Mathematical modelling of Hass avocado firmness by using destructive and non-destructive devices at different maturity stages and under two storage conditions

Devices which are used to determine firmness of non-destructive nature do not penetrate the skin or damage the underlying flesh of the fruit and do provide real-time results, avoid raw biomass loss and allow the testing of every individual fruit and repeated testing of the same fruit, thus providing many advantages for researchers and the industry alike. Contrarily, destructive methods puncture the fruit and thus only a subsample, selected to represent all fruit, can be tested. In addition, different operators can generate quite different values for the same fruit using a hand-held penetrometer. Hass avocado from two commercial orchards was collected, and fruit firmness was measured at harvest, during two storage conditions controlled atmosphere (CA) and regular air (RA), during shelf-life and at the ready-to-eat stage using both destructive (Fruit Pressure Tester, mod. FT327, Wagner Instruments, Greenwich, USA) and non-destructive devices (Model TA.XT plusC, Stable Micro Systems Ltd, England). Then, the mathematical relationship between these two devices was assessed using Spearman Correlation coefficient (rho) and p-values adjusted by Benjamini-Hochberg and Bonferroni procedures. Thus, 3,200 fruits were evaluated during two harvests and two subsequent seasons. A moderate and positive association between destructive and non-destructive devices was found (rho coefficient ranging from 0.41 to 0.51). The variance explained by the regression models ranged from 0.53 to 0.63; all of them were significant with good accuracies (i.e., 0.79; 0.78; 0.73; 0.76). The results prompt us to conclude that a non-destructive texture analyser device can be used to accurately predict firmness measured by a penetrometer in Hass avocado fruit and contribute to avoiding fruit discards.