Direct addition of vanillin improved the physicochemical properties and antibacterial activities of gelatin/sodium carboxymethyl cellulose composite film

Green packaging films made of natural macromolecular polymers can be used for food packaging, the performance of such packaging films is not satisfactory. Alternatively, crosslinkers are often used to compensate for the defects. However, studies on edible aromatic substances as cross-linking agents and their addition methods have been neglected. In this study, vanillin was added to gelatin (G) and carboxymethylcellulose sodium (CMC-Na, C) complex coacervation system in two ways: direct addition (GC-D) and emulsification addition (GC-E), and two different vanillin-polysaccharides-proteins composite films were prepared. Meanwhile, the effects of vanillin amount on physicochemical and functional properties of the composite films were explored. Results showed that vanillin significantly reduced the tensile strength (TS) of GC-D films, but significantly increased the GC-E films' TS (P < 0.05). The TS of GC-D film (61.75 MPa) and GC-E film (56.66 MPa) reached the maximum with 3% vanillin addition. Vanillin significantly reduced the UV transmittance of the two films, while tended to increase the water contact angle. XRD and FTIR analysis found that vanillin played a cross-linking role with protein imino groups in the composite system. The SEM showed that GC-D films had good microstructure, but GC-E films had honeycomb-like surface. Finally, the two films had good soil degradability and antibacterial property on Escherichia coli and Staphylococcus aureus, among which GC-D films had better antibacterial effect. In summary, this study showed that vanillin could be used as a cross-linking agent to strengthen protein-polysaccharide-based composite film, and different addition methods and vanillin amounts could significantly affect the physicochemical and functional properties of GC composite film, which provided a new idea for the development of new environmentally friendly food packaging films.