Sustainable Production and Characterization of Eumelanin from Organically Cultivated <em>Mucuna ceniza</em> Seeds: A High-Performance Biomaterial for Optoelectronic Applications

Natural melanins represent an emerging class of bio-based materials with exceptional properties for advanced technological applications. This study presents a comprehensive analytical characterization of eumelanin produced from organically cultivated Mucuna ceniza seeds through sustainable biotechnological processes. A high-quality L-DOPA extract containing 56% w/w L-DOPA was first obtained using green extraction protocols with organic acids, followed by lyophilization. Then, optimized stirred-tank bioreactor conditions achieved remarkable melanin production rates of 1526.23 ± 10.78 mg L⁻¹ h⁻¹ with complete L-DOPA conversion, yielding 9.5 g/L of purified eumelanin. Spectroscopic characterization using UV-visible, FTIR, Raman, and NMR spectroscopy confirmed the authentic eumelanin structure, characterized by a characteristic absorption at 225 nm, diagnostic FTIR bands, Raman signatures at 1380 and 1580 cm⁻¹ and NMR peaks. The elemental composition (C: 48.04%, H: 6.14%, N: 11.85%) classified the pigment as eumelanin, with an inferred empirical formula of C₄₈H₇₄N₁₀O₂₅. This melanin has already demonstrated practical utility in optoelectronic applications. By harnessing the unique biocatalytic potential of organically grown Mucuna ceniza, this study validates a green, high-yield production platform for eumelanin, paving the way for its commercially viable application in advanced functional materials.