Structural characterization and antioxidant activity of a new polysaccharide from Bletilla striata fibrous roots

•A new polysaccharide pFSP was isolated from Bletilla striata fibrous roots.•pFSP mainly consisted of mannose, galactose and glucose with Mw of 9.1 × 104 Da.•Structure of the pFSP was established by 1D and 2D NMR and chemical approaches.•pFSP exhibited stronger antioxidant abilities than polysaccharide from tuber. A new polysaccharide (pFSP) was first isolated from the originally discarded fibrous roots part of Chinese traditional herb, Bletilla striata. pFSP was composed of D-glucose, D-galactose and D-mannose in a molar ratio of 1: 2.03: 3.45 with molecular weight of 9.1 × 104 Da. It could effectively scavenge DPPH and superoxide radicals with inhibition rate of 64.47% and 72.27% at 5.0 mg/ml, higher than that of polysaccharide from Bletilla striata tuber. Structural investigations of the periodate oxidation studies and Smith-degradation as well as the FT-IR spectroscopy were performed, and combined with 1D and 2D NMR spectroscopy, the repeating unit of pFSP contained (1→4)-linked-α-D-Glcp, (1→4)-linked-β-D-Manp and (1→3,6)-linked-β-D-Manp units, together with the branches of (1→6)-linked-β-D-Galp and terminated with (1→)-linked-β-D-Manp residue.