Peel tan (apple)

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Peel tan is a storage disease of the apple that is often divided into three different forms:

Peel tan on a Rubinstar apple

to form

  • Ordinary peel tan ( superficial scald ): The usual peel tan develops in susceptible varieties only after three to four months in storage. It occurs mainly in warmer growing areas with varieties such as ' Granny Smith ' and ' Red Delicious '. In the temperate climate zones , ' Jonagold ', ' Berlepsch ' or ' Melrose ' are particularly affected. ' Gala ' and ' Fuji ' are considered to be moderately susceptible. After the apples have been removed from storage, the skin tan can quickly spread at room temperatures.
  • Age scald ( senescence scald ): The age scald can occur in almost all varieties by superimposing.
  • CO 2 -induced skin tan ( superficial CO 2 injury ): On the shady side of the apple during ripening on the tree, or in storage for light-skinned varieties.

Clinical picture

Affected apples have a large, indistinctly limited browning of the outer epidermis of the fruit peel . The tissue sinks a little in the affected areas, but the pulp is completely undamaged. The taste is not affected, but it is no longer possible to sell it as a table fruit .

Cause of illness

There is still a lot of research to be done into the exact cause of the skin tan. However, it is generally accepted that naturally occurring volatiles , the α-farnesens, remain on the fruit peel for too long and oxidize there to form a large number of other products (especially trienes ) . These oxidation products damage the cells within the epidermis of the fruit peel. Ethylene promotes the formation of α-farnesens, which ultimately oxidize to conjugated trienes under the influence of oxygen . The reason why there are differences in susceptibility between the different varieties is still unclear. However, it could be related to the naturally occurring antioxidants in the peel.

Combat

  • Reduction of the ethylene concentration during storage (ethylene scrubber )
  • Good air circulation
  • Low oxygen concentrations of 1.0 to 1.5% ( ULO storage)
  • Humidity with susceptible varieties maximum 92%
  • Good pruning for an even exposure of the fruit
  • Right harvest time

Others

In many countries, skin tan is prevented with the help of post-harvest treatment. To do this, the apples are treated with antioxidants such as diphenylamine (DPA) or ethoxyquin , the latter of which can cause damage to certain apple varieties. This treatment should be done within a week of harvest. Treatment with mineral oil or vegetable oil has also proven effective . These seem to absorb the α-farnesene , which means that further oxidation is no longer possible. In Germany, however, any form of post-harvest treatment is prohibited, which is why the skin tan can only be prevented by good growing and storage conditions.

Individual evidence

  1. ↑ a b c d e M. Ingle, MC D'Souza. Physiology and control of superficial scald of apples: a review. In: Hort Science. 24, 1989, pp. 28-31.
  2. ↑ a b c d e Fritz Winter: Lucas' instructions for fruit growing . Ulmer, 2002, p. 363.
  3. ↑ Schalenbräune - Competence Center Fruit Growing-Bodensee Bavendorf . As of November 23, 2014.
  4. ↑ James Lyons: Low Temperature Stress In Crop Plants: The Role of The Membrane. Elsevier, 2012, p. 92.