“Written by Dr Malcolm Dodd (Cold Chain Solutions)”
The classification of fruits into the two respiration categories, namely: climacteric and non climacteric has been in existence for around eighty years and is helpful in assisting with the post harvest management of fruits.
The role ethylene plays in these respiratory behaviours was first described in 1960. However, as with most biological systems there is variability within fruit kinds as to the reaction and response to ethylene. Citrus as a group of fruits are classified as non-climacteric, therefore INCORRECTLY, current wisdom says that managing ethylene in the storage environment will not benefit the storage and shelf life of such fruit. HOWEVER, like most products of plant origin they do respond and are sensitive to ethylene.
In the de-greening process ethylene is added to the storage air and the fruit is kept at a high temperature under this gas for several days. The flavedo (skin) colour development, such an important indicator of ripeness to most customers, is accelerated by this process. Thereafter the fruit is placed under cooling (citrus type dependant) and held at that temperature until sale. It is a widely thought that citrus ,particularly soft citrus and navels that have been subjected to ethylene treatment for colouration/degreening purposes, appear to be more prone to issues of skin infections/rind break down during post treatment storage. Consequently, it is just good practise to limit the presence of ethylene and other volatile gases that encourage development of moulds and rot from storage situations as effectively and quickly as possible by using the process of air purification called scrubbing .
The transition of fruit from its picking thru to its final packing and loading at the pack house invariably , despite all the due care taken in physical handling , results in a certain level of fruit whose rind is bruised or damaged. The response of the subtending damaged fruit tissue is to produce ethylene. This then stimulates further ethylene production in an auto catalytical process and so the ripening process is accelerated.
Similarly, fungi (responsible for most post harvest disease), when present as spores on the surface of fruit, are stimulated to germinate by ethylene and other volatile gases. Research has shown that by “scrubbing” the air in the storage environment, to remove ethylene and these volatiles, results in a much lower incidence of postharvest disease breaking out.
In addition by removing ethylene ( from whatever source) from the soft citrus storage environment by the scrubbing of the air using ethylene filters, the risk of fruit ripening being accelerated will be reduced.
This helps to ensure that the soft citrus varieties of fruit , and the fractious navel orange varieties will hold their packed colour , not soften too quickly nor develop the to the same level of typical post harvest infection due to fungi for fruit that has been stored in unscrubbed atmospheres.
The result…….. improved citrus fruit marketability, appearance, lower losses due to quality issues and an overall better maintained value for the exported produce.
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Dax Rowlands
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