Screening and Tolerance of Degrading Nitrite-Lactant Bacteria in Fermented Yak Milk of Western Sichuan Plateau

In this paper,195 strains of lactic acid bacteria isolated from the yak milk from the western Sichuan Plateau were used as the research object. The nitrite degradation ability was determined by colorimetric method,and the strain with strong nitrite degradation ability was screened out. These dominant strains were cultured in artificial gastric juice,artificial intestinal juice,artificial bile and high salt in four simulated artificial gastrointestinal digestive environments,and their tolerance was measured.The results showed that the degradation rate of 195 lactic acid bacteria nitrite ranged from 35.79% to 96.51%,among which the strain with degradation rate of 80%~90% accounted for 54.87%,and only 1.54% of the strains had nitrite degradation rate below 50%. There were 3 strains with strong nitrite degradation ability(degradation rates were more than 95%). The viable counts of these three strains in artificial gastric juice decreased with the prolongation of culture time. After 3 h of culture,the viable counts of strains 5,26 and 150 at pH5.5 were 3.7,3.6,4.1×10⁸ CFU/mL. After 4 h of culture in artificial intestinal juice,the viable counts of strains 5,26,and 150 were 4.3,6.8,and 5.3×10⁸ CFU/mL,respectively. After cultured for 24 h in different bile salt gradient medium,the number of viable bacteria of the 3 strains decreased with the increase of bile salt concentration,and remained above 10⁸ CFU/mL. The number of viable bacteria after 24 h culture in high salt environment decreased with the increase of salt concentration,and the number of viable bacteria was 10⁸ CFU/mL or more. Conclusion:The ability of 195 strains of lactic acid bacteria isolated from traditional fermented yak milk in western Sichuan Plateau to degrade nitrite is quite different. The strain with strong nitrite degradation ability has good tolerance to in vitro simulated digestion environment. It provides a theoretical basis for applications in the pharmaceutical,food and biological fields.