Enhancing gamma aminobutyric acid synthesis from defatted rice bran extract by Lactobacillus brevis VTCC-B397: technical parameters analysis

Abstract Gamma aminobutyric acid (GABA) is a biologically active compound that has attracted significant attention in recent years due to its beneficial effects on the nervous system and its role in brain synthesis processes. GABA is widely produced by fermentation method, and its microbial biosynthesis can be improved by adjusting operational parameters and supplementing nutrients during fermentation. However, the optimal fermentation conditions for GABA production vary depending on raw materials and microbial strain used. Rice bran is known as a low-cost and nutritious raw material, capable of producing greater GABA content than other substrates. This study aimed to enhance GABA production from rice bran slurry fermented by Lactobacillus brevis VTCC-B397 by adjusting fermentation conditions, including temperature (25–37 °C), pH (3.0–6.0), monosodium glutamate (MSG) concentration (0–1 M) and fermented time (0–72 hr). The effects of these factors on bacterial cell density and GABA content were assessed over the fermentation period. Furthermore, response surface methodology was applied to optimise the medium and fermentation parameters, as well as to investigate the interactions between factors that influence the fermentation process. The biosynthesis pathway of GABA was considerably impacted by temperature, pH, and MSG content. The optimal conditions for GABA production from defatted rice bran solution were found to be 0.56 M MSG, 34 °C, and pH 5.12. Under optimised conditions, the highest GABA yield achieved was 7.69 g/L.