A Schiff base-driven pH responsive dual release coating incorporated thyme essential oil nanoemulsion for strawberry...

Strawberries are susceptible to infection after harvest, resulting in significant losses every year. To address this issue, this paper prepared pH-responsive dual release coatings for preserving strawberries through Schiff base bond in carboxymethyl chitosan (CMCS)/pullulan matrix. The addition of thyme essential oil (TEO) could increase the antifungal activity of CMCS/pullulan composite coating by 94.45%. The addition of vanillin enabled the formation of Schiff base bond with CMCS and enhanced mechanical strength, UV resistance and water vapor resistance of CMCS/pullulan composite film. When strawberries were infected by fungus that gradually form a slightly acidic environment during storage, the Schiff base bond could break to release vanillin and TEO to inhibit fungus growth. Release tests showed that the release profiles of TEO and vanillin were sustained, and the release content of vanillin was 66.91% higher at pH = 5 than pH = 7. Strawberry storage experiment demonstrated that the CMCS/PUL/T/VA group had the best preservation effect, with the lowest decay rate, the highest firmness and better appearance. Soil degradation test confirmed that CMCS/PUL/T/VA films could be completely degraded within 60 d. This paper prepared natural, biodegradable, and antifungal pH-responsive dual release coatings and provided a strategy for the future development of multifunctional pH-responsive packaging.