Substrate sustained release-based high efficacy biosynthesis of GABA by Lactobacillus brevis NCL912

Gamma-aminobutyric acid (GABA) plays a significant role in the food and drug industries. Our previous study established an efficient fed-batch fermentation process for Lactobacillus brevis NCL912 production of GABA from monosodium L-glutamate; however, monosodium L-glutamate may not be an ideal substrate, as it can result in the rapid increase of pH due to decarboxylation. Thus, in this study, L-glutamic acid was proposed as a substrate. To evaluate its potential, key components of the fermentation medium affecting GABA synthesis were re-screened and re-optimized to enhance GABA production from L. brevis NCL912.

The initial fermentation medium (pH 3.3) used for optimization was: 50 g/L glucose, 25 g/L yeast extract, 10 mg/L manganese sulfate (MnSO₄·H₂O), 2 g/L Tween-80, and 220 g/L L-glutamic acid. Glucose, a nitrogen source, magnesium, and Tween-80 had notable effects on GABA production from the L-glutamic acid-based process; other factors showed no or marginal effects. The optimized levels of the four key components in the fermentation medium were 25 g/L glucose, 25 g/L yeast extract FM408, 25 mg/L MnSO₄·H₂O, and 2 g/L Tween-80. A simple and efficient fermentation process for the bioconversion of GABA by L. brevis NCL912 was subsequently developed in a 10 L fermenter as follows: fermentation medium, 5 L; glutamic acid, 295 g/L; inoculum, 10% (v/v); incubation temperature, 32 °C; and agitation, 100 rpm. After 48 h of fermentation, the final GABA concentration increased up to 205.8 ± 8.0 g/L.

L-Glutamic acid was superior to monosodium L-glutamate as a substrate in the bioproduction of GABA. Thus, a high efficacy bioprocess with 205 g/L GABA for L. brevis NCL912 was established. This strategy may provide an alternative for increasing the bioconversion of GABA.