Optimizing soaking and germination conditions to improve gamma-aminobutyric acid content in japonica and indica germinated brown rice

Germinated brown rice is a well-known functional food due to its high content of gamma-aminobutyric acid (GABA). This study was designed to test the difference of producing GABA in two domesticated rice genotypes (indica and japonica rice), and the effects of adding exogenous glutamic acid or gibberellin, and processing conditions. Soaking at 30 °C and germination at 35 °C during 36 h resulted in the highest GABA in distilled soaking water with pH 7. The indica rice showed higher GABA levels than japonica rice. GABA was increased under acidic soaking conditions or by adding L-glutamic acid (L-Glu) at the optimal concentration of 1.0 g L−1 and gibberellin A3 (GA3) at the optimal concentration of 0.25 mg L−1. The lower accumulation of GABA in japonica rice could be remedied by adding exogenous L-Glu and GA3, and providing acidic soaking conditions. The results help to efficiently produce GABA enriched functional food.