MODELING COMPRESSION OF CELLULAR SYSTEMS EXPOSED TO COMBINED PRESSURE AND PULSED ELECTRIC FIELDS

The mechanism of tissue damage under combined pressure and pulsed electric field (PEF) treatment has beeninvestigated. The relationship between the macroscopic behavior of apple tissues and the mechanical properties of individualcells has been studied using a square-lattice model and compression tests. A mathematical model was developed to simulatethe compression of cellular systems exposed to combined pressure and PEF. Apple tissue was presented as the system of cellsconnected in the square lattice. Distribution of the destroyed cells was determined by the Monte Carlo method. Elasticmodulus values were calculated for the whole system as a function of the system destruction degree. Experiments wereconducted using McIntosh apples to validate the mathematical model. Pressing was achieved in a cylindrical press-cell byusing a universal testing machine. Electric field pulses were at the field strength (1000 V/cm); pulse duration was 300 .s,pulse frequency was 1 Hz, and the number of pulses varied up to 60. Good correlation between the mathematical model andexperimental data was observed within the 95% confidence level using a square-lattice dimension of 150 . 150 and 8 cellsas intact near-neighbors of the destroyed cell. The modeling approach showed that elastic properties of near-neighbors ofdestroyed cells significantly changed due to the unbalance of turgor pressure on cell walls. Elastic modulus of the nearestintact cells surrounding plasmolized cells was similar to that of the destroyed neighbor cells. The cells elastic modulusreduced by 73% to 81% after PEF treatment. The whole tissue compression modulus decreased by 72% to 75% at theplasmolysis degree of 0.25 to 0.33. Maximum decrease of about 77% in the tissue compression modulus was observed at themaximal PEF plasmolysis degree of 1. There was an increase in apple tissue compressibility even with minimal PEF treatment.

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