Acid Production Characteristics Of Lactobacillus Casei N1115 And Its Application In Fermented Milk

Lactobacillus casei has been widely applied in dairy processing as a health-beneficial lactic acid bacterium,and together with Lactobacillus acidophilus and Bifidobacterium,they were known as "three health-promoting bacteria".In this paper,acid production characteristics of Lactobacillus casei N1115 isolated from traditional fermented dairy products and its therapeutic effect on mice with constipation were studied.To determine the acid fermentation characteristics of L.casei N1115,acid fermentation kinetics at different temperatures,pH and lactose concentration of basal medium were studied using Gompertz model.Results showed that under optimum growth temperature and pH(37?,pH5.5),and lactose concentration(5g/L),the highest rate of acid production was obtained;Although growth rate of the strain decreased at 20?,the total acid produced was unchanged in a prolonged fermentation.This indicated L.casei N1115 had a strong acid-producing capacity at lower temperatures,which commonly considered as a post-acidification causing effect in yogurt fermentation.To weaken the acid-producing activity,L.casei N1115 was treated with heating at 65? for 25 s or sonication at 140 W,8min,respectively.Results showed both treating methods can effectively weaken the acid-producing activity of L.casei N1115,but treatment with sonication deteriorated the texture of fermented milk.GC and chemical analysis of fermented milk of L.casei N1115 found three kinds of short chain fatty acids including lactic acid,acetic acid and benzoic acid.And the key enzymes of acid producing were lactase and H+-ATPase.After these tests,L.casei N1115 was added into skimmed milk as a nonstarter strain.The optimum fermentation properties of strain were studied using response surface analysis.Results showed that adding 4%(w/w)inulin would greatly increase the fermentation process at 45?.When the amount of inulin lowered to 2%,increasing inoculation amount of L.casei N1115 could achieve similar result.And addition of more than 4% of inulin greatly affected the viscosity and hardness of fermented milk.Finally,the probiotic effect of L.casei N1115,in vivo,was examined using constipation mice model caused by oral gavage of loperamide hydrochloride for 15 days.Results showed feeding different dose of fermented milk of L.casei N1115 had no effect on mice growth compared with control group.But the intestinal propulsion rate of the experimental group was significantly improved(p<0.05),and defecation volume was higher than that of the control group(p<0.05),and the two index of mice from high dose group was similar to that of healthy mice(Blank group).Short chain fatty acids in mouse feces were analyzed and the result showed that the contents and kinds of organic acids in mice fed with fermented milk of L.casei N1115 were significantly increased(p<0.05).Furthermore,the number of intestinal stromal cells in the experimental group was significantly higher than that in the control group in physiological analysis of the intestinal tract of mice.These results showed L.casei N1115 fermented milk had a positive therapeutic effect on mice with constipation.