Inactivation of microorganisms using pulsed electric fields: the influence of process parameters on Escherichia coli, Listeria innocua, Leuconostoc mesenteroides and Saccharomyces cerevisiae

This study examines the killing effect of pulsed electric fields (PEF) on four organisms suspended in a model medium. Escherichia coli , Listeria innocua , Leuconostoc mesenteroides and Saccharomyces cerevisiae differ in size, shape and cell wall construction. The electric field strength, pulse duration and number of pulses were varied in the ranges of 25–35 kV/cm, 2–4 μs and 20–40 pulses, respectively. The results showed that S. cerevisiae was the most sensitive organism with a 6-log reduction, followed by E. coli with a 5.4-log reduction, when they were exposed to 30 kV/cm, and 20 pulses with 4 μs duration. The most resistant organisms were L. innocua and L. mesenteroides with only a 3-log reduction, however, by increasing the parameters to 35 kV/cm and 40 pulses with 4 μs pulse duration; marked viability reductions of 8 and 7 log, respectively, were observed. Heat, which is generated during the process, has limited killing effect on the cells, hence the observed reduction can be ascribed to the PEF treatment. Although transmission electron microscopy of PEF treated cells did not confirm membrane damage, observations suggest that PEF treatments have profound direct or indirect effects on the intracellular organisation of microorganisms.