Abstract
Changes in the DPPH radical-scavenging activity and related components during processing of the traditional fermented soybean food, Daitokuji-natto, made in Zuihoin Daitokuji (Kyoto) were examined. Daitokuji-natto was processed from the end of July to September. The contents of genistin, daidzin and glycitin in soybean (Tsuruhime harvested in Hokaido) were all increased by steaming. However, the contents of these components gradually decreased during fermentation and maturation, in contrast to the increases of the daidzein, genisitein and glycitein contents. Fermentation for 1 week in a cellar resulted in the contents of peptides and free amino acids, especially glutamate, being increased by enzymatic degradation of the protein. The melanoidin-related compounds gradually increased during the progress of maturation under sunlight in the summer for 2 months. Although the DPPH radical-scavenging activity was significantly related to the polyphenol contents (p<0.01), the components mainly responsible for the radical-scavenging activity of Daitokuji-natto were found to be melanoidin-related compounds.
