CHANGES IN SONIC RESONANCE OF DELICIOUS AND GOLDEN DELICIOUS APPLES UNDERGOING ACCELERATED RIPENING

Apple growers need to measure the firmness of their fruit when it is harvested and during and after storage to make management decisions. Freshly harvested 'Delicious' and 'Golden Delicious' apples from Pennsylvania were stored for 55 days at almost-equal-to 22-degrees-C to accelerate ripening. The sonic transmission spectrum of each apple was measured periodically as it ripened and resonant frequencies were determined by examination of each transmission spectrum. The resonant frequencies for each apple were found to decrease monotonically with time in a pattern similar to the decrease in Magness-Taylor firmness, but more consistently and with less scatter There was a small difference in the functional relationship between frequency and duration of ripening for the two cultivars of apple tested, an additional difference was shown in the case of 'Delicious' which had been heavily waxed. The effect of surface restraint by the skin on the resonant frequency was found to be negligible. The advantages of the sonic measurement are that it is nondestructive, it is representative of the entire fruit, and it has the potential to be adapted for on-line sorting.