Novel bioconversion of sodium glutamate to γ-poly-glutamic acid and γ-amino butyric acid in a mixed fermentation using Bacillus subtilis HA and Lactobacillus plantarum K154

Abstract

Both γ-poly-glutamic acid (γ-PGA) and γ-amino butyric acid (GABA) were produced from sodium glutamate in a mixed fermentation. A culture broth was obtained using a defined medium including 3% glutamate and Bacillus subtilis HA for 3 days at 42°C, with 1.20×108 CFU/mL viable cells, a 0.46 Pa·sn consistency index, and a 1.94% mucilage content. In a second fermentation using Lactobacillus plantarum K154 at 37°C for 3 days, 1.29% of the remaining glutamic acid in the viscous culture broth was converted to 0.86% GABA. Glutamic acid in the first culture broth fortified with 5% skim milk was completely converted to GABA. The final co-cultured broth had 0.48% GABA, a 0.294% tyrosine content, and viable cells of 1.06×109 CFU/mL (L. plantarum K154) and 5.42×105 CFU/mL (B. subtilis HA). Serial co-culturing of these two bacteria can provide novel ingredients fortified with γ-PGA, GABA, peptides, and probiotics.