Stability of isoflavone glucosides during processing of soymilk and tofu

The stability of isoflavone glucosides during processing of soymilk and tofu from soybean was studied. A fast HPLC method was used to monitor the different forms and concentration changes of isoflavones. Results showed that the concentrations of the three aglycones, daidzein, glycitein and genistein increased with increasing soaking temperature and time, while a reversed trend was found for the other nine isoflavones, nine glucosides. During processing of soymilk, an increase of concentration for glucosides (daidzin, glycitin and genistin) and acetylgenistin was shown, whereas malonylglucosides (malonyldaidzin, malonylglycitin and malonylgenistin) exhibited a decreased tendency and the aglycones did not show significant change. Also, no acetyldaidzin and acetylglycitin were detected. Tofu made with 0.3% calcium sulfate (protein coagulant) was found to contain the highest yield (2272.3 mug/g) of total isoflavones. Whereas, a higher level (0.7%) of calcium sulfate resulted in a lower yield (1956.6 mug/g) of total isoflavones in tofu. (C) 2004 Elsevier Ltd. All rights reserved.