INACTIVATION OF LISTERIA INNOCUA AND PSEUDOMONAS FLUORESCENS BY PULSED ELECTRIC FIELDS IN SKIM MILK: ENERGY REQUIREMENTS

Pulsed electric field energy applied over a short duration of time was effective in the inactivation of Listeria innocua and Pseudomonas fluorescens inoculated into 0.2% skim milk. Additionally, the energy consumption was reasonable for industry applications compared with the alternative of thermal pasteurization. The energy densities required to achieve three log reductions of the microorganisms were 120, 212 and 270 kJ/Lfor L. innocua corresponding to input voltages of 30, 35 and 40 kV, and 88, 105 and 128 kJ/L for P. fluorescens under the same input conditions. Treatment times were, respectively, 145 \is and 290 μs, and exponentially decaying wave pulses with time duration of 3 μs were selected. For L. innocua, the inactivation of viable cells was significantly different (P < 0.05) between energy inputs of 120, 212 and 270 kJ/L. Meanwhile, the inactivation of P. fluorescens exhibited significant differences (P < 0.05) between energy inputs of 88 and 128 kJ/L, but not between inputs of 105 and 128 kJ/L. These results consistently indicated that microbial inactivation in skim milk increased as the energy intensity and the treatment time increased.