Application of Impedance Measurement Using Noise-FFT to Monitoring of Physical Properties of Cellular Agricultural Products

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Agricutural products composed of cellular tissues can be macroscopically regarded as systems in which cell membranes electrically isolate intracellular electrolytes from extra cellular ones ; a process which causes the movement of electrolytes or moisture through cell membranes can be detected using an impedance spectroscopic method with an electrical equivalent model.In this study, an impedance measurement based on the FFT algorithm was applied to the analyzes of the relationship between the heat and mass transfer properties of cellular agricultural products and the parameters in an electrical equivalent model through the experiments of heating and drying.The impedance of vegetables and fruits could be expressed as two series arcs corresponding to beta_1 and beta_2 dispersions in the complex plane called the Cole-Cole plot. The first arc observed at the lower frequency than 100kHz was successfully predicted by the modified Hayden model.An increase in the extra cellular resistance in the model showed a good correlation with a decrease in moisture content of a carrot root during drying. Thus, the impedance measurement can be applied for monitoring the moisture of the agricultural products during drying.The temperature of the potato tubers during heating was successfully estimated by the extra cellular and intracellular resistance at the lower temperature than 50ﾟC.At the higher temperature than 50ﾟC,gelatinization of the starch granular in the cells caused the movement of electrolytes inside a cell to the outside. Therefore, the gelatinization could be also detected by the impedance measurement.Through the results, it was concluded that the model of the physical properties of the cellular agricultural products should be developed based on the properties of the inside-cell and outside-cell components and the configuration of them in a cellar material.