Antimicrobial effects of ZnO nanoparticles may be attributed to several mechanisms:
1) induction of oxidative stress due to ROS generation especially interior or out of cell H2O2 which leads to interaction with proteins, DNA, and lipids causing death ;
2) membrane disorganization due to accumulation of ZnO nanoparticles in the bacterial membrane and also their cellular internalization ;
3) release of Zn ions that may be responsible for antimicrobial activity by binding to the membrane of microorganisms.
However, the toxicity of ZnO nanoparticles is not directly related to their entering into the cell, rather their intimate contact onto the cell causes changes in the microenvironment in the vicinity of the organism-particle contact area to either increase metal solubilization or to generate ROS, that may ultimately damage cell membrane .
Moreover, the toxicity of ZnO nanoparticles is not only affected by the light via ROS production, but may also happen in the dark although its mechanism is not yet defined .
Jin et al. (2009) studied several approaches (powder, film, PVP capped and coating) for the application of nano-ZnO in food systems and concluded that nano-ZnO exhibits antimicrobial effects against L. monocytogenes and S. enteritidis in liquid egg white and in culture media.