Fruit and vegetable atmosphere preserved storage

Fruit and vegetable atmosphere storage and preservation in recent years, fruit and vegetable storage and preservation technology has developed rapidly, in which the use of cooling, oxygen, carbon dioxide and ethylene control of the modified atmosphere is the world's most advanced storage of fruits and vegetables. This article introduces the principle of air-conditioned storage and preservation, the method of adjusting the atmosphere, and the process conditions of fresh-keeping of fruits and vegetables. First, the principle of controlled atmosphere storage and preservation of fruits and vegetables Atmosphere storage, referred to as CA, refers to the method of refrigeration in a specific gas environment. The oxygen content in the normal atmosphere is 20.9% and the carbon dioxide content is 0.03%, while the controlled atmosphere storage is based on the low temperature storage, adjusts the content of oxygen and carbon dioxide in the air, that is, changes the gas composition of the storage environment and reduces the oxygen content to 2%-5%, increase the content of carbon dioxide to 0-5%, such a storage environment can maintain the freshness of fruits and vegetables at the time of picking, reduce losses, and have a long shelf life and no pollution; compared with cold storage, the atmosphere is stored fresh Technology is more perfect. After harvesting, fresh fruits and vegetables are still undergoing vigorous respiration and evaporation. They absorb oxygen from the air, decompose and consume their own nutrients, and produce carbon dioxide, water and heat. Since breathing requires the consumption of nutrients from fruits and vegetables after harvesting, the key to prolonging the storage period of fruits and vegetables is to reduce the respiratory rate. The change of the gas composition in the storage environment has a significant effect on the physiology of fruits and vegetables after picking: low oxygen content can effectively inhibit the respiration, to a certain extent reduce evaporation, microbial growth; appropriate high concentrations of carbon dioxide can slow the respiration, the breathing The transitional fruits and vegetables have the effect of delaying the initiation of the respiratory jump, thereby delaying ripening and aging of fruits and vegetables. Ethylene is a ripening agent for fruits and vegetables. Controlling or reducing the ethylene concentration is very beneficial for delaying the ripening of fruits and vegetables. Lowering the temperature can reduce the respiration rate of fruits and vegetables, and can inhibit the evaporation and growth of microorganisms, but it is still high for some cold-sensitive fruits and vegetables. The use of a modified atmosphere storage method can effectively inhibit the respiration of fruits and vegetables, delay aging (mature and aging) and related changes in physiology and biochemistry to achieve the purpose of prolonging the storage and preservation of fruits and vegetables. Therefore, the air-conditioned storage and preservation technology has become an advanced fruit and vegetable storage method recognized by various countries in the world for the past two decades. In recent years, China's Shandong, Shaanxi, Henan, Beijing, Hebei, Liaoning, Guangdong, Fujian and other places have established a comprehensive air-conditioned cold storage. Second, the method of adjusting the atmosphere There are four commonly used methods of adjusting the atmosphere: the gas film of the plastic film, the atmosphere of the silicon window, the oxygen reduction of the catalytic combustion, and the oxygen reduction of the nitrogen gas. 1, the plastic film accounted for the gas modulation method: the use of plastic film oxygen and carbon dioxide have different permeability and the principle of low water permeability to inhibit the respiration of fruits and vegetables in the storage process and water evaporation storage method. Plastic film is generally 0.12mm thick non-toxic polyvinyl chloride film or 0.075-0.2mm thick polyethylene plastic film. Because the plastic film selectively permeates the gas, the gas components in the bag can naturally form a state of controlled atmosphere storage, thereby delaying the consumption of nutrients in the fruits and vegetables and delaying aging. For plastic accounts that require rapid oxygen reduction, after the account is closed, a mechanical oxygen reduction machine is used to quickly achieve the conditioning conditions. However, due to the respiration of fruits and vegetables still exist, the concentration of carbon dioxide in the account will continue to rise, and special instruments should be used regularly for gas detection in order to timely adjust the ratio of gas components. 2. Silicon window air-conditioning method: According to different fruits and vegetables and the temperature and humidity conditions of storage, select different areas of the silicone rubber fabric film to heat the storage account made of polyethylene or polyvinyl chloride, as a gas exchange window, referred to as silicon window. Silicone membranes have a good permeability to oxygen and carbon dioxide and an appropriate air permeability, which can be used to regulate the gas composition of fruits and vegetables storage environment to achieve the purpose of controlling respiration. The plastic account made of suitable silicon window area can be automatically weighed with oxygen content of 3%-5%; carbon dioxide content is 3%-5%. 3. Catalytic combustion and oxygen reduction method: Catalytic combustion and oxygen reduction machine is used to combust the combustion reaction of gasoline, liquefied petroleum gas, etc., and high-oxygen gas extracted from the storage environment (in storage). After the reaction, the oxygen-free gas is returned to the atmosphere storage tank, and the cycle is repeated until the oxygen content of the gas in the storage tank is reduced to the required value. Of course, this combustion method and the respiration of fruits and vegetables will increase the concentration of carbon dioxide in the storage tank. In this case, a CO2 removal machine can be used to reduce the carbon dioxide concentration. 4. Oxygen reduction and oxygen reduction method: The oxygen-enriched air is pumped out from the air-conditioning warehouse with a vacuum pump, and then filled with nitrogen. The two air-exhausting and full processes are alternated so that the oxygen content in the warehouse is reduced to the required value. The sources of nitrogen used are generally two types: one is nitrogen filling with a liquid nitrogen cylinder; the other is nitrogen filling with a carbon-dividing screen, and the second method is generally used for a large-scale air-conditioned storage.