Effects of culture conditions on γ-aminobutyric acid accumulation during germination of foxtail millet (Setaria italica L.)

Effects of two buffer solutions—citrate solution and acetate solution—on γ-aminobutyric acid (GABA) accumulation during germination of foxtail millet (Setaria italica L.) and optimization of culture conditions, namely culture temperature, air flow rate and pH values, on GABA yield in germinated foxtail millet were investigated in this paper. The optimization processes were conducted using response surface methodology. The results showed that citrate buffer at 10 mmol L−1 was most effective as culture medium. Box–Behnken experimental design showed that the optimal conditions for GABA accumulation during millet germination were at a temperature of 33 °C; an air flow rate of 1.9 L/min; and a pH value of 5.8. Under these conditions, the maximal observed production of GABA (26.96 mg 100 g−1FW) was obtained. Analysis of variance for quadratic polynomial regression model indicated that the model was extremely significant (P < 0.0001), the determination coefficient (R2) was 0.9594, which implied that the model can forecast the changes of GABA accumulation during millet germination excellently.