Spray-Deposited Epigallocatechin Gallate-Based Metal–Phenolic Networks as Innovative Edible Coatings for Fresh Produce Preservation

Postharvest spoilage of fresh produce is a major contributor to global food loss, with existing preservation methods often constrained by sustainability or scalability. Metal–phenolic networks (MPNs), formed through coordination between metal ions and polyphenols, offer a promising alternative due to their inherent antioxidant and antimicrobial properties. This study presents a systematic evaluation of epigallocatechin gallate (EGCG)-based MPN coatings for fresh produce preservation, focusing on the effects of varying concentrations and metal ion types under controlled conditions. Using strawberries as a model, spray-applied Fe3+–EGCG and Zn2+–EGCG coatings delayed spoilage by at least 1.3-fold while maintaining key quality indicators. Notably, Zn–EGCG coatings reduced weight loss by up to 27% and retained 21% more firmness compared to uncoated controls over 5 days. While Zn–EGCG coatings, particularly at higher concentrations, demonstrated superior oxidative stability and moisture barrier properties, Fe–EGCG coatings showed reduced performance over time, likely due to iron-induced redox activity. Antibacterial assays showed Fe–EGCG to be more potent than Zn–EGCG, but high-concentration Zn–EGCG also inhibited both Gram-positive and Gram-negative bacteria. These findings highlight EGCG-based MPNs as an effective, scalable, and biocompatible strategy for extending shelf life and reducing postharvest food waste.