Preparation of intelligent and active κ-carrageenan-based packaging film incorporating bayberry anthocyanins and iron-doped carbon dots for fresh shrimp preservation

This study developed a multifunctional, intelligent packaging film (bayberry anthocyanins/Fe-CDs/κ-Carrageenan/gelatin) based on a stepwise strategy for the high-value utilization of bayberry processing residues. Anthocyanins were extracted from bayberry residue, and iron-doped carbon dots (Fe-CDs) were synthesized from the remaining biomass to achieve comprehensive resource recovery. The structural characterization and performance evaluation confirmed that the synergistic integration of anthocyanins with Fe-CDs within the κ-Carrageenan/gelatin matrix endowed the film with a more compact structure and essential functionalities. The addition of bayberry anthocyanins and Fe-CDs enhanced the thermal stability and barrier properties of the composite film. Furthermore, the film demonstrated freshness-indicating capability through broad-spectrum pH responsiveness, strong ammonia sensitivity, and acid-induced color recovery. Antibacterial efficacy was significantly enhanced by incorporating Fe-CDs, achieving inhibition rates of 89.95 % against Staphylococcus aureus and 94.60 % against Escherichia coli , and the antibacterial mechanisms of Fe-CDs at the cellular level was explored. In a fresh shrimp preservation model, the film containing 1.5 wt% Fe-CDs extended its shelf life by three days and enabled real-time visual monitoring of spoilage. This study provides valuable insights for the application of metal ion-doped carbon dots in food packaging materials and offering diversified development perspectives for plastic alternatives and multifunctional food packaging.