Isolation, structure and activity of a novel water-soluble polysaccharide from Dioscorea opposita Thunb

A previously unknown, water-soluble polysaccharide, named DOTP-B, was isolated from the roots of the plant Dioscorea opposita Thunb, a well-known edible and medicinal plant in China. DOW-B was found to be neutral in charge, with an average molecular weight of 5623 Da. Monosaccharide composition analysis by GC-MS revealed that DOTP-B was a hetero-polysaccharide consisting of glucose and galactose at a molar ratio of 14.6:1.0. Structural features of DOTP-B were investigated with a combination of chemical and instrumental methods, including complete acid hydrolysis, periodate oxidation, methylation, GC-MS, FTIR and several NMR spectra. Highly correlated results demonstrated that the main chain of DOTP-B consisted of -> 4)-alpha-D-glc(1 -> residues, with about 6% internal -> 6)-beta-D-gal(1 -> residues. The antioxidant activity of DOTP-B was also evaluated as the EC50 values against DPPH and PTIO radicals were 2.1 +/- 0.1 mg/mL and 1.6 +/- 0.1 mg/mL, respectively. Therefore, the polysaccharide DOTP-B could be possibly developed as a promising natural antioxidant for application in medical and food industries. (C) 2019 Published by Elsevier B.V.