Screening and Optimization of Fermentation Conditions for γ-Aminobutyric Acid-Producing Enterococcus faecium and Analysis of Probiotic Properties

In order to broaden and evaluate the microbial resources with capability of producing γ-aminobutyric acid (GABA), lactic acid bacteria (LAB) strains were isolated from Sichuan pickles. The higher GABA-producing LAB strain was identified using physiological and biochemical tests and phylogenetic analysis. And the fermentation conditions were also optimized using the response surface methodology. Meanwhile, the probiotic properties of GABA-producing strain were analyzed. The results showed that strain AB157 produced higher yield of GABA analyzed by high performance liquid chromatography (HPLC), and the content of GABA reached 1.08 g/L. Then the strain AB157 was further identified as Enterococcus faecium using physiological and biochemical tests and 16S rRNA gene sequence analysis. The optimal fermentation conditions were as follows:L-glutamate sodium concentration 5.2 g/L, fermentation temperature 31℃, initial pH7 and fermentation time 70 h. Under the optimized conditions, the production of GABA by E. faecium AB157 reached 1.60 g/L. The probiotic characteristics results showed that strain AB157 presented high survival rates in pH2.0 and 3 g/L bile salt circumstances, reached 39% and 59% respectively. Meanwhile, the cholesterol-reducing activity of the strain reached 18.09 μg/mL. According to these results, E. faecium AB157 had better stress tolerance to acid and bile and stronger cholesterol-reducing activity. Therefore, E. faecium AB157 can be used as a potential functional LAB resource for further study.