Black Soybean Fermentation using a rpoB Mutant Strain of Bacillus subtilis (natto)

Abstract

A new Bacillus subtilis natto-fermenting strain, Miyagi-4100, showing enhanced exoenzyme production and developed from the parental Miyagi-4 strain, was used to prepare natto from hard-hulled black soybeans. In this study, we evaluated the ability of Miyagi-4100 to ferment black soybeans, based on the amount of viscous substances, poly-gamma-glutamic acid and levan, as well as the degree of hardness of the fermented black soybean component. Miyagino, a commercial starter strain, and Miyagi-4 were compared to Miyagi-4100. Black soybean natto produced with Miyagi-4100 contained much more levan than that produced with Miyagi-4, and showed a tendency for decreased hardness. Therefore, we conclude that Miyagi-4100 is highly applicable to fermenting black soybeans to natto.