Empirical modelling of postharvest changes in the firmness of kiwifruit

Several different types of empirical mathematical models were used to chara cterise the softening behaviour of 'Hayward' kiwifruit (Actinidia deliciosa (A. Chev) C.F. Liang et A.R. Ferguson) during storage at 0 degrees C. Our purpose was to determine whether or not the softening behaviour of fruit co nformed to a limited number of patterns. If this were so, such models, coup led with measurements made in a short period after harvest, might form the basis of a quantitative tool that would allow the industry to segregate bat ches of fruit with differing storage potentials. Initially, three simple mo dels were used to characterise firmness data: a Complementary Michaelis-Men ten type (CMM), Exponential (EXP), and Complementary Gompertz (CG). However , these were unable to characterise firmness changes with sufficient accura cy, either in the early, middle or latter stages of storage. Instead, the f irmness data were better characterised by two more complex models that were identified during the course of the study: a segmented Jointed Michaelis-M enten type (JMM) and Inverse Exponential Polynomial (IEP). With the JMM mod el, different functional relationships were assumed for different regions o f the time domain although its parameters were difficult to estimate accura tely when the number of data points for a region of the time domain was lim ited. The IEP model best characterised the firmness data although its abili ty to predict the softening behaviour of fruit was poor given a limited win dow of data. None of the equations that were studied provided a standard cu rve that could be useful as a predictive model for firmness in storage. Nev ertheless, the more complex equations did accurately characterise our firmn ess data and have potential value for comparing treatment effects in experi mental programmes. (C) 2000 Elsevier Science B.V. All rights reserved.