Screening, identification and flask fermentation optimization of a high-yield γ-aminobutyric acid Enterococcus raffinosus strain

Abstract:

[Objective] A high-yield γ-aminobutyric acid (GABA) producing lactic acid bacterium (LAB), strain M1 was isolated from pickled Chinese vegetables by our laboratory. [Methods] Its physiological and biochemical characteristics and 16S rDNA sequence were analyzed. GABA fermentation medium, based on MRS medium, was optimized using single factor test and orthogonal design, as well as the shake flask condition for GABA fermentation. [Results] The results indicated that the morphological, physiological and biochemical characteristics of strain M1 were accorded with Enterococcus family. The identity between the obtained 16S rDNA sequence of strain M1 and Enterococcus raffinosus SS1278 was up to 99%, strain M1 was accordingly identified as Enterococcus raffinosus. Moreover, its GABA fermentation medium was optimized, and the shake flask condition for GABA fermentation was: inoculum of 10%, growing temperature at 30 °C, initial pH at 5.5, fermentation period of 60 h and monosodium glutamate substrate concentration of 10%. Under these conditions, GABA yield by flask fermentation achieved a 1.22-fold increase. [Conclusion] The isolated E. raffinosus M1 strain reveals its potential for industrial fermentation of GABA.

Key words:γ-Aminobutyric acid, Enterococcus raffinosus, Pickled Chinese vegetables, Isolation and identification, Medium and fermentation optimization