Photothermal controlled-release packaging films based on chitosan-gelatin incorporated with pickering emulsions for tea tree oil delivery and their application in freshness preservation of berries.
Natural antimicrobial agents are both environmentally friendly and safe, and exhibit excellent biocompatibility. However, their instability and rapid release characteristics limit their application in food preservation packaging. In this study, a photothermal-responsive packaging film was developed by incorporating a Pickering emulsion of soy protein isolate-tannic acid-Fe3+(STF) nanoparticles stabilizing tea tree oil (TTO) into a chitosan (CS)/gelatin (Gel) matrix. The STF nanoparticles, synthesized via coordination-driven self-assembly, stabilized the Pickering emulsion and achieved an encapsulation efficiency of 84% for TTO. Under near-infrared (NIR) irradiation, STF nanoparticles transform light energy into thermal energy. On the one hand, the localized increase in temperature provides the film with a certain sterilizing effect. On the other hand, the film allows for the rapid, controlled release of tea tree oil as needed. Through the synergistic effect of localized thermal therapy and controlled release of essential oils, the film exhibits over 98% antibacterial activity against E. coli and S. aureus. Furthermore, the resultant film has outstanding mechanical strength, barrier properties, and antioxidant effects. Preservation experiments were ultimately carried out using strawberries and grapes as representative berries, and the results showed that the film can extend the shelf life by 3-8 days depending on the fruit type. These results demonstrate the application potential of this photothermal controlled-release film in the field of berry preservation.