Evaluation of using a combination of enzymatic hydrolysis and lactic acid fermentation for γ-aminobutyric acid production from soymilk

The production of fermented foods enriched with γ-aminobutyric acid (GABA) is a current trend in the food industry. In this study, the release of free glutamic acid (Glu) and its conversion to GABA in soymilk were conducted through enzymatic hydrolysis using Alcalase (Al) and Flavourzyme (Fl), following by the fermentation using Lb. plantarum LMG6907 (at 30 °C for 96 h). Results showed that a degree of hydrolysis of 90% was achieved when soymilk was treated with a mixture of Al:Fl in a ratio 1:1 (final enzyme concentration of 2 mL/100 mL). Both the free Glu and the GABA content were significantly increased in soymilk hydrolysate, which is a product obtained after enzymatic hydrolysis of soymilk. After 72 h of fermentation, the GABA content in soymilk hydrolysate reached 859 mg/L while the remaining Glu was 2467 mg/L. Fermentation of soymilk hydrolysate at the optimal conditions for glutamate decarboxylase activity (initial pH 4.7, 50 °C), the enzyme catalyzing the conversion of Glu to GABA, also did not show a higher GABA production.