Study On The Functional Properties Of Two Lactobacillus Plantarum Strains And Their Improvement In The Quality Of Goat Yogurt

Goat milk is rich in protein,lipid,minerals and vitamins and also abundant in biologically active ingredients,such as lactoferrin,epidermal growth factor and insulin-like growth factor,which have high nutritional value and health benefits.The dairy goat industry in Shaanxi Province has developed into the most advantageous characteristic industry in China,among which the development of functional goat yogurt products has become a vital research field of the industry.However,the lack of functional lactic acid bacteria strains has severely restricted the development of functional goat yogurt products.To solve this problem,this project intends to screen out lactic acid bacteria（LAB）with cholesterol-lowering ability and antioxidant activity from the Shaanxi Jiangshui,traditional fermented food.This could provide new strains and theoretical basis for the development of functional goat yogurt.The dominant LAB from Shaanxi Jiangshui were isolated and identified in this study,and then evaluated their cholesterol-lowering ability,antioxidant activity,acid production ability,cell surface hydrophobicity and gastrointestinal tolerance.LAB with high cholesterol-lowering function and antioxidant activity were selected,and their functional characteristics in vivo and the influence on the quality of goat yogurt were investigated.The obtained results are as follows:1.Screening of functional LAB in Jiangshui and study on their probiotic characteristicsA total of 38 Lactobacillus were isolated and identified,which were classified into Lactobacillus plantarum,Lactobacillus fermentum and Lactobacillus delbrueckii sp.The strains of L.plantarum JS5 and L.plantarum JS19 showed good acid production ability,excellent surface adhesion,and tolerance to acid and bile salt.Meanwhile,L.plantarum JS5 performed stronger cholesterol-lowering ability and L.plantarum JS19 showed higher antioxidant activity.Therefore,these two strains of Lactobacillus plantarum will be used for subsequent functional characteristics and application studies.2.Study on the improving hypercholesterolemia by L.plantarum JS5L.plantarum JS5 was fed to mice with high cholesterol diet,and mice’ serum indices and intestinal flora were analyzed to evaluate its functional characteristics.It was found that L.plantarum JS5 could significantly reduce the body weight growth rate and epididymal fat index,relieve liver tissue damage,lower the levels of AST,ALT,and TC in serum.Meanwhile,L.plantarum JS5 could restore the intestinal flora diversity of high cholesterol mice,and promote the growth of some probiotics,such as Eubacterium coprostanoligenes_group,Faecalibaculum,Blautia,etc.According to the COG function prediction,L.plantarum JS5 showed improvement in defense mechanism,signal transduction mechanism and cell activity pathway.The results indicated that L.plantarum JS5 can reduce serum cholesterol,improve intestinal flora structure,effectively control dietary obesity in mice,and prevent the deterioration of hypercholesterolemia in mice.3.Study on the alleviating injury of colitis mice by L.plantarum JS19Through the establishment of acute and chronic colitis injury models,the intervention effect of L.plantarum JS19 on model mice was studied.It was found that administration of L.plantarum JS19 relieved weight loss and shortening of the colon caused by acute and chronic colitis.The levels of anti-inflammatory cytokines IL-4 and IL-10 were increased while the pro-inflammatory cytokines IL-1 and TNF-α were slightly decreased.L.plantarum JS19 also enhanced the activity of SOD and GSH-Px in the liver,decreased the content of MDA,and attenuated the MPO activity of the colon.In addition,L.plantarum JS19 up-regulated the relative abundance of beneficial microflora such as Bacteroidaceae,Prevotellaceae and Eubacterium,and down-regulated the relative abundance of Enterobacteriaceae,Anaerostipes,and Escherichia-Shigella,which indicated that L.plantarum JS19 could alleviate the colon damage of mice by enhancing the body’s antioxidant capacity,partially eliminating the damage of inflammatory factors to the intestine,and adjusting the structural balance of intestinal flora.4.Research on L.plantarum JS5 and JS19 to improve the quality of goat yogurtL.plantarum JS5 and JS19 were used to assistant ferment goat milk and evaluate its performance.The result showed that L.plantarum JS5 and JS19 had poor coagulability when they were fermented individually in goat milk.Taking the only YO-MIX187 fermented as the control group,the addition of L.plantarum JS5 and JS19 could improve the titratable acidity and apparent viscosity,lower the hardness and adhesiveness of goat yogurt,and increased total number of LAB colonies in goat yogurt.It could also increase the content of acetaldehyde and diacetyl,reduce the cholesterol content in goat milk,and enhance its antioxidant activity.Therefore,these two strains of Lactobacillus plantarum can be used as accessory starter to improve the quality of goat yogurt.In summary,the L.plantarum JS5 with strong cholesterol-lowering ability and the L.plantarum JS19 with high antioxidant activity screened out from Jiangshui showed excellent probiotic properties in vitro,and exerted the functional properties of lowering blood cholesterol and enhancing the liver antioxidant activity in vivo.Further both of these two Lactobacillus plantarum strains could be used as accessory starter for milk fermentation to improve the yogurt flavor and increase its functional characteristics,which has a broad application prospect for the development of functional goat yogurt.