Study On The Relationship Between The Exopolysaccharides Production And Environmental Stress Tolerance Of Lactobacillus Plantarum

Exopolysaccharide(EPS)has many physiological activities,such as regulating immunity,anti-tumor,anti-oxidation,reducing cholesterol and so on.At present,many studies are based on the structure,functional characteristics and biosynthesis of EPS,but the regulation mechanism of EPS synthesis is not clear.Therefore,Lactobacillus plantarum was isolated and identified from feces and saliva samples of longevous people in Guangxi Province and traditional fermented dairy products from Xinjiang Province.The correlation between the yield of EPS and environmental tolerance was studied to explore the potential influencing factors of EPS synthesis regulation,so as to provide theoretical basis for revealing the potential regulatory mechanism of EPS of L.plantarum.The main research contents are as follows:1.Isolation and identification of L.plantarum.101 strains of lactic acid bacteria were isolated from feces and saliva from longevous people which 11 strains were L.plantarum(10 strains from feces and 1 strain from saliva),accounting for 10.89%of the total number of lactic acid bacteria;44 strains were isolated from traditional fermented dairy products from Xinjiang,among which 5 strains were L.plantarum,accounting for 11.36%of the total number of lactic acid bacteria.2.Study on the growth and metabolic characteristics of L.plantarum.The dynamic process of growth and metabolism of 16 strains of L.plantarum were explored by measuring the pH,acidity,viable count and EPS production of L.plantarum in SDM medium.The results showed that the maximum amount of EPS produced by 16 strains of L.plantarum ranged from 9.2 mg/L to 26.05 mg/L,and the highest production was L.plantarum 58.In the first 6-10 h,the acid production rate of the strain increased rapidly,including the rapid decline of pH value and the rapid rise of acidity,and the EPS was in the rapid accumulation stage.When the fermentation time was 20 h,the number of viable bacteria began to decline,while the EPS was still in the rapid growth stage,and most L.plantarum strains reached the maximum value of EPS at 24 h.3.Tolerance of L.plantarum to environmental stress.The tolerance of L.plantarum strains with different EPS production to gastrointestinal(simulated gastric juice pH 2.5 and 3.0,simulated intestinal juice),heat,freezing,oxidative(2 mmol/L and 5 mmol/L),9%ethanol and freeze-drying stress were studied.The survival rate of L.plantarum 58,67 and 128 with high EPS production was more than 100%when exposed to simulated gastric juice at pH 3.0.The survival rate of 16 strains of L.plantarum under other stresses had no obvious tendency in different groups.Among them,L.plantarum 97 has strong tolerance to simulated gastric juice of pH 2.5;L.plantarum 67 has strong tolerance to simulated intestinal juice;L.plantarum 58 and 11 have strong tolerance to bile salt;L.plantarum Y-5 has superior heat,freezing and freeze-drying resistance;L.plantarum 58 can tolerate 5 mmol/L hydrogen peroxide;L.plantarum p-12 and 11 had good tolerance to 9%ethanol.4.Study on the correlation between EPS of L.plantarum and its tolerance to environmental stress.The correlation between EPS of L.plantarum and its survival rate under environmental stress was analyzed by analysis software.The results showed that the total EPS of 16 strains of L.plantarum were significantly and moderately positively correlated with the survival rate under simulated gastric juice pH 3.0 stress(p<0.01).Among them,the total EPS production of L.plantarum from human origin was highly significantly and moderately positively correlated with the survival rate of simulated gastric juice pH 3.0,simulated intestinal juice and 2 mmol/L hydrogen peroxide stress(p<0.01),and the total EPS production of L.plantarum from no-human origin was highly significantly and strongly correlated with the survival rate of simulated gastric juice pH 3.0(p<0.01).The average EPS production of 16 strains of L.plantarum was significantly and moderately positively correlated with simulated gastric juice pH 3.0 and survival rate under simulated intestinal juice stress(p<0.01).The average EPS production of L.plantarum from human origin was significantly and moderately positively correlated with simulated gastric juice pH 3.0 and intestinal juice(p<0.01).The average EPS production of L.plantarum from no-human origin was significantly positively correlated with the survival rate and 9%ethanol stress(p<0.01).The results showed that the EPS synthesis of L.plantarum might be related to simulated gastric juice pH 3.0 and simulated intestinal juice environment.