Optimization And Characterization Of Exopolysaccharide Production From A New Lactic Acid Bacterium:Weissella Cibaria 27

Exopolysaccharide(EPS)from lactic acid bacteria(LAB)is a carbonhydrate compound,which synthesized and secreted to extracellular during the cell growth process.Due to its special physicochemical properties and qualities,like anti-oxidant and bacteriostasis,EPS is widely applied in food(additives for dairy products),medicine(blood plasma substitutes)and other fields.In this study,sucrose addition with optimization of culture conditions was performed to improve the yields of EPS from Weissella cibaria 27(W27).The physicochemical properties of the EPS,as well as the biological characteristics,hydrophobicity and bacteriostasis of W.cibaria 27 were further analyzed.The results are shown as follows:W.cibaria 27 is found to be a good exopolysaccharide producer with sucrose as additive and the yield of EPS could be improved from 0.082 g/L to 9.8 g/L while 2%(w/w)sucrose was added at 30?.The results of single-factor assay indicated that the EPS production declined when the cultivation temperature increased or initial pH value decreased.Meanwhile the cultivation duration had to be controlled at a proper time,too long or too short significantly affecting the yield.The optimum yield of EPS(25.65 g/L)was obtained when 6%(w/w)sucrose was added and cultured at pH 6.2,22? for 24 hours.In this study,the major component of EPS was dextran(87.2%),which is mainly made up of glucose(97%in dextran),and its structure is identified as?-(1?6)-dextran.Analysis by High Performance Size Exclusion Chromatography(HPSEC)showed that the molecular weight of EPSs varied from 1.2×107 to 3.9×107 Da and the viscosity was enhanced while the sucrose concentration increased from 0 to 6%(w/w).Scanning electron microscope(SEM)and contact angle results revealed that the W27 cells become shorter,stickier and more hydrophobic when sucrose was added.From the results of bacteriostatic tests,W27 cultured with sucrose was able to inhibit the growth of Bacillus cereus and Escherichia coli more sufficiently,but no inhibition on Staphylococcus aureus.W27 could use sucrose and glucose as carbon source,but can not utilize lactose.Besides,the metabolic compounds of lactic acid(LA),acetic acid(AA)and ethanol were synthesized during the growth of W27.Finally,we provided a new approach to improve the yields of EPS,which is from 0.082 g/L to 25.65 g/L by adding sucrose.The properties and structure of the EPS were investigated and will be helpful for the application of EPS.