Preparation and characterization of deep eutectic solvent-plasticized zein films embedded with cinnamaldehyde nanoparticles and their application in the preservation of green oranges

To address the brittleness and inadequate barrier properties of conventional zein films, this study explored a composite zein film plasticized with choline chloride-citric acid deep eutectic solvent (DES) and loaded with cinnamaldehyde nanoparticles (namely DES-plasticized zein/nanoparticle film, abbreviated as DZNF), whose structural, physicochemical and functional attributes were evaluated by comparing with DES-plasticized zein film (DZF), glycerol-plasticized zein film (GZF) and glycerol-plasticized zein/nanoparticle film (GZNF). Subsequently, the preservation effect of prepared composite films on green oranges was investigated. The characterization results demonstrated that DES modified protein structure of zein, which significantly enhanced the tensile strength, thermal stability and water vapor barrier permeability. DZNF showed the highest antioxidant capacity and antimicrobial activity among all tested films. DZNF showed a slower release of cinnamaldehyde than GZNF. Further observation by SEM revealed that DZNF formed a denser and smoother microstructure compared to GZNF, DZF and GZF. Coating application of composite films to green oranges inhibited the changes in fruit quality parameters, as indicated by delayed weight loss, discoloration and soluble solid loss, with the optimal preservation effect being achieved by DZNF. The results indicate that DZNF, with its enhanced material properties, exhibits significant potential for citrus fruit preservation.