Improvement of Okara by fermentation with Bacillus subtilis

The utility of Okara, a by-product of the soybean processing industry

Abstract

Okara (by-product of tofu manufacturing) was fermented by Bacillus subtilis in order to improve it as good taste and high processing characteristics as food stuff, and the morphological, physicochemical properties and composition of physical properties of okara fermented with B. subtilis (ON) were investigated. 1. After 24 hr of fermentation, the amount of free amino acids, free fatty acids, inorganic phosphorus increased and dietary fiber decreased as compared to the starting levels. In ON leucine and phenylalanine among free amino acids were the predominate, and in dietary fiber, the pectic substances increased, while hemi-cellulose decreased. 2. The temperature of ON increased rapidly with increasing CFU of B. subtilis in 5 to 10 hr of fermentation and rose up to 50°C at 15 hr. The hydrolysis ratio of proteins (formol nitrogen / total nitrogen × 100) increased with increasing protease activity. The ammonia content and pH value increased rapidly after 15 hr, and the pH value of ON at 30 hr was 8.2. 3. Scanning electron microscopic observation of ON at 24 hr revealed that the cell wall was completely disintegrated. The amount of particles less than 10 μm diameter increased with the further progress of fermentation. 4. The in vitro digestibility of protein in ON was similar to that in okara. The water absorption and oil absorption were also same in both okara. However, the emulsifying activity and emulsion stability were higher in ON than in okara.