Antibacterial Activity And Mechanism Of Metallic Nano-oxides Against Foodborne Pathogens

The objects of this research were Staphylococcus aureus, Salmonella and Listeria monocytogenes, which are the commonly detected foodborne pathogens. Effects of Zn O and Mg O nanoparticles on the growth curve of the 3 kind of pathogenic bacteria were studied.The antibacterial mechanism were also discussed through the changes in morphological,physiological, and biochemical indexes. Zn O nanoparticles film was prepared to study the antibacterial properties and the effects on quality of chilled pork. The results of this research were as follows:The growth of S. aureus and L. monocytogenes was well inhibited by Zn O nanoparticles at 37℃. The inhibitory effects was enhanced as the concentration increased.Mg O nanoparticles have strong antibacterial activity against the 3 kind of foodborne pathogens and can inhibit the growth of L. Monocytogenes and exterminate S. aureus and Salmonella. In present study, the antibacterial effects of Zn O nanoparticles and Mg O nanoparticles were firstly evaluated at 4 ℃ and-18 ℃. The Zn O nanoparticles, Mg O nanoparticles and low temperature demonstrated a cooperatively antimicrobial property on tested foodborne pathogens. There were evidented by a 2 Log(CFU/ml)reduction for L.monocytogenes, or even totally inactivation for S. aureus after 120 and 96 h of storage,compared to the group without Zn O or Mg O supplement at 4℃. On the condition of-18℃,the growth of S. aureus, Salmonella and L. monocytogenes were completely inhibited when treated by Zn O nanoparticles for 120, 96 and 72 h respectively. The growth of the 3 kind of foodborne pathogens were totally inactivated by Mg O nanoparticles when treated for 120,72 and 72 h respectively. However, the Zn O nanoparticles showed no inactivation effect on Salmonella at 37℃ and 4℃.Scanning electron microscopy(SEM) and transmission electron micrographs(TEM)were used to characterize the changes of morphological and internal structure of S. aureus and L. monocytogenes before and after Mg O or Zn O nanoparticles treatments. The results showed that normal S. aureus had rough surface, ambiguous cell wall and cell membrane,disorganized internal structure and the bacteria was transparent and ruptured when treated by Zn O nanoparticles. Mg O nanoparticles treatments distorted the normal L. Monocytogenes morphological by elongating, bending cells, and shrinking cell membrane. Cytoplasm-cell wall separation and internal organization condensation were also observed. The results alsoshowed an increase in the content of O2- and SOD activity increased, which indicated that the treatment of Mg O or Zn O nanoparticles caused oxidative stress.Zn O nanoparticles were further combined with CMC to form a nanocomposite film using drying method. When the film was applied as a packaging material for chilled pork meat during storage, it showed significant inhibition on the growth of pathogenic S. aureus,L. monocytogenes, as well as the total viable cell numbers. Meanwhile, the increases of TVB-N and p H values as meat quality indicators were also retarded. By delaying the meat corruption and maintaing the sensory quality, the shelf-life of chilled pork meat was 10 d extended compared to that packaged using no Zn O nanoparticles coated film. Thus, the Zn O nanoparticles coated film have a great potential in the application of chilled meat to reduce harmful bacterial contaminations, retain meat fresh, as well as extend the shelf life.