Effects of components in culture medium on glutamate decarboxylase activity and [gamma]-aminobutyric acid accumulation in foxtail millet (Setaria italica L.) during germination

The effects of glutamic acid (Glu), pyridoxal-5-phosphate (PLP) and calcium chloride (CaCl[sub]2) in culture medium on glutamate decarboxylase (GAD) activity and [gamma]-aminobutyric acid (GABA) accumulation in foxtail millet (Setaria italica L.) during germination were investigated in this study. The components in culture medium for GABA accumulation were optimised using response surface methodology (RSM). Results showed that GAD activity and GABA yield were dependent on the addition of Glu, PLP and CaCl[sub]2 into the culture medium. Box-Behnken design indicated that the optimal culture components for GABA accumulation were: Glu at a concentration of 1.2 mg/ml, PLP at a concentration of 50 [micro]M and CaCl[sub]2 at a concentration of 2.5 mM. Under the optimal conditions, the maximal production of GABA (42.9 mg/100 g FW) was obtained. Analysis of variance for the regression model suggested that the model can quite exactly predict GABA accumulation in millet during germination.