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Application of AC Impedance Spetroscopy Analysis for Solid Foods

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  036145,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.13918) @2003
Authors:   Wen-Rong Fu, En-Lin Lin
Keywords:   Impedance, alternating current, conductivity, dielectric constant, dielectric loss, solid food

The study used alternative current (AC) impedance spectroscopy analysis and direct conductivity measuring device to measure dielectric constant, dielectric loss and electric conductivity of solid foods. Electrical properties in the frequency range of 10~100kHz was analyzed. Problems associated with electrode-solid sample contact were eliminated by applying an adequate pressure (0.2kg/cm2). Equivalent circuits, consisted of resistors and capacitors, of foods obtained could describe foods impedance property at various frequencies to realize the ionic conductivity. Higher conductivity was obtained when vascular tissue/muscular fiber was aligned with AC electric fields. The electric conductivity of vegetables and fruits decreased, while the dielectric constant and loss increased slightly, with decreasing frequency at the frequency range 10k~100kHz when charge transferred mainly by dielectric induction. Bound water started to result in increased dielectric loss of all vegetables and fruits at about 10kHz. Ionic conduction predominated and the conductivity was independent on the frequency. Dielectric constant remained uncharged at these frequencies. At frequencies below 100Hz, ions and charged molecules underwent space charge polarization and ionic conductivity decreased while dielectric loss of vegetables and fruits increased sharply. Ionic conduction persisted even at the highest frequency (100kHz) for meats. Space charge polarization occurred at frequencies below 1kHz. Fatty constituents in meats would increase relaxation time and thus decrease electric conductivity.

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