RIPENING OF NECTARINE FRUIT - CHANGES IN THE CELL-WALL, VACUOLE, AND MEMBRANES DETECTED USING ELECTRICAL-IMPEDANCE MEASUREMENTS

Electrical impedance measurements were used to characterize changes in intracellular and extracellular resistance as well as changes in the condition of membranes during ripening of nectarines (Prunus persica [ L.] Batsch cv Fantasia). These measurements were related to changes in fruit texture assessed by flesh firmness and apparent juice content. An electrical model indicated that, during ripening (d 1-5) of freshly harvested fruit, the resistance of the cell wall and vacuole declined by 60 and 26%, respectively, and the capacitance of the membranes dec reased by 9%. Accurate modeling of the impedance data required an addi tional resistance component. This resistance, which declined by 63% du ring ripening, was thought to be associated with either the cytoplasmi c or membrane resistance. Changes in tissue resistance measured using low frequencies of alternating current were closely related to flesh f irmness. After storage at 0 degrees C for 8 weeks, the nectarines deve loped a woolly (dry) texture during ripening at 20 degrees C. The main difference between these chilling-injured nectarines and fruit ripene d immediately after harvest was the resistance of the cell wall, which was higher in woolly tissue (4435 Ohm after 5 d at 20 degrees C) than in nonwoolly tissue (2911 Ohm after 5 d at 20 degrees C). The results are discussed in relation to physiological changes that occur during the ripening and development of chilling injury in nectarine fruit.