Partial characterization and antioxidant activities of polysaccharides sequentially extracted from Dendrobium officinale

Six polysaccharide fractions (DOP30, DOP40, DOP50, DOP60, DOP70, and DOP80) were purified successfully from Dendrobium officinale by the ethanol precipitation method, and their physicochemical characterizations and antioxidant properties were investigated by the chemical methods, high performance liquid chromatography (HPLC), UV–vis (UV) and Fourier transform infrared spectroscopy, and 1,1-diphenyl-2-picrylhydrazyl radical scavenging ability, 2,2-azinobis-6-s (3-ethylbenzothiazoline sulfonic acid) (ABTS) radical scavenging activity, hydroxyl radical scavenging activity, and reducing power, respectively. Results estimated their weight-average molecular weight (Mw) to be 361.4, 242.6, 192.3, 100.5, 23.7, and 8.2 kDa, respectively. Mannose and glucose were the major monosaccharide components presenting in the polysaccharide fractions. However, monosaccharide compositions were significantly different among the DOPs, namely, DOPs with a smaller Mw contained more species of monosaccharides. All six polysaccharide fractions displayed antioxidant activities in vitro according to the antioxidant tests, and a small molecular weight of polysaccharides (DOP80 and DOP70) showed stronger antioxidant activities. The present results suggest that DOPs could potentially be used as a natural antioxidant, especially the small molecular weight ones.