Abstract: The aim of this study was to investigate the influence of medium components on γ-aminobutyric acid (GABA) enrichment during soybean sprouting and further to optimize the variables by response surface methodology (RSM). Furthermore, the mechanism of GABA accumulation in germinated soybean under low salt stress was also preliminarily investigated. The results demonstrated that soybean germination in the optimized medium containing 1.0 mg/mL sodium glutamate (MSG), 2.0 mmol/L pyridoxal phosphate (PLP), 2.0 mmol/L CaCl2 and 100 mmol/L NaCl yielded accumulation of a high level of GABA, (269.93 ± 4.73) mg/100 g dry weight, which was around 11 times higher compared with ungerminated soybeans (control). With increasing concentration of NaCl and extending stress time, glutamine acid decarboxylase activity and GABA content of sprouted soybean increased. Correlation analysis indicated that there was a significantly positive correlation between the GABA content of sprouted soybean and sprout length, glutamine acid decarboxylase activity, free amino acids content or soluble protein content. The germination of soybeans was restrained, the GAD activity was enhanced, and the contents of free amino acid and soluble protein were increased under low salt stress. Finally, GABA was accumulated at a high level.

Key words: γ-aminobutyric acid, response surface methodology, salt stress, enrichment process