Development of an automated monitoring device to quantify changes in firmness of apples during storage

An automated firmness monitoring system for apples was developed to estimate loss of firmness during storage and determine the time when cool stores should be opened. The non-destructive acoustic impulse response technique was chosen to measure firmness. This technique was very reproducible and its sensitivity to firmness changes was greater than the sensitivity of penetrometer measurements with a materials testing device. The correlation between the acoustic impulse response technique and penetrometer varied according to the apple cultivar and freshness. The developed automated fruit firmness monitoring system is composed of a rotating disc on which a representative fruit sample is located, an electromagnetic excitation mechanism, and an optical sensor to detect the position of the apples. A microphone records the apple vibrations at impact and is linked to a computer with a data acquisition and analysis programme, which is placed outside the cool store. A first-order degradation model, fitted to the measured firmness data, is used to estimate the time when the cool stores should be opened to guarantee an average firmness after storage. (C) 2000 Elsevier Science B.V. All rights reserved.