Synergic effect and biosafety of chitosan/zinc complex nanoparticle-based carboxymethyl cellulose coatings for postharvest strawberry preservation

Nanotechnology represents a burgeoning field that revolutionizes various industries and sectors, including food applications. In this study, chitosan nanoparticles (CS NPs), zinc oxide nanoparticles (ZnO NPs), and chitosan-zinc complex nanoparticles (CS/Zn NPs) were prepared and incorporated into carboxymethyl cellulose (CMC) coatings to examine their strawberry preservation efficiency. CS NPs, synthesized <i>via</i> ionic gelation, appeared with a spherical shape and a relatively uniform size below 50 nm. ZnO NPs, produced through a green electrochemical method, formed larger aggregates. CS/Zn NPs were formed due to the chelation of CS NPs with Zn²⁺ present in the fresh zinc electrochemical solution. In antibacterial tests against <i>Escherichia coli</i> and <i>Staphylococcus aureus</i>, CS/Zn NPs exhibited significantly lower MIC and MBC values compared to CS NPs and ZnO NPs individually, indicating a synergistic antibacterial effect between the components. CMC coatings containing these nanoparticles were applied to strawberry surfaces and the fruits were stored at room temperature (25 °C) and in a refrigerator (5 °C). The CS/Zn-CMC coating demonstrated the most pronounced effect in preventing weight loss and decrease of titratable acidity (TA) and ascorbic acid (AA) content over storage. It effectively preserved the original appearance of strawberries, delaying browning until day 15, while the control and other coated samples were completely spoiled within this period. The cytotoxicity assessment indicated the safety of CS/ZnO-CMC coating, suggesting its potential application in fruit preservation.