Screening For Cholesterol-lowing Lactic Acid Bacteria In Traditionally Fermented Yak Milk And Its Probiotic Effect In Rats Fed A High-cholesterol Diet

Studies have indicated that high level of cholesterol in the blood is closely related to cardiovascular disease. At present, cardiovascular diseases have become the leading cause of death in worldwide. In recent years, studies have shown that some of the probiotic lactic acid bacteria or its fermented products have cholesterol-lowering function. More and more people pay attention to lactic acid bacteria (LAB) with probiotic properties. In this study we isolated115strains of LAB from traditional yak yoghourt in four different pastoral herdsmen home in the Golog Tibetan Autonomous Prefecture in Qinghai Province. In combination of16SrRNA sequence analysis with cholesterol-lowering ability of strains, we screened out21candidate strains. Through in vitro experiments we screened best strain with resistantence to gastrointestinal fluid and adhesion in the intestine. At last, the probiotic effect of the screened LAB strain in rats fed a high cholesterol diet was studied. The results are as follows:The results showed that115isolates could be classified as9species and subspecies. Among these strains,59strains were Lactobacillus plantarum,13strains were Lactobacillus delbrueckii suhsp. lactis,12strains were Lactobacillus paracasei,5strains were Enterococcus durans,7strains were Enterococcus faecalis,8strains were Enterococcus gallinarum,8strains were Leuconostoc mesenteroides,2strains were Leuconostoc mesenteroides subsp. mesenteroides and1strain was Lactococcus lactis subsp. lactis.In the present experimental conditions, the115strains had different ability of cholesterol-lowering, In the115strains, there are44strains (38.26%) with above50%of cholesterol clearance rate. The best ability of cholesterol-lowering was observed on the strain of Lactobacillus plantarum Lp1with75.91%cholesterol clearance rate.We selected Lactobacillus plantarum Lp3that has a good resistant performance through in vitro simulation experiment. After3h of incubation in artificial gastric juice, strain of Lp3had92.48%final survival rate. Survival rate of the strain in the artificial intestinal juice after24hours digestion was61.24%. The strain was not sensitive to bile salts, and in0.3%bile salts its lag phase was0.71h. The surface hydrophobic rate was58.41%, which indicated that the strain has a strong adhesion to the cell.Animal experimental results showed that Lactobacillus plantarum Lp3had no obvious side effects in rats and had a good cholesterol-lowering effect in high fat model rats. Lactobacillus plantarum LP3can significantly reduce serum total cholesterol, triglycerides and LDL-cholesterol levels in rats fed a high fat diet compared with the control group (P<0.05), but no difference was observed in high-density lipoprotein cholesterol.Long-term consumption of high-fat feed could reduce fecal water content of model rats and led to intestinal flora imbalance. In comparison with other two groups of rats, number of E. coli in feces of high fat fed rats group (HC) had obvious increase, the number of Bifidobacterium and Lactobacillus decreased significantly. But in high fat and LAB fed rats group (HL), the number of Lactobacillus in the feces was slightly higher than that in control group. The number of E. coli and Bifidobacteria were almost the same with the control group. The results indicated that Lactobacillus Lp3could maintain the balance of intestinal flora and increase the moisture content in faeces about6.44%compared with HC group.Analysis of cholesterol and triglyceride levels in liver tissue, cholesterol and triglyceride in the liver tissue of the high fat fed rats group (HC) were significantly higher than high fat and LAB fed rats HL group (P<0.05). It indicated that Lp3could reduce lipid deposition in liver tissue. From histology of liver steatosis, we can also draw out the above conclusion. Cholesterol and bile acid contents in feces of HL group were higher than the HC group. The result indicated that Lp3may be in the form of coprecipitation to promote cholesterol excretion and lowering cholesterol levels in the body. All the above results suggested that Lactobacillus plantarum Lp3had good probiotic effect on fatty rats.