Detailed Explanation of Key Points of Mushroom Storage and Fresh-Keeping Technology

I. Storage Characteristics and Varieties

Mushrooms are rich in amino acids and protein and have a delicious flavor. However, after harvest, mushrooms have vigorous respiration and quickly open their caps, turn brown, develop off-flavors, and deteriorate in quality at room temperature, so they can only be stored short-term. Dried mushrooms are easy to preserve, but their nutritional value declines, and serious losses can occur if processing is not carried out in time. Therefore, measures must be taken after harvest during storage, transport@#@136@#@, and sales and before processing to prevent a decline in mushroom quality. There are many cultivated varieties of mushrooms, and common ones include oyster mushroom, shiitake, button mushroom, enoki mushroom, and Phoenix mushroom.

II. Harvesting

1. Timely Harvesting

If mushrooms are harvested too early, the caps have not grown fully, which affects yield; if harvested too late, the fruiting bodies are not suitable for storage and quality declines. Oyster mushroom should be harvested when the cap is fully expanded, the color has become lighter, white downy material is present in the depressed center, and the edge has just begun to curl upward but has not yet released a large number of spores. If harvested too late, the stipe becomes hard, the edge cracks, the texture becomes tough, and it often has a bitter and unpleasant taste, reducing eating quality. Shiitake should be harvested before the veil opens. Button mushroom is generally harvested before the cap exceeds 4 cm and before the veil opens; if harvested too late, it easily opens and turns brown, shortening the storage period. Enoki mushroom should be harvested when

the stipe stops growing, the cap diameter reaches 1.5--2.0 cm, and the cap edge begins to flatten; if harvested too late, the mushroom loses weight.

2. Harvesting Methods

Do not spray water on the day of harvest in order to maintain firmness, but stopping water too early will cause the caps to dry out and become brittle and cracked; in some cases, a small amount of water may be sprayed in the early morning. When harvesting, turn each mushroom upward to harvest it, tilt the cap outward, and do not pull it directly out of the bed. Clamp the base of the mushroom with the fingers of the left hand, and use a knife in the right hand to cut off the base of the mushroom base; when fruiting bodies grow in clusters, such as with oyster mushroom, a knife can be used close to the bed surface to cut the entire cluster from the base of the stipe; for enoki mushroom, simply hold the mushroom gently and pull it out. After harvesting, place the mushrooms in a basket with the stipes facing up, and precool as soon as possible or trim and grade them in a cold place; they may also be trimmed immediately after harvest and then put into baskets. For varieties with larger fruiting bodies and shorter stipes, shortening the stipes can extend the storage period. For example, after harvest, oyster mushroom is best left with a stipe length of 2--3 cm. When button mushroom is harvested, the stipe length is generally 5--10 mm. The main edible part of enoki mushroom is the stipe, so it should not be shortened. During trimming, remove opened mushrooms, diseased mushrooms, insect-damaged mushrooms, and mechanically damaged mushrooms that are unsuitable for storage. After trimming, refrigerate the mushrooms as soon as possible.

III. Storage Conditions

The suitable conditions for mushroom storage are 0°C and 95% relative humidity. Mushroom water loss is related to black stipes and cap opening, and packaging with plastic film or maintaining relative humidity above 95% can reduce water loss. Controlled atmosphere storage can inhibit mushroom browning, and controlling oxygen at 2--4% and carbon dioxide at 5--10% helps maintain the whiteness of mushrooms and extend storage life. Treatment with brine, citric acid, ascorbic acid, sulfur dioxide, or steam heat can all deactivate polyphenol oxidase activity and prevent enzymatic browning; during storage and transport, metal containers should be avoided for holding mushrooms in order to prevent non-enzymatic browning.

IV. Storage and Treatment Methods

1. Controlled Atmosphere Storage

(1) Spontaneous modified atmosphere Place mushrooms in polyethylene bags 0.04--0.06 mm thick, using the mushrooms' own respiration to create a low-oxygen and high-carbon dioxide environment inside the bag. The packaging bag should not be too large; generally, a filling capacity of 2--4 jin is suitable, and quality remains unchanged for 5 days at 0°C.

(2) Carbon dioxide filling Place mushrooms in polyethylene bags 0.04--0.06 mm thick, fill with nitrogen and carbon dioxide, and keep them at 2--4% and 5--10% respectively; at 0°C this can inhibit cap opening and browning.

(3) Vacuum packaging Place mushrooms in polyethylene bags 0.06--0.08 mm thick and vacuum them to reduce oxygen content; they can be kept for 7 days at 0°C.

2. Ice Storage Method

During transport, add ice cubes to lower the temperature of the mushrooms. Line the packaging container with a layer of plastic film, place 4--6 cm thick crushed ice at the bottom, place ice packs in the middle, and place mushrooms around them. When filled to about 80% capacity, fold the plastic film inward, cover the film with about 5 cm of crushed ice, and finally cover and transport.

3. Vat Storage Method

Place cold water 3--4 cm deep at the bottom of a washed vat, set a wooden rack above it, stack the mushrooms on the rack, then seal the opening with plastic film, and store at low temperature.

4. Chemical Treatment

(1) Brine. After harvest, wash mushrooms with 0.6% cold brine and soak for 10 minutes, which can precool them and prevent browning; drain the water and store. If after washing with brine they are then rinsed with 0.1% ascorbic acid or 0.1% citric acid before storage, the effect is better. Drain and place in plastic bags for cold storage.

(2) Sodium metabisulfite. After harvest, wash off debris with 0.02% sodium metabisulfite, then place in 0.05% sodium metabisulfite for half an hour, rinse with clean water, drain, and store; this has a very good color-protecting effect.

5. Irradiation

Gamma ray irradiation can prevent fresh mushrooms from discoloring and inhibit respiration and cap opening, with a dose of 200--300 rad.