Application of Electrical Resistance in Nondestructive Postharvest Quality Evaluation of Apple Fruit

Nondestructive physical tests can be considered as recent trends for quality evaluation of agricultural products. Required information on postharvest quality of fruits and vegetables makes it possible to use their electrical properties as a novel method for nondestructive quality evaluation purposes. In this study, the electrical resistance of harvested apple fruits (Golden Delicious variety) was nondestructively measured by developing and employing special plate electrodes using a load cell to adjust the force holding the samples between two electrodes. Electrical resistance measurements were performed at two frequencies; 120 Hz and 1 kHz. Precise fruit weight was also measured along with electrical resistance measurements. The relationship between the electrical resistance and the weight loss was investigated during the storage period. The experiment ran for a total of 24 days. Results showed that in the 15 initial days of experiment, the electrical resistance decreased by increasing the storage period. But with further increase in the storage period, the electrical resistance also increased. The loss of the fruit moisture content, during the early stage of storage, may be attributed to the decrease of the fruit electrical resistance. However, as the stored apples lost more moisture, the concentration of ions, in soft tissues of samples, highly increased and this could be responsible for the increase of apple electrical resistance during the final days of the experiment.