Static decolorization of polysaccharides from the leaves of Rhododendron dauricum: Process optimization, characterization and antioxidant activities

Abstract

In this study, polysaccharides from the leaves of Rhododendron dauricum L. (RDPs) were decolorized using the static macroporous resin adsorption method. The RDPs were characterized and their antioxidant activities were investigated. An analytical hierarchy process (AHP) and a response surface method (RSM) were used to determine the optimum decolorization conditions as: a polysaccharide concentration of 8 mg/mL, decolorization time of 70 min, liquid–solid ratio of 6 mL/g, and decolorization temperature of 52 °C, with D101 as the best resin. Furthermore, two novel polysaccharides (RDP-1 and RDP-2) were isolated from R. dauricum leaves and characterized, which demonstrated that RDP-1 and RDP-2 were both composed of mannose, glucose, galactose, and arabinose in different molar ratios. These RDPs also exhibited a triple helix conformation, and primarily contained →6)-Glcp-(1→, →5)-Araf-(1→, →2,4)-Manp-(1→, →6)-Galp-(1→ and Glcp-(1→ residues with different connection sequences. Biological activity tests showed that the two polysaccharides possessed scavenging capacity against 1,1-Diphenyl-2-picrylhydrazyl (DPPH), hydroxyl, and 2,2-Azino-bis-(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) radicals. The results indicated that the antioxidant activities of the RDPs obtained by the static decolorization method improved, which lays a theoretical foundation for developing techniques for utilising R. dauricum.