Detailed Explanation of High-Yield Cultivation, Drying, and Candied Fruit Processing Techniques for Edible Mushrooms

Core Tip: Edible mushrooms are edible fungi; fungi is a general term for higher fungi that can form large fleshy (or gelatinous) fruiting bodies or sclerotial tissues.

Edible mushrooms are edible fungi; fungi is a general term for higher fungi that can form large fleshy (or gelatinous) fruiting bodies or sclerotial tissues. Currently, more than 120,000 species of fungi have been described worldwide, more than 6,000 species can form large fruiting bodies or sclerotial tissues, and more than 2,000 species are edible.

China is rich in edible mushroom resources and is also one of the earliest countries to cultivate and utilize edible mushrooms. The protein content of mushrooms is generally 1.5-6% for fresh mushrooms and 15-35% for dried mushrooms, which is higher than that of ordinary vegetables. Moreover, their amino acid composition is relatively complete, and most mushrooms contain the eight essential amino acids for the human body. Among them, mushrooms, straw mushrooms, and enoki mushrooms are rich in lysine, which is lacking in grains, and lysine is beneficial to children's physical constitution and intellectual development. Mushrooms contain various vitamins and various mineral elements with physiological activity. Such as VB1, VB12, Vc, Vk, VD and phosphorus, sodium, potassium, calcium, iron and many trace elements, which can supplement the deficiencies in other foods [4].

Edible mushrooms are not only delicious but also rich in nutrition, and are often called health foods by people. They not only contain various essential amino acids for the human body, but also have the effect of lowering blood cholesterol and treating high blood pressure. In recent years, it has also been found that shiitake mushrooms, button mushrooms, enoki mushrooms, and lion's mane mushrooms contain substances that enhance the human body's anti-cancer ability.

Edible mushrooms contain bioactive substances such as high-molecular polysaccharides, beta-glucans and RNA complexes, natural organic germanium, nucleic acid degradation products, cAMP and triterpenoid compounds, etc., which have important utilization value for maintaining human health.

In recent years, health foods, health beverages, wines and medicines produced and processed with edible mushrooms as raw materials have been widely used in medical clinical practice and put into the health product market. Therefore, edible mushrooms, as a green food, are increasingly valued by people of all countries.

1. Drying of Edible Mushrooms

Edible mushrooms have high water content, tender fruiting bodies, and strong after-ripening. They are easy to rot. During batch production or large-scale cultivation, the quality of drying processing will directly affect the economic benefits of producers. The drying methods for edible mushrooms include two categories: natural drying and artificial drying. During the drying process, the speed of drying has a decisive impact on the quality of the dried product. The faster the drying speed, the better the product quality.

At present, the equipment widely used in China includes linear temperature-rise drying rooms, same-fire temperature-rise drying rooms, hot-air dehydration dryers, steam dehydration dryers, infrared dehydration dryers, and other equipment. The dehydration and drying processes for edible mushrooms are varied. Taking shiitake mushrooms as an example, in order to achieve a round mushroom shape, thick rolled cap edges, bright yellow gill color, rich aroma, and a water content reaching the 12% export standard, the following links must be well controlled: 1. Strictly control harvesting; 2. Spread to air in time; 3. Arrange and load for baking; 4. Master the heat. Low-temperature drying; 5. Pay attention to moisture removal and ventilation.

1.1 Drying Techniques

Drying processing of edible mushrooms. There are two methods: natural drying and mechanical drying.

1.1.1 Natural Drying

Using sunlight as the heat source and natural wind as an auxiliary for drying, it is suitable for varieties such as bamboo fungus, silver ear fungus, wood ear fungus, enoki mushrooms, and reishi mushrooms. This method is simple, ancient, and requires low investment. During processing, spread the fruiting bodies flat on bamboo curtains without pressing each other and sun-dry them. When turning them to dry, do so gently to prevent damage. Generally, they can be sun-dried in 2-3 days. This method is suitable for small-scale processing plants. Some processing plants, in order to save costs, carry out baking only after they are half-dried, but this needs to be flexibly controlled according to weather, water content of the fruiting bodies, and other conditions, to prevent deformation, discoloration, or even rotting of the mushrooms.

1.1.2 Mechanical Drying

The method of using ovens, drying cages, drying rooms, or heat sources such as charcoal hot air, electric heat, and infrared rays for baking to dehydrate and dry the fruiting bodies. At present, the widely used equipment includes linear temperature-rise drying rooms, return-fire drying rooms, hot-air dehydration dryers, steam dehydration dryers, infrared dehydration dryers, etc. [5].

1.2 Factors Affecting Drying

1.2.1 Temperature of the Drying Medium

In the drying of edible mushrooms, preheated air is used as the drying medium, but it is not dry; it is a mixture of air and water vapor. To make the mushroom (fungus) bodies dry continuously, the temperature of the air and water vapor must be continuously increased. In this way, the moisture in the mushroom (fungus) bodies evaporates easily, and the drying speed accelerates. When the relative humidity in the air decreases by 10%, the saturation deficit increases by 100%, so the drying quality can be improved by raising the temperature while lowering the relative humidity.

During the drying of edible mushrooms, especially in the initial stage, excessively high temperatures are generally not suitable. Otherwise, due to sudden high temperature, the juice in the tissues expands rapidly, which easily causes cell walls to rupture and internal solutes to be lost. The sugars and other organic matter in the raw materials are often decomposed or scorched due to high temperature, damaging the appearance and flavor of the product. High temperature and low humidity in the initial stage easily cause case hardening, affecting moisture diffusion [2].

1.2.2 Humidity of the Drying Medium

As the air temperature rises, the relative humidity decreases. Under the condition of constant temperature, the lower the relative humidity, the greater the saturation deficit of the air, and the faster the drying speed of edible mushrooms. If the temperature is raised while the relative humidity is lowered, the greater the difference between the partial pressure of water vapor in the raw material and the outside, the easier the evaporation of moisture.

1.2.3 Speed of Airflow Circulation

The faster the flow speed of dry air, the faster the moisture on the surface of edible mushrooms evaporates. Increasing the airflow speed has two effects: first, it helps quickly transfer the heat of the air to the raw material to maintain its evaporation temperature; second, it quickly takes away the evaporated moisture from the raw material and continuously replenishes fresh unsaturated air. This promotes continuous evaporation of moisture on the surface of the raw material. According to measurements, when the wind speed is below 3 m/s, the moisture evaporation rate is roughly proportional to the wind speed [2].

1.2.4 Types and States of Edible Mushrooms

Different types of edible mushrooms have different chemical compositions and tissue structures, so their drying speeds are also different. The size of the cut raw material is directly related to the drying speed. The smaller the cut, the larger the evaporation area. The faster the drying speed.

1.2.5 Loading Amount of Raw Materials

The amount and thickness of loaded mushrooms should be based on the principle of not hindering air circulation. The amount and thickness of loaded raw materials affect the drying speed of the raw materials. If more raw material is loaded on the baking tray and the thickness is greater, it is not conducive to air circulation. This affects moisture evaporation. During the drying process, the thickness can be changed according to changes in the volume of the raw material. It is better to make it thinner in the early stage of drying and thicker in the later stage of drying [1].

2. Candied Fruit Processing of Edible Mushrooms

Edible mushroom candied fruit is a refined edible mushroom product boiled with thick syrup. It is a leisure food with a unique flavor and rich nutrition, and can also be used as an auxiliary material for producing pastries, eight-treasure rice, and instant soup mixes, with a relatively large consumer market. Edible mushrooms suitable for making candied fruit include button mushrooms, oyster mushrooms, enoki mushrooms, lion's mane mushrooms, silver ear fungus, small ear fungus, etc. The raw materials are required to be fresh, fine in texture, and low in fiber content. For products with a relatively moist surface, no syrup, and a water content of 30%, they are generally called edible mushroom candied fruit; for products with a relatively dry surface, no syrup, and lower water content, they are called edible mushroom preserves [3].

2.1 Production Process of Oyster Mushroom Candied Fruit

Material selection: Select young and tender fruiting bodies with complete mushroom bodies, thick flesh, and basically unopened caps as processing raw materials. Because the texture difference between the cap and stipe tissues of oyster mushrooms is relatively large, the two should be processed separately. The caps are best kept intact and generally are not trimmed; the stipes can be cut into mushroom strips 2-3 cm long and 1.00-1.15 cm thick, rinsed and drained for later use. For processing with dried stipes, first soak them in clean water for 4-6 h, and wash them after softening.

Blanching: The caps should use a two-time blanching method. The first blanching water temperature is 95-100°C, blanching for 25-30 min; the second blanching water temperature is 80-85°C, blanching for 5-7 min. The stipes use a one-time blanching method, water temperature 95-100°C, blanching for 7-8 min. After removing, quickly place them in cold water to cool.

Hardening treatment: Soak in a calcium chloride aqueous solution with a mass fraction of 0.4%-0.5%, the mass ratio of oyster mushrooms to water is 1:2, treatment time is 8-10 h, then wash off the residual liquid with clean water. The second blanching of the caps is carried out at this time. A 5% lime water by mass fraction can also be used as the hardening agent. For treatment, the cap boiling time is 60 min, and the pot can be removed when the sugar liquid is concentrated to a mass fraction of 72%. During sugar boiling, the color of the mushroom bodies will change (gray-white gray-light yellow-yellow-remaining yellow).

Drying (sugar coating) and packaging: Move the semi-finished product into the drying room and dry it at 50-55°C. The temperature must not exceed 65°C. Dry for about 4 h, turning frequently during the period. After cooling, it can be packaged. If candied fruit is made from stipes, after drying it can be separately coated with refined sugar, that is, add white sugar to water, boil until it forms threads, then pour the dried stipes into the pot and stir-fry so that it wraps around the surface of the mushroom bodies, forming a white sugar coating. Then rinse with clean water for 48 h, changing the water 5-6 times during this period. Cold soaking in sugar: Drain the rinsed mushroom bodies and place them in a 40% sugar liquid by mass fraction. Cold-soak for 5-6 h so that the mushroom bodies initially release water, in order to reduce damage and fragmentation during sugar boiling.

Sugar boiling: First prepare the syrup. The syrup has a mass fraction of 70%-80%, citric acid 0.8%-1.0%, and sodium benzoate 0.05%. Put them into water in sequence. After boiling, add the cold-soaked oyster mushrooms and boil over high heat, then switch to low heat, keeping the sugar liquid slightly boiling. During boiling, replenish evaporated water at any time to prevent scorching, and keep the sugar mass fraction above 55%, then package. Candied fruit packaging is generally divided into 2 layers. First wrap with cellophane, 1 piece per package for large mushroom bodies, and 2-3 pieces per package for small ones, then put them into plastic bags and seal. The finished oyster mushroom candied fruit basically maintains the fan-shaped structure of fresh mushrooms, is golden amber in color, has strong transparency, and has a good mouthfeel. It can be stored for 1 year at room temperature [3].

2.2 Straw Mushroom Candied Fruit

Material selection and treatment: Select straw mushrooms with plump bodies, unopened caps, and no mechanical damage. After harvesting, immediately place them in a 0.03% sodium metabisulfite solution for 8 hours, then rinse them clean with clean water.

Blanching and hardening: Put the treated straw mushrooms into boiling water and blanch for 2-3 minutes to kill enzyme activity. After blanching, immediately remove them and place them in cold water to cool. After cooling, remove them. Place them in a 0.5%-1% calcium chloride solution and soak for 1-2 hours. After hardening, rinse with clean water 3-4 times to remove residual liquid. Then remove and drain the water, place them in 85°C hot water and keep for 5 minutes, then transfer to clean water and rinse 3-4 times.

Cold soaking in sugar liquid: Place the rinsed straw mushrooms in a 40% sugar liquid and cold-soak for 12 hours.

Concentration: After cooling, add more white sugar so that the sugar liquid concentration reaches 60%. Pour the straw mushrooms and sugar liquid into a stainless steel pot or aluminum pot. Boil over high heat, then use low heat, and remove from the pot when the sugar liquid temperature reaches 108-110°C and the sugar liquid concentration is about 75% (measured with a saccharimeter).

Baking and sugar coating: The drying room temperature must not exceed 60°C. Bake for about 4 hours, while turning frequently until the surface of the straw mushrooms is no longer sticky to the hand. Then coat with white sugar powder (place white granulated sugar at 60-70°C, dry and grind into powder). The amount used is 10% of the straw mushrooms. After stirring evenly, sift off excess sugar powder. Then package according to predetermined specifications [4].

2.3 Lion's Mane Mushroom Candied Fruit

Material selection and treatment: Select fresh lion's mane mushrooms with normal shape, white or slightly yellow color, no mold, and no scars as raw materials. Cut off the base. Remove debris and impurities adhering to the spines. Immediately soak in 2% salt water and process as soon as possible.

Hot blanching: Put clean water in a pot. Add an appropriate amount of citric acid. Put in the lion's mane mushrooms and boil for 5 minutes, then remove. Quickly rinse cool with cold water. For larger individuals, cut them appropriately to make the mushroom bodies uniform, and remove seriously damaged mushroom bodies.

Medicinal liquid soaking: Prepare a solution containing 0.2% sodium metabisulfite, and add an appropriate amount of calcium chloride. After dissolving, put in the mushroom bodies and soak for 6-8 hours. Remove and rinse clean with clean water.

Salting: According to the weight of the mushroom bodies, add 40% white sugar for salting. After 24 hours, filter out the sugar liquid, heat to boiling, and adjust the sugar liquid concentration to 50%. Pour it into a vat while hot, with the sugar liquid submerging the mushroom bodies, and continue pickling for 24 hours.

Heating and concentration: Pour the mushroom bodies together with the sugar liquid into a pot. Heat and boil, and gradually add sugar and an appropriate amount of invert sugar liquid. Boil the mushroom bodies until they have a transparent feeling. When the sugar liquid concentration reaches above 60%, pour the sugar liquid and mushroom bodies into a soaking vat. After soaking, remove and drain the sugar liquid.

Baking: Put the mushroom bodies with the sugar liquid drained into a tray and spread them flat. Send them into the drying room. Bake at 60-65°C for 8-10 hours. When the moisture content of the mushroom bodies drops to 24%-26%, take out the baking tray. After moisture regain for 16-24 hours, shape them, pressing the mushroom bodies into flat round mushroom slices, then send them into the drying room for a second baking. Control the temperature at 55°C. Bake for about 6-8 hours. When the water content drops to 17%-19% and they are no longer sticky to the touch, they can be taken out of the drying room. After moisture regain treatment, they can be packaged [8].