Improved eumelanin production, phenolic content, flavonoid content, and antioxidant activity by Streptomyces lasalocidi NTB 42 following copper sulfate supplementation

The demand for natural pigments, including microbial melanin, is rapidly increasing in the pharmaceutical industry. Eumelanin, a black pigment produced by Streptomyces lasalocidi NTB 42, exhibits high antioxidant activity. This pigment can be produced in large quantities using copper sulfate (CuSO₄.5H₂O). This study aimed to evaluate the effect of CuSO₄.5H₂O on various parameters related to eumelanin production in S. lasalocidi NTB 42 and antioxidant activity. The addition of 0.04 % CuSO₄.5H₂O to the production medium significantly enhanced tyrosinase activity by 4.52-fold. Additionally, it resulted in a 46.75-fold increase in eumelanin production (3.74 g/L), a 1.83-fold increase in eumelanin concentration (875 mg/g eumelanin dry weight), a 1.44-fold increase in total phenolic content (TPC) (127.76 mg GAE/g eumelanin), a 0.89-fold increase in the 2,2-diphenyl-1-picryl-hydrazyl scavenging assay (IC₅₀) (66.75 μg/mL), and a 7.68-fold increase in ferric reducing antioxidant power (875.95 mg AAE/g eumelanin) (p < 0.05). Furthermore, the addition of 0.03 % CuSO₄.5H₂O resulted in a 1.30-fold increase in total flavonoid content (TFC) (76.93 mg QE/g eumelanin) and a 0.328-fold increase in total antioxidant capacity (191.41 mg AAE/g eumelanin) (p < 0.05). The obtained eumelanin, which is characterized by UV–VIS and FT-IR analysis, has the same character as the previously found eumelanin. These findings suggest that CuSO4.5H₂O concentrations between 0.03 % and 0.04 % significantly enhance eumelanin production, levels of major chemical compounds, and antioxidant activity in S. lasalocidi NTB 42. This study underscores the potential for increased eumelanin production and antioxidant activity of S. lasalocidi NTB 42 to meet the demands of pharmaceutical applications as an antioxidant agent.