Behavior of isoflavone conjugates of soybeans during the rehydration and heating process

Abstract

In order to utilize the isoflavone of soybean, which is expected to have higher functionality, we investigated changes in composition and behavior of isoflavone conjugates of soybean following rehydration with different temperatures, duration of and heating rates. The conditions were selected in consideration of home cooking processes and industrial processes, and 12 isoflavones were analyzed by HPLC. For 12 -hour rehydration at 5, 20 and 30°C, the composition of isoflavones was nearly identical to that before rehydration. With rehydration at 40°C, malonyl-glucosides decreased 13% and aglycon increased slightly, and at 60°C rehydration, malonyl-glucosides decreased 54%, and daidzein and genistein of aglycons increased 10- and 12-fold, respectively. Besides increasing aglycon at rehydration at 60°C, daidzin and genistin of glucosyl-glucosides increased 2.5-fold. For rehydration time of 24 hours, these trends became more pronounced. The isoflavone composition of soybeans cooked for 1 hour at 60°C was similar to that for soybeans cooked at 95°for 30 min with a 2°/min heating rate. Malonyl-glucosides decreased slightly, equivalent to the increase in aglycons. With heating rates of 9°/min and 30°/min, malonyl-glucosides decreased 38% and 40%, respectively, and glucosyl-glucosides increased two-fold.