Optimization of Orange Peel Extract Nanoemulsions and Their Incorporation into Chitosan/Gelatin Biodegradable Films: Physicochemical and Functional Properties

In this study, orange peel extract (OPE), obtained from Citrus sinensis processing by-products, was encapsulated in nanoemulsions and incorporated into chitosan/gelatin-based biodegradable films to enhance their functional performance. A Box–Behnken design combined with response surface methodology was employed to optimize nanoemulsion formulation. Polyphenolic profiling revealed that flavanones, particularly hesperidin and narirutin, were the predominant compounds in both the extract and the optimized nanoemulsion, with retention efficiencies exceeding 80% for major flavonoids. The incorporation of OPE-loaded nanoemulsions into chitosan/gelatin films significantly modified film structure and functionality. Nanoemulsion-containing films showed increased thickness and opacity, reduced solubility and swelling capacity, as well as enhanced UV-visible light barrier properties compared with control films. Furthermore, nanoencapsulation increased polyphenol recovery within the film matrix, preserving up to 80% of total polyphenols after film formation. Both free-extract and nanoemulsion-loaded films exhibited markedly enhanced antioxidant activity compared with control films. Release studies demonstrated that nanoemulsion incorporation promoted a more sustained and controlled release of polyphenols, with the characteristic release time more than doubling relative to films containing the non-encapsulated extract. No antibacterial activity was detected against the tested bacterial strains; this result may be attributed to the relatively low availability of antimicrobial compounds in the film matrix or their limited diffusion into the surrounding medium; nevertheless, the incorporation of OPE-loaded nanoemulsions improved stability, antioxidant performance, and controlled release behavior, highlighting the potential of nanoemulsion-assisted incorporation strategies. The developed chitosan/gelatin films containing OPE-loaded nanoemulsions represent a promising approach for the development of active biodegradable food-packaging systems.