Abstract: Gelatin (Gel) and carboxymethyl chitosan (CMCS) were used as the film-forming matrix to prepare ternary composite films via covalent imine bonding between cinnamaldehyde (Cin) at varying concentrations (0%–20%) and the Gel-CMCS matrix. The effect of Cin on the physicochemical properties of the composite films was investigated, and the pH-responsive release characteristics of Cin and the antibacterial activity of the composite films were evaluated as well as the application effect for the quality preservation of fresh blueberries during room-temperature storage. The results showed that the composite film with 15% Cin exhibited the best comprehensive performance, with a tensile strength of 13.350 MPa, an elongation at break of 181.523%, a water vapor transmission rate of 4.690 g·m/(m2·d·kPa), and a water contact angle of 75.7°. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyses confirmed that Cin was bonded to the film-forming matrix through Schiff-base reactions and uniformly distributed therein, resulting in a compact structure. The composite film displayed an obvious burst release of Cin in acidic environments (pH 3–5) and sustained release under neutral conditions, demonstrating a pH-triggered “on-off” release behavior. At pH 5, the film exhibited significant inhibitory effects against Escherichia coli and Staphylococcus aureus. Furthermore, the composite film effectively delayed mass loss, firmness reduction, and anthocyanin degradation in blueberries, significantly inhibited microbial growth, and extended the shelf life from 4–6 to 8 days. The pH-responsive “on-off” active packaging developed in this study can provide a novel strategy for the design and development of intelligent packaging materials.

Key words: cinnamaldehyde; controlled release; preservation; antibacterial activity; active packaging