Chitosan-Starch-Modified ZnO Cross-Linked Composite Films for Food Packaging

The CS-c-ST-c-mZnO composite films as active food packaging films were developed using chitosan (CS) and starch (ST) as the film-forming substrates, mZnO (KH-550 modified nano-ZnO) as the antimicrobial agent, and citric acid as the cross-linking agent by the solution-casting method. The research indicated that mZnO prepared using the KH-550 modified nano-ZnO could effectively improve the thermal stability, mechanical properties, barrier properties, and antimicrobial properties of the composite films. Rheological testing results demonstrated that the film-forming fluid can create a more stable film structure. When the mZnO content was 3 wt %, the thermal degradation temperature of the cross-linked composite films increased by 8 °C (DTG peak of 343 °C). The tensile strength and the elongation at break were 16.50 ± 0.23 MPa and 181.65 ± 4.46%, and the water vapor transmission rate and oxygen transmission rate were 7.3 ± 0.3 g/(m2·24 h) and 36.9 ± 1.7 cm3/(m2·24 h·atm). The composite films exhibited significant broad-spectrum antimicrobial activity, demonstrating inhibition zones of 17.3 ± 0.3 mm against S. aureus and 16.5 ± 0.2 mm against E. coli, along with a high inhibition rate of 89.1% against B. cinerea. With the increase of mZnO content, the transparency of the cross-linked composite films decreased yet it still maintained a high level of clarity. Compared with the commercial PE packaging films, the strawberries packed with the CS-c-ST-c-mZnO-3 maintained high fruit hardness after 8 days of storage, and the rotting was not observed, which effectively prolonged the shelf life of the strawberries. The results indicated that the CS-c-ST-c-mZnO composite film had great potential for application in the packaging of fruits and vegetables during transportation.