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Applied and Environmental Microbiology, December 1999, p. 5364-5371, Vol. 65, No. 12
Microbiology & Preservation, Unilever
Research Vlaardingen, 3133 AT Vlaardingen, The Netherlands
Received 7 May 1999/Accepted 9 September 1999
The effects of pulsed electric field (PEF) treatment and processing
factors on the inactivation kinetics of Listeria innocua NCTC 11289 were investigated by using a pilot plant PEF unit with a
flow rate of 200 liters/h. The electric field strength, pulse length,
number of pulses, and inlet temperature were the most significant
process factors influencing the inactivation kinetics. Product factors
(pH and conductivity) also influenced the inactivation kinetics. In
phosphate buffer at pH 4.0 and 0.5 S/m at 40°C, a 3.0-V/µm PEF
treatment at an inlet temperature of 40°C resulted in
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Effects of Pulsed Electric Fields on Inactivation
Kinetics of Listeria innocua

6.3 log
inactivation of strain NCTC 11289 at 49.5°C. A synergistic effect
between temperature and PEF inactivation was also observed. The
inactivation obtained with PEF was compared to the inactivation obtained with heat. We found that heat inactivation was less effective than PEF inactivation under similar time and temperature conditions. L. innocua cells which were incubated for a prolonged time
in the stationary phase were more resistant to the PEF treatment, indicating that the physiological state of the microorganism plays a
role in inactivation by PEF. Sublethal injury of cells was observed after PEF treatment, and the injury was more severe when the level of
treatment was increased. Overall, our results indicate that it may be
possible to use PEF in future applications in order to produce safe products.
*
Corresponding author. Mailing address: Microbiology & Preservation, Unilever Research Vlaardingen, Olivier van Noortlaan 120, 3133 AT Vlaardingen, The Netherlands. Phone: 31-10-4605028. Fax: 31-10-4605188. E-mail: Patrick.Wouters{at}Unilever.com.
Present address: TNO Voeding, 3700 AJ Zeist, The Netherlands.
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