Physicochemical properties of poly- gamma-glutamic acid produced by a novel Bacillus subtilis HA isolated from cheonggukjang.

摘要

A novel bacterium isolated from cheonggukjang (chungkook-jang) was identified as glutamate-dependent Bacillus subtilis HA with 98.3% similarity to B. subtilis Z99104. Optimization of poly( gamma-glutamic acid) ( gamma-PGA) production by modulating fermentation factors including C sources, N sources, inorganic salts and fermentation time was studied. Optimum culture broth for gamma-PGA production consisted of 3% glutamate, 3% glucose and various salts, resulting in a PGA production of 22.5 g/l by shaking culture for 72 h at 37 degrees C. Average mol. wt. of gamma-PGA was determined to be 1220 kDa using MALLS analysis. The gamma-PGA solution showed a typical pseudoplaslic flow behaviour and a large decrease in consistency below pH 6.0 regardless of the same mol. wt. of gamma-PGA. The mol. wt. of isolated gamma-PGA was decreased markedly by heat treatment in various acidic conditions, resulting in different hydrolysis of gamma-PGA. The consistency of gamma-PGA solution was decreased with an increase in heating time in acidic conditions.