Physicochemical characterization and antioxidant activity of cell-bound exopolysaccharides from Lactobacillus fermentum Si obtained by two extraction methods

This study investigated the physicochemical characteristics and antioxidant activities of cell-bound exopolysaccharides (c-EPS) from Lactobacillus fermentum S1 extracted using either phenol (CFP) or ethylenediaminetetraacetic acid (CFE). The extraction products, CFP and CFE, were homogeneous polysaccharides with molecular weights of 2.89 x 10(5) and 2.44 x 10(5) Da, respectively. Both CFP and CFE were composed of five kinds of monosaccharides. They had a main chain of beta-D-Glcp-(1 -> 2), alpha-L-Rhap-(1 -> 2), beta-D-Galp-(1 -> 3), alpha-D-Glcp-(1 -> 3), alpha-D-Galp-(1 -> 3) and beta-L-Rhap-(1 -> 3,4) residues, and a tail of alpha-D-Manp-(1 -> ) residue, but with different molar ratios. Trace amounts of D-Galp-(1 -> ) and L-Araf-(1 -> 2,5) residues were randomly distributed in the sugar chains. Although both CFP and CFE were in triple-helical conformation, they differed from each other in relation to surface morphology and thermal properties. The two c-EPS had different performances in radical scavenging and ferric reducing antioxidant power assays in vitro. The antioxidant capacity of both c-EPS extracts was confirmed in vivo using Caenorhabditis elegans, whose total antioxidant capacity and total superoxide dismutase activity increased after c-EPS treatment. Overall, the extraction method significantly affected the structure and biological activity of c-EPS. Moreover, the potent antioxidant activities of CFP and CFE support their use as natural antioxidants in dietary supplements or food additives.