Liquid Foods Treatments by PEF –A deep Analysis owing to Electromagnetic Theory

It was observed that applying pulsed high voltages of the order 20kV or more with durations of 0 to 10 μs or less can destroy some micro organisms like Saccharomyces Cerevisiae which are commonly encountered in tropical liquid foods. The amplitude of the applied high pulsed signals, their durations, and the number of pulses per second seem experimentally necessary to obtain good results in terms of the number of destroyed micro organisms. Few studies have yet clearly explained quantitatively the mechanism of the observed destruction due to the application of very fast and intense electric fields on the undesired micro organisms in the foods. In this paper we attempt to contribute such explanations by using the theory of distributions applied in electromagnetism which seems more adequate for the analysis of fast phenomenon like the one that appears in the cells when they receive the pulsated electric field. We carefully consider in the study different real situations, where, we have the plates that carry the high voltage pulses, the media in which the micro organisms are immersed, as well as the micro organisms. Firstly we state some assumptions like the bipolarisation reactions of the micro organisms due to either natural polarization of some cell internal components, or to induced polarization of the cell that comes from the applied high voltages. We then analyse many cases using different variations of the parameters of, the electric source, the media, or the micro organisms. We begin the study with a case in which only one micro organism with holes is considered. Then we increase the number of micro organisms in the same medium. We also consider micro organisms with holes on their cell wall which is a more realistic case. We then derive a model for each case, replacing the applied high voltages in a static regime, and in a pulsated one where the applied voltage and the electric reactions of the micro organisms can be replaced by distribution models, which seem here to be more adequate to explain the physical interactions and phenomenon that appear in the studied system. We used “FlexPDE Solutions” Professional Version 6, a finite element code, that has made it possible to obtain the electrical quantities and consequently the mechanical forces inside the micro organisms, and inside their membrane; thus explaining the observations in the literature of the importance of some parameters like, the amplitude, the duration, and the number of applied pulses. Those variables have been experimentally observed by nearly all scientists as key factors in PEF sterilizations. The study also shows the possibility to simulate some changes brought to the sources, the medium, as well as to the micro organisms.