Physicochemical Properties of Poly-γ-glutamic Acid Produced by a Novel Bacillus subtilis HA Isolated from Cheonggukjang

A novel bacterium isolated from Cheonggukjang was identified as a glutamate-dependent Bacillus subtilis HA with 98.3% similarity to Bacillus subtilis Z99104. Optimization of poly-γ-glutamic acid (γ-PGA) production by modulating fermentation factors including carbon sources, nitrogen sources, inorganic salts and fermentation time was investigated. Optimum culture broth for γ-PGA production consisted of 3% glutamate, 3% glucose and various salts, resulting in the PGA production of 22.5 g/L by shaking culture for 72 hr at 37℃. Average molecular weight of γ-PGA was determined to be 1,220 kDa through MALLS analysis. The γ-PGA solution showed a typical pseudoplastic flow behavior, and a great decrease in consistency below pH 6.0 regardless of the same molecular weight of γ-PGA. The molecular weights of isolated γ-PGA were drastically decreased by heat treatment in various acidic conditions, resulting in different hydrolysis of γ-PGA. The consistency of γ-PGA solution was greatly decreased with increase heating time in acidic conditions.