Characterization and antioxidant activity of eumelanin produced by Streptomyces lasalocidi NTB 42

Melanin, a macromolecule derived from the oxidative polymerization of phenolic compounds, possesses notable bioactive attributes and serves as a crucial biological safeguard against deleterious environmental factors. Melanin originates in Streptomyces and is known for its antioxidative properties. This study aimed to characterize and evaluate the antioxidant activity of melanin obtained from Streptomyces lasalocidi NTB 42. Based on 16 S rRNA identification, strain NTB 42 was identified as Streptomyces lasalocidi NTB 42 (OR710932). During melanin biosynthesis, S. lasalocidi NTB 42 had the highest tyrosinase activity on day 5 and the highest L-3,4-dihydroxyphenylalanine concentration on day 6. Melanin NTB 42 exhibited polymorphic and irregular morphology. Melanin NTB 42 characteristics were analyzed using the A₆₅₀/A₅₀₀ ratio, UV–visible spectroscopy, Fourier transform infrared spectroscopy, high-performance liquid chromatography, dispersive X-ray spectroscopy, and thermal degradation products based on pyrolysis-gas chromatography-mass spectrometry were identified as eumelanin. The scavenging ability of NTB 42 melanin, as determined by the half maximal inhibitory concentration (IC₅₀), was 70.60 ± 0.40 μg/mL for 2,2-diphenyl-1-picrylhydrazyl and 176.76 ± 0.93 μg/mL for 2,2′-azino-bis(3-ethylbenzothiazolin-6-acid sulfonate radicals. The Fe-reducing power and total antioxidant capacity values were 114.05 ± 0.41 mg AAE/g melanin and 145.10 ± 0.56 mg AAE/g melanin, respectively. This study is the first attempt to characterize the antioxidant properties of eumelanin from S. lasalocidi NTB 42. The antioxidant ability of eumelanin NTB 42 against various free radicals shows promise for further development as an antioxidant.