Application of AC Impedance Spetroscopy Analysis for Solid Foods

Abstract

The study used alternative current (AC) impedance spectroscopy analysis and directconductivity measuring device to measure dielectric constant, dielectric loss and electric conductivityof solid foods. Electrical properties in the frequency range of 10~100kHz was analyzed. Problemsassociated 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 coulddescribe foods impedance property at various frequencies to realize the ionic conductivity. Higherconductivity 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 lossincreased slightly, with decreasing frequency at the frequency range 10k~100kHz when chargetransferred mainly by dielectric induction. Bound water started to result in increased dielectric loss ofall vegetables and fruits at about 10kHz. Ionic conduction predominated and the conductivity wasindependent on the frequency. Dielectric constant remained uncharged at these frequencies. Atfrequencies below 100Hz, ions and charged molecules underwent space charge polarization andionic conductivity decreased while dielectric loss of vegetables and fruits increased sharply. Ionicconduction persisted even at the highest frequency (100kHz) for meats. Space charge polarizationoccurred at frequencies below 1kHz. Fatty constituents in meats would increase relaxation time andthus decrease electric conductivity.