Constituents actually responsible for the antioxidant activities of crude polysaccharides isolated from mushrooms

The major chemical constituents and antioxidant activities of water-soluble polysaccharide (PS) fractions isolated from three edible mushrooms were investigated. Crude PS (CPS) isolated from the mushroom hot water extract by ethanol precipitation contained 15-30% (w/w) total protein and 2-5% phenolics. The CPS were fractionated by ion exchange chromatography and the neutral, and slightly ionic PS fractions (eluted with 0 and 0.1 M NaCl) contained 70-80% carbohydrate with low protein and phenolic contents, while the ionic PS fractions (eluted with 0.3 M and 0.7 M NaCl) had higher contents of protein (20-70%) and phenolics (2-13%). The antioxidant activities of all PS fractions were significantly correlated with the total phenolic and protein contents but not with the carbohydrate content. Purified PS free of phenolics and proteins had no significant activities. Therefore, the phenolic and protein components instead of carbohydrates were mainly responsible for the antioxidant activities of mushroom PS.