one. The origin of MAP In the past decade, people's lifestyle changes have far exceeded our expectations. At the same time, food is not only a basic need, but also a measure of living standards. Today, consumers value the pure taste of perishable foods, long shelf life and attractive appearance packaging. Therefore, the food industry develops new food packaging technologies to meet the needs of customers. The use of improved gas packaging for perishable foods has evolved into a market trend due to the development of society and the ever-increasing demand for high quality by customers. Modified atmosphere packaging is also known as MAP or CAP, domestically called modified atmosphere packaging or replacement gas packaging, and inflatable packaging. It is packaged with packaging materials with gas barrier properties. According to the actual needs of customers, a certain proportion of O2+CO2+N2, N2+CO2, O2 + CO2 mixed gas is charged into the package to prevent food from occurring in physical, chemical and biological aspects. The quality declines or slows down the quality, thus extending the shelf life of food and increasing the value of food. The history of the development of modified atmosphere packaging As early as the early 12th century, when fresh beef was shipped from New Zealand to the UK, it was transported or stored by adding CO2 and O2 in the cabin or warehouse. In 1930, American researchers found that the breathing activity of apples and pears in sealed refrigerators reduced the O2 content in the warehouse, increased the CO2 content, significantly reduced the fruit breathing rate, and made the fresh-keeping period reach 6 months. It has been extended by a factor of 1. In 1950, this method of using the breath of the breath itself has been greatly developed throughout the United States. In 1970, the Danish retail chain of Irma retailed in the Copenhagen distribution center to produce fresh meat modified atmosphere packaging for the first time successfully supplied to Denmark. , In 1976, in cooperation with Danish advanced meat products manufacturers, MULTIVAC and WITT-GASETECHNIK made the first package of fresh meat with a mixed gas. In 1980, British vacuum packaging and modified atmosphere packaging accounted for about half of the market for packaged food in Europe. About 38% of fresh red meat is packaged in modified atmosphere, and by 1982 the total sales increased by 300%. Since the 21st century, about 80% of the sales of beef in the United States and Canada have been supplied by meat packaging manufacturers to retailers, hotels, restaurants and institutional canteens in the form of vacuum-packed meat. In the UK, all foodstuffs in the food retail chain are selling modified foods. In France, a large portion of the fresh food market is particularly successful in the packaging of modified bread. In the German air conditioning package The dress is applied to instant noodles, pizza and fresh cut vegetables. About 10% of cured meat and 72% of pies in Italy are packaged in modified atmosphere. In the late 1990s, China began to research and develop food packaging equipment and processes. For example, Shanghai meat processing enterprises introduced foreign modified atmosphere packaging equipment to develop fresh pork modified atmosphere packaging market, which laid a foundation for the application of China's food modified atmosphere packaging market. basis. Since the 21st century, the research and market application of food modified atmosphere packaging has entered a period of development. Many universities and research institutes and far-sighted enterprises have done a lot of practice and research in the atmosphere packaging technology. two. Why apply MAP People want food at any time, anywhere, fresh, attractive and of high quality. In order to realize these expectations, manufacturers and distributors have to solve huge logistics problems. The high stability of the cargo guarantees long distance transport. In addition, packaged foods are attractive enough for people to buy. Consistent quality (taste, freshness, etc.) is a must for strong customer loyalty. The freshness and corrosion resistance of perishable goods such as meat, fish and seafood depends not only on the raw materials themselves but also on the environmental impact. Microbial and biochemical reactions are the cause of deterioration of perishable foods, which is of particular concern for fresh meat and seafood. Deterioration begins after slaughter, which is difficult to stop because the microbes have already reached it. A well-known method that has the potential to reduce or slow down its activity is freezing. Of course, frozen foods are not considered fresh products. In addition, the goods must be constantly frozen during transportation, which is a high-cost, high-input method compared to MAP packaging. A large number of practices have proven to be significant after applying modified atmosphere packaging: A better product quality and longer shelf life - prevent oxidation, spoilage and discoloration - Improved atmosphere can inhibit the growth characteristics of bacteria and fungi — mechanical protection of products that are prone to chipping - maintain the freshness, appearance, smell and flavor of the product to maintain its freshness — Extended shelf life, replaceable food transportation methods, and significantly reduce transportation costs How to apply MAP? Due to the different characteristics of the food itself and the conditions encountered in the transportation and sales of the food, the requirements for packaging vary greatly. There are many factors to be considered when using the food modified atmosphere packaging technology, including the following four elements. (1) Gas replacement The vacuum pump is used to draw out the air in the bag or the box to form a certain degree of vacuum, and then the mixed fresh gas is charged. The process of gas replacement is completed so that the amount of residual oxygen in the package is less than 1%. (2) Gas mixing 1 Commonly used mixed gases and characteristics 1) CO2 Carbon dioxide can inhibit most aerobic bacteria and molds. There is no doubt that carbon dioxide is the most important gas for gas conditioning in food packaging. In general, the higher the concentration of carbon dioxide, the longer the corrosion-resistant period of perishable foods. However, in the packaging process, fat and water absorb carbon dioxide easily. The high concentration of carbon dioxide also affects the taste of the food and consumes the humidity and concentration of the food (called the vacuum effect). Therefore, we should consider it carefully! As for how long the shelf life and how much consumption depends on the amount of carbon dioxide used. If the purpose of carbon dioxide is to inhibit the growth of bacteria and mold, the recommended concentration is at least 20%. 2) N2 Nitrogen is an inert gas used to expel air, especially oxygen, from the package. It is also used as a filling gas for perishable foods and has the same effect as carbon dioxide. Nitrogen reduces the vacuum effect and is a natural part of the air. 3) O2 Oxygen is a very important gas for all organisms, and it also supports the deterioration of perishable foods. It is a condition for the growth of aerobic microorganisms. In general, no oxygen is applied to the MAP, but in some cases, quantitative oxygen brings quite good results. * It makes perishable foods look natural in color (the effect of freshness). * It allows food to breathe, especially fruits or vegetables. * It inhibits anaerobic microorganisms in various fish and vegetables. 2 How to mix accurately? The classic gas mixer, through the double isobaric principle, adjusts the proportion of various gases through the proportional valve. The gas ratio and accuracy are not affected by the change of the gas source pressure and the fluctuation of the gas flow, so as to provide stable and accurate gas supply. With the advancement of technology, the KM and MG series gas mixers produced by WITT of Germany can realize the simultaneous and continuous simultaneous operation of one equipment, and the accuracy of the mixed gas is better than 1%. The blender with excellent performance has also been loved by the world's leading packaging machine manufacturers, and has reached a global strategic partnership with several packaging machine companies such as MULTIVAC, WEBOMATIC and ILACAK. (3) Packaging materials: 1 commonly used packaging materials 1) Polyolefins: polyethylene (PE) and polypropylene (PP). 2) Vinyl polymer class: ethylene vinyl acetate copolymer (EVA), polyvinylidene chloride (PVC), polyvinylidene chloride Copolymerization (PVDC), ethylene-vinyl alcohol copolymerization (EVOH), 3) Polystyrene (PS) 4) Polyamide (PA) 5) Polyester (PET) 2 should pay attention to the problem when using packaging materials — The box should be made of high barrier material, and the boxed film will vary depending on the product characteristics. — The package should be effectively blocked in terms of moisture permeability, oxygen permeability and light transmission; — The commonality of the packaging film is anti-fogging, the light transmittance is reduced to the lowest value, and the air permeability is different. Selecting different characteristic membranes, such as the respiration of fruits and vegetables, will affect the proportion of mixed gases. The gas permeability of the barrier membrane must be relied upon to maintain the balance of the gas ratio; (iv) Storage environment: The optimal storage environment for modified atmosphere packaging is refrigerated. At present, the temperature of refrigerated food in supermarket refrigerated display cabinets is about 33% higher than 7 °C, about 5% is higher than 13 °C, and the average temperature of household refrigerators is 10 to 13 °C. Obviously, the current cold chain conditions are not sufficient to meet the refrigeration temperature and condition requirements of modified or vacuum-packed chilled foods. Many non-breathing refrigerated fresh foods (eg, livestock, poultry, fish) are recommended for refrigerating temperatures of 0-2 ° C. Many refrigerated fresh foods (eg apples, strawberries, mushrooms) are recommended for refrigerating temperatures of 0-5 ° C. The ambient temperature also directly affects the freshness of the food.