Pulsed Electric Field Effects on Bacteria and Yeast Cells

Cell suspensions of yeasts and bacteria in the exponential growth phase were subjected to pulsed electric fields of 12.5 kV/cm intensity to study inactivation. Up to 20 pulses of 0.3 ms duration were applied at a maximum temperature of 30C. The yeasts Saccharomyces cerevisiae and Candida stellata were reduced by >3 log. These reductions were due to nonthermal effects. Reductions of approximately 1 log or less were obtained for the bacteria Escherichia coli and Listeria innocua. However, by acidifying the L. innocua suspension from pH 6.6 to 3.8, a 3 log reduction was achieved. In contrast, acidification of the E. coli suspension had no effect on inactivation.