Physicochemical characterization and antioxidant activity of cell-bound exopolysaccharides from Lactobacillus fermentum S1 obtained by two extraction methods

Abstract

Abstract 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 × 105 and 2.44 × 105 Da, respectively. Both CFP and CFE were composed of five kinds of monosaccharides. They had a main chain of β-D-Glcp-(1→2), α-L-Rhap-(1→2), β-D-Galp-(1→3), α-D-Glcp-(1→3), α-D-Galp-(1→3) and β-L-Rhap-(1→3,4) residues, and a tail of α-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.