Structure characterization and biological activities of a pectic polysaccharide from cupule of Castanea henryi

A pectic polysaccharide (CHIP3) was fractionated from the natural cupule of Castanea henryi. It contained mannose (10.70%), rhamnose (8.70%), galacturonic acid (38.21%), galactose (13.75%) and arabinose (28.63%) with a molecular weight of 2.44 × 10⁴ g/mol by multi-laser light scattering. The structure was elucidated by using FT-IR spectroscopy, methylation analysis and NMR analysis. Results showed that the backbone of CHIP3 consisted of 1, 4-α-linked d-GalpA residues containing the non-methyl-esterified carboxyl groups, interspersed with a few 1,2-α-l-Rhap units. Its side chains were attached by two branches to O-4 of Rhap with 1,4-β-linked d-Galp units and 1,5-α-l-linked Araf units bearing 3,5-substituted α-l-linked Araf residues as branching points. AFM data revealed it existed as a flexible chain in 0.1 M NaNO₃ aqueous solution. Furthermore, CHIP3 was demonstrated to have notable antioxidant activity of FRAP, ABTS⁺ radical scavenging and reducing power. Cytotoxicity assay showed it displayed inhibitory activity against HepG2 cells with IC₅₀ values of 242.6 μg/mL.