Metal–Organic Framework-Encapsulated Transglutaminase Biocatalyst: Enhancing Operational Stability and Freshness Retention in Food Coatings

Food packaging films, enzymatically cross-linked using transglutaminase (TG), have demonstrated significant potential for eco-friendly packaging applications due to their biodegradability and nontoxicity. However, the inherent fragility of natural enzymes, such as instability and nonreusability, poses significant challenges for TG in the fabrication of these films. Herein, TG was immobilized within HKUST-1 (a copper-based metal-organic framework) via in situ biomineralization with ultrasound assistance and employed to cross-link zein for preparing biodegradable films. TG@HKUST-US demonstrated 140% enzymatic activity compared to the free enzyme, while also enhancing thermal and pH stability. The composite further improved the pH tolerance and exhibited significantly enhanced stability in organic solvents. Furthermore, the addition of TG@HKUST-US to zein-based polymeric matrices resulted in improved water holding capacity, which could effectively slow down the weight loss of fruits and vegetables (reductions of 41.5% for apples, 34.1% for pears, and 29.5% for lettuce compared to those without any treatment group). Moreover, the films prepared through the reuse process exhibited no toxicity, with copper ion leaching levels significantly lower than the safety threshold. Therefore, this study developed TG@HKUST-US to catalyze zein protein cross-linking for eco-friendly films, establishing a novel immobilization strategy of enzyme and sustainable platform for advanced food packaging.