Soymilk processing with higher isoflavone aglycone content

The objective of this work was to optimise conversion of β-glucoside isoflavones to aglycones in soymilk processing and to evaluate their thermal stability. The soymilk was assessed for time and temperature effects of incubating supplied to central composite design 22. The response functions were investigated for β-glucosidase activity and isoflavone contents. The β-glucosidase activity was reduced through soybean slurry incubation at approximately 64 °C and 3.42 h. Maximum conversion of β-glucosides into isoflavone aglycones involved soaking the soybeans at 5 °C for 14 h at a 1:3 ratio (soybean:water, w:v), homogenising them at a 1:8 ratio (soybean soaked:water, w:v) and incubation at 50 °C for 2.7 h. In evaluation of thermal stability of isoflavones in soymilk at 97 °C for 25 min, the daidzein and genistein aglycone contents were maintained, the glycitein and β-glucosides contents increased and the malonylglucoside content decreased.