Physicochemical characterization and antioxidant activity of melanin from a novel strain of Aspergillus bridgeri ICTF-201

Aims: The aim of the study is to isolate and characterize a melanin pigment from a new strain of Aspergillus bridgeri isolated from rhizosphere soil of Eucalyptus tree and to investigate its antioxidant activity. Methods and Results: The extracellular pigment was alkali soluble, acid-resistant and insoluble in organic solvents and water. The pigment was precipitated on treatment with FeCl3, ammoniacal AgNO3 and potassium ferricyanide and was bleached in the presence of oxidants and reductants. It was confirmed as melanin based on the Fourier transform infrared and electron paramagnetic resonance spectroscopy techniques apart from chemical analysis. Inhibition of melanin production by inhibitors like tricyclazole, 6-hydroxyflavanone, 4-hydroxy-7-methoxy-3-phenyl-coumarin, 7-hydroxy-4-phenyl-coumarin and 7-hydroxy-3,4,8-trimethylcoumarin confirmed that melanin produced by A. bridgeri is synthesized by 1,8-dihydroxynaphthalene (DHN)-melanin pathway. The melanin showed good free radical scavenging activity by DPPH method with an EC50 of 54.12 mu g ml(-1). Conclusions: The results of the study indicate that the melanin produced by the newly isolated A. bridgeri strain is a member of DHN melanin family and exhibited significant free radical scavenging activity. Significance and Impact of the Study: This is the first report on characterization of DHN melanin produced by a novel strain of A. bridgeri and may find potential application as a natural antioxidant in the cosmetic and pharmaceutical industries.