Design, development and test of apparatus to measurement of electrical resistance and impedance of fruit

Electrical properties of fruits are accepted indicators for detecting fruit quality. Electrical resistance one reluctance can detect quality factors and are sensitive to variations in the concentration and state of water. Therefore، these properties can be associated with maturity، damage، overripe condition، decay or other quality factors. In most of previous research on electrical resistance and impedance of fruits، sensors pushed into the fruit to measure electrical resistance of the sample between two electrodes. Needle type electrodes usually are used which results in damages to the fruit. Thus in every tests، samples should change. In this experiment، especial electrodes for measuring electrical resistance were developed and used which did not damage the fruit. Electrical sensors for electrical resistance measurement consisted of two copper plates. Fruit sets between two plate electrodes where constant force was applied on it. The overall construction of the apparatus was made up of the following main components: LCR Meter، Load cell، Indicator، Base، Frame، and Probes. Red apples were used in this experiment. Electrical resistance measurements were performed at two frequencies; 120 Hz and 1 kHz. Water loss of the whole fruit also contributed in decreasing the mobilization of ions، thus، increasing of electrical resistance of the ripen fruit. The results indicated that the relationship between the electrical resistance and the weight loss، during the storage period، was also investigated. The results indicated that، the electrical resistance decreases by third degree equation and the weight of apple decreases linearly with increase in storage period.