Effect of extraction and precipitation conditions during soybean protein isolates production on the genistein series content

SPERONI AGUIRRE, F.J., MILESI, V., AÑÓN, M.C.

JOURNAL OF THE AMERICAN OIL CHEMISTS SOCIETY (JAOCS)

Año: 2007 vol. 84 p. 305 - 314

0003-021X

Abstract The influence of the conditions for isolationof soy protein on the content of genistein and its conjugatedforms was studied. The major components ofthe genistein series isolated from soybean flour weremalonyl genistin (54.3%), genistin (36.9%), and equalamounts (4.4%) of genistein and acetyl genistin. Amodification in the conjugation profile of genisteinbetween pH 4.5 and 8.0 and above pH 10 was attributedto the action of b-glucosidase and the saponifi-cation reaction, respectively. A decrease in the contentof total genistein in the insoluble flour residue and inthe soy protein isolate (SPI) with increasing extractionpH was detected, while in the whey, the total genisteincontent was not affected by pH. The effect of pHvariation during acid precipitation on the content ofgenistein and its conjugated forms, at a constantextraction pH (8.0), was also studied. Under theseconditions, the highest absolute content of total genisteinin the SPI was obtained at pH 3.5 and the lowestwas obtained at pH 5.6. The total genistein content inthe whey followed an inverse trend compared with thatof the protein yield. A temperature increase did notsubstantially affect the distribution of the differentgenistein forms or their total contents. The content oftotal genistein was higher in the glycinin than in theb-conglycinin protein fraction. The effect of the pHduring the alcohol/water extraction of the isoflavoneswas also analyzed. The efficiency of the extraction waslower at pH values between 3.25 and 3.5 than at otherpH values.