Long-term Storage Methods in Cold Room for Fruits:
The long-term storage and preservation of fruit is to provide suitable storage environment and conditions to maintain its normal metabolism in accordance with the requirements of the biological characteristics of fruit, so as to reduce the quality decline and decay loss of fruit and extend the edible period. The long-term storage methods of fruits are as follows:
1. Room temperature moisture storage is the most energy-saving and the lowest cost. The earliest and most common folk traditional methods are used. It is not necessary to add auxiliary equipment to control temperature and humidity, but only to build a shed and kiln that can use natural conditions to create a suitable environment. The temperature and humidity in the shed and kiln are regulated by natural ventilation. The shed and kiln with normal temperature and moisture preservation are generally built in the place with high terrain, low groundwater level and good ventilation.
2. Low temperature storage is the most complete method, which has been widely used in commercial. The method can be divided into two types: low temperature storage at about 0 ℃ and low temperature storage below the general temperature. Cold storage needs refrigeration device, and low-temperature storage only needs ventilation device. Bottom temperature storage can reduce fruit respiration, speed of bio chemistry, reduce nutrition loss, and inhibit the vitality of bacteria. The temperature of the cold storage should be kept at the level that can remove the heat of respiration. Just like the circulation fresh-keeping, the warm storage also needs a refrigeration system, namely, the low-temperature precooling, the heat preservation transportation and the sale of the freezer, so as to keep the low temperature of the fruits from the post harvest treatment to the hands of the consumers. Japan is studying a stack ventilation storage method, also known as intermittent ventilation circulation stack ventilation storage method. This method is to use fruit respiration and transpiration to obtain the conditions of high humidity and higher carbon dioxide concentration than the atmospheric composition under the low temperature condition. At the same time, it can remove harmful gases such as ethylene and prevent the phenomenon of over humidity through appropriate air exchange. This method can keep the appearance of fruit quality and is easy to operate, so people pay attention to it.
3. Plastic packaging storage is a kind of storage method which uses the different permeability and water permeability of plastic film to restrain the evaporation and respiration of fruits during storage. This method can make the fruit keep good quality for a long time. Plastic packaging storage is divided into cold storage and normal temperature storage. Cold storage can reduce the respiration and oxygen consumption of fruits, slow down the rate of carbon dioxide accumulation, and make the gas in the bag form a natural state of controlled atmosphere storage, thus delaying the loss and maturity of fruit nutrients. When the packaging film is stored at room temperature, holes must be made to improve the air permeability. Because the fruits that breathe a lot at high temperature, after sealing for 1-2 days, the oxygen is exhausted and the carbon dioxide is increased rapidly. This not only can't keep fresh, but also can cause physiological poisoning and make the fruit go bad.
4. Irradiation preservation is to use the electron beam and X-ray and r-ray produced by radioisotope or particle accelerator to irradiate the fruit, so as to achieve the purpose of sterilization, Inhibiting Germination, ensuring quality and prolonging storage period. Irradiation preservation has the advantages of less investment, low energy consumption, less pollution, convenient operation, safety and reliability.
5. Controlled atmosphere storage is a kind of cold storage method which can keep fresh by adjusting the gas composition in the storage environment. Controlled atmosphere storage not only needs to control the content of oxygen and carbon dioxide in the air, but also needs to control the temperature, the three can achieve the purpose of fresh-keeping properly. There are many methods of controlled atmosphere storage, such as natural oxygen reduction method, rapid oxygen reduction method, nitrogen filling method, carbon dioxide filling method, silicon window method and so on. Silicon window has a greater permeability to ethylene, which can rapidly reduce ethylene concentration, delay fruit aging and improve storage effect, so it develops rapidly. Controlled atmosphere storage requires sealed low temperature storage and devices for regulating gas and pressure. At the same time, it is difficult to determine the amount of carbon dioxide and oxygen required by fruits. If not mastered well, physiological poisoning will occur. Therefore, at present, only short-term storage and expensive fruits are used abroad.
6. During the storage of chemical preservation fruits, fumigation or direct coating with various chemicals are used to achieve the purpose of preservation. Thousands of drugs have been developed abroad. It has been used as preservative peracetic acid, niclosamide, etc., and physiological regulator 2.4-d. They are cyanin, naphthyl acetic acid, sodium o-chlorophenol, aldrin, paraffin, etc. These drugs can keep the freshness of fruits and prolong the storage period.
7. Low-pressure storage is the most advanced storage method, which can make all fruits mixed. By removing 90% of the air, the air pressure and oxygen concentration are reduced to one-tenth of the normal value. Under such conditions, the amount of ethylene produced in plants can be controlled. It can reduce the respiration rate of fruit, and the storage period of low-pressure storage fruit can reach 3-5 times that of general low-temperature storage. After low-pressure storage, the air will be dry. Fresh, moist and reduced pressure air must be supplied through a humidifier. Because of the high cost of investment and operation, low-pressure storage has not yet entered the stage of commercial application in foreign countries.