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Pepper, Capsicum annuum / Solanaceae
Postharvest Atmosphere Management
After the harvest, it is important to cool the peppers down as soon as possible so as to reduce water losses. The pre-cooling is made in tunnels, lowering the temperature below 12ºC in less than one and a half hours; the best method is humid forced air.

If they are stored at temperatures over 7,5ºC, they loose more water and they wrinkle; and if the temperatures are too low, they may suffer from chilling injuries. Temperatures over 10ºC favour maturation and the growth of bacteria.

Peppers behave as not-climacteric fruit and give off very low ethylene levels. Moreover, the latter has little effect. In order to accelerate the maturation or the colour change, the most effective process is to keep peppers with a partial coloration at lukewarm temperatures of 20-25ºC and high relative humidity, over 95%.

The controlled atmosphere ha little effect on the pepper. If the concentration of O2 is low (2-5%), it hardly influences the quality of the fruit; on the contrary, a high CO2 concentration (more than 5%) may damage the peppers, specially at temperatures below 10ºC.

For more information on the basic processes of postharvest handling for peppers, consult the Internet address of the University of Davis ( http://postharvest.ucdavis.edu ).
Postharvest Problems
Due to the high rate of transpiration of peppers, their life is not longer than 2-4 weeks. In that stage, the main problems affecting them are: loss of weight , , diseases< and other alterations detailed below.

1. Loss of weight
The lower the relative humidity of the storage, the greater the loss of weight and softening of the fruit is, since the loss of weight is a direct consequence of the loss of water. Besides, the peppers loose firmness, the surface wrinkles and the meat softens. Therefore, it is recommended to keep the fruit in a saturated atmosphere so as to avoid the loss of water.

2. Apical rot
It is caused by the lack of water and calcium, and it may occur at higher temperatures if the peppers grow too fast.
It is characterized by the appearance of a slight atypical colouring or a more serious damage, dark and depressed in the tip of the fruit.

3. Pepper mottles
The cause of this physiological disorder is unknown. Some mottled damages penetrate in the wall of the fruit. Some varieties are more susceptible than others.

4. Chilling injuries
Peppers suffer from chilling injuries below 7ºC. Between 0 and 2ºC they occur in few days. This disorder brings about the pitting of the fruit surface, some watery areas, increasing the susceptibility to rots (specially Alternaria), and an abnormal colouring of the internal cavity, as well as a brown colour in the seeds. Peppers also loose taste and aroma.

5. Botrytis or grey mould
This fungus is quite common in the pepper, causing rots and developing a grey mycellium that carries the spores. It is favoured by the exposition to low temperatures. Its effects diminish if the field is clean and there are no damages in the fruit.

6. Alternaria
It causes the " fruit rot" and attacks mainly the peppers weakened for multiple reasons. It causes dark wet spots, of circular shape and different sizes, that extend along the surface. On the injuries there is a green olive down that carries the fungus spores. The inner tissues suffer from a rot that may affect the whole surface.

The most susceptible fruits are those that have been exposed to frequent rainfall or high relative moisture, temperatures between 20 and 22ºC, with sun damages or caused in the handling process, with symptoms of apical rot or attacks of parasitic diseases.

7. Rhizopus rot
This fungus causes a wet rot, with a whitish mycellium, with black small spots formed by the fruiting bodies.

The injuries and the high humidity and temperatures favour the attacks.

8. Bitter rot
Caused by a soil fungus called Geotrichum candidum, that usually attacks tomatoes and carrots. The fruit looses cellular juice very quick through the cracks of the skin. The fruit is reduced to the epidermis, giving off a characteristic vinegar smell. If the environmental conditions are the appropriate, the fruit shows a dirty white mycellium on the affected area.

High temperatures and relative humidity favour the development of this disease.

9. Soft rot
Caused by the bacterium Erwinia carotovora, that damages a wide range of vegetables. The injuries generally begin in the damages in the area of the peduncle insertion; the tissues suffer from a wet rot that spreads along the surface and inside the fruit. At the beginning, the epidermis creases; afterwards it breaks releasing a liquid full of bacteria that may damage the nearby fruit.

The preservation at temperatures between 7 and 10ºC controls the development of the bacterium.
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