RIPENING AND DEVELOPMENT OF CHILLING INJURY IN PERSIMMON FRUIT - AN ELECTRICAL-IMPEDANCE STUDY

Electrical impedance spectroscopy was used to follow ripening and chil ling 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 respons es to both ripening at 20 degrees C and storage in modified atmosphere at 7 degrees C were distinct and easily detected using electrical imp edance spectroscopy. Plots of reactance against resistance at each ser ies of frequencies traced a semicircular are. During ripening, the arc s dilated between Days 1 and 21, then contracted, until at Day 35 they were smaller than at Day 1. Electrical modelling indicated that the d ilation occurred as a result of a 43, 115, and 17% increase in resista nce R-1 (cell wall resistance), R-2 (cytoplasm resistance), and R-4 (v acuole resistance), respectively. After 35 days of ripening, R-1 was 3 9% lower and C-3 (membrane capacitance) was 19% higher than at Day 1. Chilling injury developed with increasing time at 7 degrees C in modif ied atmosphere storage (MA), until severe symptoms were observed after 5 weeks. Chill-injured fruit differed from other fruit in that R-2 wa s significantly lower upon removal from storage, although it rapidly i ncreased when fruit were transferred to 20 degrees C for ripening. The se results are discussed in relation to the physiological changes that occur during ripening and development of chilling injury in persimmon .