Identification of pivotal components on the antioxidant activity of polysaccharide extract from Ganoderma atrum

• PSG was fractionated into five fractions with different content of sugar, proteins and phenolic compounds.
• Antioxidant components were enriched in the high charge density fractions (F0.5 and F2).
• Acidic fractions (F0.2 and F0.5) were responsible for the immunomodulatory activity of PSG.
• Phenolic and proteins were clarified to be the pivotal antioxidant components in PSG.

The pivotal components responsible for the antioxidant activities of polysaccharide from Ganoderma atrum (PSG) were identified by chemical composition and antioxidant activity analysis after separating PSG into different fractions. PSG was determined to be a mixture with neutral fraction and acidic fraction, as well as protein and phenolic compounds. The fractions with different ionic density were separated by anion exchange chromatography (AEC). The neutral fraction (Fw) was identified as a (1→6)-linked-heterogalactan, while the ionic fractions (F0.2, F0.5 and F2) were acidic (1→3, 1→6)-linked-heteroglucans with non-sugar components. Phenolic compounds and proteins bonded/crosslinked with PSG were enriched in the very ionic fractions (F0.5 and F2). Antioxidant activities of PSG and its fractions via chemical assays showed good correlation to the total phenolic and protein contents, while cell culture assay indicated that acidic (1→3, 1→6)-linked-heteroglucan could significantly stimulate the macrophage cell RAW264.7 to release nitric oxide. These results clarified that the antioxidant activities of PSG ascribed to the phenolic and protein components, rather than the carbohydrates part which would be more responsible to the immunomodulatory activity of PSG.

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