Optimum conditions for the hydrolysis and extraction of isoflavones in defatted soybean meal were determined. The best condition for the hydrolysis of bound isoflavones was to digest the dry sample in 1 M hydrochloric acid for 2 hr at 98-100 deg C. Absolute ethanol was the most efficient among two extraction solvents (methanol and ethanol) at four concentration levels (25, 50, 75, and 100). The optimum ratio of the absolute ethanol to the defatted soybean meal was 20:1 (v/w). The pH of the solvent was critical in the extraction of isoflavones in which the maximum extraction was at pH 7, and the optimal extraction temperature was 50 deg C. In addition, the extraction with absolute methanol at 50 deg C for 9 hr gave the highest concentration of the total free isoflavones (113.73 #mu#g/g of free daidzein plus free genistein). Under the optimal conditions, defatted soybean meal contained 610.09 #mu#g/g of total daidzein and 667.86#mu#g/g of total genistein, where about 8.81 of the total daidzein and 8.99 of total genistein existed as their free forms.
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