2008-Optimisation of ultrasound-assisted extraction from wh(4)

J.Wangetal./FoodChemistry106(2008)804–810807

3.Resultsanddiscussion

3.1.Thetotalphenoliccontentofwheatbranextractedwithvarioussolvents

Aqueousalcoholsandacetone,withdi erentlevelsofwater,havebeenwidelyusedtoextractphenoliccompo-nentsfrombotanicalmaterials,especiallyherbs.Anextrac-tionsolventsystemisgenerallyselectedaccordingtothepurposeofextraction,polarityoftheinterestedcompo-nents,polarityofundesirablecomponents,overallcost,andsafety(Yuetal.,2002).Inthispaper,thee ciencyofmethanol,ethanol,andacetoneontheextractionofthetotalphenoliccontentfromwheatbranwas

compared,whichwasexpressed

asgallicacidequivalents(GAE).Fig.1showsthetotalphenoliccontentsofwheatbranextractedwithvarioussolvents.Signi cantdi erenceintotalphenoliccontentwasobservedamongthevarioussol-ventextracts.Ethanolextractscontainedthehighestcon-tentoftotalphenolics,followedbymethanolextractsandacetoneextracts.Inaddition,ethanolislesstoxicandcanbeeasilyrecoveredbyreducedpressuredistillation.There-fore,ethanolwasusedastheextractionsolventinthefol-lowingstudy.

3.2.E ectofethanolconcentrationonextractionoftotalphenoliccompounds

Addingacertainamountofwaterinethanolmightimprovetheextractinge ciency(Yuetal.,2002).Etha-nol–watermixtureswereusedastheextractionsolventinthestudy.Thee ectsofethanolconcentrationintheextractionsolventonthecontentofphenolicsinwheatbranextractsareshowninFig.2.Whenethanolconcentra-tionincreasedfrom20%to60%(v/v),thetotalphenoliccontentoftheextractsincreasedfrom1.67to2.81mgGAE/gofwheatbrantested.Whenethanolconcentrationreached80%(v/v),thetotalphenoliccontentinbranextractsdecreasedquickly,andataconcentrationof95%(v/v),thetotalphenoliccontentwas1.48mgGAE/gofwheatbran.When95%(v/v)ethanolwasusedtoextractwheatbran,somelipidcomponentswerealsoextracted,whichmaylimittheextractionofphenolicsinwheatbran.Asimilare ectwasreportedintheextractionofphenolicantioxidantsfrompeanutskins(Neptoe,Grosso,&Guz-ma

´n,2005).3.3.E ectofextractiontemperatureonextractionoftotalphenoliccompounds

Fig.3showsthee ectofextractiontemperatureundersonicationonthecontentsoftotalphenoliccompoundsextractedfromwheatbran.Asigni cantincreaseofthetotalphenoliccontentwasobservedovertheextractiontemperaturerange(25–75°C),andthetotalphenoliccon-tentreachedamaximumofaround2.80mgGAE/gofwheatbranat65°C.Atahighertemperature,thesolubility

ofphenoliccompoundsinwheatbrancouldbeenhanced,andtheviscosityofwheatbranextractswasdecreased,acceleratingthewholeextraction.