Structural characterization of a low-molecular-weight polysaccharide from Angelica pubescens Maxim. f. biserrata Shan et Yuan root and evaluation of its antioxidant activity

•A novel low-molecular-weight polysaccharide was obtained from A. Pubescentis roots.•Its structure was elucidated by chemical analyses and NMR for the first time.•DF80-2 can effectively scavenge DPPH, and hydroxyl radicals, and chelate ferrous ions.•The antioxidant activities may be attributed to its special structural features. A novel heteropolysaccharide with about twenty sugar residues named DF80-2 was obtained from Angelica pubescens Maxim. f. biserrata Shan et Yuan root, one of the most widely used traditional Chinese medicines for thousands of years in China. The possible structure of DF80-2 was proposed considering the comprehensive results of physicochemical properties, methylation analysis, and 1D/2D NMR spectroscopy, which showed that its main chain was composed of (1→3)-, and (1→4)-linked-α-d-Glcp, (1→4)-linked-β-d-Galp, (1→6)-linked-α-d-Manp, and (1→3)-linked-α-l-Araf, and the branch was present as the α-d-Glcp-(1→3)-β-d-GalpA disaccharides stretched from O-6 position of (1→4)-linked-α-d-Glc moiety in the main chain. Congo red analysis, scanning electron microscopy and atomic force microscopy showed that DF80-2 possessed a triple helical conformation, and its branched monomers were interlaced with one another forming a regular network structure. DF80-2 exhibited antioxidant activity by effectively scavenging DPPH, and hydroxyl radicals, and chelating ferrous ions.