A Chitosan-Based Dual-Functional Packaging Film Integrated Carbon Dots with Enhanced pH Sensing Ability for Fish Freshness Monitoring and Maintenance

Research into novel functional packaging materials can address the issues of food waste and food-borne illness caused by food spoilage. In this study, carbon dots (CDs) with good biocompatibility were prepared using a hydrothermal method and integrated with chitosan (CS) and purple potato anthocyanin (PPA) to manufacture a range of functional composite films for fish preservation. The introduction of CDs improved their mechanical properties, water resistance ability, and UV block performance, which were beneficial for the protection of foods. In contrast to pure CS film, the developed CS/PPA/CDs film exhibited high scavenging capacity against ABTS• (~ 87.99%) and DPPH• (~ 44.07%) and effectively inhibited the growth of Escherichia coli and Staphylococcus aureus. Notably, with the addition of 0.5 wt.% CDs, the pH sensing rate and color change of the film were more pronounced. In the preservation of fish, the CS/PPA/CDs film displayed lower weight loss, pH, TVB-N, and TVC values than CS film, confirming the effectiveness of the prepared film in controlling food contamination. Additionally, the intelligent film extended the shelf-life of fish and provided a reliable indication of fish freshness by a visual color change from purplish red to blue. This work constructs a new strategy for monitoring and maintaining fish freshness.