Abstract
Purpose of this paper is to investigate the impact of changes of moisture content and growth of fungi on the electrical impedance characteristics of brown rice. Brown rice was stored in the constant temperature and humidity chamber (30°C, 90% RH) in order to change the moisture content of brown rice. During the storage, the electrical impedance of the sample was monitored by using insertion type electrodes. As a result, the electrical impedance characteristics of brown rice were modeled by the parallel circuit model composed of resistance and constant phase element (CPE). Focusing on the relationship between moisture content and model parameters, resistive component R decreased and capacitive component C increased with increasing moisture content. Especially R has a strong exponential correlation with the moisture content. The moldy brown rice was prepared by 40 days storage under the condition of 30°C, 90% RH. As is the case with the ordinary brown rice, R decreased and C increased at higher moisture content. However, variations of these parameters with respect to the moisture content were quite small compared to the ordinary brown rice. It was considered that the changes of electrical characteristics were due to the shedding of the aleurone layer caused by the growth of fungal filament and changes in composition of brown rice by metabolism of fungi. These findings obtained from above results would be useful in evaluating the quality of brown rice.
