Self-Assembled Metal–Phenolic–Agar Microparticle-Derived Coatings Enable Scalable and Sustainable Fresh Produce Preservation

Abstract

The burden of food waste highlights the need for effective, scalable preservation strategies. Herein, we developed a natural, biocompatible, plant-based, and consumer-friendly metal–phenolic–agar (MPN–Agar) coating for postharvest preservation. The coating was formed through coordination between micronutrient ions (e.g., Zn2+, Mg2+, Ca2+, and Fe3+) and tannic acid within an agar matrix, producing stable microscale colloidal particles. Applied to strawberries, grapes, and apple slices, the coating extended shelf life by at least 2-fold. In strawberries, it reduced 4 day weight loss from 30.59% to 13.36% and increased firmness from 18.53 to 41.77 N. The coating also showed antibacterial activity, no cytotoxicity in Caco-2 cells, easy removal by water rinsing, and compatibility with food-grade agar. Notably, MPN–Agar coating under room-temperature storage outperformed uncoated refrigeration for strawberries, suggesting potential to reduce cold-chain reliance. Life cycle assessment showed lower carbon footprint and freshwater ecotoxicity than refrigeration, supporting its potential as a sustainable preservation alternative.