A novel multifunctional composite film of oxidized dextran crosslinked chitosan and ε-polylysine incorporating protocatechuic acid and its application in meat packaging

Oxidized dextrans (ODex) with different oxidation degrees were prepared by periodate oxidation. Chitosan (CS) and ε-polylysine (PL) were crosslinked with ODex and incorporated with protocatechuic acid (PA) to enhance the properties of the chitosan-based films. FT-IR, XPS and XRD analysis showed that the aldehyde groups of ODex were covalently crosslinked with amino groups of CS and PL through Schiff base reaction, and PA interacted with the film components through non-covalent bonds. The results of SEM and AFM indicated that the film structure became denser with the addition of ODex. Increasing crosslinking degree resulted in deepened color and improved the UV-blocking ability of the films, which was caused by the increase of CN groups. Covalent crosslinking significantly reduced the moisture content, swelling degree and water solubility. The film with 50% ODex had the highest mechanical strength (31.72 MPa) and modulus of elasticity (885.54 MPa). The results of water vapor permeability, thermal properties and PA release experiments also indicated the crosslinking of the films by ODex. The incorporation of PA significantly improved the antioxidant activity of the films, but to some extent, the antibacterial activity of the films decreased due to the consumption of amino groups by crosslinking. In addition, application experiments suggested that crosslinked films could maintain the quality and freshness of chilled meat for a longer period than that of PE plastic films. The study suggested that the new crosslinked films might have good prospects as food packaging materials.