Abstract: Soymilk was prepared with soy thermally treated respectively at 95, 121 and 140℃ for various time lengths. Three aglycones of soy isoflavones, namely genistein, daidzein and glycitein in soy granule and the heat-processed soy milks were assayed with HPLC method to compare their thermal reliability. The results showed that at 95℃, genistein exhibits thermal reliability during the whole 60 minutes, whereas daidzein and glycitein are found degraded with the T(loss 0.5) values (time to be decreased by 50%) of 1442s and 453s respectively, indicating the order of thermal stability as: genistein>daidzein> glycitein. At 121 and 140℃, all the three aglycones are found degraded. The T(loss 0.5) values of daidzein, glycitein and genistein at 121℃ are found to be respectively 26.36, 37.88 and 1015s, while at 140℃, these T(loss 0.5) values for daidzein, glycitein and genistein are shortened as 6.94, 8.47 and 369s respectively. The results indicat that their thermal stability is in the order of genistein>glycitein>daidzein.

Key words: genistein, daidzein, glycitein, soymilk, thermal stability