Feasability of using electrical capacitance for determining the fruit ripeness of apple

Grading based on product ripeness is important for marketing fruits and vegetables. Various methods have been used to determine fruit ripeness some of which are destructive and some nondestructive. In this study for determining the fruit ripeness of apple during storage an apparatus was designed and fabricated to measure the electrical capacitance of the fruit samples as an indication of fruit ripeness. In the next stage a model was proposed to establish a relationship between the capacitance and ripeness (maturity rate) of the apple fruits. The capacitance unit was used to measure the dielectric constant of two apple varieties; Red delicious and Golden Delicious. For each variety three fruit samples of 45 mature apples were harvested on one day. Each sample was divided into three groups of small, medium and large apples. Preliminary tests indicated that the capacitance unit can establish a good relationship between dielectric constant and fruit ripeness at a frequency of 100 kHz. Remaining tests were conducted to measure dielectric constants of all samples under controlled conditions of temperature and humidity at this frequency. Analyses of the results indicated that dielectric constant decreases as the fruit ripens. This frequency level was also used to conduct other tests for measuring the fruit hardness and total soluble solids (TSS) during ripening stage. Results indicated that fruit hardness decreases and TSS increases during ripening.