Combination of Microsecond and Nanosecond Pulsed Electric Field Treatments for Inactivation of Escherichia coli in Water Samples
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Inactivation of microorganisms with pulsed electric fields is one of the nonthermal methods most commonly used in biotechnological applications such as liquid food pasteurization and water treatment. In this study, the effects of microsecond and nanosecond pulses on inactivation of Escherichia coli in distilled water were investigated. Bacterial colonies were counted on agar plates, and the count was expressed as colony-forming units per milliliter of bacterial suspension. Inactivation of bacterial cells was shown as the reduction of colony-forming units per milliliter of treated samples compared to untreated control. According to our results, when using microsecond pulses the level of inactivation increases with application of more intense electric field strengths and with number of pulses delivered. Almost 2-log reductions in bacterial counts were achieved at a field strength of 30 kV/cm with eight pulses and a 4.5-log reduction was observed at the same field strength using 48 pulses. Extending the duration of microsecond pulses from 100 to 250 μs showed no improvement in inactivation. Nanosecond pulses alone did not have any detectable effect on inactivation of E. coli regardless of the treatment time, but a significant 3-log reduction was achieved in combination with microsecond pulses.
KeywordsInactivation Bacteria Nanosecond Microsecond Electric pulse Pulsed electric field treatment Electroporation E. coli Water
The authors thank Prof. Dr. Damijan Miklavčič, who read the manuscript and provided comments and insights that improved it. This research was supported by the Slovenian Research Agency under research program P2-0249, MRIC UL IP-0510 and research project L2-4314. The research was conducted in the scope of EBAM, European Associated Laboratory.
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