Structural characterization and antioxidant activities of a novel fructan from Achyranthes bidentata Blume, a famous medicinal plant in China

•Achyranthes bidentata Blume is a well-known traditional Chinese medicine yet underutilized plant.•A novel fructan (ABP70-2) was firstly isolated from the roots of Achyranthes bidentata Blume.•We reported for the first time the structure characterization and conformation of ABP70-2.•ABP70-2 comprises a backbone of (2 → 6) linked β-d-Fruf with (2 → 1) linked β-d-Fruf branched chains.•ABP70-2 exerted excellent activity of DPPH radical scavenging with an EC50 of 1.05 μM.

Achyranthes bidentata is one of the most important medicinal plants in Henan Province of China. Due to the excellent ethnopharmacological uses and scientifically proved biological properties, A. bidentata is worth investigating. In this manuscript, a novel water-soluble polysaccharide (ABP70-2) with a low molecular weight (Mw) of 3406 Da was isolated from the roots of A. bidentata by hot water extraction and further successively purified through DEAE-cellulose 52 and Sephacryl S-100HR columns. ABP70-2 was composed of glucose and fructose in a molar ratio of 1:18. Its exact structural features were first elucidated by a combination of monosaccharide analysis, infrared spectroscopy, methylation, gas chromatography–mass spectrometry (GC–MS) analysis, and NMR studies (1H, 13C, NOESY, HSQC, and HMBC). The data obtained indicate that ABP70-2 possessed a backbone of (2 → 6)-linked β-d-fructofuranosyl (Fruf), with (2 → 1)-linked β-d-Fruf branched chains, and terminated with Glc and Fru residues. Advanced structures and conformation of ABP70-2 were preliminarily investigated by scanning electron microscope (SEM), circular dichroism spectroscopy (CD), and Congo-red assay (CR). The in vitro antioxidant activity showed that ABP70-2 possessed a concentration dependent 1, 1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity, with an EC50 value of 1.05 μΜ.

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