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Pistachio nut, Pistachia vera / Anacardiaceae
Postharvest Atmosphere Management
When pistachios are harvested, they have between 30-40% of moisture; this percentage should lower to 7% to maintain the quality once peeled; the drying process can be carried out in two phases. The optimal temperature is 0 to 10ºC and the levels of oxygen and carbon dioxide in the atmosphere also influence in the preservation period.

The drying process is done in two phases; the first one lasts three hours, under temperatures up to 82ºC reaching a humidity of 12 or 13%; the second one is made under environmental temperature or below 49ºC, during one or two days, and moisture decreases to 4-7%. If the amount of fruits is small they can dry in 8 hours at temperatures of 60ºC. Another alternative is sundrying, between 3 and 5 days, although this method brings along problems with fungi. It is advisable that the drying process takes place as soon as possible to prevent them; therefore, it is recommended to harvest the fruits that can be peeled and dried in the same day or to store them until the peeling, 8 hours in cool storage rooms at 0ºC and 80% of relative humidity.

Pistachios are less susceptible to become rancid than other dry fruits, probably because they contain a smaller proportion of fatty acids polyunsaturated.

By controlling the conditions of relative humidity and environmental temperature of the warehouse, the fruit qualities will be better preserved. With a level of humidity inferior to 7% and a temperature lower than 25ºC, the development of the fungi is interrupted. If they must be preserved for more than a year, temperatures between 0 and 10ºC are recommended, since it reduces the possibility of fungi development, and the risk of fat oxidation is lower, decreasing the flavour quality.

In addition, by controlling the levels of the atmosphere components we can also influence in the preservation of the product. Therefore, in controlled atmospherewith oxygen concentrations lower than 1%, rancidness and other symptoms of deterioration are delayed. Oxygen concentrations below 0.5% balanced with nitrogen, and/or carbon dioxide levels higher than 80% in the air may be effective to control the insects from attacking stored products, and may be an alternative to chemical fumigation.
Postharvest Problems
There may be physiological disorders like cold damage and diseases caused by fungi.

There is a series of physiological disorders like physical damage, that is to say, that the shell breaks and thus the storage period is shorter. Then, the damage by ammonium to which they are very sensible, that causes the blackening of the external tissues, may appear.

In addition, several insects can damage the stored fruits. In order to diminish the attacks of insects there must be good hygiene, and fumigate if possible. Other ways to control are by means of irradiation, heat treatment and using controlled atmospheres. These fruits are also very attractive for squirrels and some birds.

The diseases that affect the fruits are mainly produced by fungi.

Aspergillus flavus:

The infection of fruits sometimes begins before harvest and its development is favoured by a rainy and humid weather, and when pistachio nuts are damaged by insects. The best way to avoid fungi in already harvested products is to maintain them in optimal temperature and relative humidity conditions when handling takes place.
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