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Orange rind damage is self-inflicted
Supermarket shoppers are familiar with beautiful displays of unblemished fruit, carefully presented to induce purchase. However, these high standards can cause problems for growers who may be unable to avoid the conditions that cause surface damage. One such condition is oleocellosis, a specific type of lesion in orange rind resulting from exposure to oils produced by the rind itself. In nature, excessive release of rind oils may occur because of damage of various types, but undamaged fruit may also suffer as a result of contact with damaged fruit. But how exactly is the damage caused? Knight et al. (University of Adelaide, pp. 765-773) have subjected oranges to controlled rind damage and have also applied rind oil externally (to mimic the effect of contact with damaged fruit). They then examined, in detail, the structure of cells in the layers of rind tissue. Mechanical damage caused breakage of the oil glands beneath the epidermis and leakage of oils into the underlying cell layers, which collapsed within 12 h. Application of oil to the rind caused damage to the epidermis, followed by discolouration, and more severe damage to the underlying layers. The first ultrastructural changes in membrane integrity were observed within 30 min and may be associated with the ability of the oil to enter and accumulate in the cells. Loss of membrane integrity also led to a breakdown in compartmentation prior to total cell collapse; enzymes such as polyphenol oxidases may be released with the potential to contribute further to discolouration of oil-damaged epidermis. Oleocellosis typifies situations in which a toxic compound arrives in the wrong place, thus causing self-harm. This is interesting in the context of natural selection but perhaps we might also say retailers have imposed an un-natural selection against this phenomenon.
Professor J. A. BryantUniversity of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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