Structural characterization of a novel acidic polysaccharide from Rosa roxburghii Tratt fruit and its alpha-glucosidase inhibitory activity

A novel acidic polysaccharide (RTFP-3) was isolated and purified from Rosa roxburghii Tratt fruits. Structural analyses revealed that RTFP-3 is a homogeneous polysaccharide with a molecular weight of 67.2 kDa and mainly consists of arabinose (37.20%), galactose (34.40%), glucose (10.02%) and fucose (18.30%). The structural chain of RTFP-3 was proven to be composed of 6)--d-Galp-(1, 4)--d-GalpA-(1, 5)--l-Araf-(1, 4)--d-Glcp-(1, -d-Glcp-(1 and 3,4)--l-Fucp-(1 residues by periodate oxidation-Smith degradation, methylation, and 1D- and 2D-NMR analyses. Bioassay results showed that RTFP-3 exerted favorable mixed type inhibitory activities against -glucosidase, and its half inhibitory concentration (IC50) value was determined as 4.15 mg mL(-1). RTFP-3 showed static type quenching of the intrinsic fluorescence of -glucosidase, during which the binding process induced the conformational change of -glucosidase. These results suggest that RTFP-3 has the potential to be a novel -glucosidase inhibitory agent for use in functional foods.