Postharvest Atmosphere Management
After the harvesting it is recommended to put mushrooms under pre-cooling. Afterwards they are stored at –0.5-1ºC and relative moisture of 90-95%.
It is recommended to put mushrooms under pre-cooling to cool them quickly and therefore, to avoid the loss of water and the development of bacteria. Among the different methods available, the most suitable is vacuum cooling, although humid air is also appropriate. The optimal temperature for storage is from –0.5 to 1ºC, although freezing must be avoided. The lowest the temperature the longer the period of storage. The optimal level of moisture is 90-95%.
In theory, mushrooms can be stored up to 21 days if they are kept at atmospheric pressures under the normal. This can be attained at pressures between 10 and 15mm of mercury, at 0ºC and relative moisture around 95%, although this method is not carried out in practice.
There are also references concerning the effects of controlled atmosphere. The minimum limit of oxygen they bear is very low, next to 0%, whereas concentrations of carbon dioxide over 15% may cause some damages. According to some authors, they may have positive effects, inhibiting the development of mould and the opening of the cap if the concentration is around 20%, but actually it is not used.
Post-harvest problems can be caused by inadequate conditions of temperature and moisture. These may give rise to browning, drying, opening of the cap, elongation of the stem and physiological alterations like "crocodile skin‘, and be affected by diseases and pests.
Due to their high metabolic activity, mushrooms have a short post-harvest life and may undergo deterioration for several reasons. It may cause browning or spotting, drying, opening of the cap and elongation of the stem.
During selection, mushrooms Íwh ich do not fulfil the minimum quality requirements demanded by the standard in force must be removed, and some of the reasons for selection are due to physiological alterations, pests and diseases.
Mushrooms affected by this alteration show protuberances in the cap. It may be caused by low relative moisture in the atmosphere, excessive application of some pesticides, formol steaming, etc.
Dry bubble disease
It may be caused by several fungi, among them Verticillium malthoussei, giving rise to malformations, such as bifurcations and onion-shaped buds.
The fungus Dactylium dendroides grows spreading its mycellium, of a whitish colour or with pink-tinged on the caps.
Wet bubble disease
Caused by the fungus Mycogone perniciosa. It causes deformations and twisting on the cap and in advanced stages they give off a viscous brown fluid of unpleasant smell.
Mould of the gill
This disease is caused by fungi of the genus Cephalosporium and gives rise to an abnormal coloration on the laminae.
Bacterial blight or ‘drop’
The so-called bacterium Pseudomonas toolasi causes the appearance of yellowish spots on the cap that turn into a brown colour and become sticky.
Damping off or blight
The fungi causing this disease are Fusarium martii and F. Oxysporum. The mushrooms become cork-like and the peduncles are dry, hollow and brown inside.
It gives rise to deformations in the carpophores caused by the Mushroom Virus 1 and 2.
The presence of this mite of the Tyrogliphus group causes the appearance of irregular cavities, humid texture in the stem and the cap.
These insects attack the crop and make small holes and confer a dry appearance to the surface of the affected cap.
The larvae of insects belonging to several species of dipterous dig galleries in the stem or the cap.