Effect of soaking and germination conditions on gamma-aminobutyric acid and gene expression in germinated brown rice

Four pigmented land races (Madew Zag-1, Madew Zag-2, Tangdhar Zag and Karnah Zag) and one high yielding variety (cv. Jhelum) were tested for production of gamma-aminobutyric acid (GABA) rich brown rice through germination. Central composite rotatable design was used to determine the effect of germination conditions, i.e., soaking time (h), germination time (h), germination temperature (degrees C), and relative humidity (%) on GABA content. Regression model developed was highly significant (P < .0001) with high coefficient of determination (R-2 = 0.98). The optimized conditions obtained were soaking time: 5.76 h; germination time: 40 h, and germination temperature: 35 degrees C. The genetic variation among genotypes was also studied with respect to three glutamate decarboxylase cDNAs; OsGAD1, OsGAD2, and OsGAD3. The maximum GABA synthesis during germination was recorded in Jhelum (48.18 mg/100 g) followed by Tangdhar Zag (44.40 mg/100 g). Gene expression of OsGAD3 was also upregulated maximum in Jhelum followed by Tangdhar Zag with a fold change of 22.368 and 19.472, respectively.