Techniques for predicting damage during postharvest handling of perishable products

In order to address the critical issue of mechanical damage to perishable product, research needs to focus on two areas; 1) the handling system and the typical forces exerted on the produce, and 2) how they respond to these forces. A new method for describing produce damage susceptibility has been developed. This model, based on the logistic function, describes susceptibility in terms of the proportion of a population of product that will sustain damage above some threshold. The attraction of the approach is that the threshold is often commercially defined, as part of a QA programme. The model has been shown to be suitable for apples, but is also applicable for products such as nectarines and potatoes which have a highly variable damage response. The model has been tested against other techniques for describing susceptibility. It has also been used to study the major factors which affect the damage susceptibility for New Zealand apples. A method has been developed to combine the individual fruit impacts recorded using an Impact Recording Device (IRD) with the susceptibility model to predict levels of damage for specific handling events. Technology has also been developed to enable, for the first time, force measurements to be made in situations where compression damage is likely to result. These flat sensors have been trialed in an orchard bin handling evaluation aimed at comparing different bins and tractor mounted forks. These studies have identified various shock events that are the primary causes of damage in bulk handling systems. The thesis also includes discussions on related topics which were studied as part of the overall programme. These include: optimal techniques for estimating the size of an apple bruise, primary influences on damage susceptibility for apples, aspects of the use of the IRD, levels of damage in apple bins and comparisons of bin design