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Mandarin, Citrus reticulata / Rutaceae
Postharvest Atmosphere Management
Mandarin
Mandarins are very sensitive to low temperatures, for which they develop spots in the skin, reducing their commercial quality. For that reason, each variety has its own cooling characteristics. Temperatures around 5ºC and 90% of relative humidity will be applied to fruit in case we ignore the suitable conservation conditions.

The main cause of physiological deterioration in citruses is the water stress when the fruit is removed from the tree. In the case of mandarins it worsens because they have a very high surface in relation to the volume and a thinner skin that favours dehydration. The transpiration that takes place in the fruit causes the skin to dry, wrinkle, soften and it accelerates the aging of the fruit. At the same time that the fruit softens, the acidity, the content in vitamin C, the organoleptic flavour characteristics and the quality of the texture decrease.

The application of low temperatures to stored mandarins is useful for the lengthening of the fruit’s self life, to reduce transpiration and to avoid the proliferation of fungi. It is usually thought that the lower the temperature is, the longer the fruit lasts without loosing its quality. Nevertheless, there are two limitations when applying low temperatures. First of all, the freezing temperature of mandarins, which is around 0-1,5ºC ,must not be surpassed. On the second hand, mandarins are very sensitive to low temperatures; they develop spots in the skin and different alterations that make them to lose commercial quality.

To each variety they usually apply cooling conditions consisting in the application of higher temperatures whenever the fruit has greater sensitivity to damages by cold. On the other hand, relative humidity must be around 90%. Thus, the optimal conditions of storage for some varieties are the following ones:

CULTIVAR::TEMPERATURE (ºC)::Approximate time of conservation (weeks)
Clementina::4 - 5::6 - 1
Ellendale::5 - 6::8 - 10
Fortune::9 - 10::4 - 6
Nova::9 - 10::2 - 4
Ortanique::5 - 6::10 - 12
Satsuma::1 - 2::4 - 6


Source: II Congreso de Citricultura de la Plana (23,24,25 of March 1995)

When we do not know the characteristics of a given variety, general storage conditions of 5ºC and 90% of relative humidity are applied.
Distribution
During transport, mandarins must be protected against the atmospheric agents. When the transport is made by road, the trucks must maintain the box at temperatures and humidity suitable for the fruit they transport, stressing on the correct circulation of the coolant current.

Since all citruses, including the mandarin, are perishable, certain adequate conditions must be maintained during the transport, so the fruit reaches the point of sell in perfect conditions. Mandarins must be protected from rain, insolation, wind, etc.

The transport trucks must maintain the temperature of the box around 0ºC and a relative humidity around 85-95%. The load must never lean on the walls or ceiling and there must be an adequate space between the packages for a correct circulation of the coolant current. If packages of different size are used or the load is not full, the holes must be filled up with empty packages.

The trucks will have temperature and humidity registries to verify that the conditions of transport have been the suitable ones.

The means of transport will be chosen according to the distance, the conditions of the fruit, the market location, etc. For the European Union countries it is done by road, for the countries of eastern Europe by railway and for countries like Japan, the United States or Canada it is transported by boat.

The transport by road is the mostly used for its rapidity, unloading comfort and more reduced cost.
Postharvest Problems
Mandarins are very sensible to cold and in many occasions there appear dark spots in the rind. In addition there can also appear, like in most citruses, rots caused by different fungi.

Mandarins are very sensible to low temperatures and prone to injuries by cold. One of these is "pitting", the commonest, characterized by round depressions on the rind with a certain decolouring that darkens with the time. If the fruit is overmatured, there can appear dark spots of irregular shape in the rind, spread on the surface of the fruit. This alteration is also due to cold and is called scald.

If the fruit is put under high humidity conditions during the storage appears the so-called ‘oil-darkening" or blackening of the oleiferous glands, that contain the essential oils; it can be confused with scald when it spreads all over the rind.

Another type of alteration by cold, although less common, is the so-called " watery break-down", characterized by a spongy and soft appearance of the fruits, as if they had been frozen.

All these damages by cold appear more frequently when the storage in the rooms is longer and the temperature is lower. The symptoms can be visible in the rooms and they show when the fruit is put under environmental temperatures.

Another type of alterations that mandarins may undergo are the fungi that cause rots in all citruses. Thus we can find:
- green rot, caused by Penicillium digitatum, characterized by green spores.
- blue rot, caused by Penicillium italicum, characterized by blue cottony spores.
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