J.Wangetal./FoodChemistry106(2008)804–810809

Fig.5.Responsesurfaceplotshowingthee ectofethanolconcentration(%)andextractiontemperature(°C)onthetotalphenoliccontentfromwheatbran.Extractiontimeisconstantatthezerolevel,20

min.

aturetested.Thee ectofethanolconcentrationandextractiontimeshowninFig.6demonstratedthatthetotalphenoliccontentincreasedrapidlywiththeincreaseofeth-anolconcentrationata xedextractiontime,whileanincreaseinextractiontimeata xedethanolconcentrationalsoledtoamarkedincreaseintotalphenoliccontent.Fig.7re ectsthee ectofextractiontemperatureandextractiontimeontheextractionofphenoliccompounds

Fig.6.Responsesurfaceplotshowingthee ectofethanolconcentration(%)andextractiontime(min)onthetotalphenoliccontentfromwheatbran.Extractiontemperatureisconstantatthezerolevel,50°

C.

Fig.7.Responsesurfaceplotshowingthee ectofextractiontemperature(°C)andextractiontime(min)onthetotalphenoliccontentfromwheatbran.Ethanolconcentrationisconstantatthezerolevel,60%.

fromwheatbran.Asimilarlinearincreaseinthetotalphe-noliccontentwithincreaseinextractiontemperatureata xedextractiontime,whileanobviousquadratice ectofextractiontimewerebothobserved,andthetotalphenoliccontentreacheditshighestvalueatanextractiontimeofabout25minata xedextractiontemperature.

Theoptimalconditionsobtainedusingthemodelwereasfollows:ethanolconcentration,64%;extractiontemper-ature,60°C;andextractiontime,25min.Underoptimalconditions,themodelpredictedamaximumresponseof3.08mgGAE/gbran.Tocomparethepredictedresultwiththepracticalvalue,experimentalrecheckingwasperformedusingthisdeducedoptimalcondition.Ameanvalueof3.12±0.03mgGAE/gbran(n=3)obtainedfromrealexperimentsvalidatedtheRSMmodel.Thegoodcorrela-tionbetweentheseresultscon rmedthattheresponsemodelwasadequatetore ecttheexpectedoptimisation(Table5).

Ithasbeenreportedthatsomestatisticallysigni cantdi erencesintotalphenoliccontentwereobtained

among

Table5

Optimumconditions,predictedandexperimentalvalueofresponseunderthoseconditionsOptimumconditionsTotalphenolicscontent(mgGAEeq.a/gbran).Ethanol

ExtractionExtractionExperimentalb

Predicted

concentrationtemperaturetime(min)(%)

(°C)64

60

25

3.12±0.033.08

aGallicacidequivalent.

b

Means±standarddeviation(n=4).