Production, purification and structural study of an exopolysaccharide from Lactobacillus plantarum BC-25

The exopolysaccharides (EPS) produced by Se-enriched Lactobacillus plantarum BC-25 was purified to illustrate its structure and conformational characterization. The yield of EPS (324.80 mg/l) was obtained with a sodium selenite concentration of 6 μg/ml. The results indicated that the EPS was soluble in water, but insoluble in organic solvents. The molecular weight of this highly thermal stability EPS was 1.83 × 104 Da and 1.33 × 104 Da with or without Se enriched respectively. The EPS was composed of mannose, galactose and glucose in a molar ratio of 92.21:1.79:6.00 and 91.36:2.44:6.20 with or without Se. This compound had a backbone of (1 → 2)-linked Man, (1 → 2.6)-linked Glc, (2 → 6)-linked Man, and (2 → 6)-linked Gal confirmed by GC–MS. IR analysis suggested that the EPS belonged to heteropolysaccharide with a pyran group, with possible presence of SeO and CSeC residues that Se may substitutes CH3 in −OCH3 in the polysaccharide as confirmed by NMR spectroscopy.