Light-activated Zein–curcumin films for the photodynamic inactivation of bacterial biofilms: Continuous vs. intermittent illumination

The development of protein-based films derived from plants and agricultural sources has gained significant attention in the medical and food industries due to their broad applicability, sustainability, low cost, and non-toxic nature. Over the years, numerous studies have reported (photo)antimicrobial films aligned with the principles of the circular economy. In this study, zein-based films immobilized with curcumin as a photosensitizer (2.5 % and 5 % w/w) were synthesized and fully characterized using UV–Vis spectroscopy, fluorescence analysis, FT-IR, thermogravimetry (TG), and water contact angle measurements. Their potential for photodynamic applications was assessed through photobleaching analysis, confirming the generation of reactive oxygen species (ROS) at both concentrations. Furthermore, microbiological evaluations were conducted against Staphylococcus aureus biofilms under two different lighting regimes: continuous and intermittent exposure at specific time intervals (0, 6, 12, 18, and 24 h). The films demonstrated promising antimicrobial activity, achieving bacterial inactivation of up to 3.5 log reductions. These findings highlight the potential applications of zein-curcumin films as coatings for medical devices (e.g., endotracheal tubes, catheters) and as sustainable food packaging materials. The incorporation of photoantimicrobial properties into biodegradable films opens new perspectives for their use in healthcare and food preservation.