Dielectric properties of apples in the range 0.1-100 kHz

Capacitance and conductance spectra are measured between 100 Hz and 100 kHz for three varieties of apple. Analysis of the spectra for several types of electrode material indicates that electrode effects may be neglected for frequencies above 1 kHz. Power-law responses are observed with C approximately f super(-0.3) for the capacitance and G sub(a.c) approximately f super(+0.9) for the a.c. conductance. Activation energies were found to be of the order of 0.05-0.15 eV for the three apple varieties and found to be frequency dependent. Comparison is made with an apple in which the cellular structure has been damaged by freezing. Freezing produced a significant increase in the high-frequency activation energy for conductance and a decrease in the power-law exponent to + 0.3 for a.c. conductance. It is suggested that the dielectric properties result from a combination of relatively free ionic diffusion in the extracellular medium and the hopping of counterions along trap sites on the cell wall.