Optimization of GABA Production and Partial gad Gene Identification of Potential Probiotic Levilactobacillus brevis F064A Isolated from Thai Fermented Sausage

Abstract

Gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter, can be produced by lactic acid bacteria. Levilactobacillus brevis F064A, a high potential probiotic, is capable of producing GABA. To elucidate its glutamic acid decarboxylase (GAD) enzyme responsible for GABA production, partial gad genes were examined. It was found that both partial gadA and gadB genes were existing in L. brevis F064A genomes. Some influencing effects on GABA production by Levilactobacillus brevis F064A were determined. The highest GABA production of 4.18 ± 0.07 mg/mL was achieved with the optimal conditions of initial media pH of 5.5, 2% (w/v) of glucose, 2% (w/v) of monosodium glutamate (MSG) and 48 h at 37°C of incubation. Pyridoxal 5′-phosphate (PLP) had no effect on its GABA production. At 48 h of incubation, the viable cells were increased as well as the culture pH. Moreover, the optimum conditions based on the response surface methodology (RSM) model were pH of 5.26, 2.71% (w/v) of glucose and 2.96% (w/v) of MSG yielded 4.53 ± 0.08 mg/mL GABA content (p < 0.05). Additionally, total lactic acid of 10.30 ± 0.91 mg/mL was also produced. Promisingly, L. brevis F064A is a good candidate for GABA production and for functional food development in the future.