Fig. 3.

Concentration of GABA produced by Lactiplantibacillus plantarum Y7 in modified-MRS broth. (A) The optimal temperature was determined at various temperatures (25 °C, 30 °C, 35 °C, 37 °C, 40 °C, and 43 °C) supplemented with 50 mM MSG. (B) The optimal initial pH was investigated at different pH conditions (pH 3.5–9.5) supplemented with 50 mM MSG at 37 °C. (C) The optimal carbon

source was determined using 9 different carbon sources (glucose, mannitol, maltose, lactose, lactulose, galactose, fructose, xylose, and sucrose) supplemented with 50 mM MSG at 37 °C and pH 6.5. (D) Optimal fructose concentration was determined at the concentration range of 1–5% supplemented with 50 mM MSG at 37 °C and pH 6.5. (E) The optimal nitrogen source was investigated using 7 different nitrogen sources (control, peptone, soytone, malt extract, beef extract, proteose peptone No. 3, and tryptone) supplemented with 50 mM MSG and 2% fructose at 37 °C and pH 6.5. (F) Optimum peptone concentration was investigated within the range of 1–5% supplemented with 50 mM MSG and 2% fructose at 37 °C and pH 6.5. (G) Effect of MSG supplementation was evaluated under various concentrations (25 mM, 50 mM, 75 mM, 100 mM, 125 mM, 150 mM, 175 mM, and 200 mM) substituted with 2% fructose and 2% peptone at 37 °C and pH 6.5. (H) Effect of PLP supplementation was performed at various concentrations (0 μM, 25 μM, 50 μM, 75 μM, 100 μM, 150 μM, and 200 μM) supplemented with 175 mM MSG, 2% fructose, and 2% peptone at 37 °C and pH 6.5. MSG, monosodium glutamate; PLP, pyridoxal 5′-phosphate