Progress in the principle and application technolo

Advances in the principle and application technology of reduced pressure storage of fruits and vegetables

the storage of fruits and vegetables is an old and often new topic. Since the surplus of agricultural products produced by people, our ancestors have been constantly exploring practical ways to accumulate and store agricultural products. The so-called storage of agricultural products is to keep the quality of agricultural products unchanged for a certain period of time, that is, to maintain the use value and commodity value of agricultural products, which is determined according to all the physical, chemical and biological characteristics and conditions of agricultural products. The purpose of storage is to maintain its unique flavor, maintain its use value and improve its commodity value. Agricultural products gradually deteriorate after harvest due to the extension of storage time. Therefore, the gross profit margin of viscose staple fiber of tanxinxiang chemical fiber in recent years is very low. Scientific storage will be responsible for the development of advanced Materials with cost-effectiveness and solutions for manufacturing large aviation and automotive composite structures. The method is to find out the reasons for the deterioration of these characteristics and take measures to prevent them from deterioration, which is the content of storage work

fruits and vegetables are perishable and difficult to store agricultural products. Although our ancestors, based on long-term production experience, used natural cold sources and some simple heat preservation measures to prolong the preservation time of agricultural products, they have great limitations, especially for some special varieties that are difficult to store and keep fresh, they must adopt the storage and preservation technology of modern agricultural products in order to achieve better storage and preservation results

1. The rise of modern fruit and vegetable preservation technology

modern fruit and vegetable preservation technology originated in the 19th century, and has experienced three revolutions so far. James Harrison, the father of modern refrigeration in Australia, designed and manufactured the world's first refrigeration compressor and its auxiliary equipment in Jilong, Victoria, Australia in 1851, and used it for fruit and vegetable preservation, which is considered to be the first revolution in the history of fruit and vegetable preservation. It really gets rid of the seasonal and regional restrictions caused by the use of natural cold sources to preserve fruits and vegetables, and greatly improves the accuracy of storage temperature control, which expands the geographical and seasonal application range of low-temperature fresh-keeping fruits and vegetables, greatly improves the fresh-keeping quality of fruits and vegetables, and extends the storage period, which has been widely used in commerce. After entering the 20th century, industrialized countries have widely used large-scale mechanical refrigerators to store pears, apples and other agricultural products. After the founding of the people's Republic of China, some mechanical refrigerators were also built, but they were mainly used to store aquatic products and livestock products. The use of refrigerators for the commodity storage of fruits and vegetables began in the 1970s

on the basis of previous studies, Kidd and west of Britain in 1917 further discussed the influence of atmospheric composition on the respiration of fruits and vegetables and its preservation effect. The results show that on the basis of controlling low temperature, reducing the concentration of O2 in the air and increasing the concentration of CO2 in the air can further reduce the respiratory metabolism of fruits and vegetables than simple cold storage, and prolong the storage period by more than twice as long as cold storage. They formally put forward the theory of controlled atmosphere storage in 1920. In 1928, the theory was applied to build the world's first controlled atmosphere storehouse in Britain to store apples, which was a commercial success. After the Second World War, the air conditioning technology has developed rapidly. If there is a power failure, it changes from spontaneous air conditioning to mechanized air conditioning, and then to automatic control air conditioning, and is widely used for the storage of agricultural products. At present, agricultural products in developed countries have basically realized cold chain and controlled atmosphere storage, and 80% of apples in countries such as the United States and Japan have adopted controlled atmosphere storage technology. In the late 1970s, China began to introduce air-conditioned cold storage for the storage of agricultural products. In recent years, China has made great progress in the research and manufacturing of supporting equipment for controlled atmosphere reservoirs. At present, China has developed more than 100 controlled atmosphere reservoirs by strengthening the supervision of announced enterprises during and after the event. This is considered to be the second revolution in the history of fruit and vegetable preservation

later, more extensive and in-depth studies were carried out on the modified atmosphere preservation of fruits and vegetables. It was found that although the quality of the modified atmosphere preservation of fruits and vegetables was greatly improved compared with the ordinary cold storage, and the storage period was greatly extended, there were also limitations, which were shown as follows: 1. It was not easy to form an ultra-low oxygen (0%~2%o2) storage environment; 2. It is not easy to form a low CO2 or CO2 free storage environment; 3. It cannot accelerate the outward diffusion of ethylene and other volatile gases in fruit and vegetable tissues. In order to further improve the fresh-keeping quality of fruits and vegetables and extend their storage life, we should introduce new technical measures. In 1957, workman and Hummel found at the same time that the storage life of some fruits and vegetables can be significantly prolonged by adding the condition of reducing air pressure on the basis of cold storage, compared with the conventional controlled atmosphere. In 1966, Burg et al. Of the United States put forward a complete theory and technology of reduced pressure storage. Since then, extensive research has been carried out in many countries, and the test scope has rapidly expanded from the first apple to other varieties of fruits and vegetables; Decompression storage equipment for commercial use has been available in the United States since 1975. In 1991, through years of research, Chinese scientific and technological personnel made a key breakthrough in the production of vacuum storage tank wall. In 1997, the first decompression fresh-keeping warehouse was built in Baotou. This is considered to be the third revolution in the history of preservation, and will play a great role in perishable and difficult to store fruits and vegetables

2. Theoretical and technical characteristics of vacuum preservation

vacuum preservation technology is based on the development of vacuum technology, replacing atmospheric storage with gas replacement storage in vacuum environment. This method can quickly change the atmospheric pressure in the storage container, and can accurately control the gas composition to achieve a stable ultra-low oxygen environment. Therefore, vacuum preservation has its unique characteristics both in theory and technology

2.1 theoretical characteristics

2.1.1 can achieve the effect of low O2 and ultra-low O2

place fruits and vegetables in a closed container, extract part of the air in the container, and reduce the internal pressure to a certain extent. The partial pressure of various gas components in the air will be reduced accordingly, and the O2 concentration will also be reduced accordingly. For example, when the air pressure is reduced to 1/10~1/20 of the normal pressure, the relative proportion of each component in the air does not change, but their absolute content is reduced to the original 1/10~1/20. At this time, the content of O2 is only equivalent to 1.1%~2.1% of the normal pressure. Therefore, reduced pressure storage