Gamma-aminobutyric acid fermentation and its fermented extracts on α-glucosidase inhibition and anti-obesity effect.

Levilactobacillus brevis KCL010 was fermented in a simple medium containing 8% (w/v) of rice bran extract. We modified the carbon, nitrogen, and initial pH conditions using 10 g/L of sucrose, 10 g/L of yeast extract, and 5.0 of pH, respectively. To minimize the pH increase due to decarboxylation, we fermented 100 mL of modified synthetic medium containing citrate-phosphate buffer (CPB, pH 5.0) of 25-200 mM in 250 mL Erlenmeyer flasks. After 72 h of fermentation with 50 mM CPB, the maximum GABA concentration and conversion efficiency were 3.42 g/L and 22.39%. Furthermore, the potential α-glucosidase inhibitory activity, MTT assay, and oil red O staining were determined by fermented extracts of L. brevis KCL010. At the highest concentration of 500 μg/mL, the α-glucosidase inhibition percentages for non-fermented rice bran (NFRB), rice bran fermented by L. brevis (RBFL), and GABA (analytical standard) extracts were 55.03%, 58.37%, and 59.48%, respectively. All extracts exceeded 80% viability, suggesting that there was no cytotoxic to 3T3-L1 adipocytes. The rice bran fermented by L. brevis (RBFL) extract shows a high inhibition of lipid accumulation by 29.33% compared to those of extracts.