Detailed Explanation of Controlled Atmosphere Storage and Preservation Technology for Mushrooms

Mushrooms have a tender and delicate texture, a pure white color, and rich, unique nutrition, making them deeply loved by consumers. However, due to their high water content, tender tissues, and lack of a protective surface structure, both respiration and transpiration are relatively intense, and they are also susceptible to pathogen infection and mechanical damage, leading to rot and deterioration. Under normal temperature and normal air conditions, harvested mushrooms will discolor, deteriorate, and open their caps within 2-3d, reducing their edible quality and commercial value. Given the physiological characteristic that mushrooms are highly prone to aging and browning, there is currently not much research both domestically and internationally on mushroom storage and preservation, so it is very necessary to study the optimal storage and preservation technology for mushrooms.

The controlled atmosphere storage and preservation technology for mushrooms is based on the biological characteristic that mushrooms are prone to aging, browning, and regrowth after harvest. First, low temperature is used to inhibit respiration and transpiration, while extremely low O2 concentration and high CO2 concentration are used to further inhibit respiration and prevent the mushrooms from opening their caps and browning, thereby significantly improving the preservation effect and extending the storage period of mushrooms to 25-30d. The technology is described as follows:

I. Harvesting

Mushrooms should be harvested at the appropriate time, generally when the fruiting bodies have fully grown and no longer show obvious increases in volume. If harvested too early, the fruiting bodies have not fully grown, the mushroom quality is poor, and yield is reduced; if harvested too late, the fruiting bodies are more likely to age, open their caps, and discolor. During harvesting, handle them gently, place them gently, and load them gently to reduce mechanical damage as much as possible. At the same time, harvesting tools and packaging containers should be cleaned and disinfected.

II. Pre-storage Treatment

After harvesting, trim off the mushroom stems. If any mushrooms have yellowed or browned, place them in a 0.5% citric acid solution and rinse for l0min, then remove and drain off the water droplets, and then quickly pre-cool the mushrooms. Pre-cooling mushrooms is very important, because at relatively high temperatures, various physiological activities in the mushroom bodies are promoted, accelerating nutrient consumption, water loss, post-ripening and aging, and browning reactions.

III. Low-temperature Controlled Atmosphere Storage

Place the pre-cooled mushrooms into storage bags made of 0.025m thick polyethylene plastic film, with each storage bag holding about lkg of fresh mushrooms. After sealing the opening, place the mushrooms in a cold storage room for storage, and reduce the mushroom body temperature to 0°C-3°C within 4-5h, maintaining a relative humidity of 95%-100%. Mushrooms store well when the O2 concentration is 1% and the CO2 concentration is 10%-15%, and the mushroom bodies remain white in color with very few opening their caps. When the mushrooms are first put into storage, the temperature is relatively high, generally above 10°C, and the respiration of the mushrooms is relatively vigorous. At l0°C, the respiration intensity of mushrooms is Rco2=l00.lmg/kg h, so while lowering the temperature after loading, that is, within 4-5h, the O2 concentration in the storage bag can be reduced to below 3%, and the CO2 concentration can be raised to above 10%. When the temperature drops to the suitable storage temperature for mushrooms of 0°C-3°C, respiration gradually weakens (at 0°C, the respiration intensity of mushrooms is Rco2=28.3mg/kg h). The O2 concentration slowly decreases, and the CO2 concentration slowly increases. After ld, the O2 concentration in the bag reaches about 1%, and the CO2 concentration is about 13%. At this time, prick a small hole in the bag with a thin needle, which can basically maintain the ratio of O2 and CO2 concentrations. In subsequent management, humidification measures should be taken for the cold storage room to ensure that the relative humidity in the bag remains above 95%.

IV. Precautions

1. During mushroom storage, a constant low temperature must be maintained, and temperature fluctuations up and down should be avoided, otherwise discoloration and aging will be accelerated.

2. Mushrooms have a high water content and no protective surface structure, so water evaporation is very intense. Therefore, using plastic bags for packaging and preservation can not only maintain the controlled atmosphere indicators required by the mushroom bodies, but also maintain humidity, prevent water evaporation, reduce weight loss, and maintain freshness.

3. Because different plastic films have different gas permeability, before storage, the permeability of the film to O2 and CO2 must be measured.

4. Reducing the O2 concentration and increasing the CO2 concentration can effectively inhibit the respiration intensity of mushrooms, but unsuitable concentrations of O2 or CO2 have a stimulating effect on the growth of the mushroom bodies. For example, a 4% O2 concentration can stimulate the growth of the mushroom cap, causing the mushrooms to open their caps; when the CO2 concentration is 5%, it can stimulate the elongation of the mushroom stem, but when O2 drops to 1% or the CO2 concentration rises to 10%, it can completely inhibit the growth of the mushroom caps and stems, while also inhibiting respiration.