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Orange, Citrus sinensis / Rutaceae
Postharvest Atmosphere Management
The oranges collected with a good level of internal maturity but with little external ripeness, that is to say, that are still green, are put under a process of degreening with ethylene.

The conservation in suitable conditions in cold storage rooms help to maintain the fruit’s organoleptic characteristics in perfect conditions.

After the harvesting, oranges are transferred to the fruit and vegetable premises where they are put under several processes. With the conveyor belt, oranges go through ultraviolet cameras where the rotten areas are detected. Later on, they are washed in big pools with the use of foam curtains and water. After a predrying, the oranges will be waxed (always after the degreening) and polished and finally put under hot air tunnels to dry. Then, the commercial classification of the fruit is carried out by diameter and colour, with mechanical graders.

As it has been explained in previous points, the fruit’s internal and external maturity is governed by different processes; for that reason some orange varieties reach the optimal maturity level before they change colour. In these cases, in order to advance the sale, fruits will be treated with ethylene in special cameras, to cause coloration. This process is called degreening; the ethylene degrades the bark’s chlorophyll and favours the formation of carotenoids, responsible for the orange colour.

With so low concentrations of 1 ppm (parts by million) of ethylene an appreciable effect takes place in the process of degreening, however, it is not recommended to surpass 10 ppm since it favours softening.

For a correct degreening process, the temperature of the cameras must be around 18-24ºC and at the same time there should be a uniform circulation of the air in the camera to avoid the CO2 accumulations that are responsible of bad flavours in the fruit. On the other hand, the relative humidity of the cameras will be as high as possible, to avoid physiological disorders.

One of the key problems for the orange preservation is the loss of water after harvesting. Low temperatures and high relative humidity around 95% reduce transpiration, slow down senescence and reduce the development of pathogens; therefore, they help to lengthen the fruit’s life.

Low temperatures in the storage rooms have two limitations: on the one hand temperatures must never reach the level of freezing, between 1.5 and 2ºC, and, on the other hand, some physiological disorders are very sensitive to low temperatures. The optimal temperature is around 3-8ºC.

In order to reduce the fruit sensitivity to cold temperatures, several techniques have been developed that are based on the modification of the atmosphere during preservation. One of these techniques is the controlled atmosphere, consisting of 2% reduction of O2 concentration and 10% increase of CO2 in the environment surrounding the fruit. Nevertheless, due to the high economic cost, this system is not very used nowadays.
Distribution
During transport, oranges must be protected against the atmospheric agents.

During the transport of fruit to the consumption point, oranges must be protected from rain, insolation, wind, etc.

The transport trucks will keep the box temperature around 0ºC and a relative humidity around 85-95%. The freight must never lean on the walls or ceiling and there must be enough space between the packages for a correct circulation of the cooling current.
Postharvest Problems
Many alterations may damage the fruit, and diverse diseases, plagues or virosis attack the tree. Among the fruit alterations we emphasize swellings, cracks and brown marks.

Fruit alterations:

- Swellings or " Creasing"
Presence of cracks or absence of skin in certain areas due to an enzymatic failure during the fruit formation.

- Fruit crack or " Splitting"
Presence of cracks due to the growth at different speed of the skin and the flesh. If the flesh increases its size very quickly, and the skin cannot follow the rate, there is a breakage of the latter since the dimensions of the fruit are too big.

- Skin collapse
Very frequent alteration in the Navelate variety. It consists of the creation of depressions on the surface that evolve into brown marks. They take place when the fruit is put under very strong relative humidity variations.

Plagues

- Mediterranean fly
It is one of the most important plagues, also called Ceratitis capitata. It is a dipterous insect that lays its eggs inside the fruit. The larvae will be fed from the pulp, decomposing the orange until it drops from the tree.

Diseases

- Phytophthora
It is a fungus that attacks the neck of the plant and produces rubber exudations. If it attacks the tree’s circulatory vases, it can block the absorption of the roots producing the weakening and causing the tree to die. The symptoms in the fruit are usually a noticeable alcoholic smell.

- Postharvest fungi
There are a lot of postharvest fungi, like the Penicillium type, that causes a bluish cottony mould. It is better controlled in the warehouses applying different pesticides.
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