The moisture content of fresh vegetables can reach 65% -96%, but it will gradually lose water and wilting during storage and transportation after harvest, which will result in the continuous reduction of product weight and direct economic loss. In addition, dehydration can also cause product loss. In general, wilting and shrivelling occur when vegetables lose 5% water, and some of them do not reach the level of wilting, but water loss has affected its taste, crispness, color and flavor.
Slight wilting can cause imbalance in the metabolism of vegetables and increase the activity of hydrolytic enzymes. For example, dried sweet potatoes are sweetened because dehydration causes the hydrolysis of starch into sugar. When vegetables and vegetables are seriously dehydrated, the concentration of cell fluid increases, and some ions, such as ammonia and hydrogen ions, are too high, causing cell poisoning and even destroying the alternate structure of the protoplasm. Excessive tissue dehydration also causes increased abscisic acid levels and stimulates ethylene synthesis, accelerating organ aging and shedding. In addition, wilting can also cause the decrease of cellular turgor pressure and changes in the mechanical structure characteristics, which will inevitably affect the storage tolerance and disease resistance of vegetables. The greater the degree of tissue dehydration and wilting, the more susceptible it is to infection by microorganisms, and the faster the disease resistance declines. Therefore, in the process of post-harvest processing, storage, and transportation of vegetables, water loss should be controlled as much as possible. However, there are some exceptions, such as onions, garlic, proper drying before storage to accelerate the drying of the scales, promote product dormancy Chinese cabbage should be moderately dry before storage, make the leaves slightly dehydration, can reduce the freezing point, improve the ability of cold resistance.
Measures to prevent water loss after harvesting vegetables are as follows
First, packaging, waxing or coating
The easiest way to reduce the loss of water in vegetables is to use a plastic film or other waterproof material to cover the product, or to put it in a bag, box or carton. Polyethylene film is a better waterproof material. However, it must be noted that packaging reduces the water loss of the product while also reducing the cooling rate of the product. In addition, the water absorption capacity of packaging materials can not be ignored. Packaging with compound wax or rosin can prevent the packaging from absorbing water. Although the cost is high, it has practical value in the business. It is also possible to wax or paint the surface of the product and then add appropriate packaging to prevent the product from losing water.
Second, increase the air humidity
Another effective way to reduce the loss of water in vegetables is to increase the relative humidity of the air. However, high humidity is beneficial to the growth of bacteriolytic enzymes and can be used in combination with fungicides. Increase the air humidity The automatic humidifier can be used to spray fog or steam into the storage space. It is also possible to sprinkle water on the ground or hang wet grass curtains in the storage area, or to increase the humidity of the evaporator condensation tubes to maintain the temperature below the storage temperature of 2-3. One in the range of °C. In short, keeping the relative humidity in the warehouse at about 95% can prevent the product from losing water.
Third, proper ventilation
Whether it is a mechanical or natural ventilation warehouse, sufficient ventilation is necessary, it can take away the heat load inside the warehouse, and prevent the temperature inside the warehouse from being uneven, but try to reduce the wind speed, 0.3-3m/s Wind speed has little effect on product moisture.
Fourth, use the sandwich cold storage
The storehouse of the sandwich cold storage is composed of two walls. The middle is circulated by cold air. The outer wall is both heat-insulated and moisture-proof. The inner wall is not insulated. The evaporator is placed between the two walls and is conducted through conduction and storage. Hot swap. Since the evaporator is not in the reservoir, it will not capture the moisture in the product and it will be frosted. The humidity inside the reservoir is high, which prevents the product from losing water.
Fifth, use the breeze library
The cold wind of the breeze storehouse is sent to the storehouse through the multi-hole on the top of the storehouse or the cold air is humidified before being sent to the storehouse, which can effectively prevent water loss.
Preservation of fruits and vegetables is an important aspect of improving quality, and it is necessary to properly treat the product according to the circumstances and effectively maintain its optimal freshness.
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