Metal‑Doped ZIF‑8 Nanoparticles Coated with Hyaluronic Acid and Loaded with Oregano Essential Oil for Inactivation of Listeria monocytogenes on Spinach ( Spinacia oleracea )

Abstract

This work evaluates an antimicrobial ZIF‑8−based nanocomposite developed through Ag/Cu doping, hyaluronic acid (HA) surface functionalization, and oregano essential oil (OEO) encapsulation to enhance activity against foodborne pathogens, including Listeria monocytogenes. The combined incorporation of metal dopants, a biopolymer coating, and a natural antimicrobial enables complementary physicochemical and antimicrobial functions within a single nanostructure. Nanoparticles were synthesized via ambient-temperature precipitation and comprehensively characterized using SEM, TEM, FTIR, XRD, zeta potential, particle size, and DSC tests. The triple-modified variant (OEO-Ag-ZIF-8-HA) demonstrated superior antibacterial efficacy, with MIC and MBC values of 125 μg/mL and 375 μg/mL, respectively, significantly lower (p < 0.05) than undoped ZIF-8 (MIC: 2000 μg/mL, MBC: 8000 μg/mL). Cytotoxicity evaluation demonstrated favorable biocompatibility, with greater than 90% cell viability at 250 μg/mL for OEO-Ag-ZIF-8-HA. Testing on spinach leaves yielded reduced initial aerobic plate counts to 2.89 log CFU/g, sustaining <4 log CFU/g over 5 days and a 3.38 log CFU/g reduction of L. monocytogenes within 15 min (p < 0.05), showing greater antimicrobial performance than a standard chlorine control under the tested conditions. Treated spinach leaves retained a fresher appearance compared to controls over 5 days at 21 °C. These results demonstrate the potential of OEO‑Ag‑ZIF‑8‑HA as a biocompatible antimicrobial material for food safety applications.