Isolation, purification, and physio-chemical characterization of melanin pigment from nigerseed hulls (Guizotia abysinica)

Abstract

Plant melanin, a natural pigment, has gained significant attention recently due to its potential therapeutic and industrial applications. In this study, melanin pigments were extracted from Nigerseed hulls (NH) via alkali and acid extraction methods, followed by acid hydrolysis, organic solvent treatment, and repeated precipitation. The solubility of NH melanin was assessed, revealing solubility in alkali and dimethyl sulfoxide (DMSO) but insolubility in other common organic solvents. High-performance liquid chromatography (HPLC) was employed to measure the purity of NH melanin in comparison to standard melanin, while elemental analysis indicated a similarity between melanin extracted from nigerseed hulls and the standard counterpart. LC-MS data revealed a molecular weight of NH melanin. Furthermore, the stability of melanin was evaluated under varying conditions including temperature, oxidants, reducing agents, light exposure, and metal ion presence. Results demonstrated significant effects of Mg2+, Cu2+, and Fe2+ metal ions on melanin stability, with a minor effect observed for Ca2+, while sodium hyposulfite was found to destabilize the pigments. Our findings suggest that nigerseed hulls hold promise as a novel source for efficient melanin production, with potential applications in the food sector, food packaging, and biomedical fields.