Antibacterial activity and mechanism of high voltage electrostatic field (HVEF) against Staphylococcus aureus in medium plates and food systems

Inhibitory effects of three kinds of electric fields, high voltage electrostatic field (HVEF), alternating electric field (HVAEF) and prick electrostatic field (HVPEF) against Staphylococcus aureus (S. aureus) were investigated in medium plates and food systems. The results showed that S. aureas was more sensitive to HVPEF than to HVEF and HVAEF, especially when growing on the surface of solid culture medium, and the mortality rate was over 99.9% when the voltage was higher than 10 kV. The kinetics study showed that with the increase of processing time, the mortality rate increased linearly and then plateaued. The change of cell morphology and leakage of intracellular materials indicated that HVPEF damaged cell membrane and increased the membrane permeability. Flow cytometry with double staining demonstrated cell membrane integrity was destroyed, and nonspecific esterase activity was reduced by HVPEF. The intracelluar reactive oxygen species (ROS) generated by HVPEF increased significantly compared with the control as voltage rose. And the effect of HVPEF on S. aureus incubated on food surface was further studied, the mortality rate increased with the increase of electric voltage and treatment time, the rates attained 98.3 +/- 0.2% (Salmon), 98.6 +/- 0.3% (Griskin), 99.8 +/- 0.1% (Cheese) and 99.6 +/- 0.1% (Sausage) at 13 kV for 30 min, respectively. HVPEF had great antibacterial effects against S. aureus on solid surfaces, and the results provided a theoretical guidance for the possible application of HVPEF technology in non-thermal food sterilization.