Research and application analysis of the hottest m

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Editor's note: in the past 30 years, the scope of application of map technology has been expanding, including raw and cooked meat products, fish, poultry, shellfish, fruits, sauces, crisps, coffee, tea, vegetables, bread, etc. At present, map has become the main packaging form of some products, and its market share is also increasing. In recent years, modified atmosphere packaging map has become a research hotspot

modifiedatmospherepackaging, referred to as map, can be defined as "the technology of regulating the gas environment of food in materials that can prevent gas from entering and leaving". One of the importance of map is to store the gas components in the initial adjustment package, so as to inhibit the decay and deterioration, maintain the quality of perishable food in the normal shelf life or extend its shelf life. Therefore, modified atmosphere packaging is also called activeatmospherepackaging

I. current situation of modified atmosphere packaging the origin of modified atmosphere packaging can be traced back to the 1930s. At that time, fresh beef and mutton were stored and transported in large packaging bags, and its application in aquatic products began in 1930. However, the large-scale commercial application of this technology began after 1970. In 1979, British Mark & Spencer company launched map meat products, which were applied to fish, ham and other aspects two years later. As early as 1955, marceland of the Plant Physiology Laboratory of Gerhard National Research Center in the United States began to study the storage of apples and pears with various PE films, and systematically studied the changes of oxygen (O2) and carbon dioxide (CO2) in the storage environment. In 1960, he published a research report, which was called physiological packaging storage

modified atmosphere packaging in China started in the 1990s. The national agricultural products preservation engineering and technology center developed 24 formulations of PVC fresh-keeping films for fruits and vegetables in 1988, from which 32 varieties and 47 specifications were selected for the practical application of fresh-keeping film bags such as garlic stalks, cucumbers, celery, grapes, apples and Yali pears.

second, the composition of the modified atmosphere packaging system. There are two main influencing factors in the storage process of fruits and vegetables, That is, aerobic bacteria and oxidation reaction, both of which need 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 less than 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. Map technology is specially designed for the problems existing in vacuum packaging, which can further inhibit microbial corruption and product shrinkage. Like vacuum packaging, map products are usually combined with refrigeration. 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 map technology include oxygen, nitrogen and carbon dioxide

(I) the ideal condition for fresh-keeping of oxygen fruit and vegetable 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

(II) carbon dioxide and CO2 can inhibit the reproduction and growth of bacteria and fungi, but the specific mechanism is not very clear. It is certain that this depends on the gas diffusion in the package for the following reasons: (1) the inhibition effect is directly related to the presence 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) The solubility of CO2 is inversely proportional to the storage temperature. Therefore, low temperature has a synergistic effect. (3) When the CO2 concentration is very high, if there are some hydrolytic 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 cause a slight change in the appearance, and sometimes make people mistakenly believe that it is the lax packaging and the defects of the 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

it should be pointed out that the references cited above about the CO2 inhibition effect use questionable experimental methodology (such as using unbuffered medium, changing several variables in an experiment, etc.), and there must be some potential errors as the results

(III) nitrogen nitrogen is an inert and tasteless gas, which 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

to sum up, the design of modified atmosphere packaging system should consider many factors, among which the most important factor is the relative content of CO2 and O2 in the package, which is mainly determined by the gas concentration in the package and the permeability of packaging materials

III. application and development of modified atmosphere packaging for fruits and vegetables fresh fruits and vegetables also have strong respiration and evaporation after picking. It absorbs oxygen from the air, decomposes and consumes its own nutrients, and produces carbon dioxide, water and heat. The main nutrient during respiration is sugar, so the respiratory reaction is mainly the oxidation reaction of sugar. When the oxygen supply is not sufficient, this kind of respiration is called anoxic respiration, that is, intermolecular respiration. Incomplete oxides such as alcohol will be produced during hypoxic respiration

fruits and vegetables undergo aerobic respiration during normal oxygen supply, and anaerobic respiration during hypoxia. Too fast aerobic respiration or anaerobic respiration will cause fruits and vegetables to age or rot. The degree of two kinds of respiration of fruits and vegetables is proportional to the concentration of oxygen in the environment. Controlling the oxygen concentration in the environment can make fruits and vegetables produce only weak aerobic respiration without anaerobic respiration. Fruits and vegetables packed in plastic bags consume O2 and produce CO2 under the action of respiration, gradually increase CO2 in environmental elasticity, stiffness and other index data and reduce the concentration of CO2. Using high permeability plastic film can exchange gas with the atmosphere, supplement the consumed O2 and eliminate CO2. When the penetration rate of the body from the film is equal to the respiration rate of the fruits and vegetables, the gas in the packaging bag reaches a certain equilibrium concentration, so that the fruits and vegetables maintain a weak respiration rate without anaerobic respiration, so as to delay the ripening of the fruits and vegetables and get fresh-keeping. There are many factors that affect the gas equilibrium concentration in the packaging bag, such as the respiration rate of fruits and vegetables, the permeability ratio of the film to O2 and CO2, storage temperature, etc. There are two packaging methods for modified atmosphere packaging of fruits and vegetables. One is called passive modified atmosphere, that is, the current supermarket supply uses plastic film to exchange gas to adjust the content of O2 and CO2; One is called active air conditioning, which fills the mixed gas of hypoxia and carbon dioxide according to the respiratory intensity of fruits and vegetables, and uses different breathable films for gas exchange, so as to balance the gas exchange in the packaging bag as soon as possible. Obviously, active air conditioning is better than passive air conditioning. However, the technology is complex and limited by the limited variety of high permeability films. The shelf life of fresh fruits and vegetables depends on the physiological aging and water loss of fruits and vegetables. Modified atmosphere packaging can effectively control the above influencing factors and prolong the shelf life of some important commodities. During storage, when sugar and acid decompose, the sensory quality of fruits and vegetables begins to change, and the rate of change is determined by their respiration. Therefore, shelf life must be closely related to respiration. Map is to reduce the anaerobic respiration rate by reducing the oxygen content

because the packaging system must allow the gas exchange of respiration. Vacuum packaging can not meet this requirement. Although inflatable packaging sometimes uses the specific function method of the square aluminum rope tensile testing machine of natural packaging, it is most commonly used to design a packaging system, which should achieve a suitable gas atmosphere to balance the respiration and the permeability of the packaging. In such body series, the permeability of the packaging film (such as the entry of O2 and the elimination of CO2) should be selected according to the respiratory rate of the product (such as the consumption of O2 and the production of CO2), in order to adjust the gas composition from 20.95% O2 and 0.03% CO2 to 2% - 5% and 3% - 8% during storage

however, in fact, the application of map is very complex, because respiration and the permeability of packaging film are constantly changing

the respiratory rate depends on many factors, such as the type of vegetables and different varieties of fruits and vegetables (such as different varieties of lettuce, the respiratory rate is definitely different), maturity (such as the respiratory rate of mature bananas is 4-5 times that of green bananas), and the degree of damage in the preparation process (such as the respiratory intensity of striped carrots is 6-7 times that of non sliced carrots). Temperature is also one of the most important factors. Every 10% increase in temperature. c. The respiratory rate is generally increased by 2 ~ 3 times. However, in spite of this, normal temperature storage is very common, because the cost of cold storage is too high. In fact, CO2 is more effective than low temperature, and the general respiration can be controlled to 4 ~ 5 times that of low temperature

source: desktop network

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