PENETROMETER MEASUREMENT OF APPLE AND KIWIFRUIT FIRMNESS - OPERATOR AND INSTRUMENT DIFFERENCES

Flesh firmness is a characteristic used to indicate fruit quality, Exp erimental design and data analysis are important when comparing device s that measure fruit firmness, We compared the Effegi penetrometer ope rated by hand, mounted in a drill press and then operated by hand, and mounted on a motorized drive and operated remotely; the hand-operated EPT pressure tester; the Instron with an Effegi probe; and a hand-ope rated prototype of the twist tester, Devices varied in operator differ ences and precision, Comparisons between devices were at the within-fr uit level of variability and, therefore, more precise than comparisons where different device-operators used different fruit, We demonstrate statistical methods that are appropriate for making the comparisons o f interest and discuss the possible cause of differences between opera tors and between devices. We also discuss how the mechanical propertie s of the devices may affect results and consider implications for thei r practical use. In this study, we found the precision of discriminati on between soft and hard apples was best using the Instron in 1992, wh ile the Instron and hand-held Effegi penetrometer were comparable in 1 991, For kiwifruit, the hand-held Effegi penetrometer consistently gav e the most precise measurements of softening in 1991, while the twist test was the most precise in 1992.