-tionedintothesoybeverage,whileonlyone-thirdfractionatedintotheby-product,okara(Table2).Theproteincontentofokarawassimilartothatofsoybeverageandtofu(about5%)suggestingthatasignifi-cantportionofthenutritionalcontentofthesoybeanisbeinglostalongwiththeokara.Therefore,thereisagreatpotentialforutilizingtheokaraasananimalfeedwithagoodsourceofproteinandisoflavones.Therewasagreaterpercentageofaglycones(15.4%),glu-cosides(28.9%)andacety-genistin(0.89%)intheokaraascomparedwiththesoybeverage(5.41%aglycones,22.2%glucosidesand0.34%acetyl-genistin)(Table3),likelyduetothelowsolubilityofaglyconesintheaqueousmedia.Inthesoybeverage,agreaterpercent-ageofmalonyl-glucosides(72%)werepresentthaninokara(54.9%)(Table3).
Theyieldoftofuwas2.75gfreshtofupergramdrysoybean(404gfreshtofufrom147gdrysoybeansinstartingmaterial),andthetofucontained36%oftheisoflavonespresentedinthestartingmaterial(i.e.260mgisoflavonesintofurelativeto720mgisoflavonesinrawsoybeans,Table2).Therewasa67%recoveryofisoflavonesintofuwhenthesoybeveragewascoagu-latedusingGLDtoformtofu(i.e.260mgisoflavonesintofurelativeto390mgisoflavonesinsoybeverage,withlittlechangeinthedistributionofisoflavonecom-ponentsbetweensoybeverageandtofu(Table2).
Whenestimatedfromtheamountofisoflavonespresentinthesoybeverageandtofu,assumingnolossduetoheatingandcoagulation,themaximumisoflavonecontentinthewheywouldbeabout18%ofthetotalisoflavonepresentinthestartingmaterial.Incontrast,WangandMurphy[17]observed44%ofisoflavoneinwhey.Thedifferentresultscouldbepartlyduetothemannerinwhichthetofuwaspreparedusingdifferentcoagulant,thewheywascollected,orthesoybeanvarietyused[20,26].Thepercentageofeachofthecomponentsinthesoybeverageandtofuwasverysimilar,exceptthatabout5%ofthemalonyl-glucosideswereconvertedtoglucosidesinthetofuderivedfromthesoybeverage(Table3).Theheatingprocessin-volvedinmakingtofufromthesoybeveragewaslikelyresponsibleforthisconversion[25].Resultsindicatethatthelossofisoflavoneswassignificantwhenthesoybeverageiscoagulatedtoformtofu,andthetypeofcoagulantmayhavedifferentinfluence.Isoflavonesmaybeassociatedwithproteins,andthelossesof
Table2
Impactofprocessingonyield,percentmoisture,percentproteinandisoflavonecontents(threeaglycones)insoybeansproductsandby-productsProduct
Yield(g)
%Moisturea%Proteinb(wetweight)–
19.590.9–
4.6490.014.5490.065.0390.05
Daidzeinc(mg)
Genisteinc(mg)
Glyciteinc(mg)
Totalisoflavone(mg)720A690B550D390E220F260FRawsoybeanSoakedsoybeanSoakedwaterCookedslurrySoybeverageOkaraTofuWhey1479031393NCd110090682938418938404917NCd9.7790.0642.690.487.99088.990.182.191.187.590.3
250A240A200B140D84E95E450A430B340D240E130E160F18A19A6.0BD10B4.0D6.8BTheyield,%moistureand%proteinvaluesrepresentthemean9standarddeviation;n=3.Thedaidzein,genistein,glyciteinandtotalisoflavonecontentsineachcolumnwithdifferentsuperscriptsaresignificantlydifferent(PB0.05).aPercentmoisturewascalculatedfromthedifferencebetweenwetandfreeze-driedsamples.bPercentproteinwascalculatedbytheDumascombustionmethod(AOAC992.23).cToestimatethetotalisoflavonecontent,individualisoflavoneglycosideandaglyconeformswerenormalizedfortheirmolecularweightdifferencesandsummed.Valueswerecalculatedindrybasis.dNC,notcollected.
1122C.-J.C.Jacksonetal./ProcessBiochemistry37(2002)1117–1123Table3
EffectsofprocessingonthedistributionoftwelveisoflavonesProduct
Aglycones(mg)aDai.
RawsoybeanSoakedsoybeanCookedslurrySoybeverageOkaraTofu
3.4A6.5B40C15D22E7.8BGen.2.6A8.7B60C22D31D12EGly.NDND1.2A0.8A1.1A0.5BGlucosides(mg)aDai.130A120A105B68C48D57EGen.150A140A120B81C53C63DGly.11A12A3.7BCD5.6B2.2C4.5DMalonylglucosides(mg)aDai.330A320A200B160C64D100EGen.680A630B390C330D130E200FGly.20A23A6.8B11C2.8D6.5BAcetylglucosides(mg)aDai.NDNDNDNDND1.3
Gen.4.7A7.6B8.7C2.4F3.2D2.9DGly.NDNDNDNDNDND
1325A1267B933D695C355E455FTotal(mg)
Differentsubscriptsinacolumnrepresentsignificantdifferences(PB0.05);Dai.,daidzein;Gen.,genistein;Gly.,glycitein;ND,notdetectable.aValueswerecalculatedondryweightbasisasmgofindividualcomponent(mgpergdryweight).
isoflavonesinwheymaybeduetoprotein-associatedisoflavonesbeingreleasedintothewhey.Itisnecessaryinfuturetodevelopoptimumconditionsforcoagula-tionofsoybeverageintotofutoretainthemaximumamountofisoflavonesinthefinalproduct.
Theestimatedtotalmassofisoflavoneslostinthesoakingwater,okaraandwheywere30,220,and13mg,respectively.Thesevaluesrepresentisoflavonelossesof4,31and\\18%,respectively(relativetothetotalisoflavoneinstartingmaterial,720mg),through-outtheprocessingsteps(Table2).Thesoakingandcookingstepsinsoybeverageandtofuproductionyieldedhigherconcentrationsofaglyconesandglu-cosideswithdecreasedconcentrationsofmalonylderivatives,whichwere,observedpreviously[17].Therewereslightincreasesinthelevelsofacetyl-genistinandacetyl-daidzinthroughouttheprocessingofsoybeanstosoybeverageandtofu.
Inconclusion,itwasshownthatsomeisoflavoneswerelostintheprocessingsteps,whichinvolvedheat-ing,grinding,andvariousfractionations.Theisoflavones,whichremainintheby-products(okaraandwhey),arenotcurrentlyutilizedfullyinNorthAmericaasfoodorfeedsources.Thisstudysuggeststhatthedevelopmentofefficientprocessingtechniquesiswarrantedforbetterutilizationofsoybeaninsoybeverageandtofupreparation,aswellas,tomakeuseoftheirby-productsinvalue-addedfoodsoranimalfeeds.
Acknowledgements
ThisresearchwasfundedbyOntarioSoybeanGrow-ersandtheworkwascarriedoutcollaborativelywithUniversityofGuelphandGPCRC-AAFC,Harrow,Ont.,Canada.Thesoybean(RCATAngora)waskindlyprovidedbyGaryAblettattheUniversityofGuelphandthepreparationofsoybeverageandtofuwereperformedbyD.JessopatGPCRC-AAFC,Har-row,Ont.,Canada.
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