Purification, structural characterization, and antioxidant activity of the COP-W1 polysaccharide from Codonopsis tangshen Oliv

A new polysaccharide named COP-W1 was extracted from the root of Codonopsis tangshen Oliv using hot water extraction and ethanol precipitation. COP-W1, with a molecular weight of 2.34 x 10(4) Da, was purified using gel permeation chromatography. The monosaccharide composition of COP-W1 was mannose, rhamnose, glucose, and galactose, and its molar ratio was 20.32:1:1.27:36.13. Structural characterization of COP-W1 was confirmed by Fourier transform infrared spectrometry (FT-IR), gas chromatograph-mass spectrometry (GC-MS), and nuclear magnetic resonance (NMR) analysis. The results indicated that the backbone of COP-W1 was composed of (1 -> 3)-linked-galactose, (1 -> 3, 6)-linked-mannose, (1 -> 4)-linked-mannose, and (1 -> 6)-linked-mannose residues, which branched at O-3. The branches consisted of (1 -> 2, 6)-linked-galactose, (1 -> 6)-linked-galactose, and (1 -> 4)-linked-galactose, each terminating with alpha-galactose. In addition, antioxidant assays demonstrated that COP-W1 has strong 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (half maximal inhibition concentration, IC50, at 0.610 mg/mL), and suggested that COP-W1 has the potential to be used as a natural antioxidant.