Nondestructive Sonic Firmness Measurement of Apples

Abstract

Firmness is critical to fresh apple quality. Sonic resonance testing is a potential method for nondestructive measurement of firmness. Firmness changes in Delicious and Golden Delicious apples were measured before and after storage by three methodssonic vibrational spectra, Magness-Taylor puncture, and axial compression of excised specimens. Changes in all measurements over storage were greater in Golden Delicious than in either of two Delicious sports. For Delicious apples, sonic measurements were more closely related to mechanical stiffness than to maximum forces. Sonic stiffness coefficients were satisfactory predictors of the firmness of Golden Delicious apples as measured by maximum force in compression or puncture (r = 0.85 to 0.88), but were poor for Delicious (r = 0.50 to 0.59).