Self-enhancement of GABA in rice bran using various stress treatments

Gamma-aminobutyric acid (GABA) may be synthesized in plant tissues when the organism is under stressful conditions. Rice bran byproduct obtained from the milling of brown rice was treated under anaerobic storage with nitrogen at different temperatures (20–60 °C) and moisture contents (10–50%) up to 12 h. For the GABA synthesis, the storage at 30% moisture content and 40 °C appeared optimal. Utilisation of an electrolyzed oxidizing water (EOW, pH 3.3) for moisture adjustment and addition of glutamic acid increased the GABA content in rice bran. The maximum GABA content in rice bran (523 mg/100 g) could be achieved by the anaerobic storage at 30% EOW for 5 h at 40 °C after an addition of glutamic acid (5 mM). This amount was approximately 17 times higher than that in the control (30 mg/100 g). The use of EOW also prevented bacterial growth by decreasing the colony counts almost by half.