2006 Volume 53 Issue 7 Pages 365-372
In order to examine the bioavailability of soybean isoflavone and to obtain basic nutritional data, we measured separately the quantities of each of twelve kinds of isoflavone contained in soybeans : malonyl glucosides, acetyl glucosides, glucosyl glucosides and aglycon. First, we analyzed six types of soybean generally seen in the market. Differences in total isoflavone content, some greater than 100%, were observed depending on the type of bean. Second, we analyzed the compositional changes of isoflavone, using a heating method that reflected the domestic cooking process, with soybeans of known quantities. Isoflavones were not eluted to a significant extent by immersion in water, but after boiling for 3 min, 8∼9% of the isoflavones dissolved in water, which was drained off. By boiling for 30 min and 60 min, 24% and 30%, respectively, of the total isoflavone contents in soybean broth were dissolved. Upon heating, the content of glucosyl glucosides decreased and that of malonyl glucosides increased ; this tendency became more marked as the heating time was extended. Although heating time was shorter when a pressure cooker was used, elution of isoflavone was no greater than when the broth was boiled normally. When a steamer was used for heating, only small amounts of isoflavones could be eluted.