Penkwan Chompreeda

Optimizing time and temperature of enzymatic conversion of isoflavone glucosides to aglycones in soy germ flour.

Five factors (enzyme concentration, substrate concentration, pH, incubation temperature, and incubation time) were initially screened for the conversion of isoflavone glucosides to aglycones in soy germ flour. The incubation temperature/time most significantly affected aglycone yield; subsequently, a full 5 (35, 40, 45, 50, and 55 °C) × 6 (1, 2, 3, 4, 5, and 6 h) factorial design and response surface methodology were employed to attain an optimal incubation time/temperature condition. The optimum condition producing soy germ flour with a high concentration of daidzein, glycitein, and genistein was as follows: soy germ flour:deionized water (1:5, w/v), β-glucosidase at 1 unit/g of soy germ flour, pH 5, and incubation temperature/time of 45 °C/5 h. Under this optimal condition, most isoflavone glucosides were converted to aglycones with daidzein, glycitein, and genistein of ≥ 15.4, ≥ 6.16, and ≥ 4.147 μmol/g, respectively. In contrast, the control soy germ flour contained 13.82 μmol/g daidzin, 7.11 μmol/g glycitin, 4.40 μmol/g genistin, 1.56 μmol/g daidzein, 0.52 μmol/g glycitein, and 0.46 μmol/g genistein.