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.

Antimicrobial activity of chitosan coating containing ZnO nanoparticles against E. coli O157:H7 on the surface of white brined cheese.

White brined cheese may serve as an ideal medium for the growth of foodborne pathogens including E. coli O157:H7. The objectives of this study were i) to evaluate the inhibitory effects of zinc oxide (ZnO) nanoparticles against E. coli O157:H7 at 10 or 37 °C using broth dilution; ii) to address the post-process contamination of white brined cheese with E. coli O157:H7 by using chitosan coating with or without ZnO nanoparticles during storage for 28 d at 4 and 10 °C; and iii) to study the physicochemical characteristics of chitosan coating containing ZnO nanoparticles. ZnO nanoparticles at ≥0.0125% inhibited the growth of three E. coli O157:H7 strains at both 37 and 10 °C. The chitosan coating with or without ZnO nanoparticles significantly reduced the initial numbers of E. coli O157:H7 in white brined cheese by 2.5 and 2.8 log CFU/g, respectively, when stored at 4 °C or by 1.9 and 2.1 log CFU/g, respectively, when stored at 10 °C. The chitosan-ZnO nanoparticle coating was not significantly different (p > 0.05) but was slightly better than chitosan alone as an active, smart packaging material in food applications.