Efficient sterilization of bacteria by pulse electric field in micro-gap

Pulsed electric field sterilization is an appropriate treatment for fresh foods. However, the energy efficiency is not high enough and high voltage is required for the sterilization operation. In the present work, a high-efficient system with a micro-gap reactor was proposed for pulsed electric field sterilization. The applied voltage was reduced to the order of 100 V and the sterilization characteristics for Escherichia coli were improved significantly. In addition, the adjustment of electrical operating parameters was made possible using a semiconductor switch in a pulse generator circuit. Therefore, quantitative change of the sterilization characteristics was investigated with respect to various electric fields, repetition frequencies and pulse widths. A sterilization effect occurred over an electric field of 10 kV cm−1. The energy efficiency for sterilization was raised with an increase in the electric field strength. Besides, there was hardly difference in the energy efficiency for the repetition frequency. Their results suggest that Maxwell stress, which is defined as the stress tensor of an electromagnetic field, is extremely dominant compared with electrolysis or thermal effect in the sterilization mechanism. The optimum value of pulse width was estimated to be 100 μs on the basis of experimental and theoretical considerations. With long-pulse treatment, excess energy was consumed in Joule heating of the suspension.