Date of Award

Summer 2001

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical Engineering

Committee Director

Karl H. Schoenbach

Committee Member

Ravindra P. Joshi

Committee Member

Linda L. Vahala

Call Number for Print

Special Collections LD4331.E55 A59 2001

Abstract

Pulsed electric fields are widely used for bacterial decontamination of water and liquid food [I]. Depending on pulse amplitude and duration, a certain percentage of the bacteria suffer irreversible damage and, consequently, cell death. We have explored the effect of microsecond pulses of 13 kV/cm and 15 kV/cm electric field amplitude on the viability of Escherlchia coli. The pulse duration was varied from 4 μs to 32 μs, and the pulse number of 4 μs pulses from one to eight, Finally, the effect of separation between pulses was studied. The pulses were generated by means of a generator where IGBTs were used as closing and opening switches. The maximum voltage was 1.5 kV at a maximum current of 160 A. The load was a cuvette with plane I cm aluminum electrodes, 1mm apart and filled with a solution (LB Broth) that contained E. coli bacteria at a concentration of approximately 3x105 cells/ml. The viability of the E. coli after electric field application was measured by using manual counting for E coli colonies in cultured agars. The bacterial decontamination rate was found to increase with pulse duration up to 8 μs and then to decrease again.

This maximum decontamination rate is assumed to be related to dipole formation in the rod-shaped bacteria. It causes a reorientation of the E. coli into the direction of the electric field and consequently a higher possibility for irreversible damage. The experimental results with varying temporal separation between two consequence pulses show that independent of field amplitude (in the relatively narrow range of 13 kV/cm to 15 kV/cm), the decontamination rate decreases logarithmically with increasing separation. This effect is assumed to be due to the randomization of the directions of the axis of rod-shaped bacteria in the broth after exposed to an electric pulse.

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DOI

10.25777/e57z-ka93

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