Isolation Of Exopolysaccharide-producing Leuconostoc Pseudomesenteroides XG5 And Structure And Properties Analysis Of Exopolysaccharide

Microbial exopolysaccharides(EPSs)have been widely used in food,medicine,chemistry and other fields because of their biological activities and physicochemical properties,such as antitumor,anti-inflammatory,antiulcer,antioxidant,antibiofilm,immunomodulatory and high water holding capacity.Our country has abundant products fermented by lactic acid bacteria(LAB),and the resources of LAB are rich,the objectives of this work were to isolate and identify EPS-producing LAB strain from homemade wine,and the structural characterization and physico-chemical properties of EPS was investigated.One EPS-producing strain named XG5 was isolated from homemade wine by combining with appearance of“ropy”strand colony formed on the screening plate and the EPS yield.The strain XG5 was identified as Leuconostoc pseudomesenteroides through morphological,biochemical,physiological tests and 16S rDNA sequencing analysis.The strain L.pseudomesenteroides XG5 was cultivated in MRS-S medium supplemented with 12.5%sucrose at 30?for 48 h under a static condition,to gain the fermented milk containing EPS.After centrifugation,eliminating the proteins,ethanol precipitation,dialysis and lyophilization,the crude EPS was obtained.The further purification of the crude bacterial EPS solution was subjected by gel-filtration chromatography using a Sephadex G-100 column.The purified EPS solution was pooled,concentrated,lyophilized and yielded.The yield of purified XG5 EPS achieved to 35.5 g/L.The purity determination of the EPS was conducted by UV spectroscopy,the result appeared that the EPS had the absence of nucleic acid and peptide.High-performance size-exclusion chromatography showed the Mw was 2.6×10~6 Da.The gas chromatography showed that the EPS was a dextran composed exclusively of glucose.Fourier transform infrared spectra and nuclear magnetic resonance spectra revealed that the EPS was a dextran containing D-glucose residues in a linear chain with consecutive?-(1?6)linkages.Scanning electron microscopy of the EPS appeared a highly branched and porous structure.Rheological studies showed that the EPS had higher viscosity in 0.1 M KCl solution,at 25?,or at pH=4,the viscosities were 635,685 and 651 mPa,respectively.Thermal gravimetric analysis and differential scanning calorimetric indicated that the EPS had excellent thermal stability with a degradation temperature of 313.80?and melting point at 274.14?.Water solubility index and water holding capacity of XG5dextran were 90.2%and 412%respectively.In the study,the EPS produced by L.pseudomesenteroides XG5 had a high yield,and the EPS was a linear dextran.The dextran showed high viscosity,excellent thermal behavior,high water solubility and water holding capacity promoting its application in foods,medicine,cosmetics and other fields.