Development of capacitance based nondestructive ripening indices measurement system for sapota (Manilkara zapota)

The study aimed to develop a nondestructive sensing system to determine the ripening indices of sapota fruit, based on the principle of dielectric capacitance measurement. The unripened sapota fruit contains starch, which gets converted to simple sugars during ripening. This conversion increases the electrical energy storability (i.e., electrical capacitance) of the fruit. A capacitance measurement system was developed, which consists of two standard copper-coated printed circuit board (PCB) electrodes and a microprocessor. The capacitance of fruit was determined at 9 V D.C. input voltage. Physicochemical properties such as total soluble solids (TSS), titrable acidity, firmness during ripening were studied for the fruits stored at ambient condition (30 +/- 2 degrees C). The changes in physicochemical properties and their correlation with capacitance were studied during ripening. The capacitance of the fruit increases with the increase in total soluble solids content of the fruit. With the correlation observed (R-2 = .9727), an algorithm has been developed for sensing the ripening stages (mature green, semi-ripe, and ripe) of the fruit. The system shows an accuracy of 90.74% in determining the stages of fruit ripening. Practical Applications The developed system helps in nondestructively determining the ripening stages (mature green, semi-ripe, ripe) of sapota at low cost. The detection process is less time-consuming. Also, the fruit does not undergo any tissue damage since the fruit is not applied with any force in the capacitance measurement process.