Screening And Functional Evaluating Of Anti-oxidative Lactic Acid Bacteria In Traditional Fermented Milk

10 traditional fermented yoghurt,which were collected from Shangri-La region of Yunnan,were isolated and purified by traditional microbial isolation and culture techniques.Experiments were conducted to evaluate the antioxidant properties,acid and bile resistance properties of Lactic Acid Bacteria in vitro.Combined with its antioxidant properties and digestive resistance,screening for Lactic Acid Bacteria with high antioxidant activity and good resistance.At the same time,the target strain was identified by API 50 CH physiological and biochemical identification method and 16 S rDNA sequence homology analysis.Aging mouse model,which was induced by D-galactose,was constructed to evaluate the antioxidant activity of Lactic Acid Bacteria.The main results of this paper are as follows:(1)18 strains of Lactic Acid Bacteria were obtained from traditional fermented yoghurt collected from Shangri-La,including 10 Lactobacillus plantarum strains,4 Lactobacillus paracasei strains,4 Lactobacillus fermentum strains.12 strains have up to 100% homology to the Lactic Acid Bacteria known in GeneBank database;while 6 strains have up to 99% homology.(2)Study on the antioxidant activity of the intact cells and cell-free extracts(109 CFU/mL),we found that L4,L5,L8,L14 and L18 showed higher antioxidant activity.The cell-free extract of L4 demonstrated high hydroxyl radical scavenging ability by 34.89%,equivalent to 0.40 mg /mL of vitamin C.The intact cells of L8 showed highest superoxide anion free radicals by 22.89%,while the cell-free extract of L12 demonstrated highest superoxide anion free radicals by 28.78%,equivalent to 0.20 mg/mL of vitamin C.The intact cells and cell-free extract of L5 showed highest reducing power by 86.18% and 89.69%,respectively.In addition,the reducing power of intact cells and cell-free extract showed a certain relevance.The intact cells of L14 demonstrated the highest anti-lipid peroxidation capacity by 62.48%,while the cell-free extract of L13 and L14 showed the higher anti-lipid peroxidation capacity by 48.04% and 46.21%,which were equivalent to 0.30~0.40 mg/mL of vitamin C.(3)The survival rate of Lactic Acid Bacteria in gastric acid at pH=3.0 and the tolerance to different concentrations of bile salt and NaCl were studied.The results showed that L6 and L14 had good resistance ability.(4)Combined antioxidant activity with resistance ability,L14 was the target strain of the 18 strains.L14 was identified as Lactobacillus paracasei subsp.Paracasei by physiological and biochemical characteristics identification.Named Lactobacillus paracasei subsp.Paracasei L14.(5)The effects of L14 on the antioxidant system of aging mice were carried out by animal experiments.The results showed that L14 could increase the activity of superoxide dismutase(SOD),total antioxidant capacity(T-AOC),glutathione peroxidase(GSH-Px)and decrease the content of malondialdehyde(MDA)in the serum of aging mice.In addition,a significant reduction in triglyceride(TG),low density lipoprotein cholesterol(LDL-C),total cholesterol(T-CHO)and increase in high density lipoprotein cholesterol(HDL-C)in serum of aging mice.At the same time,we found that L14 can improve the pathological changes of liver,increase the expression of Catalase,SOD1,SOD2,Gsh1 in liver and spleen,which indicated that L14 had good antioxidant effect in the body and could improve the antioxidant activity of mice in a certain extent.