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

由细胞组织组成的农产品在宏观上可以看作是细胞膜电隔离胞内电解质与胞外电解质的系统；导致电解质或水分通过细胞膜运动的过程可以使用具有电等效模型的阻抗光谱方法进行检测。本研究采用基于FFT算法的阻抗测量方法，通过加热和干燥实验，分析细胞农产品的传热传质特性与电等效模型参数之间的关系。蔬菜和水果的阻抗可以表示为复合平面上对应于β _1和β _2色散的两个串联弧，称为Cole-Cole图。用改进的Hayden模型成功地预测了在低于100kHz频率下观测到的第一个电弧。模型中细胞外阻力的增加与胡萝卜根干燥过程中水分含量的减少有很好的相关性。因此，阻抗测量可以应用于农产品干燥过程中的水分监测。在低于50℃的温度下，通过胞外电阻和胞内电阻成功地估算了马铃薯块茎在加热过程中的温度。在高于50°C的温度下，细胞内淀粉颗粒的糊化导致细胞内电解质向外移动。因此，也可以通过阻抗测量来检测糊化。结果表明，应根据细胞内和细胞外组分的性质及其在地窖材料中的配置，建立细胞农产品的物理性质模型。

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.