Pulsed electric field breakage of cellular tissues: visualisation of percolative properties

Abstract

Results of numerical and experimental investigation of the electric breakage of a cellular material in pulsed electric fields (PEF) are presented. The numerical model simulates the conductive properties of a cellular material by a two-dimensional array of biological cells. The application of an external field in the form of an idealised square pulse sequence with a pulse duration t i , and a pulse repetition time Δ t is assumed. The simulation model includes the known mechanisms of temporal and spatial evolution of the conductive properties of different microstructural elements in a tissue. The kinetics of breakage at different values of electric field strength E, t i and Δ t was studied in the experimental investigation. A 5×55-mm cylindrical slab of apple was taken as a sample. The results of the experimental and numerical studies were compared. A hypothesis for the nature of tissue properties evolution after PEF treatment was proposed. This phenomenon was considered as a correlated percolation governed by two key processes: resealing of cells and moisture transfer processes inside the cellular structure. The breakage kinetics was shown to be very sensitive to the repetition times Δ t of the PEF treatment. Correlated percolation patterns were observed in a case when Δ t exceeded the characteristic time of the moisture transfer processes while random percolation patterns were observed in other cases. The long-term mode of the pulse repetition times in PEF treatment allows the experimental visualisation of macroscopic percolation channels in the sample. Considerable differences were observed between the damage kinetics at long and short repetition times both for experimental and simulation data.