EFFECT OF GROWTH STAGE AND PROCESSING TEMPERATURE ON THE INACTIVATIONOF ESCHERICHIA-COLI BY PULSED ELECTRIC-FIELDS

The effect of growth stage and processing temperature on the inactivat ion of Escherichia coli subjected to pulsed electric fields was studie d. Simulated milk ultrafiltrate (SMUF) inoculated with E. coli was sub jected to high-intensity exponentially decaying or square-wave pulses with a field strength of 36 kV/cm and pulse duration of 2 mu s at sele cted temperatures ranging between 3 and 40 degrees C. The rate of inac tivation increased with an increase in the processing temperature. Fur thermore, square-wave pulses were more lethal than exponentially decay ing pulses. At 7 degrees C after 100 mu s, square-wave pulses produced a 99% decrease while exponential decaying pulses produced a 93% decre ase in bacterial cell population. Cells harvested at lag, log, and sta tionary phases were subjected to 2 and 4 pulses with an electric field intensity of 36 kV/cm at 7 degrees C. Logarithmic-phase cells were mo re sensitive than stationary- and lag-phase cells to the pulsed electr ic field treatment.