Structural elucidation and antioxidant activities of exopolysaccharides from Lactobacillus helveticus MB2-1

In the present study, the crude polysaccharides (EPS) from Lactobacillus helveticus MB2-1 were fermented with reconstituted whey medium and further fractionated on DEAE-52 cellulose and Sephadex G-100 chromatography to afford three purified fractions of EPS-1, EPS-2 and EPS-3. Then, their preliminary structures and antioxidant activities in vitro were investigated. Three purified EPS fractions (EPS-1, EPS-2 and EPS-3) had similar molecular weight distributions (about 2 × 105 Da), and it was composed of galactose, glucose and mannose with a molar ratio of 1.33:2.75:1.00, 1.00:1.43:9.34 and 1.17:1.00:2.96, respectively. In addition, the antioxidant activity of EPS-1, EPS-2 and EPS-3 was evaluated with the in vitro scavenging abilities. The results indicated that both crude and purified EPS showed strong scavenging activities on three kinds of radical and chelating activities on ferrous ion, and their antioxidant activities decreased in the order of crude EPS > EPS-3 > EPS-2 > EPS-1.