Map technology and application of the hottest modi

2022-08-16
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Modified atmosphere packaging (map) technology and its application

preface

modified atmosphere packaging, referred to as map, refers to filling the packaging with certain ideal gas components, improving the atmosphere of the environment in the packaging under certain temperature conditions, and maintaining relative stability for a certain period of time, so as to inhibit the deterioration process of products and extend the shelf life of products. One of the importance of modified atmosphere packaging is to store the gas components in the initial regulated packaging, so as to inhibit decay and deterioration, maintain the quality of perishable food in the normal shelf life or extend its shelf life

1 overview of modified atmosphere packaging

the development of food from vacuum packaging to modified atmosphere packaging is an upgrading process from quality assurance to fresh preservation. Keeping fresh is to ensure the original flavor of food, and it is a big step forward on the basis of quality assurance. Food preservation is not only the need of the current market, but also the manifestation of the improvement of people's living standards. There are many ways to keep food fresh. Modified atmosphere packaging is one of the advanced methods, which is a new change in food packaging today. In the 1930s, Europe and the United States began to study the use of carbon dioxide gas to preserve meat food; In the 1950s, canned beef and cheese cans that replaced air with nitrogen and carbon dioxide gas were developed, effectively extending the shelf life; In the 1960s, due to the development of various air tight plastic packaging materials, many foods such as dairy products, meat processing products, peanuts and so on successfully adopted the gas filling packaging technology; In the 1970s, the inflatable packaging of fresh meat was widely used in Europe and the United States [1]. So far, the modified atmosphere packaging products of food have made great progress in the European and American markets, with an annual growth rate of 25%, and the total packaging volume of more than 5billion boxes. The products include fresh food (fish, meat, fruits and vegetables), cooked meat products, baked goods and noodles [5]. Since the early 1990s, China began to develop and research the modified atmosphere packaging technology and equipment for food in the field of household appliances, and now it has the preliminary conditions for commercial application, but so far the market development is still in the primary stage. Under the condition of rapid economic development in China, the modified atmosphere packaging is becoming more and more important, which is not only a new topic of food engineering, but also an inevitable law of historical development

2 principle of modified atmosphere packaging and gas composition

2.1 principle of modified atmosphere packaging

the modified atmosphere packaging system is a closed system, in which there are two processes at the same time: one is the physiological serialization process of products, that is, the respiratory process of metabolism; Second, the air permeability of packaging materials leads to the exchange process between the product and the gas in the packaging. These two processes make the controlled atmosphere system a dynamic system. The principle of modified atmosphere packaging can be summarized into two points: ① destroy the environment on which microorganisms rely for survival and reproduction. ② It can maintain a certain activity of cells in food, delay its life process, and maintain a certain degree of freshness

there are two main influencing factors during food storage, namely aerobic bacteria and oxidation reaction, both of which require O2. Therefore, in order to prolong the shelf life or maintain the quality of fruits and vegetables, it is necessary to reduce the O2 content of the environment. The test shows that when the O2 content in the package is 1%. The growth of various bacteria decreases rapidly, and when it decreases to 0.5%, its growth is inhibited and its reproduction stops. However, the decay and deterioration of some fruits and vegetables are due to anaerobic/micro aerobic microorganisms and non oxidative reactions. In fact, it is difficult to effectively use vacuum packaging alone, and the products are inevitably shrunk and not suitable for many foods. Modified atmosphere packaging technology is specially designed for the problems existing in vacuum packaging, which can further inhibit microbial corruption and product shrinkage. Like vacuum packaging, modified atmosphere packaging technology is usually combined with cold storage. Its core is to regulate the gas around fruits and vegetables to contain low oxygen and high carbon dioxide compared with the normal atmosphere, and cooperate with appropriate temperature conditions to extend the shelf life of fresh products. The regulating gases of modified atmosphere packaging technology include oxygen, nitrogen and carbon dioxide. The air conditioning system is set up because the pressure increases, which increases the injection speed. After the mold filling process is accelerated, on the one hand, the melt temperature is increased and the activity resistance is reduced due to the shear heating of the plastic melt; On the other hand, it can also enter the pressure maintaining and feeding stage earlier when the melt temperature is still high and the activity resistance is small. The principle of the meter can be represented by a simple diagram, as shown in Figure 1

2.2 gas composition of modified atmosphere packaging

2.2.1 oxygen

the ideal condition for modified atmosphere packaging is to eliminate O2. However, when packaging fresh fruits and vegetables, O2 is essential. Because fruits and vegetables must be breathed after harvest (such as consuming O2 and producing CO2), and anaerobic respiration will be carried out if O2 is lacking, which will accelerate the change of sensory quality and decay. For oxygen, its main functions are as follows: ① maintain the color of food with oxygen, such as the red of meat. ② Maintain the respiration of fruits and vegetables. ③ Inhibit the growth of anaerobic microorganisms

2.2.2 carbon dioxide

co2 can inhibit the reproduction and growth of bacteria and fungi, which depends on the gas diffusion in the package. There are the following reasons: ① the inhibition effect is directly related to the existence of CO2. Gill and Tan (1980) pointed out that the inhibition effect was linear with CO2 concentration until its concentration reached 50% - 60% (atmospheric volume ratio), while further increasing the concentration had no obvious effect on most microorganisms. Shay and Egan (1987) and gill and Penney (1988) both believe that more than 50% - 60% will be diffused into the product, which can achieve the best effect. Therefore, the packaging volume and the air permeability and surface area of packaging materials should be taken into account. ② CO2 solubility is inversely proportional to storage temperature, so low temperature has a synergistic effect. ③ When the CO2 concentration is very high, if there are some inert gases containing carbonic acid, it will produce sour taste. ④ The absorption of gas by the product will reduce the volume of the gas, so it will cause the collapse of the product, which will slightly cause changes in the appearance, and sometimes make people mistakenly believe that it is the lax packaging and the defects of packaging materials

in addition, the antibacterial effect of CO2 also depends on the growth stage of the existing microorganisms. CO2 can increase the delay period and reduce the reproductive efficiency of logarithmic long-term; However, the effect of the former is more obvious, so the inhibition effect will weaken when the bacteria transition from the delayed period to the logarithmic long-term. In this way, CO2 in the early stage of inflatable packaging will be more effective

2.2.3 nitrogen

nitrogen is an inert, odorless gas that can control chemical reactions. Nitrogen is the main component of air, accounting for about 78%. It is neutral in contact with food, so it can be used for food preservation. Compared with other commonly used gases, nitrogen is not easy to penetrate the packaging film, and it is mainly used as the filling gas in the modified atmosphere packaging system

3 materials and machinery for modified atmosphere packaging

the selection of modified atmosphere packaging materials must be able to control the penetration rate of the selected mixed gas and the penetration rate of water vapor. Generally speaking, the modified atmosphere packaging of fruit and vegetable products should choose materials with good air permeability, and pay attention to the transmission ratio of o2/CO2 (suitable range 1:8-10). For modified atmosphere packaging materials used for muscle food and baked products, packaging materials with high barrier should be selected to maintain the ideal atmosphere inside the packaging for a long time. Generally, it is required to have good resistance to nitrogen, carbon dioxide and oxygen. Composite packaging films based on OPP, ALU, PE, pet, OPA, etc. are often selected, and different composite materials have different properties. For example, opp/alu/PE composites have good mechanical impedance and processing performance; Opa/alu/pe composites have high barrier property and high mechanical impedance; Opa/pp composite, with high transparency, is suitable for heat treatment; Paper pe/alu/pe composite, easy to eat; Pve/evoh/pe composite, which can be hot formed, has good stiffness and high barrier property; Pet/m/pe composite material has high barrier property without aluminum foil [6]. We should choose packaging materials according to different products. If the delivery time does not need to be very long, generally barrier pa/pe or pet/pe can meet the requirements. If the delivery time is long, it is best to use high barrier PVDC or EVOH composite materials. The packaging machinery of modified atmosphere packaging mainly has two forms: first, flushing compensation type. Flushing compensation is to use mixed gas to drive out the air in the packaging container several times, and then package, so as to prolong the shelf life and transportation period of food in an ideal environment. This air conditioning method is not suitable for oxygen sensitive food packaging because there is residual oxygen content in the container during flushing, so the vacuum degree is not high, the compensation air time is short, and the production efficiency is high, but it is not suitable for oxygen sensitive food packaging. 2、 Vacuum displacement type. Vacuum displacement modified atmosphere packaging machine is to extract the air in the packaging container first, then fill in the mixed gas suitable for delayed food preservation, and then heat seal to make the pressure inside and outside the box equal. This kind of modified atmosphere packaging container has low oxygen content and a wide range of applications, but the work efficiency is slightly lower due to the long extraction time [1]. Although all kinds of packaging machines use air conditioning as a means, their working principles are different. The compensation type works in a semi sealed state, and the replacement type pumps, fills and seals in a fully sealed container. Obviously, the replacement manufacturing process is more complex and expensive than the compensation type

4 problems that should be paid attention to in modified atmosphere packaging

due to the different physiological characteristics of food itself and the different conditions encountered in the transportation and marketing of food, the requirements for packaging change greatly, and there are many factors to be considered when using modified atmosphere packaging technology, mainly including the following four elements

4.1 gas mixture with appropriate proportion

the most commonly used modified atmosphere packaging is nitrogen, carbon dioxide, oxygen or their mixture

nitrogen is stable in nature. It is generally used to eliminate oxygen, so as to slow down the oxidation and respiration of food. Nitrogen can also inhibit the growth of bacteria. In addition, nitrogen is basically insoluble in water and grease. Food has little adsorption on nitrogen, and it will not shrink gradually due to the absorption of gas during packaging

carbon dioxide is the most critical gas in modified atmosphere packaging. It can inhibit the growth of bacteria and fungi. When used in fruit and vegetable packaging, increasing carbon dioxide has the effect of strengthening oxygen reduction and reducing respiratory intensity; However, when using carbon dioxide, we must pay attention to the high solubility of carbon dioxide in water and oil. The formation of carbonic acid after dissolution will change the pH value and taste of food. At the same time, after the dissolution of carbon dioxide, the amount of gas in the package will be reduced, which is easy to lead to the shrinkage and incompleteness of food packaging and affect the appearance of food. The use of carbon dioxide in modified atmosphere packaging must consider many factors, such as storage temperature, food moisture, microbial species and quantity. In the process of modified atmosphere packaging, we should add a 24 bit high-precision low noise high-speed AD converter to eliminate oxygen as much as possible, but we should analyze the amount added according to specific problems

4.2 packaging materials

packaging materials are the most important part of modified atmosphere packaging. It must have high gas barrier performance to ensure that the mixed gas in the packaging does not leak out. In addition, for fruits and vegetables, because their respiration will change the proportion of mixed gas, in this case, it is also necessary to make the mixed gas achieve dynamic balance, that is, to maintain the ideal proportion of mixed gas by using the air permeability of packaging materials. Modified atmosphere packaging has very strict requirements on the permeability of packaging materials. In addition, we must also consider the thermoformability of materials and the reliability of sealing

at present, the commonly used materials are polyester (PET)

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