Preparation screening, production optimization and characterization of exopolysaccharides produced by Lactobacillus sanfranciscensis Ls-1001 isolated from Chinese traditional sourdough.

The present study focused on preparation screening, production optimization and characterization of exopolysaccharides (EPS) produced by Lactobacillus sanfranciscensis isolated from a Chinese traditional sourdough sample. In addition, in vitro antioxidant activity of pure EPS was determined. A total of 51 strains of L. sanfranciscensis were screened, and L. sanfranciscensis Ls-1001 was proved as the most abundant crude EPS producing strain, which was selected for further EPS optimization and characterization. The optimized conditions resulted in around 31% increase in EPS production (final yield: 249.30 mg/L) and included: maltose 25 g/L, yeast peptone 10.24 g/L and fresh yeast extractives (FYE) 12.92 mL/L. HPLC analysis showed that pure EPS contained only glucose monomers, indicating that it was a kind of homopolysaccharides. FTIR spectroscopy revealed the presence of hydroxyl and carbonyl groups. NMR analysis confirmed that EPS contained α-glycosidic bond and pyranose residue. The EPS showed strong in vitro antioxidant activity.