pH-triggered starch/ordered macroporous ZIF-8 smart films: synergistic antioxidant–antibacterial activity via clove oil encapsulation for sustainable food packaging

Abstract

Plant essential oil is acclaimed for its antibacterial and antioxidant qualities; however, it presents challenges in terms of stability and compatibility with natural polymers. This investigation centers on the application of single-crystalline ordered macro-microporous ZIF-8 (SOM-ZIF-8) for loading clove essential oil (CEO), which was later combined with starch/gellan gum to fabricate starch-based packaging films. This study meticulously explores the structural and property aspects of these films. SOM-ZIF-8, distinguished by its macroporous structure, reveals a CEO loading capacity of 660.6±2.4 mg/g. Starch-based films containing CEO@SOM-ZIF-8 demonstrate outstanding mechanical robustness, superior gas barrier properties, low moisture absorption, pronounced antioxidant activity, and potent antibacterial efficacy against key pathogens (Escherichia coli and Staphylococcus aureus). Blueberries packaged with the 4% (mass fraction) CEO@SOM-ZIF-8 film maintained the highest firmness (18.7±0.2 N) and soluble solids content (5.4%±0.1%). The film with 4% CEO@SOM-ZIF-8 consistently preserved the highest total phenol content (110.92 mg/L, P<0.05), a result significantly superior to the PE group and directly correlated with its efficacy in delaying quality deterioration by suppressing metabolic and microbial activity in blueberries. A key feature is the gradual and sustained release of CEO from CEO@SOM-ZIF-8, with release kinetics accurately described by the Ritger-Peppas equation. Importantly, the pH-responsive nature of this release provides a major advantage for preserving fruits and vegetables by extending shelf life.