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Pea, Pisum sativum / Leguminosae (Fabaceae)
Postharvest Atmosphere Management
Pre-cooling is a fundamental practice in order to keep a high quality. Hydro-cooling by means of using water at 0-2ºC is the simplest method. Good results are also obtained with vacuum pre-cooling; the produce must be dampen before in order to avoid damages by dehydration.

Storage is carried out at a temperature between -1 and 0ºC, and high relative moisture (95%). The peas must be previously pre-cooled. Under these conditions they are kept up to one or two weeks. The best preservation is obtained without peeling the product, since the pod renders protection to the vegetables and prevents from the stress of podding. The packages must not carry a great burden since it would complicate the ventilation and the maintenance of low temperatures.

The purpose of applying controlled atmosphere with an oxygen concentration of 5-7% and a carbon dioxide concentration of 5-10% is to store the product for 9 weeks. The peas cannot withstand high concentrations of carbon dioxide, but a concentration of 5%, as previously remarked, is an optimal percentage to obtain good results in storage.

For further information on the basic indications of post-harvest handling, consult the University of Davis Internet address ( http://postharvest.ucdavis.edu )
Distribution
Relative moisture during transport must be around 90-95% and the temperature between 0 and 2ºC. The produce must be cooled down before loading.

At the end of the transfer and during the marketing of the produce, drastic increases of the temperature must be avoid, in order to prevent condensations on the produce that would favour the development of diseases.
Postharvest Problems
Peas have a extremely high metabolic activity, resulting in a short post-harvest life. The main problems that peas may undergoes after harvesting are: self-scald, blight, pod yellowness, hardening of the seeds, sugar degradation and diseases.

Self-scald
These damages occur when the produce is not pre-cooled immediately after harvesting. It is caused by the product’s heat when exposed to the sun rays combined with the heat generated by respiration.

Blight
Peas are very prone to loose water. This occurs very fast if the atmosphere has a percentage of relative moisture below 90%. The effect of this phenomenon is usually reduced with the use of plastics and low temperatures.

Pod yellowness
During long periods of storage, over 14 days, the pods loose chlorophyll and they turn into a yellowish colour.

Hardening of the seeds
This phenomenon is quite serious with excessively long storage. The loss of tenderness means a significant reduction of quality.

Sugar degradation
The taste of peas depends mainly on the sugar content. These compounds degrade quite easily unless the product is kept at low temperatures (0ºC) immediately after harvesting. Another reason for the loss of sugar at high temperatures is the transformation into starch.

Diseases
There are several pathogens growing in the already harvested product. Among them, Sclerotinia sp., Botrytis cinerea (that causes grey rot), as well as the bacteria Pseudomonas pisi and Erwinia sp. Pseudomonas pisi causes some spots that may appear in the pod as in the seed and Erwinia produces wet rot.
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