Identification and antioxidant activity of melanin isolated from Hypoxylon archeri, a companion fungus of Tremella fuciformis

Melanin produced by Hypoxylon archeri, a companion fungus of Tremella fuciformis, was purified from the submerged culture medium and designated as HM. Ultraviolet-visible and FTIR spectra of the purified HM showed significant similarities with those of the synthesized melanin derived from tyrosine. Thus, the HM melanin was identified to be derived from the precursor molecule of tyrosine or dihydroxyphenylalanine (DOPA). The antioxidant activity of HM melanin, synthetic melanin and vitamin C were compared by inhibition of the oxidation of 5-thio-2-nitrobenzoic acid (TNB) caused by hypochlorous acid (HOCl) and hydrogen peroxide (H2O2). The HM melanin is likely to be more efficient eliminating oxygen free radicals generated by H2O2 than by HOCl At a concentration of 100 mg . l(-1), the HM melanin protected 80.95% of TNB oxidation by H2O2, slightly higher than the synthetic melanin. Inhibition curves as a function of time also revealed the HM melanin was a more effcient inhibitor of H2O2 oxidation with an average TNB (TNBacr) consumption rate of 0.0553 mmol l(-1) . min(-1) during the inhibition phase. Therefore, HM melanin is an efficient scavenger of peroxide free radicals.