Systematic Investigation of Metal–Phenolic Network-Capped Starch Nanoparticles as Sustainable Coatings for Postharvest Fruit Preservation

Abstract

Sustainable coatings have emerged as an alternative for preserving fruit freshness, reducing food loss, and waste. Metal–phenolic network (MPN) offers broad applicability in the agri-food sector by modifying food molecules and structures, and contributes to food preservation. The study systematically investigates the formation, characterization, and functional performance of a sustainable coating composed of MPN-capped-starch nanoparticles (MCS) using various combinations of metal ions (Fe³⁺, Zn²⁺) and polyphenols (tannic acid (TA), epigallocatechin gallate (EGCG) for postharvest fruit quality maintenance. The incorporation of starch nanoparticles (SNPs) effectively enhanced the barrier properties of MPN coatings by reducing gas exchange and water loss. Among the formulations, Fe–TA–MCS showed the strongest performance in limiting weight loss and maintaining firmness due to the dense network structure. Fe-based coatings also exhibited notable antimicrobial activity. Zn–EGCG–MCS was most effective in preserving surface color, titratable acidity, soluble solids, and phenolic content. Overall, Fe–TA and Zn–EGCG systems formed robust MPN crosslinks, and once capped onto SNPs, MPN-capped-starch nanoparticles formulations enable superior multifunctional performance in postharvest preservation compared with MPN formulations. This study provides a first demonstration and systematic analysis of the preservation performance of various MPN and MPN-formulated MCS coatings in grape preservation, offering insights for the future design and engineering of MPN systems customized for specific functional applications in food packaging and coating.