Structure, physical property and antioxidant activity of catechin grafted Tremella fuciformis polysaccharide

•A purified TPS fraction with the molecular weight of 5.82×105Da was obtained.•Catechin-g-TPS was prepared with the grafting ratio of 265mgCAE/g.•Catechin-g-TPS was characterized by FT-IR, 1H NMR, TGA, XRD and SEM.•Catechin-g-TPS exhibited higher antioxidant activity in vitro than TPS. In this study, structural characterization, physical property and antioxidant activity of catechin grafted Tremella fuciformis polysaccharide (catechin-g-TPS) were investigated. Crude polysaccharides were isolated from the fruit bodies of T. fuciformis and further purified on DEAE-52 and Sepharose CL-4B chromatography to afford a main purified fraction (named TPS). The molecular weight of TPS was determined as 5.82×105Da by HPLC. Then, the free radical mediated grafting of catechin onto TPS was achieved by using a redox system. As compared with the unmodified TPS, catechin-g-TPS showed new bands within the range of 1300–1600cm−1 in FT-IR spectrum, and exhibited new signals at around δ 6.00 and 6.80ppm in 1H NMR spectrum. Thermogravimetric analysis indicated the thermal stability of catechin-g-TPS was higher than TPS. X-ray diffraction spectrum of catechin-g-TPS exhibited two sharp narrow diffraction peaks at 14.2 and 32.1°, corresponding to the crystalline peaks of catechin. Scanning electron microscopy observation revealed the surface of TPS was smooth, whereas the surface of catechin-g-TPS was much rough. These results all confirmed the successful grafting of catechin onto TPS. Moreover, catechin-g-TPS had higher 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity and reducing power as compared to TPS.