Key Points of Mushroom Harvesting, Storage and Fresh-keeping Techniques

I. Storage Characteristics and Varieties

Mushrooms are rich in amino acids and protein and have a delicious flavor. However, after harvest, mushrooms respire vigorously and at room temperature quickly open their caps, turn brown, develop off-flavors and deteriorate in quality, so they can only be stored for a short time. Dried mushrooms are easy to preserve, but their nutritional value decreases, and delays in processing can cause serious losses. Therefore, measures must be taken after harvest during storage, transport @#@136@#@ and sale 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 fully grown, which affects yield; if harvested too late, the fruiting bodies do not store well and quality declines. Oyster mushroom should be harvested when the cap is fully expanded, the color has become lighter, white cottony material is present in the depressed center, and the margin has just begun to curl upward but has not yet released large numbers of spores; if harvested too late, the stipe becomes hard, the margin cracks, the texture becomes tough, and it often has a bitter and off-flavor, 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 its cap 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 margin 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, so a small amount of water may be sprayed in the early morning. When harvesting, twist each mushroom upward, tilting 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 cut off the base of the mushroom base with a knife in the right hand; when fruiting bodies grow in clusters, such as oyster mushroom, a knife can be used close to the bed surface to cut off the entire cluster at 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 them 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. Button mushroom is generally harvested with a stipe length of 5--10 mm. The main edible part of enoki mushroom is the stipe, so it should not be shortened. During trimming, remove open-cap mushrooms, diseased mushrooms, insect-damaged mushrooms and mechanically damaged mushrooms that are unsuitable for storage. Trimmed mushrooms should be refrigerated as soon as possible.

III. Storage Conditions

The suitable conditions for mushroom storage are 0°C and 95% relative humidity. Water loss in mushrooms is related to black stipes and cap opening, and water loss can be reduced by packaging with film or keeping relative humidity above 95%. Controlled-atmosphere storage can inhibit mushroom browning; maintaining 2--4% oxygen and 5--10% carbon dioxide helps keep mushrooms white and extends storage life. Treatment with brine, citric acid, ascorbic acid, sulfur dioxide or steam heat can inactivate 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, and use the mushrooms' own respiration to create a low-oxygen and high-carbon dioxide environment inside the bag. The bags should not be too large; a capacity of 2--4 jin is generally 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, vacuum to reduce the oxygen content, and 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 of crushed ice at the bottom, place ice packs in the middle, and arrange mushrooms around them. When filled to about 80% capacity, fold the surrounding film inward, cover the film with another layer of crushed ice about 5 cm thick, and finally cover and transport.

3. Jar Storage Method

Place cold water 3--4 cm deep in the bottom of a washed jar, 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 them for 10 minutes; this can precool them and prevent browning. Drain the water and store. If, after washing with brine, they are further rinsed with 0.1% ascorbic acid or 0.1% citric acid before storage, the effect is even better. Drain and put into plastic bags for cold storage.

(2) Sodium metabisulfite. After harvest, wash away 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.