EFFECT OF APPLE SHAPE ON ACOUSTIC MEASUREMENTS OF FIRMNESS

The acoustic impulse response technique can be used for non-destructive measurements of apple firmness. It is based on the relationship between Young's modulus and the resonant frequency of the various spherical mode shapes of vibrating apples. The main sources of error for estimating apple firmness using this method were studied. From finite element simulations the sensitivity of the firmness measurements to variations in the apple shape was analysed. Measurements were carried out on Jonagold apples for experimental analysis of the relationship between the variability of apple shape and the variability of measured frequency for different positions on the apple surface. Some suggestions to reduce the error or uncertainty in the apple firmness estimation based on acoustic measurements are given. One of them is the use of multiple measurements along the fruit equator. © 1993 Silsoe Research Institute.