| Kiwi fruit is known as the king of VC. Because of its unique taste, rich nutrition and huge market demand, it leads to the phenomenon of the abuse of pesticides and swelling agents. Plant growth regulator was used frequently to improve the yield of kiwi fruit in recent years. But the use of plant growth regulator often caused low internal quality and deformity of fruits. The expanded kiwi fruit easily decays after softening. It is necessary to explore the effect of plant growth regulator on kiwi fruit tissue during the growth and ripening process. Up to now, the traditional chemical methods and the other modern techniques such as NIR, FTIR and NMR have been adopted to analyze the influence of plant growth regulators on fruit tissues. But these approaches are either complex and expensive or time-consuming, it was difficult to achieve fast and cheap measurement. In order to provide green pollution-free kiwi fruit for people, it is an urgent need to develop a detection method which is cheap, safe, non-toxic, easy to operate, information-rich, effective and feasible for the plant growth regulator at the moment. When currents with different frequencies flow through the biological tissue, cytomembrane, the extracellular and intracellular fluid would show different electrical properties. Therefore, EIS has the potential to be used for detecting the change of kiwi fruit cell microstructure during the growth and ripening process. During kiwi fruit growth period, we treated the’Hayward’kiwi fruit with the process of spraying plant growth regulator. When picking up kiwi fruit, we store kiwi fruit according to the classification of the fruit with plant growth regulator and normal fruit in temperature controlled cold storage at 0 ℃. In the process of kiwi fruit growth and late ripening, we use the LCR impedance detector combined with electrical impedance spectroscopy to calculate the electrical characteristics of the kiwi fruit organization corresponding to structure. Choosing the’Hayden model’as equivalent electrical model this model is composed of three circuit elements with four parameters which are extracellular resistance, intracellular resistance, membrane capacitance and phase angle. The complex nonlinear least square (CNLS) method was applied to the measured data in order to determine the model parameters. Meanwhile, kiwi fruit pulp was also investigated by means of using scanning electron microscopy. The results clearly indicated that Electrical Impedance Spectroscopy (EIS) technique is an efficient method for distinguishing the kiwi fruit of spraying plant growth regulator from normal kiwi fruit.1) In order to explore the effect of plant growth regulator on the electrical impedance spectroscopy of growth by kiwi fruit, this paper test the electrical impedance spectroscopy of expended kiwi fruit handled with CPPU method and control kiwi fruit without treated during the growth process. During the growth process of kiwi fruit, we analysed two kinds of kiwi fruit every 20 days using electrical impedance spectroscopy method until they were picked to store. We found that during the growth process, the total impedance of the two kinds of kiwi fruit gradually reduced with passing by the time. And during the beginning stage of growing process, the resistance of expended kiwi fruit was less than that of control kiwi fruit. But with the growth of the fruit, the resistance of two kinds of fruits was becoming consistent. We determined and found that the Cole-cole photographs of the two types of fruits were both an arc which were consistent with the typical electrical characteristics of biological tissues. And the membrane impedance of control kiwi fruit and expended fruits decreased and then tend to be stable by time passing. The membrane inside and outside liquid resistance of control kiwi fruit and expended fruits was also first decreased and then being stabilized finally. The electrical impedance spectroscopy method reveals electrical impedance characteristics variation of control kiwi fruits and expended fruits during the growth process.2) EIS technique was used to analyze the change of biological tissue at the cellular level during the ripening process of the expanded and control kiwi fruit by using an equivalent electrical circuit. Hayden model was chosen to analyze ripening process of kiwi fruit, which is composed of extracellular resistance, intracellular resistance and constant phase element representing the cytomembrane. Complex nonlinear least square (CNLS) method was used for fitting the EIS data and determining the parameters of Hayden model. The results indicated that the impedance magnitude of the expanded and control fruits decreased with increasing frequency, and impedance magnitude decreased with ripening only at low frequencies. It was obvious during the ripening process that the impedance of control fruits was decreased more quickly than that of the expanded fruits. The phase angles of two types of kiwi fruit increased sharply and then decreased quickly with the increase of frequency, and reached the maximum values at 12 kHz. Cole-cole plots of kiwi fruit tissues presented the semicircles with different radiuses, which represent the characteristics of typical biological tissue. Cytomembrane impedance of expanded kiwi fruit changed minimally during the ripening process of 15 days, but after 7 days, cytomembrane impedance of the control fruits dropped sharply. Extracellular fluid resistance of two types of kiwi fruit initially decreased, then increased and finally decreased with ripening process. Extracellular fluid resistance of expanded fruits was larger than that of control fruits, and extracellular fluid resistance of control fruits dropped more quickly than that of expanded fruits after 7 days. Variation of intracellular fluid resistance of two types of kiwi fruit was not obvious. Because plant growth regulator could alleviate the damage of cell membrane, EIS properties of two types of kiwi fruit were different. So electrical impedance spectroscopy is useful for the identification of expended kiwi fruit from untreated kiwi fruits by the impedance properties, such as the extracellular fluid resistance and cytomembrane impedance. Consequently use of EIS to analyze the ripening process provides a foundation of research for the detection of expanded fruits. |
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