초록
Neutralization of H<SUP>+</SUP> enhances the substrate conversion rate and affords high product concentrations during lactic acid fermentation. Glutamate decarboxylase (GAD) consumes H<SUP>+</SUP> and catalyzes the α-decarboxylation of glutamate to generate neutral γ-aminobutyric acid (GABA). In this study, the glutamate decarboxylation reaction, mediated by immobilized GAD, was applied to consume the H<SUP>+</SUP> ions produced during lactic acid fermentation by Rhizopus oryzae As3.819. The glutamate decarboxylation reaction could neutralize the H<SUP>+</SUP> produced during fermentation, thereby stabilizing the pH during lactic acid production, while lactic acid fermentation provided H<SUP>+</SUP> for GABA production. By coupling the two biochemical processes (pH 4.7-5.0), a lactic acid concentration of 80.2g/L with a yield of 67% from glucose and a GABA concentration of 44.8g/L with 96.7% conversion from glutamate were obtained. These results indicated that the two biochemical processes could be coupled in a single reactor, thereby enabling the production of lactic acid and GABA simultaneously and economically.