Characterization and Antioxidant Activity Analysis of Daylily Polysaccharides

Daylily is a traditional and typical dry product in our country. In order to explore the functional components from daylily, daylily polysaccharides were extracted with water adjusted to pH1.8 using nitric acid. Proteins were removed by the Sevag method. The basic characteristics, physical and chemical properties and in vitro antioxidant activity of the daylily polysaccharides were analyzed. The results showed that the yield of daylily polysaccharides after protein removal was 0.72%, the polysaccharide content was 34.91%, and the galacturonic acid content was 26.42%. Daylily polysaccharide contains high-ester pectin, and the degree of methyl esterification was 96.13%±0.3%. The neutral sugar of daylily polysaccharide was mainly composed of galactose, glucose and xylose, and its molar ratio was 62.50:17.31:11.30. Microscopic observation revealed that the daylily polysaccharide had a flocculent structure, and the surface was uneven and discontinuous. The Fourier transform infrared (FTIR) diagram showed that the daylily polysaccharides contained more ester bonds. Analysis of the rheological properties showed that as the shear rate increased, the apparent viscosity of the daylily polysaccharide solution decreased rapidly and then maintained at a low level. At each concentration, its G' was greater than G''. The molecular weight of daylily polysaccharide peak 1 was relatively high, with Mw of 1310.32 kDa. Peak 2 molecular weight was relatively small, with Mw of 83.81 kDa. The rheological properties of the daylily polysaccharide solution showed that the apparent viscosity of the polysaccharide decreased rapidly as the shear rate increased, its G' was greater than G" at all concentrations. Results from antioxidant analysis showed that daylily polysaccharides possessed strong 2,2'-azinobi-(3-ethylbenzthiazoline-6-sulphonate) radical (ABTS⁺·) scavenging ability and Ferric reducing antioxidant power (FRAP) ability. This study could provide a profound understanding on the physical and chemical properties of daylily polysaccharides and provide a basis for the development and utilization of their biological activities.