Firmness is a critical quality attribute for kiwifruit, as it is for most commodities. Firmness is related to flesh elasticity and rigidity which, along with geometry and density, determine vibrational behavior. Firmness changes in kiwifruit were followed during storage at 0C by three methods: sonic vibrational spectra from 0 to 2000 Hz, dynamic force/deformation (F/D) in the range 40 to 440 Hz, and Magness-Taylor puncture (MT) on an Instron. Frequencies of sonic resonances and dynamic F/D peaks, as well as MT maximum force, decreased as storage time increased. Sonic resonance frequencies were highly correlated with MT maximum force and apparent elasticity (r=0.79 and 0.88). Frequencies of peaks in the dynamic F/D traces were correlated with MT maximum force and apparent elasticity (r=0.68 and 0.72) and with resonance frequency (r=0.81). Further data processing improves the ability of the nondestructive vibrational measurements to estimate the destructive MT test values.
The sonic vibration characteristics of 5 major apple (Malus domestica Borkh.) cultivars were evaluated. The resonant frequency (f) and the mass (m) of individual intact apples were measured over 4 weekly harvests and again after 2½ and 5 months in storage. A nondestructive index of firmness, f2m, for each apple was calculated and compared with other measures of fruit texture. The f2m index was directly correlated with Magness-Taylor pressure test measurements of firmness and with sensory ratings of crispness, juiciness, and firmness, especially crispness. It was inversely related to mealiness. Correlations were affected by differences among cultivars; results were best and most consistent for ‘Golden Delicious’ and ‘Rome Beauty’.