Peel tan (apple)
Peel tan is a storage disease of the apple that is often divided into three different forms:
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
- ↑ 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.
- ↑ a b c d e Fritz Winter: Lucas' instructions for fruit growing . Ulmer, 2002, p. 363.
- ↑ Schalenbräune - Competence Center Fruit Growing-Bodensee Bavendorf . As of November 23, 2014.
- ↑ James Lyons: Low Temperature Stress In Crop Plants: The Role of The Membrane. Elsevier, 2012, p. 92.