NONDESTRUCTIVE SONIC FIRMNESS MEASUREMENT OF APPLES

Firmness is critical to fresh apple quality. Sonic resonance resting i s a potential method for nondestructive measurement of firmness. Firmn ess changes in 'Delicious' and 'Golden Delicious' apples were measured before and after storage by three methods-sonic vibrational spectra, Magness-Taylor puncture, and axial compression of excised specimens. C hanges in all measurements over storage were greater in Golden Delicio us than in either of two Delicious sports. For Delicious apples, sonic measurements were more closely related to mechanical stiffness than t o maximum forces. Sonic stiffness coefficients were satisfactory predi ctors of the firmness of Golden Delicious apples as measured by maximu m force in compression or puncture (r = 0.85 to 0.88), but were poor f or Delicious (r = 0.50 to 0.59).