Characteristics of Potential Gamma-aminobutyric Acid-producing Bacteria isolated at Korean and Vietnamese Fermented Fish Products.

Gamma-aminobutyric acid (GABA) is a neurotransmitter that exerts several physiological functions and positive effects on human health. The aim of this study was to isolate and characterize the strains that had GABA-producing abilities from various fermented fish products. A total of 91 acid-producing strains were isolated from 41 samples of fermented fish products, and 27 strains showing GABA-producing abilities were identified by the 16S rDNA sequences. The 31% strains tolerated at high salty environment of 10-20% in the complete fermentation of fish sauces. All the 27 isolates produced GABA at various concentrations in the range of 5 to 454 mM. GABA-producing isolates were identified as lactic acid bacteria of 14 strains, which included 12 Lactococcus lactis , one Enterococcus faecium , and one Lactococcus pentosus ; eight Bacillus cereus group, which included seven B. thuringiensis and one B. cereus ; and five Staphylococcus spp. Interestingly, with Vietnamese fish sauces, we mostly identified species of B. thuringiensis and Staphylococcus spp., while with Korean fermented fish products, the majority of the strains identified belonged to L. lactis . Among the strains, B. thuringiensis LH2134 produced the high levels of GABA of 366 mM among the strains identified from Vietnamese fish sauces, whereas L. lactis LA43, a new strain isolated from Korean Jeotgal -salted shrimp paste, produced the highest amount of GABA of 454 mM and the glutamate concentration in the medium was essential for GABA accumulation. Therefore, such the isolates might be the good starters for development of more GABA reinforced foods of fermented fish products.