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Corn, Sweet corn, Zea mays / Gramineae
Postharvest Atmosphere Management
It is important to lower the produce temperature as quick as possible at levels between -1 and 0ºC. Pre-cooling is necessary because the metabolic activity is very high, the sugar is converted in starch, and the produce gradually looses the sweet taste. The produce may be subject to fermentation if the temperature is lowered too late. The pre-cooling is made with humid air, water or vacuum.

Normally, the sweet maize is not stored, although it may be stored for short periods when there is an excessive supply in the market. The optimal temperature is 0ºC and 95% of relative humidity; in these conditions it may last up to two weeks.

Concerning modified atmospheres, there are several opinions on their effects, according to different authors. Thus for instance, Kader et al. (1985), American authors, consider a modified atmosphere bearing concentrations of 2-4% of oxygen and 10-20% carbon dioxide to have a good effect (degree 2, in a scale from 1 to 4, where 1 is the maximum beneficial effect), although the commercial use of this method in this country is scarce.
Postharvest Problems
Due to its high metabolic activity, the sweet maize has a limited period of storage. The main factors that take part in the loss of quality are sugar decay, drying, the grains dent, bract yellowness and some diseases.

Sugar decay
Sugar decay is considered as an important factor in the quality decrease, since sweetness is one of the most appreciated characteristics in maize. The temperature recommended in order to slow down the process of sugar decay during storage is 0ºC; the higher the temperature is, the greater the sugar decay. Thus, at 10ºC it is 3 or 4 times faster than at 0ºC, 6 times faster at 20ºC, 12 times at 30ºC and 24 at 40ºC. However, the rate of sugar decay depends also on the variety; thus, the richer in sucrose the variety is, the longer the storage period. The extra-sweet varieties show less quality loss when they are not quickly pre-cooled.

Drying
The drying occurs when the maize grains loose water. In order to avoid it, the pre-packaging is recommended to be in plastic, both stretchable or retractile, since they maintain high levels of relative moisture (95-100%).

Dent of the grains
It is a direct consequence of water loss, they loose their rounded shape and there appear some dips that diminish their quality.

The application of pricked ice on the produce causes the temperature lowering and help to maintain a humid environment. This method is used in the United States, although not in Europe.

Diseases
The main micro-organisms affecting maize cobs in post-harvesting are bacteria and yeast in a greater extent, and fungi. Among the bacteria we find Pseudomonas fluorescens, Flavobacterium sp., Xanthomonas sp. or Pseudomonas maltofila, Enterobacter agglomerans, E. cloacae and Serratia rubideae. Some of the common yields are Rhodotorula sp., Criptococcus sp., Candida sp. and Kloeckera sp. The most recurrent fungi are Penicilium oxalicum, P. expansum, P. funiculosum, Aspergillus niger and Cladosporium cladosporioides.
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