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.