Abstract:Phlebopus portentosus polysaccharide（PBP）was extracted from the fruiting bodies by the hot water extraction method. The structures of PBP and PBP-I were characterized，and the in vitro antioxidant activities of PBP and PBP-I were studied.The results showed that PBP had the total sugar content of 70.97%，the protein content of 8.14%，the glucuronic acid content of 5.60%，and the reducing sugar content of 4.16%. UV spectral scanning showed strong absorption peaks of PBP and PBP-I around a wavelength of 200 nm，which was consistent with the UV absorption characteristics of polysaccharides.PBP and PBP-I were composed mannose，galacturonic acid，glucose，galactose，and fucose at different ratios.The molecular weight distribution of PBP encompassed 4.54×107，1.41×107 Da，and 6.63×105 Da. The molecular weight of PBP-I was mainly 1.20×107 Da，accounting for 90.4%.The infrared spectroscopy results indicated that PBP and PBP-I contained pyranose with βglycosidic bonds.The results of the Congo Red test indicated that PBP contained a triple helix structure.X-ray diffraction analysis showed that PBP presented an amorphous structure. Scanning electron microscopy showed that the surface of PBP exhibited irregular sheet-like adhesion and aggregation，while PBP-I exhibited irregular fibrous filamentous aggregation. The in vitro antioxidant activity assays of PBP and PBP-I showed that the median inhibition concentration（IC50）values of PBP and PBP-I were 3.08 mg/mL and 2.82 mg/mL for scavenging DPPH radicals and 1.21 mg/mL and 2.65 mg/mL for scavenging ABTS+ radicals，respectively. In addition，PBP and PBP-I showed the median effect concentrations of 5.30 mg/mL and 18.15 mg/mL，respectively，for reducing iron ions.