Abstract
Tubu-natto and hikiwari-natto (which are made from whole and split soybeans, respectively) are mainly produced in Japan. The production process consists of splitting (performed only for hikiwari-natto), soaking, and boiling of soybeans, followed by fermentation with Bacillus subtilis (natto). In this study, we examined changes in the contents of various types of soy isoflavone during the production of these two kinds of natto. There was little leakage of soy isoflavones throughout the process of tubu-natto production, but during production of hikiwari-natto, about 9.8% of isoflavones were lost as soybean powder generated during splitting. During processing of both kinds of natto, malonyl isoflavones were found to decrease after the soybeans were boiled, and succinylated isoflavone glycosides increased after fermentation with B. subtilis (natto).
