Ripening and development of chilling injury in persimmon fruit: An electrical impedance study

Abstract

Electrical impedance spectroscopy was used to follow ripening and chilling injury development in persimmon fruit (Dyospyros kaki L. ‘Fuyu'). Tissue resistance and reactance were measured at frequencies between 50 Hz and 1 MHz, and then fitted to an electrical model. Fruit responses to both ripening at 20°C and storage in modified atmosphere at 7°C were distinct and easily detected using electrical impedance spectroscopy. Plots of reactance against resistance at each series of frequencies traced a semicircular arc. During ripening, the arcs dilated between Days 1 and 21, then contracted, until at Day 35 they were smaller than at Day 1. Electrical modelling indicated that the dilation occurred as a result of a 43, 115, and 17% increase in resistance R\\ (cell wall resistance), R2 (cytoplasm resistance), and R4 (vacuole resistance), respectively. After 35 days of ripening, R1 was 39% lower and C3 (membrane capacitance) was 19% higher than at Day 1. Chilling injury developed with increasing time at 7°C in modified atmosphere storage (MA), until severe symptoms were observed after 5 weeks. Chill‐injured fruit differed from other fruit in that R2 was significantly lower upon removal from storage, although it rapidly increased when fruit were transferred to 20°C for ripening. These results are discussed in relation to the physiological changes that occur during ripening and development of chilling injury in persimmon.