Structural characterisation and structure-antioxidant activity relationship of polysaccharides from Dendrobium catenatum Lindl

Dendrobium catenatum Lindl. has been long used in China as a functional food and traditional Chinese medicine and polysaccharides from Dendrobium catenatum Lindl. (DOP) exhibited extensive bioactivities. However, studies on the structure-activity relationship of DOP are rarely reported. Here, two polysaccharides named DOP-1 and DOP-2 were obtained, which differed in the ratio of monosaccharide composition and molecular weight. Structural characteristics were elucidated by spectral and chemical analysis. The main structures of DOPs were the linkage of beta-(1 -> 4)-D-Manp, with some attached 2-O- or 3-O-acetylated groups. Additionally, the DPPH, hydroxyl and superoxide radicals scavenging assays of DOP-1 and DOP-2 showed that DOP-2 exhibited the higher antioxidant activity, which might be related to its lower molecular weight, higher mannose proportion and lower degree of acetylation, and higher phenolic content. Our results provide a more accurate basis for the application of DOPs in the pharmaceutical and food industries.