Interaction of pulsed electric fields with cell membrane

Pulsed Electric Fields (PEF) allow non-thermal pasteurization and sterilization of liquids, involving the application of high intensity electric field pulses (20-80 kV/cm) of short duration (1-10 microseconds). The electric field interacts with microorganisms at the level of plasma membrane, through the mechanism of electroporation, but, although many theories have been proposed to describe this phenomenon, a satisfactory explanation has not been found yet. An extensive description of the state of the art of the knowledge on this field is given, along with the current research needs and the main obstacles to a wide diffusion of PEF applications. The time course of cell transmembrane voltage is studied, developing an analytical expression for planar, spherical, cylindrical and prolate spheroidal membranes, with the aim to evaluate the charging time constants and the steady state intensity upon variation of treatment conditions. The results of this approach are used to investigate the impact of the electric field in rod-like bacteria. The electric field distribution in test chamber is studied by means of computer simulations for various electrode geometries, optimizing the shape for intensity and uniformity of electric field. The impact on PEF treatment of a normal distribution of cell dimensions in a microbial population and the rotational movement of bacteria inside treatment chambers are also investigated. Computer simulations are used to obtain a possible explanation to the deviations from first order inactivation kinetics, and to the intrinsic variability of microbial laboratory results. PEF inactivation experiments of Escherichia Coli are carried out in a test system under different conditions of treatment duration and microbial concentration. Inactivation kinetics is compared to theories of electroporation and computer simulations previously carried out. Experimental evidence of a variation in the effectiveness of PEF as a function of bacterial concentration is discovered and a possible explanation proposed. The application of high permittivity ceramics materials to PEF is also studied, with the aim of increasing the volumes of treatment chambers, improving the duration of electrodes, and allowing the use of the most energy efficient square wave pulses to large volumes of liquid. These materials can also be used to test the possibility of a relation between energy deposited in treatment chambers and microbial inactivation, in order to acquire more insight on the interaction between Pulsed Electric Fields and cell membranes. A novel chamber is prepared with the use of a high permittivity non-toxic material (Sodium Potassium Niobate) and it is ready to be tested in PEF applications.