Screening And Characterizing Of Lactic Acid Bacteria With High Antioxidant Activity From The Tibetan Plateau

As a natural antioxidant,lactic acid bacteria has been given an increasing amount of attention on account of the safe and effective characteristics.Due to the strong ultraviolet rays and hypoxia characteristics in the Qinghai Tibet Plateau,the local lactic acid bacteria may have the ability to resist oxidative stress in such extreme environments.In this experiment,34 strains of lactic acid bacteria isolated from traditional fermented yak yogurt and natural Elymus nutans silage in the Tibetan plateau,as well as standard bacteria Lactobacillus rhamnosus GG(LGG;ATCC53103),were chosen for test strain.Initially,lactic acid bacteria with high antioxidant activity were screened through an in vitro antioxidant test.The enzymatic mechanism of lactic acid bacteria with antioxidative activity were studied.The probiotic characteristics of lactic acid bacteria with high antioxidant activity were evaluated in vitro,and the lactic acid bacteria strains with good characteristics were selected to carry out in vivo antioxidant test.The following results were obtained:(1)All lactic acid bacteria showed some tolerance ability to hydrogen peroxide.Among them,11 strains of lactic acid bacteria can grow satisfactorily at 2 mmol/L hydrogen peroxide,which showed strong tolerate ability to hydrogen peroxide.Certain free radical scavenging abilities were observed in 11 strains of lactic acid.Among them,strains 24-7 and BX62 were the standouts.When the cell concentration or the cell-free extract concentration was 1010 CFU/mL,the scavenging rate of 24-7 and BX62 on DPPH radical were 73.88% and 75.17%,respectively.The scavenging rate on hydroxyl radical were 82.46% and 81.13%,respectively,and the scavenging rate on superoxide anion radical were 62.75% and 65.85%,respectively.(2)24-7 showed the strongest tolerance ability to hydrogen peroxide and scavenging ability on hydroxyl radical,which also had the highest GSH-Px levels.BX62 showed the strongest scavenging ability on the superoxide anion radical,and also had the highest SOD levels.It was further confirmed that GSH-Px expressed the antioxidant activity by scavenging hydrogen peroxide and hydroxyl radical,while SOD expressed the antioxidant activity by scavenging superoxide anion radical.The T-AOC levels in the supernatant liquid were all higher than that in the 1010 CFU/mL of cell-free extracts.The T-SOD levels in the 1010 CFU/mL of cell-free extracts were all higher than that of the supernatant liquid.There was not detected activity of GSH-Px in the supernatant liquid,and it had high levels of GSH-Px in the cell-free extracts.(3)In the simulated gastrointestinal tract test,there were 7 strains of lactic acid bacteria showing a survival rate of over 90%,with the survival rate of the other strains were all over 87%.Strains 3-4,24-7,BX62 and LGG all displayed a survival rate of over 60% after being digested in simulated gastric juice for 24 h,exhibiting sufficicent tolerance to simulated intestinal juice.When grown in the MRS culture medium containing 0.3% bile salt,the lag phase of the lactic acid bacteria were all within 3 h during the bile salt tolerance test,demonstrating that all strains had definite tolerance ability to bile salt.Among them,XS14,BX62 and LGG were the standouts,the lag periods were all within 2 h.BX62 and LGG displayed strongest hydrophobicity capacity,being 43.09% and 46.15%,respectively.In addition,strains 21,24-7 and XS40,BT36 also showed a strong hydrophobic capacity.(4)The intake of L.casei 24-7 and L.plantarum BX62 could significantly increase the weight gain of aging model mice.There were noteworthy effects on the brain and liver of mice,though not on the spleen or kidney.Compared with the aging model group,the T-SOD,GSH-Px,T-AOC levels and MDA content in the liver,brain and serum of mice fed with lactic acid bacteria had significantly improved.The GSH-Px and T-AOC levels in liver and T-SOD levels in brain and serum even returned to normal levels.The above results indicate that the two strains of L.casei 24-7 and L.plantarum BX62 screened in this study can be used as the candidate probiotics characterized by high antioxidantive activities,and have potential application value in the future.