The Study Of Physiological Activity In Vitro Of Streptococcus Thermophilus And Their Metabolic Products Exopolysaccharide

The Streptococcus thermophilus Q4 isolated from naturally fermented yak yogurt in Tibe tan was test object in this study.Afteractivated and cultured,which antioxidant activity,degradation ability of cholesterol and antibacterialablity were respectively studied in vitro.Then fermentation conditions of expolysaccharide produced by Q4 were optimized,and the expolysaccharide was further purified.Finally,antioxidant activity,degradation ability of cholesterol and antibacterial ablity of expolysaccharides of before and after purification were studied in vitro.The results were as follows:1 Different components?supernatant,mycelidium,no cell free extracts and heat and killed bacteria?of Q4 had different antioxidant activity and degradation ability in vitro,and which increased with increasing of the concentration.The antioxidant activity of supernatant and mycelidium were stronger,the antioxidant activity of no cell free extracts and heat and killed bacteria were weaker.The degradation abilityof supernatant was better than other contents,and itsdegradation rate was?58.64±2.37?%when the concentration was up to10¹⁰CFU/mL.Best bacteriostatic effectof supernatant,mycelidium,no cell free extracts and heat and killed bacteriaagainst different pathogenic bacteria was Staphylococcus aureus,and inhibitionzone was?18.7±0.81?mm,inhibition zone of Bacillus subtiliswas?14.36±0.34?mm,which against bacteriostatic effect of ohther pathogenic bacteria were weaker.against the same pathogenic bacteria was supernatant>no cell free extracts>mycelidium>heat and killed mycelidium.2 The optimal fermentation conditions on the yield of?Q4?expolysaccharide were determined by response surface methodology?RSM?:initial pH 6.8,fermentation time 33 h and fermentation temperature 41?.Under the optimal conditions the corresponding response value for extracellular expolysaccharide production was 268.42 mg/L,compared with the previous EPS contents?89.43 mg/L?,which was increased 3 times.3 After the crude EPS was purified by DEAE Cellulose-52 column chromatography and gel filtration purification Sepharose CL-6B,then the purity of them were identificated and obtained neutral expolysaccharide EPS1 and acidic expolysaccharides EPS2 of higher purity and homogeneous distribution.4 Expolysaccharide of before and after purification had different antioxidant activity in vitro,and which graduallyenhanced with increasing of theconcentration of expolysaccharide.Antioxidant activities of them was the CEPS?crude EPS?>EPS2>EPS1.Polysaccharide of before and after purification against different pathogenic bacteria was Aspergillus Niger,Staphylococcus aureus,Bacillus subtilis,E.coli,Saccharomyces cerevisiaeyeast,and against the same pathogenic bacteria was CEPS>EPS2>EPS1.The minimum inhibitory concentration of CEPS with the best antibacterialeffectwere 2.5mg/mL,5mg/mL,5mg/mL,10mg/mL and10mg/mL against Aspergillus Niger,Staphylococcus aureus,E.coli,Bacillus subtilis and Saccharomyces cerevisiaeyeast,respectively.In conclusion,The Streptococcus thermophilus Q4 with goodpropertiessolated from naturally fermented yak yogurt in Tibetan and its secondarymetabolites called expolysaccharide had better antioxidant activityand degradation ability and antibacterial effect in vitro,which not only can providetheoretical foundation and guiding significance for development and utilization of lactic acid bacteria resources in yak milk,but can providescientific theoretical basis for functional food of lactic acid bacteria fermentated for the further research.