Technical Guide for Disease Control, Fresh-keeping, Storage and Processing of Edible Fungi
Fresh edible fungi after picking are prone to rot and deterioration at room temperature, and are also easily damaged during packaging and transport, reducing quality and causing losses. To sell edible fungi fresh during the peak production season, and to collect and process edible fungi products during the hot season, fresh-keeping and storage must be done well. In order to regulate and enrich the market supply of edible fungi and meet the needs of domestic and international markets, the processing of edible fungi must be done properly. The most commonly used fresh-keeping, storage and processing methods for edible fungi are introduced below.
(1) Fresh-keeping and Storage Methods
1. Cold storage method: Temperature is the most important factor affecting the respiration of agricultural products. Within 5-35°C, for every 10°C rise in temperature, the respiration intensity increases 3 times, which in turn raises the ambient temperature even higher. However, the cold storage temperature should not be too low either, and is usually controlled between 0-8°C. Ice is most commonly used in production; add salt or calcium chloride to the ice, and place the ice above the stored edible fungi.
2. Controlled atmosphere storage method: The principle is to reduce the oxygen concentration and increase the carbon dioxide concentration, thereby inhibiting respiration. Oxygen below 1% can inhibit cap opening in edible fungi, while at 5% it stimulates cap opening; high concentrations of carbon dioxide can inhibit cap opening, but too high a concentration will promote anaerobic respiration in edible fungi and produce toxic effects. Controlled atmosphere methods: (1) Place the edible fungi in a container with a certain degree of transparency and let the oxygen decrease naturally; (2) Artificial oxygen reduction method, that is, filling with carbon dioxide and nitrogen. The combination of controlled atmosphere and cold storage gives better results.
3. Radiation treatment method: Using gamma rays emitted by cobalt-60 or palladium-137 as a radiation source to treat edible fungi by radiation can ionize the water and other substances in their bodies, producing free radicals or ions, which can effectively inhibit cap opening, delay the discoloration process of the fungal body, and kill or inhibit the activity of spoilage microorganisms and pathogens, thereby achieving a fresh-keeping effect; the effect is better when combined with cold storage. A radiation dose of 200,000 rad is more suitable.
4. Plant hormone treatment method: Some hormones can inhibit the respiration of edible fungi, delay aging, and prolong storage time; some hormones can also inhibit cap opening. The hormones that can be used include: chlormequat (ccc), 2,4-d, maleic hydrazide (mh), indoleacetic acid (iaa), naphthaleneacetic acid (naa), and daminozide (n-dimethylaminosuccinamide). The concentration used varies with different fungal species, generally from a few to several hundred ppm.
(2) Common Processing Methods
1. Drying processing method: The drying process is the process of evaporating the water contained in the edible fungi. When edible fungi come into contact with dry hot air, the surface moisture is released to the external environment, forming a moisture content gradient from the inside to the outside. The greater the gradient difference, the faster the water moves outward, and vice versa; the movement of water stops only when the moisture content inside and outside is consistent. Drying is a widely used processing and preservation method, but not all edible fungi must be dried and processed. For example, after drying, mushrooms are inferior to fresh mushrooms in umami and flavor; oyster mushrooms, lion's mane mushrooms and slippery mushrooms are generally better eaten fresh; although enoki mushrooms can be dried, they should first be steamed in a pot for 10 minutes before drying; while shiitake mushrooms, black wood ear and silver ear are mainly dried. One drying method is sun drying: spread the fresh mushrooms (or ears) thinly on a reed mat or bamboo curtain and expose them to the sun until dry. When spreading them out to dry, attention should be paid to turning them frequently and handling them carefully to prevent damage. Generally, fresh mushrooms can be sun-dried in two sunny days; after sun drying, put them in plastic bags, seal quickly, and then store. Another method is oven drying: place the fresh mushrooms in a drying oven, drying cage or drying room, and heat and dry with electricity, charcoal fire or far-infrared, keeping the temperature at 60-65°C, and controlling the temperature fluctuation to no more than 7°C. If a drying room is used for drying, the air inlet and outlet holes should be opened every 5-6 hours for ventilation and moisture removal, and the time should preferably be 10-15 minutes. After drying, bag and store.
2. Salting processing method: Place the edible fungi in a high-concentration salt solution. The high osmotic pressure generated by the salt puts the microorganisms carried inside and outside the edible fungi into a state of physiological dryness, causing the protoplast to shrink. Although these microorganisms are not killed, they cannot be active, ensuring that the edible fungi can be stored for a long time without spoiling. Mainly mushrooms, oyster mushrooms, slippery mushrooms and lion's mane mushrooms use the salting processing method. The specific processing steps are:
(1) Selection of raw material mushrooms: They should be fresh mushrooms harvested at the right time, with impurities removed and moldy, diseased or insect-damaged ones discarded. For mushrooms, cut off the base of the mushroom; for oyster mushrooms, separate the clusters one by one and trim off the aged part of the stem base; for slippery mushrooms, cut off the hard root.
(2) Pre-boiling: Soak the edible fungi in 5%-10% refined salt water, boil in a pot for 5-7 minutes, then remove and drain off the water.
(3) Salting: At a ratio of 12.5-15 kg of salt per 50 kg of edible fungi, first put a layer of salt at the bottom of the vat, add a layer of pre-boiled edible fungi, then add salt again, repeating this until the vat is full. Pour boiled and cooled saturated salt water into the vat, place a cover on top of the edible fungi and apply pressure so that they are completely immersed in the salt water, and at the same time add the prepared adjustment liquid so that the pH of the saturated salt water reaches about 3.5.
(4) Management: A rubber tube should be inserted into the vat, and air should be pumped 2-3 times a day so that the salt water circulates up and down; turn the vat once every 10 days, and it will be fully salted in 20 days.
(5) Barreling: After salting is complete, they can be taken out and put into barrels for storage. The barrels should be filled full, saturated salt water should be added, and the pH should also be adjusted to 3.5.
3. Canning processing method: Seal the fruiting bodies of edible fungi in containers, and after high-temperature treatment, destroy the vast majority of microorganisms in them while preventing external microorganisms from invading again, so as to achieve long-term preservation of edible fungi at room temperature. All edible fungi can be processed into cans, but the ones most often processed are mushrooms, straw mushrooms, silver ear and lion's mane mushrooms. The entire processing procedure has eleven steps:
(1) Selection of canning containers. There are generally 3 types: tinplate cans, glass bottle cans and soft cans. A suitable container can be chosen according to the production process and market demand.
(2) Selection and handling of raw material mushrooms. The edible fungi are required to be fresh, free of pests and diseases, normal in color, and with intact caps. The stipe should be cut flat, with a length not exceeding 0.8 cm.
(3) Color protection and rinsing of the fungal bodies. Pour the selected edible fungi into a 0.03% sodium thiosulfate solution to wash away mud, sand and debris; after removing them, pour them into a 0.1% sodium thiosulfate solution with an appropriate amount of vitamin c and e added. Rinse clean with running water to prevent spoilage after canning.
(4) Heating and boiling. First put tap water into a container, heat to 80°C, add 0.1% citric acid, bring to a boil, pour the edible fungi into the boiling water and pre-boil for 8-10 minutes, continuously skimming off the floating foam.
(5) Grading. After pre-boiling, take out the edible fungi and cool them in cold water, and grade them by size.
(6) Filling into cans. Each can must not be filled too full; leave a gap of 8-10 mm from the lid. Usually a 500 g empty can should be filled with 240-250 g of edible fungi and 180-185 g of broth. Broth formula: 97.5 kg water, 2.5 kg refined salt, 50 g citric acid, heated above 90°C, filtered through gauze. The temperature when pouring the broth should not be lower than 70°C.
(7) Exhausting. The most commonly used method is heating to exhaust, that is, placing the cans below 86-90°C for 8-15 minutes to remove the air in the cans.
(8) Sealing. At present, a double-roll seam sealing machine is generally used for sealing.
(9) Sterilization. Edible fungus cans usually use high-pressure steam sterilization. Different edible fungi and different can sizes require different sterilization temperatures. For example, the sterilization temperature for canned mushrooms is 113-121°C for 15-60 minutes, while canned straw mushrooms require 130°C for sterilization.
(10) Cooling. After sterilization, the cans should be immediately placed in cold water to cool rapidly; the faster the temperature drops, the better.
(11) Printing and packaging. Cans that have passed inspection should have marks printed on the lids, then be packaged and stored.