Abstract: This study quantified and characterized polysaccharides from different aged Dendrobium officinale stems. The molecular weights of polysaccharides were measured by gel permeation chromatography, and their monosaccharide composition was analyzed by pre-column derivatization high performance liquid chromatography (HPLC). In addition, the structural characteristics and antioxidant activity of polysaccharides were investigated. The results showed that the stems of five-year-old D. officinale had the highest polysaccharide content (238.60 mg/g), followed by three-year-old D. officinale (232.74 mg/g). The molecular weight of the primary polysaccharide (1 383 kDa) in four-year-old D. officinale was the highest, followed by that (1 046 kDa) of three-year-old D. officinale. Mannose was the most abundant monosaccharide in one-year-old D. officinale, followed by the three-year-old one. The polysaccharides of three-years-old D. officinale had the strongest Fe3+ reducing power hydroxyl radical scavenging activity and total antioxidant capacity. Based on polysaccharide content and in vitro antioxidant activities, the quality of three-year-old D. officinale was the best.

Key words: Dendrobium officinale, polysaccharide, age, antioxidant activity