Microbial Melanin-Reinforced Chitosan Films with Enhanced Functional Performances

Melanin is a polymeric pigment with numerous properties like UV-visible light protection, and antioxidant and antimicrobial activities. In this study, for the first time, a microbial melanin, eumelanin-like, and biotechnologically produced by Streptomyces nashvillensis DSM 40314, was incorporated in chitosan films to develop multifunctional biobased materials. A4 films containing 1.0-4.0% (w/w) melanin were prepared by the casting method and then characterized for their physicochemical, mechanical, and biological properties, in comparison with control films. FT-IR analyses confirmed interactions between chitosan and melanin, and the films showed improved mechanical properties, such as enhanced tensile strength and flexibility. Water solubility of the films decreased with pigment insertion, while moisture content and swelling increased, suggesting changes in the polymer network. UV-visible shielding and gas barrier properties were also significantly enhanced. Films containing 4.0% melanin exhibited strong antioxidant activity (88.34 ± 0.02 μM FRAP; 49.22 ± 5.60% DPPH) and antimicrobial activity againstP. aeruginosa ATCC 27853 and Enterococcus faecalis ATCC 29212, compared to the control. Overall, microbial melanin acted as a multifunctional bioactive reinforcement in chitosan-based films, improving their functional performances useful for potential applications in food packaging and biomedical fields.