Electrophysiological model of intact and processed plant tissues: Cell disintegration criteria

Frequency versus conductivity relationships of food cell system, based on i mpedance measurements as characterized by polarization effects of the Maxwe ll-Wagner type at intact membrane interfaces, are presented. The electrical properties of a biological membrane (represented as a resistor and capacit or) are responsible for the dependence of the total conductivity of the cel l system on the alternating current frequency. Based on an equivalent circu it model of a single plant cell, the electrical conductivity spectrum of th e cell system in intact plant tissue (potato, carrot, banana, and apple) wa s determined in a frequency range between 3 kHz and 50 MHz. The electrical properties of a cell system with different ratios of intact/ruptured cells could also be predicted on the basis of a description of a cell system cons isting of elementary layers with regularly distributed intact and ruptured cells as well as of extracellular compartments. This simple determination o f the degree of cell permeabilization (cell disintegration index, p(o),) is based upon electric conductivity changes in the cell sample. For accurate calculations of p(o), the sample conductivities before and after treatment, obtained at low- (fi) and high-frequency (fh) ranges of the so-called P-di spersion, were used. In this study with plant cell systems, characteristic conductivities used were measured at frequencies fi = 3 kHz and fh 12.5 MHz . The disintegration index was used to analyze the degree of cell disruptio n after different treatments (such as mechanical disruption, heating, freez e-thaw cycles, application of electric field pulses, and enzymatic treatmen t) of the plant tissues.