A detailed guide to oyster mushroom preservation techniques: this way they keep much longer

Under ordinary conditions oyster mushrooms are difficult to store and have a short shelf life. Two days after picking, oyster mushrooms lose water and their freshness drops sharply, the caps turn yellow and an off-odor appears. Whenever the fruiting peak comes, large quantities of fresh mushrooms flood the market at once, causing prices to fall sharply; on the other hand, in the off-season and in cities far from mushroom-growing areas, there is little mushroom supply and nothing to sell. For this reason, we carried out research on the storage and preservation of oyster mushrooms, briefly described below.

Test materials: common oyster mushroom strains PL-32, PL-35 and Florida, all second-flush mushrooms, collected from farmers' mushroom gardens on the outskirts of Gutian County; the preservative (anti-rot and ethylene-removing) was prepared in-house; an ordinary clean cold store was used for storage; a refrigerated truck was used for long-distance transport.

Method: harvest oyster mushrooms at 80% maturity, remove diseased, insect-damaged and damaged mushrooms, place them in a clean, cool, ventilated spot and use an exhaust fan for 1-1.5 h of air-cooling pretreatment, then carefully load them into plastic baskets lined on the outside with PE (40-60 μm thick), about 7.5 kg per basket. Place 2 clean folded toilet papers on the mushroom surface, place on the paper a packet (wrapped in well-ventilated shoulder lining paper) of about 40 g of preservative, put the plastic basket lid on well, and immediately transport them into a cold store pre-cooled for 24 h to cool down; when the store temperature drops below 5°C, use a vacuum pump to draw air from the PE and reduce pressure until the PE is pressed tightly against the plastic basket; tie the bag opening tightly, strictly preventing air from leaking in, and stack them; then lower the temperature to 1±0.5°C for constant-temperature storage.

Test results: after storing oyster mushrooms for 35 d by the above preservation method, the good-mushroom rate of all 3 strains was above 99.5%, the mushroom bodies showed no rotting, browning or softening, and the natural moisture loss rate was within 0.5%. Measurement of the CO2 and O2 contents in the final storage environment showed that inside the PE for all 3 strains the CO2 content was 9.84%-10.31% and the O2 content was 2.54%-3.21%. Among the main nutrients of the 3 strains, protein content fell by 1.07-1.16 percentage points, carbohydrate content (dry product) fell by 2.0-2.5 percentage points, and cellulose content rose by 0.21-0.26 percentage points. In the control group (pretreated fresh mushrooms loaded into plastic baskets and stored in the same cold store as the test group), the CO2 and O2 concentrations of the storage environment were those of the store atmosphere; after 14 d of storage, the rotting rate reached 10.1%, the mushroom softening rate was as high as 100%, the natural moisture loss rate was as high as 27.2%, and the food value was 0. This shows that oyster mushrooms using the above preservation technique still basically maintained their original quality after completing a certain storage period.

3 d before removal from storage, the cold store should be gently warmed (from 1°C to 10°C; if locally @#@136@#@, the temperature should rise from 1°C to room temperature), and before shipment the PE and preservative should be removed, then the mushrooms should be transported to the sales destination in a refrigerated truck (with the temperature inside the truck box controlled at 8-12°C); practice has proved that using the pre-warming measure before removal from storage and storage in plastic baskets can overcome the serious condensation on the mushroom bodies after oyster mushrooms leave storage.

Oyster mushrooms packed in plastic baskets and PE, with preservative placed inside and subjected to pressure reduction, low temperature and other storage measures, create a storage environment high in CO2 and low in O2, which lowers the respiration intensity of the mushroom bodies, reduces the loss of respiratory substrate, prevents the accumulation and synthesis of ethylene, inhibits the activity of polyphenol oxidase, overcomes moisture loss, and prevents microbial infection and reproduction. After 35 d of storage, the good-mushroom rate still reached 99.5%, and the main biological arg of the mushroom bodies still basically remained at the level at just harvest, so the preservation was successful.

This technique requires little investment, is simple and easy to carry out, and takes effect quickly when applied in production; oyster mushrooms removed from storage after preservation are free of chemical contamination and meet hygiene standards.