NONDESTRUCTIVE DYNAMIC FORCE DEFORMATION MEASUREMENT OF KIWIFRUIT FIRMNESS (ACTINIDIA-DELICIOSA)

Firmness is a critical quality factor in kiwifruit marketing. We propo se a simple dynamic force/deformation (F/D) test to evaluate kiwifruit firmness nondestructively. Various parameters from a low-frequency dy namic F/D test were compared to data from Magness-Taylor (MT) puncture F/D curves. Resonant frequencies from dynamic F/D did not adequately predict kiwifruit firmness as measured by MT maximum force (r = 0.60), while amplitudes at low frequencies predicted better (r = 0.81). The dynamic test data were more closely related to slope of the puncture c urves than to maximum force, the parameter traditionally reported. Amp litudes near 60 Hz were found to be the best predictors of MT values ( r = 0.88). Adding amplitudes near 98 Hz to the regression equation imp roved prediction only slightly (R = 0.98). A relatively simple firmnes s tester could be devised on the basis of 60-Hz vibrations.