Abstract:An exopolysaccharide-producing bacterial strain ZX-5 was isolated from lake sediments, and identified as Paenibacillus sp. by 16S rRNA gene sequencing and phylogenetic tree analysis. The yield of exopolysaccharides was determined by the sulfuric acid-phenol method. In the meantime, single factor tests and response surface tests were carried out on six fermentation conditions including pH, temperature, carbon source and concentration, and nitrogen source and concentration, with the analysis of variance performed on the quadratic model. Results showed that sucrose concentration, temperature and sodium nitrate concentration had a great influence on sugar production, and there were significant interactions. Response surface tests revealed that the optimal sugar-producing conditions were: the initial sucrose concentration, 200 g/L; sodium nitrate, 3 g/L; K2HPO4·3H2O, 3 g/L; KH2PO4, 1 g/L; MgSO4·7H2O, 0.50 g/L; pH, 6.00; fermentation temperature, 20 ℃. Under the optimal conditions, the yield of exopolysaccharides from shake-flask fermentation with strain ZX-5 was 34.55 g/L, which was 2.01 times the base level of 17.15 g/L. The investigations on the moisturizing properties of the exopolysaccharides from the strain ZX-5 showed that in a dry environment, the moisture residual rate of the exopolysaccharide after 38 h was 50%, which had better moisturizing properties than glycerin and chitosan. In this study, on the basis of the optimal processing conditions for exopolysaccharide production by Paenibacillus ZX-5, the moisture retention property of the polysaccharide was studied, which laid a foundation for subsequent in-depth research and development.
