Isolation of high γ-aminobutyric acid-producing lactic acid bacteria and fermentation in mulberry leaf powders.

γ-Amino butyric acid (GABA) has numerous roles in physiological processes, including neurotransmission, and induction of hypotensive, diuretic and tranquilizer effects. The present study aimed to produce GABA-enriched mulberry leaf powder by using a strain of high GABA-producing SS6, which is isolated from fermented mulberry fruits. A total of 37 strains of lactic acid bacteria (LAB) were isolated from fermented mulberry fruits strains of high GABA-producing were selected. The isolated LAB was analyzed using thin-layer chromatography. SS6 was used as a starter culture for the fermentation of mulberry leaf powder to produce GABA. The mulberry leaf powder was treated with 10% saccharose, 6% peptone, 1.6% KHPO, 1% L-sodium glutamate at 35°C for 36 h (each treatment was applied whilst the others were kept constant), in a mixture with a water content of 60%, with the respective LAB strain that was fermented by incubation at 30°C for 6 h. The results indicated that the SS6 strain produced significantly higher GABA contents in the fermentation broth compared to the other strains (P<0.05). Addition of 10% saccharose, 6% peptone, 1.6% KHPO and 1% L-sodium glutamate significantly triggered the production of GABA compared with that in the groups void of those additives (P<0.05). Furthermore, the water content, treatment time, amount of LAB inoculated and the incubation temperature also significantly affected GABA production compared with untreated groups under the aforementioned conditions (P<0.05). In conclusion, 10% saccharose, 6% peptone, 1.6% KHPO, 1% L-sodium glutamate, and a 60% water content at 35°C significantly improved and enhanced GABA production. The present study provided a basis for the production of GABA, which may be utilized by the pharmaceutical and food industry.