γ-Aminobutyric acid produced by Levilactobacillus brevis using Chinese cabbage waste

To utilize Chinese cabbage waste (CCW) recovered from the pickle industry, a simple medium named Chinese cabbage medium (CCM) was developed for Levilactobacillus growth and γ-aminobutyric acid (GABA) production. The optimal medium compositions were 30% Chinese cabbage waste extracts (CCWE), 3% glucose, 0.25% yeast extract (YE), 0.25 X salts (0.25% sodium acetate, 0.1% sodium citrate, 0.1% ammonium sulfate, 0.005% magnesium sulfate and 0.0025% manganese sulfate), and initial pH 5.0 adjusted by HCl. L. brevis was incubated in this medium with 1% monosodium glutamate (MSG) at 30 °C for 24 h. Cell counts reached 4.16 × 109 CFU/ml, and the control results from MRS medium was 4.07 × 109 CFU/ml. GABA conversion rate at 18 h of this medium was 99.12%, higher than the MRS medium of 95.01%. Fructose and maltose were beneficial to the growth of L. brevis, but glucose was conducive to GABA synthesis. To obtain a high yield of GABA, CCM medium with 10% MSG was optimized by response surface methodology and resulted in 21.84% CCWE, 5.5% glucose, 4% YE, 1 X salt, 0.2% disodium phosphate, and initial pH of 4.5. GABA conversion rate reached 100% at 48 h with a final yield of 55.1 g/L.