Changes in Isoflavone content of soybeans during heating process
2006
Kasuga, A.(Kagawa Nutrition Junior Coll., Tokyo (Japan)) | Ogiwara, E. | Aoyagi, Y. | Kimura, H.
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 isofiavone 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.
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