Application of Pulsed Electric Fields to Skim Milk inoculated with Staphylococcus aureus

Application of pulsed electric fields (PEF) to skim milk inoculated with Staphylococcus aureus was conducted in the study. Skim milk samples were treated by PEF, using fluid handling systems of both circulation and stepwise modes. Parameters for the PEF were 3·7 μs pulse duration time, 250 Hz pulse repetition rate, 1 ml s−1 flow rate, 460 μs total treatment time, and 3·5 kV mm−1 electric field strength. After the PEF-treatment, the samples were plated onto both tryptic soya agar and Baird Parker agar with egg yolk tellurite enrichment to enumerate the number of inactivated and injured cells. Survivals of PEF-treated S. aureus cells were also enumerated at refrigeration temperature for 2 weeks. There was a significant decrease in S. aureus cells caused by the two fluid handling systems (probability P<0·05). The difference in the inactivation due to the PEF treatment with the fluid handling systems was not significant (P>0·05). After the PEF treatment, there was no significant injury of the PEF-treated cells (P>0·05). Relative to the control samples, there was a significant reduction in the number of the PEF-treated cells at 4°C for 2 weeks (P<0·05).