Electrical Impedance Analysis of Tea Leaves in the Steaming Process

Frequency-dependent electrical impedance spectroscopy has been used to characterize the intracellular and extracellular resistances as well as the capacitance of the cell wall and cell membranes of tea leaves in the steaming process. The intracellular resistance of the steamed leaves decreased by approximately 90% as compared to that of fresh leaves. Water in the cytoplasm was transformed into mobile water by the steaming treatment. This is the main factor that causes the decrease in the intracellular resistance. However, when the treatment duration exceeded 20 s, there was a negligible influence on the change in the resistance. Therefore, this organized behavior was considered to occur within 20 s. On the other hand, since the indissoluble pectin that constitutes the cell wall became water soluble by the steaming treatment, positive ions accumulated on the cell wall at the beginning of the treatment. Therefore, the capacitance increased temporarily due to the treatment. In addition, when the steaming treatment was prolonged, the capacitance and extracellular resistance decreased due to deterioration and shrinkage of cellular tissues. Electrochemical impedance analysis can be employed to investigate the organized behaviors that occur in tea leaves in the steaming treatment. Therefore, a numerical method to evaluate the steaming . treatment can be established using electrochemical impedance analysis.