Connection between Moisture Content and Electrical Parameters of Apple Slices during Drying

Generally the drying process of fruits is followed by weight loss. The weight loss characterizes only the global moisture content of fruits and does not give information about the inner state of tissue. Electrical impedance spectroscopy of biological tissues shows ab-dispersion band that is associated with membrane structures and is sensitive to their integrity and functionality. The aim of this study was to measure the impedance spectra of apple slices during drying and to correlate impedance parameters to moisture content in the different drying periods. The electrical impedance spectra of apple slices were determined during drying by an HP 4284A Precision LCR Meter in frequency range from 30 Hz up to 1 MHz. The measured spectra were approximated by Cole-impedance elements. Parameter values for the fitted curves that characterized the state of drying tissue showed good correlation with the moisture content calculated from weight loss in the two falling-rate drying periods.