Increase of gamma-aminobutyric acid contents in rice embryo with protein hydrolysates and pyridoxal-5-phosphate using abiotic stress

Effects of abiotic stress treatment and the addition of protein hydrolysates and pyridoxal-5-phosphate on the gamma-aminobutyric acid (GABA) accumulation in rice embryo were investigated. After adjusting the moisture content to 20% by adding an electrolyzed oxidizing water and storing anaerobically at 40 °C for 8 h, the rice embryo showed a significant increase in the residual GABA content from 79.8 to 269.9 mg/100 g. The GABA content in rice embryo could be further raised by adding protein hydrolysates: 503.4 and 406.4 mg/100 g, respectively with 4% wheat protein hydrolysate (WPH) and 8% yeast extract (YE). A minor addition of PLP (1.5 mg/100 g embryo solids) increased the GABA content to 827.6 and 725.3 mg/100 g, for the samples containing 4% WPH or 8% YE, respectively. Additionally, total amount of essential amino acids in rice embryo was significantly increased by the addition of protein hydrolysates and the abiotic stress treatment.