Chitosan-ZnO nanocomposite coating for inhibition of Listeria monocytogenes on the surface and within white brined cheese.

Several types of cheeses including white brined cheese have been linked to listeriosis outbreaks worldwide. This study aimed to (i) investigate the in vitro inhibitory activity of zinc oxide (ZnO) nanoparticles (NPs) at concentrations of 0.0125-0.1% against three Listeria monocytogenes strains at 10 or 37°C, (ii) evaluate the antimicrobial efficiency of chitosan-based coating containing 1.0% ZnO NPs against L. monocytogenes on the surface or inside vacuum-packaged white brined cheese at 4 or 10°C, and iii) determine the migration of ZnO NPs from the surface to the interior of cheeses using energy dispersive X-ray analysis (EDX). The antimicrobial activity of ZnO NPs was higher at 37°C than at 10°C. The initial numbers (4.0 log CFU/ml) of two L. monocytogenes strains were reduced below detectable levels, while the third strain was reduced by 1.2 log CFU/ml at 37°C. At 10°C, the initial L. monocytogenes numbers were reduced by 0.4-1.9 log CFU/ml. Chitosan coating containing 1.0% ZnO NPs reduced L. monocytogenes numbers by 1.5 and 3.7 log CFU/g on the surface or by 0.9 and 1.5 log CFU/g in the interior of vacuum-packed cheese stored at 10 or 4°C, respectively. The EDX results showed that ZnO NP levels remained constant on the cheese surface with no indication of migration into the cheese matrix at the end of storage. Practical Application: Chitosan and ZnO are antimicrobial agents and their combination in edible coatings has the potential for inactivating foodborne pathogens. Chitosan coating containing ZnO NPs can be used as an effective active packaging material to reduce numbers of L. monocytogenes in white brined cheese.