Effect of incubation time, buffer type and concentration on gamma-aminobutyric acid (GABA) production using Khao Dawk Mali 105 rice bran

Rice bran of Khao Dawk Mali 105 (KDML105) variety was selected for production of gamma-aminobutyric acid (GABA). The effect of incubation time on GABA production was studied and the maximum GABA was produced after 6 h of incubation. Different types of 50 mM buffers (containing 0.2% glutamic acid) consisting of Tris, citric acid, boric acid and phosphate buffer (pH 5.6) were used to stabilize the pH of the reaction system. The highest GABA content (5.05 mg/g of bran) was found in the phosphate buffer system. Therefore, the effect of phosphate buffer concentrations (0–200 mM) on GABA production was investigated. The results showed that rice bran with phosphate buffer at a concentration of 80 mM at pH 5.6 with a rice bran to phosphate buffer at a ratio of 1–8 (weight per volume) produced the highest GABA content (p ≤ 0.05). GABA production was increased about 2.7 times in the phosphate buffer system compared with the control and about 11 times compared to the initial GABA content (0.58 mg/g of bran) in the rice bran. The results indicated that incubation time, buffer type and concentration significantly affect GABA production using rice bran.