Structure and bioactivity of a polysaccharide containing uronic acid from Polyporus umbellatus sclerotia

• A novel polysaccharide (PUP80S1) was obtained from Polyporus umbellatus sclerotia.
• Structure characterization of PUP80S1 containing uronic acid was elucidated by NMR.
• Globular chain conformation of PUP80S1 was determined by Atomic force microscopy.
• Antioxidant activity of two polysaccharides having similar structure were compared.

Polyporus umbellatus is a medicinal fungus, has been used in traditional Chinese medicine for thousands years for treatment of edema, scanty urine, vaginal discharge, jaundice and diarrhea. The structure of a soluble polysaccharide (named PUP80S1), purified from the sclerotia of Polyporus umbellatus was elucidated by gas chromatography (GC), GC–mass spectrometry and nuclear magnetic resonance spectroscopy. PUP80S1 is a branched polysaccharide containing approximately 8.5% uronic acid and having an average molecular weight of 8.8 kDa. Atomic force microscopy of PUP80S1 reveals a globular chain conformation in water. Antioxidant tests, Oxygen radical absorption capacity and 2,2-diphenyl-1-picrylhydrazyl radical scavenging assays indicate that PUP80S1 possesses significant antioxidant activity. But the related polysaccharide, PUP60S2, which contains more uronic acid residues and a higher level of branching, shows better antioxidant activity. These results suggest that structure features of polysaccharides play an important role in their physiological functions.