Tailoring functional chitosan films using deep eutectic solvents extracts of propolis for active food packaging

In this study, to enhance the water resistance, mechanical properties and functional properties of the chitosan (CS) film, the deep eutectic solvents-based propolis extract (DPE) containing polyphenols was directly incorporated into the chitosan-based films. The total polyphenol and the total flavonoid content in the DPE achieved increases of 289.9% and 216.6% compared to conventional ethanol–water propolis extract for polyphenol and flavonoid content, respectively. Effect of incorporating DPE into a chitosan matrix on the structural, physicochemical, and functional properties of the resulting composite films was comprehensively investigated. SEM, FTIR, XRD, and TGA analyses confirmed the uniform dispersion of DPE within the CS matrix via hydrogen bonding, resulting in improved structural homogeneity, modified crystallinity, and enhanced thermal stability. Optical analyses revealed an increase in film coloration and excellent UV-blocking ability due to the aromatic structures of polyphenols. Mechanical tests demonstrated that DPE incorporation significantly increased film flexibility (62.3% for CS/DPE60 (the adding of DPE was 60% dry weight of the chitosan)) while moderately reducing tensile strength (36.6 MPa for CS/DPE60) compared to pure chitosan film, indicating suitability for flexible packaging applications. Additionally, the CS/DPE films exhibited improved water barrier properties, antioxidant capacity, and antibacterial activity. A practical application in strawberry preservation showed that the CS/DPE film effectively reduced spoilage, minimized moisture loss, and delayed texture deterioration during storage. These findings highlighted the potential of CS/DPE composite films as multifunctional active packaging materials for food preservation.