Chemical properties and antioxidant activity of a water-soluble polysaccharide from Dendrobium officinale

• Structural characterization of Dendrobium officinale polysaccharide.
• Mannose and glucose are the main constituent.
• The polysaccharide possesses antioxidant property.

In this report, a water-soluble polysaccharide was obtained from the dried stems of Dendrobium officinale Kimura et Migo by hot-water (70–75 °C) extraction and 85% ethanol precipitation, and successively purification by DEAE-cellulose anion-exchange chromatography and gel-permeation chromatography. The D. officinale polysaccharide (DOP) has a molecular weight of 8500 Da. Monosaccharide composition analysis reveals that DOP is composed of mannose, glucose, and arabinose with a trace of galacturonic acid in a molar ratio of 6.2:2.3:2.1:0.1. Periodate oxidation–smith degradation and 1D and 2D NMR spectroscopy analysis suggest the predominance of mannose and glucose, and it contains a 2-O-acetylglucomannan and (1 → 4)-linked-β-d-mannopyranosyl and (1 → 4)-linked-β-d-glucopyranosyl residues. Atomic force microscope shows that DOP mainly exists as rod-shaped chains, supporting high degrees of polymerization. The antioxidant activities of the polysaccharide in vitro assay indicate that DOP has good scavenging activity of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, higher scavenging activity of hydroxyl radical, and metal chelating activities.