Investigation of three lignin complexes with antioxidant and immunological capacities from Inonotus obliquus

• Three homogenous biomolecules (designated IOA1, IOA2 and IOA3) were prepared from the alkali extract of I. obliquus.
• They were characterized as lignin–carbohydrate complexes mainly comprised lignin as well as −25% carbohydrates.
• These biomolecules exhibited excellent antioxidant and immunological activities.

Mushroom Inonotus obliquus (I. obliquus), a folk medicine, has been widely used to treat several human malicious tumors since 16th century. In this study, three homogenous biomolecules (designated IOA1, IOA2 and IOA3) were prepared from the alkali extract of I. obliquus. Their molecular weights were measured to be 6.1 × 104, 2.9 × 104 and 3.5 × 104 g/mol respectively and all of them were characterized as lignin–carbohydrate complexes mainly comprised lignin as well as −25% carbohydrates. Antioxidant assays indicated that all of them exhibited pronounced reductive power and strong scavenging activities on DPPH and hydroxyl radicals in vitro. Immunological tests showed that they could also significantly stimulate nitric oxide production and phagocytic activity in RAW 264.7 macrophages. These results implied that the lignin–carbohydrate complexes extracted from I. obliquus might be used as novel natural antioxidants or immunostimulants in functional foods or pharmaceutical candidates.