• liquid foods;
  • nanoparticles;
  • pathogens;
  • zinc oxide

ABSTRACT:  Zinc oxide quantum dots (ZnO QDs) are nanoparticles of purified powdered ZnO. These were evaluated for antimicrobial activity against Listeria monocytogenes, Salmonella Enteritidis, and Escherichia coli O157:H7. The ZnO QDs were utilized as a powder, bound in a polystyrene film (ZnO-PS), or suspended in a polyvinylprolidone gel (ZnO-PVP). Bacteria cultures were inoculated into culture media or liquid egg white (LEW) and incubated at 22 °C. The inhibitory efficacies of ZnO QDs against 3 pathogens were concentration dependent and also related to type of application. The ZnO-PVP (3.2 mg ZnO/mL) treatment resulted in 5.3 log reduction of L. monocytogenes and 6.0 log reduction of E. coli O157:H7 in growth media after 48 h incubation, as compared to the controls. Listeria cells in the LEW control increased from 3.8 to 7.2 log CFU/mL during 8 d incubation, while the cells in the samples treated with 1.12 and 0.28 mg ZnO/mL were reduced to 1.4 and 3.0 log CFU/mL, respectively. After 8 d incubation, the cell populations of Salmonella in LEW in the presence of 1.12 and 0.28 mg ZnO/mL were reduced by 6.1 and 4.1 log CFU/mL over that of controls, respectively. ZnO powder and ZnO-PVP showed significant antimicrobial activities against all 3 pathogens in growth media and LEW. ZnO-PVP coating had less inhibitory effect than the direct addition of ZnO-PVP. No antimicrobial activities of ZnO-PS film were observed. This study suggested that the application of ZnO nanoparticles in food systems may be effective at inhibiting certain pathogens.