Antioxidant polyphenols from the mycelial culture of the medicinal fungi Inonotus xeranticus and Phellinus linteus

Aims: The medicinal fungi Inonotus xeranticus and Phellinus linteus in the family Hymenochaetaceae have been used as traditional medicines for the treatment of various diseases. However, the compound responsible for the antioxidant activity is still unknown. Therefore, this study was conducted to characterize the antioxidant substances present in cultured broths made from these fungi. Methods and Results: Antioxidant fractions of the cultured broths obtained from I. xeranticus and P. linteus were analysed using reversed-phase HPLC, which revealed several peaks that exhibited a potent free radical scavenging activity. To identify these antioxidant peaks, an I. xeranticus strain was mass-cultured, and the cultured broth was separated using antioxidant activity-guided fractionation. Four major active substances were purified and identified as hispidin and its dimers, 3,14'-bihispidinyl, hypholomine B, and 1,1-distyrylpyrylethan based on spectroscopic analyses. All compounds exhibited a significant scavenging activity against these radical species in a concentration-dependent manner. Conclusions: Antioxidant substances found in the cultured broths of the medicinal fungi I. xeranticus and P. linteus were identified as hispidin and its dimers, 3,14'-bihispidinyl, hypholomine B, and 1,1-distyrylpyrylethan. Significance and Impact of the Study: Polyphenol antioxidants were isolated from the cultured broth of the medicinal fungi I. xeranticus and P. linteus and identified based on extensive spectroscopic analyses. These compounds exhibited a strong antioxidant activity.