Purification and Partial Elucidation of the Structure of an Antioxidant Carbohydrate Biopolymer from the Probiotic Bacterium Bacillus coagulans RK-02

An exopolysaccharide (EPS) was isolated from Bacillus coagulans RK-02 and purified by size exclusion chromatography. The purified, homogeneous EPS had an average molecular weight of ∼3 × 10⁴ Da by comparison with FITC-labeled dextran standards. In vivo evaluations showed that, like other reported polysaccharides, this EPS displayed significant antioxidant activity. FTIR spectroscopy analysis showed the presence of hydroxy, carboxy, and α-glycosidic linkages and a mannose residue. GC analysis indicated that the EPS was a heteropolymer composed of glucose, mannose, galactose, glucosamine, and fucose as monomeric constituent units. Partial elucidation of the structure of the carbohydrate biopolymer based on GC-MS and NMR analysis showed the presence of two unique sets of tetrasaccharide repeating units that have 1→3 and 1→6 glycosidic linkages. This is also the first report of a Gram-positive bacterial polysaccharide with both fucose as a sugar monomer and 1→3 and 1→6 glycosidic linkages in the molecular backbone.