Superficial scalding is the most important postharvest chilling injury affecting the quality of the main pome fruits. It develops in the fruit after a prolonged storage period at low temperatures, thus limiting the time they can be conserved.
The most characteristic symptoms of superficial scalding are brown spots on the fruit's skin. As the damage progresses, the colour darkens and the affected surface increase. Superficial scalding is caused by the oxidation of a compound (a- farnaseno) on the surface of apples and pears.
Even though the scalding doesn't affect the fruit's pulp, flavour or texture it reduces the product's commercial value. The affected fruits are not intended to be consumed fresh and are sold to the processing industry. This disorder has caused losses of up to 50% of the fruit stored in cold rooms.
This disorder is effectively controlled by the application of anti-scald products such as diphenylamine (DPA) and ethoxyquin.
Limitations imposed by the European Commission
For more than four decades, the world pome fruit industry relied on diphenylamine and ethoxyquin to retard the oxidation of a-farnaseno. However, the European Commission has decided to exclude these chemicals from the list of permitted products. Hence, in the future, producers will no longer be able to use them in fruit destined to Europe.
The current maximum residue limit (MRL) for diphenylamine is of 5 mg/kg in apples and 10 mg/kg in pears. These MRLs will decrease, starting February 2, 2014, to 0.1 mg /kg as a temporary tolerance for cross-contaminated crops. Starting July 2015, DPA residues will no longer be allowed. This transition period was agreed upon, as there have been several cases of DPA contamination in untreated fruit. So far, none of the methods evaluated to eliminate DPA residues have been effective.
The current MRL for ethoxyquin in pears is of 3 mg/kg in the European market will remain in effect for the 2014 campaign. Unlike the DPA, there have been no reported cross-contamination problems for this product.
Estimates are, due to these restrictions imposed by the EU, superficial scald could affect 3.5 million tonnes of pears and apples in Europe and that the economic losses would exceed 1,000 million Euro per year. Thus, the production of many varieties would drop to levels that the market can absorb in a short period of time as they would be untreated.
Researchers at INTA Alto Valle and in different producing regions of the world have been working for several years in the search for alternative methods of controlling superficial scald. These methods include the application of 1-methylcyclopropene, storing the fruit with low oxygen levels, or the combination of both technologies.
