Low temperature preservation technology of shiitak

2022-08-14
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Low temperature preservation technology of Lentinus edodes

(1) dehumidification treatment. The water content of fresh Lentinus edodes just harvested or purchased is generally 85% - 95%, which does not meet the requirements of low-temperature storage, transportation, preservation and export. Therefore, dehumidification treatment is needed, that is, to eliminate the excessive water content of Lentinus edodes. The suitable moisture content for fresh mushroom export varies with the packaging form and cold storage time. Generally, the moisture content of small packages is 80% - 90%; The moisture content used for large packaging is 70% - 80%. Dehumidification methods include drying, hot air drying and dehumidifier dehumidification. (2) Sorting and grading

the cooled fresh mushrooms must be sorted and graded according to the size of the mushrooms, so that the specifications of the goods sold are consistent, which is convenient for packaging, storage, transportation and sales. At the same time, after grading and packaging according to certain commodity specifications, the price can be clearly marked, reflecting high quality and good price

classification standard 10 Unit conversion: KGF. In Japan, it is usually divided into three levels according to the size of the cap: large (L), medium (m) and small (s); According to the opening degree and appearance quality, it is divided into special grade (a) and first grade (b). There are also finer ones, such as dividing the size of the cap into four levels of 3, 4, 6 and 8 cm

at present, there is no unified classification standard in China, which is mainly determined by the requirements of customers. Generally, according to the size of the cap, the three-level system is adopted, that is, the cap with a diameter of more than 5.5 cm is the large level (L); The cap with a diameter of 4.5 ~ 5.5 cm is of intermediate (m) grade; The cap with a diameter of 3.5 ~ 4.5 cm is of small grade (s). In addition to classification according to the size of the cap, classification is also carried out in combination with individual weight

the Lentinus edodes used for fresh-keeping export should be round and neat in shape, with the mushroom handle in the middle, the mushroom meat plump, the curling neat, the color dark brown, the cap diameter of more than 3.5 cm, the mushroom body with low water content, no adhesive debris, no pest infection, and maintain the beautiful shape of natural growth

the step of selecting tick and grading is to select tick first and then grade. From the fresh mushrooms adopted or purchased, the ones whose shape, size, color, etc. do not meet the above export quality requirements and the ones whose umbrellas are excessively opened shall be removed first, and other treatments (such as fresh sale or drying, etc.) shall be made. If it meets the export requirements of fresh mushrooms, it shall be graded according to the classification standard

classification method, which adopts manual selection and classification or classification screening made of white iron sheet into classification circles of different specifications for mechanical classification, or a combination of the two

(3) precooling and refrigeration

① purpose of precooling and refrigeration of fresh mushrooms

precooling and refrigeration of fresh mushrooms are important technical links to maintain the freshness and quality of products. If fresh mushrooms are not pre cooled and directly packaged and transported at low temperature, it will not only shorten the preservation period, but also consume more cooling energy. Therefore, pre cooling or short-term refrigeration of fresh mushrooms under certain conditions can reduce the respiration of mushrooms and reduce the consumption of nutrients; Inhibit enzyme activity and prevent enzymatic browning; Delay the progress of various physiological activities, so that the fresh mushrooms pre cooled and refrigerated at low temperature have a more appropriate temperature and water content during low-temperature transportation, and can achieve better fresh-keeping effect with less cooling energy and cold preservation measures

② methods and principles of precooling and refrigeration

air cooling is the most widely used method of precooling and refrigeration of Lentinus edodes. Air cooling methods can be divided into forced ventilation and differential pressure. The latter is most suitable for mushroom precooling, but differential pressure generator is required. Forced ventilation, because the cold storage requires less and simple mechanical equipment, and is easy to operate and maintain, is currently used more in the export origin of fresh mushrooms in China

the working principle of air cooling method is to transfer the heat in the warehouse to the outside of the warehouse with the help of refrigerant in the process of circulating gas-liquid interaction. When the refrigerant exchanges heat through the evaporator, the fan will deliver the cooled cold air to all parts of the warehouse to reduce the temperature in the warehouse and maintain a constant low temperature in the warehouse

③ main facilities for pre cooling and cold storage - cold storage

cold storage includes fixed building cold storage and prefabricated cold storage. At present, small refrigerated warehouses with fixed buildings are widely used in the main mushroom producing areas in China

the fixed building type small-scale cold storage is a technical device that uses the method of mechanical refrigeration to combine the machinery that produces cooling capacity with the facilities that consume cooling capacity. The constant low temperature required by the cold storage is guaranteed by the mechanical refrigeration equipment and the heat insulation building of the cold storage. Mechanical refrigeration equipment usually adopts freon refrigeration system. Except for the suspended air cooler installed in the warehouse, other equipment is installed in the machine room outside the warehouse. The capacity of refrigeration is generally several tons to dozens of tons

④ use and management of fixed building small cold storage

precooling and warehousing and reprinting

precooling is carried out in the cold storage. Pour the dewatered fresh mushrooms into the plastic basket and stack them in a certain way after warehousing to avoid scattering. When stacking, the goods stack should be more than 30 cm away from the wall, and appropriate gaps should be left between the stacks and between the containers in the stack, so as to facilitate air circulation, cool down and maintain uniform temperature distribution in the warehouse. There should be a space layer of 80 cm between the top of the stack and the ceiling or with the cold air outlet, so as to prevent the freezing injury of fresh mushrooms due to being too close to the cold air outlet. The temperature in the warehouse shall be maintained at 1 ~ 4 ℃, and the final temperature of precooling must be above 0 ℃ to prevent freezing damage or physiological damage. Package in time after pre cooling treatment. After packaging, it may be transported at low temperature, or continue to be stored at low temperature for a short time. However, they cannot be stored and transported under normal temperature to prevent freshness and deterioration. Packaged items that have been refrigerated for a short time should be stored in separate warehouses with unpacked basket storage

temperature management

according to min shaoyuhuan (1995), different storage temperatures have a great impact on the length of preservation time of Lentinus edodes. When the storage temperature changes or the low temperature is interrupted and the temperature fluctuates to 20 ℃, the impact on the freshness is also obvious. The longer the low-temperature seeds are stored, the faster the freshness of Lentinus edodes will decline after temperature change. Therefore, during the cold storage and preservation period, the temperature fluctuation should be minimized

the lower the storage temperature, the longer the preservation period. However, the lower the temperature, the better. Generally, the lowest temperature that does not cause freezing injury is appropriate. In practice, the temperature of Lentinus edodes for cold storage and preservation should be controlled at 0 ~ 1 ℃, but should not be reduced below 0 ℃ to prevent freezing injury or irreversible physiological damage

humidity management

the relative humidity of the air trapped in cold storage is often too high due to the high water content of fresh mushrooms when entering the warehouse, especially when unloading, or the frequent entry and exit of goods, and a large amount of external hot air entering the warehouse, which is unfavorable to precooling and cold storage. Therefore, in the dehumidification treatment of fresh mushrooms, we should grasp the appropriate water content of fresh mushrooms; When entering and leaving the cold storage, the warehouse door should be closed in time, and try to avoid too many times of goods entering and leaving. The relative humidity of the air in the warehouse is generally controlled at about 75%. If the humidity is too high, dehumidifier can also be used for dehumidification if necessary

ventilation

fresh mushrooms refrigerated in the refrigerator still have weak respiration, and the metabolic processes of various substances have not stopped. If the released gases such as carbon dioxide, ethylene, ethanol, acetaldehyde accumulate to a certain extent, they will lead to physiological disharmony and poor quality of fresh mushrooms. Therefore, pay attention to ventilation. It is usually carried out at a time when the weather temperature is low. At the same time, it is necessary to start the refrigeration machinery to slow down the change of temperature and humidity in the warehouse

(4) scientific packaging scientific packaging technology, including the selection of appropriate packaging materials and the use of appropriate packaging methods for the safety devices and operating procedures of the electronic tensile testing machine that is shared by all. It is combined with low-temperature refrigeration, transportation, etc. Jinan testing machine factory testing machine experience. It is the most widely used mushroom preservation technology at home and abroad. Scientific packaging can take advantage of the respiration of fresh mushrooms, reduce the concentration of low oxygen and increase the concentration of carbon dioxide in the container of sealed packaging, and then refrigerate and transport under low temperature conditions, creating a good fresh-keeping ecological conditions - low temperature, low oxygen and high carbon dioxide, so as to achieve the following fresh-keeping effects; First, inhibit the activity of enzymes and microorganisms to prevent enzymatic browning, browning and deterioration; Second, reduce the respiration intensity and transpiration intensity of the mushroom, reduce the consumption of nutrients, and prevent the loss of brown water, so as to prevent the mushroom from losing freshness and weight; Third, delay the physiological and biochemical processes, inhibit the opening and opening of umbrellas, and extend the fresh-keeping period

after scientific packaging, fresh mushrooms can not only achieve the main purpose of freshness and brown quality, but also make goods beautiful and generous, easy to discharge on the shelf, and improve the competitiveness of goods. The key points of scientific packaging technology are as follows:

① packaging materials and packaging materials for mechanical mushroom preservation are mainly plastic products. Except for ordinary plastic vacuum packaging and bag packaging, most of them are pallet type stretched film packaging. The size of the tray varies with the amount of packaging, including 15cm x11cm x2.5cm (100g); 15cm x11cm x3cm (200g); And 15 cm X11 cm shape X4 cm (300 grams) and so on. The stretched fresh-keeping film is 300 mm wide, the length of each tube is less than 500 meters, and the thickness is 10 ~ 15 microns. In Japan, the raw materials used as trays and fresh-keeping films are:

low density polyethylene (LDPE) has the best water resistance and air permeability, and can be made into various anti fogging fresh-keeping films and trays

polypropylene (PP) is made of heat set biaxially oriented polypropylene (OPP) material, which can be made into extremely thin films. Source: new illustration of edible fungus production technology

source: Chinese agriculture

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