Characterization of mucilage produced from the solid-state fermentation of soybean grit by Bacillus firmus

Mucilage containing γ-polyglutamic acid (PGA) was efficiently generated by the solid-state fermentation (SSF) of soybean grit by Bacillus firmus NA-1. B. firmus NA-1 was shown to be a glutamate-dependent strain for PGA production. The SSF of soybean grit was optimized in order to produce mucilage with a fortification of 5% glutamate, resulting in higher levels of mucilage production (6.14%) and a higher consistency index (1.1 Pa·sec ⁿ). The sticky mucilage was comprised of 38% PGA, 7% levan, and some biopolymers. With regard to the viscoelastic properties of the mucilage solution, the viscous modulus (G'') obtained from soybean grit fortified with 5% glutamate was approximately 64 times higher than that of the mucilage solution obtained without glutamate. Although the addition of glutamate in the SSF of soybean grit influenced the rate of PGA production, the molecular weight of PGA remained unaltered, and was detected in a range between 1,400-1,440 kDa.