Purification and characterization of dextran produced by Leuconostoc pseudomesenteroides PC as a potential exopolysaccharide suitable for food applications

An exopolysaccharide (EPS)-producing bacterial strain, PC, was isolated from pickled Chinese cabbage and identified as Leuconostoc pseudomesenteroides. EPS yield was up to 30.5 g/L when bacteria were cultivated in Man-Rogosa-Sharpe (MRS) medium containing 5% sucrose at 30 degrees C for 48 h. Further analysis by gas chromatography, high performance size exclusion chromatography, and nuclear magnetic resonance revealed that the EPS consisted of glucose with alpha-(1 -> 6) linkages and had a molecular weight of 3.13 x 10(6) Da. Scanning-electron microscopy demonstrated an irregular sheet structure and porous surface, and lumps with an average height of 77.803 nm were observed by atomic force microscopy. Physical-chemical analysis showed that the EPS exhibited excellent thermal stability and possessed high viscosity at high concentration, low temperature and acidic pH, making it promising to be used in thermal processed foods and fermentation of acidic food products. Milk solidification test also suggested the promising potential for application as a dairy and food additive since the EPS could activate the solidification of sucrose-supplemented milk. Taken together, this study provides a commercial guidance for the practical application of PC EPS in food industry and other areas.