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Tomato, Lycopersicon esculentum / Solanaceae
Postharvest Atmosphere Management
Tomato
The most important factor to maintain the marketing quality is to harvest the tomatoes in their optimal stage of maturity, since the early harvesting prevents their maturation and, if it is too early, they will be too soft and excessively coloured, very sensible to handling and with a very short self life.

Tomatoes are not usually pre-cooled due to their sensitivity to chilling. The suitable keeping conditions of tomatoes depend on their maturation stage. In the case of mature green tomatoes, they must be kept at 12-15ºC and 85-90% of relative humidity, whereas mature tomatoes can be preserved at lower temperatures, at 10-12ºC if possible. The period of conservation may be of few days to a maximum of 4-6 weeks, according to the degree of maturation.

If they are kept at lower temperatures, damages may occur, causing a greater sensitivity to the attack of microorganisms. These chilling injuries can be diminished if tomatoes are kept at 36-40ºC for 3 days before their storage, and afterwards keeping them at 2ºC for 3 weeks; this procedure is known as thermic pre-treatment.

Controlled atmospheres are also used for preserving tomatoes. The suitable conditions vary according to the varieties, although in general the conditions recommended for the mature green tomato are 3-5% of O2 and 2-3% of CO2, at a temperature of 12 to 20ºC. In the case of mature tomatoes, both the level of O2 as the level of CO2 should be maintained at 3-5%; the temperature must be of 10-15ºC. Nevertheless, this technique is not very common in tomato preservation.

Tomatoes under maturation produce ethylene at a high rate, so it is recommended to store or to transport them with produce that is also sensitive to ethylene, such as lettuces and cucumbers.

If we want the fruit to ripe, the optimal temperature is of 20ºC. Under these conditions, the colour development is the optimal and the retention of vitamin C is high. Moisture levels must be kept at 90 or 95%, and ethylene must be applied to the concentration of 100ppm for 24-72 hours.
Distribution
The transport of tomatoes must be at temperatures between 8 and 14ºC, according to the length of the transport. The relative humidity must be high, between 90 and 95%. Although it is not very common, some authors mention the use of the controlled atmosphere during transport. The suitable conditions would be of 3 to 5% of oxygen and 0% of carbon dioxide.

Distribution takes place at average temperatures of 10-15ºC, with average relative humidity and ventilation. Moreover, unnecessary handling must be avoided, in order to reduce damages to the fruit.
Postharvest Problems
Stored tomatoes may show different problems caused by inadequate conditions (too much cold, not enough humidity...) or diseases caused by different fungi and bacteria, like black rot, sour rot, cottony rot or the bacterial soft rot.

Among the different problems during conservation we find the following:

- Softening: after the harvest, the hardness of the pulp diminishes, due mainly to the loss of water.

- Chilling injuries: they take place when tomatoes are put under temperatures below 10-13ºC. This brings about the spotting on the surface of the fruit. Besides, it favours the attack of different organisms that produce rots.

- Diseases are one of the most important reasons for the losses during storage, varying according to the period, the region and the handling of the produce. We usually find the following ones:

- Black rot: produced by Alternaria. This disease is found specially in tomatoes that are damaged by an excess of cold. It shows injuries covered with short black down.

- Sour rot: it is produced by the microorganism Geotrichum candidum. The disease produces the disintegration of the tissues, that soften. The skin wrinkles. It gives off a vinegar smell and it shows a yellowish white colour.

- Cottony rot: it is caused by the fungus Rhizopus stolonifer. The skin of the fruit affected by this disease shows brown spots spread all over a great surface. The tissue softens and the skin breaks, exuding a watery substance. Moreover, it shows the dark down of the fungus.

- Gray rot: it is caused by the fungus Botrytis, that produces a cottony down of gray colour.

- Bacterial soft rot: it is caused by the bacterium Erwinia carotovora. Its attack shows a wet rot.
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