Physicochemical characteristics and antioxidant activity of arginine-modified melanin from Lachnum YM-346

Seven kinds of amino acids were used to modify the non-water-soluble extracellular melanin (LEM346) from Lachnum YM-346. It was found that arginine–melanin (ALEM346) had the highest solubility, being 4.55% (g g−1) in 30 °C distilled water. Elemental analysis, infrared spectrum and mass spectrum analysis revealed that LEM346 molecule contained indole quinone structure, its molecular formula speculated to be C18H8O6N2. Infrared spectrum analysis showed that ALEM346 had characteristic absorption peaks at 1672.346 and 1637.679 cm−1. Mass spectrum analysis indicated that ALEM346 contained three types of arginine–melanin molecules. When the ALEM346 concentration was 500 mg L−1, its total antioxidant capacity was equivalent to α-tocopherol of 46.65 mmol L−1, the DPPH and O2− scavenging rates and the Fe2+ chelating rate were 89.05%, 93.81% and 80.18%, respectively, suggesting that the antioxidant activity of ALEM346 was stronger than that of LEM346.