Production of Fibrinolytic Enzyme from Soybean Grits Fermented by Bacillus firmus NA-1

Abstract

Bacillus firmus NA-1 producing fibrinolytic enzyme was isolated from Japanese traditional fermented soybean (Natto). Seed starter was cultured in 5% soy milk prepared with micronized soybean powder. To optimize the production of fibrinolytic enzyme, the soybean grits were mixed with 1 volume of water and sterilized at 121°C for 5 minutes, and then used as the medium for solid-state fermentation at 42°C. The fibrinolytic enzyme activity of the fermented grits was 1,120 plasmin units/100 g (wet weight) after fermentation for 24 hours. The water extract of the fermented grits showed the highest viscosity after fermentation for 12 hours. However, the tyrosine content was the highest (962 mg%) after fermentation for 60 hours. The color of raw soybean grit was affected by heat treatment. The activity of fibrinolytic enzyme was stable after freezing-drying, but was completely destroyed by heating at 70°C for 10 minutes. The color of soybean grit was greatly darkened by increasing fermentation time. Soybean grits were completely converted into valuable functional ingredients containing fibrinolytic enzyme, peptide, and mucilage by the solid-state fermentation.