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Asparagus, Asparagus officinalis / Liliaceae
Postharvest Atmosphere Management
Asparagus
The asparagus has a high rate of respiration, reason why it is essential to pre-cool it as soon as possible after its harvesting. This process can be carried out before or after packaging. The temperature must be put down to at least 4ºC, the nearest as possible to 0ºC. The methods used are water cooling, vacuum cooling and air cooling, although the best is the first one, since it allows to lower the temperature in 10-15 minutes.

When the turions are destined to far markets, it is recommended to dip the cut surface in a solution of calcium hypochlorite, thus controlling the bacterial infections.

The asparagus can only be stored for short periods of time; at best, the consumption must preferably take place within the week following the harvesting. If they are stored at temperatures between 0 and 2ºC with moisture levels around 100%, the turions may last up to 15-20 days. For longer storage it is recommended to raise the temperature to 2-3ºC, since temperatures near 0ºC may damage the produce if it is kept for too much time. Turions must not be stored together with species that produce ethylene, since this gas accelerates the hardening of the asparagus.

Whenever modified atmospheres are used, the asparagus may last for a month; in short storage, this method improves the quality of the produce. The conditions recommended are to maintain the levels of carbon dioxide at 10-14% for temperatures between 0 and 3ºC, or 5-9% for temperatures between 3 and 6ºC. Oxygen must not be modified. By means of these modifications there is a decrease of rots caused by fungi and bacteria.

If non-perforated plastic coverings are used, it is necessary to select the suitable time of exhibition, the type of plastic and atmosphere handling, otherwise there occur unsuitable environments for the turions storage.
Distribution
During distribution, temperatures must be kept below 10ºC and the relative humidity must be high, specially if the produce is not protected with plastic. If they are placed on a humid surface they keep turgidity for a greater length of time. The produce that is spare or in reserve must be protected from the light, and it is better to dip the base in water.

The transport of asparagus must be carried out at temperatures between 0 and 5ºC, according to the length of the journey. In case of sea transport, the optimal temperature is 2.2ºC, 90 to 95% of moisture and levels of carbon dioxide around 5 and 10%.
Postharvest Problems
The asparagus may undergo some modifications that reduce their quality during storage, such as the increase of fibreness, blight, bending, loss of taste and aroma and changes in their composition. They may also be affected by diverse microorganisms, like the bacterium Erwinia carotovora or the fungi Fusarium moniliforme, Penicillium hirsutum and Botrytis cinerea.

The asparagus has a high rate of respiration, so they can only be preserved for short periods of time, since there occur fast modifications that reduce their quality. They may also be subject to parasitic diseases.

Among the possible modifications we find the following ones.

Increase of fibreness: it increases from the base upwards, diminishing the proportion of edible surface. This process is accelerated if the turions are exposed to ethylene.

Blight: it is caused by the loss of water, due to transpiration. It is shown in the loss of weight of the produce; there also occur longitudinal streaks. Sometimes the base of the asparagus is immersed in buckets of water, thus controlling the problem, although this method may lead to the development of bacteria. Another method used is the covering with plastic.

Bending and lengthening of the turions: the lengthening of the asparagus is greater at high temperatures. If the turions are kept in horizontal position and they receive direct sunlight, they will bend upwards, thus reducing their quality.

Loss of taste and aroma: the lower the temperatures are, the faster the process occurs.

The white asparagus may show a pink colouring if they are placed in direct sunlight right after their cutting or if they are not sufficiently cooled down.

During storage there also occur some changes in the composition of the asparagus. The levels of vitamin C and sugar decrease, whereas the acidity increases.

Among the parasitic diseases that may affect the asparagus we find the following:

Erwinia carotovora is a bacterium that produces a soft wet rot that gives off an unpleasant smell. The development of this disease takes place both in the base as in the apex of the turions. The white asparagus are more resistant than the green ones.

Fusarium moniliforme is a fungus that causes an initial necrosis on the tissue affected, which soon develops a pinky white coloured down. As the infection spreads, the area affected turns into a dark green colour and wet appearance.

Penicillium hirsutum is one of the fungi that affect mainly the postharvested asparagus. It attacks specially the area where the asparagus is cut, being the place where the fungus grows.

Botrytis cinerea is a fungus that causes a soft rot covered by a grayish-white down. The turions are infected in the field, mainly when the weather before the harvest is cold and rainy.
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