Mechanism of gamma-aminobutyric acid (GABA) production by a lactic acid bacterium in yogurt-sake

We examined the gamma-aminobutyric acid (GABA) content of various kinds of fermented alcoholic beverages, including sake, shochu and yogurt-sake, and found that yogurt-sake contains a high concentration of GABA, higher than the sum of the concentrations in the sake and yogurt starting materials. To investigate the GABA production mechanism, we isolated the lactic acid bacteria (LAB) probably responsible for GABA production in the liquor and identified Streptococcus thermophilus Hp as a high GABA-producer and S. thermophilus Lp as a low GABA-producer. Cell extract from S. thermophilus Hp showed much higher glutamate decarboxylase activity than that from S. thermophilus Lp. During production of yogurt-sake using commercially available sake and yogurt produced with S. thermophilus Hp, the GABA increased over time, while the L-Glu was almost completely consumed. Moreover, by using sake supplemented with L-Glu, we successfully elevated the GABA concentration in yogurt-sake. By contrast, no GABA production was detected in yogurt-sake prepared using S. thermophilus Lp. These results indicate that LAB with highly active glutamate decarboxylase is responsible for GABA production in yogurt-sake. Our findings suggest GABA-enriched drinks are easily produced using yogurt and provide potentially useful information for production of other GABA-enriched foods.