Screening and Identification of Lactic Acid Bacteria with High Yield of γ-Aminobutyric Acid in Traditionally Fermented Yak Yogurt in Western Sichuan Plateau

In order to screen out a lactic acid bacterium with high yield of γ-aminobutyric acid(GABA), 300 strains of lactic acid bacteria isolated from traditional fermented yak milk in the Western Sichuan Plateau were used as the research object. The qualitative and quantitative analysis of its GABA production capacity was carried out by paper chromatography and high performance liauid chromatogram, and then the high-yielding strains were subjected to in vitro tolerance experiments and intestinal adhesion experiments, and the species of dominant strains were determined. The results showed that among the 300 strains to be tested, 24 strains had the ability to produce GABA. The five strains with higher yields are: Strain 84(1.587 g/L), strain 155(1.352 g/L), strain 32(1.124 g/L), strain 146(1.115 g/L) and strain 172(1.007 g/L). Strain 84 had a survival rate of more than 20% after being treated for 3 hours in different pH environments, with a maximum of 50.83%, which was the highest survival rate among the 5 strains. The survival rate of strain 32 can be maintained at 10% to 20%, and it changes steadily in various pH environments. This indicates that strain 84 and strain 32 have good gastric juice tolerance, and the remaining three lactic acid bacteria were not tolerant to acidic environments. After reacting in simulated intestinal juice for 4 hours, the survival rate of lactic acid bacteria of strain 84 was 37.57%, and that of 32. The tolerance of strain 32 to bile salts was lower than that of strain 84. Although strain 84 had better tolerance to NaCl, it had a certain gap compared with strain 32 and it was less stable. In the adhesion experiment to intestinal cells, the adhesion ability of strain 84 was higher than that of strain 32. Through morphological characteristics, physiological and biochemical experiments and 16S rDNA gene identification, the strain 84 was determined to be Lactobacillus fermentum. This study provides a reference for the research on functional probiotics in traditional fermented yak yogurt in western Sichuan.