Structural characterization and antioxidant property of released exopolysaccharides from Lactobacillus delbrueckii ssp bulgaricus SRFM-1

Three released exopolysaccharide fractions (r-EPS1, r-EPS2 and r-EPS3) were isolated from the fermented milk of Lactobacillus delbrueckii ssp. bulgaricus SRFM-1 and purified by anion exchange chromatography, and characterizations of the structures were conducted. The r-EPS1 and r-EPS2 were homogenous with the average molecular weights of 3.97 x 105 Da and 3.86 x 10(5) Da, respectively. Three r-EPS fractions were composed of galactose and glucose with a molar ratio of 1.23: 1.00, 1.33: 1.00 and 1.00: 1.34, respectively. Structural characterization indicated that the r-EPS1 contained a backbone of -> 6-beta-d-Galp-(1 -> 4)-beta-d-Glcp-(1 -> 4)-alpha-d-Galp-(1 ? 4)-beta-d-Galp-(1 -> 6)-beta-d-Galp-(1 -> 4)-beta-d-Glcp-(1 -> 4)-alpha-d-Galp-(1 -> 4)-beta-d-Galp-(1 -> 4)-alpha-d-Glcp-(1 ->, and had three branching points which existed in terminal with D-Glcp residues with alpha/beta-d-(1 -> 6) linkages. The r-EPS2 was composed of -> 6-beta-d-Galp-(1 -> 4)-beta-d-Glcp-(1 -> 6)-alpha-d-Galp-(1 -> as the backbone chain with a branching point which also existed in terminal D-Glcp residue with beta-(1 -> 6) linkage. In addition, three r-EPS fractions exhibited strong scavenging activities on superoxide radical, hydroxyl radical, DPPH radical and chelating activity on ferrous ion, and their antioxidant activities decreased in the order of r-EPS1 > r-EPS2 > r-EPS3. (C) 2017 Elsevier Ltd. All rights reserved.