Modified Atmosphere Packaging (MAP) Technology (I)

First, the status 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 kept in large bags for fresh storage and transportation, and their application in aquatic products began in 1930. But the commercial application of this technology on a large scale began only after 1970. In 1979, Mark & ​​Spencer of the United Kingdom introduced MAP meat products, which was applied to fish, ham and other products after two years. Research on the fresh-keeping of fruits and vegetables, as early as 1955, Marcelan of the Plant Physiology Laboratory of Gerhard National Research Center in the United States began to study the storage of various PE films for apples and pears, and for the oxygen (O2) and carbon dioxide in the storage environment. Changes in (CO2) were systematically studied and published in 1960 as a physical packaging storage.
China's modified atmosphere packaging started in the 1990s. In 1988, the National Agricultural Product Engineering Technology Center developed 24 formulas for PVC and cling film for fruits and vegetables. 32 varieties were selected and 47 varieties were used for garlic sprouts, cucumbers, celery, and grapes. The practical application of plastic wrap bags such as apples and pears.
II. Results of the modified atmosphere packaging system There are two main influencing factors in the vegetable storage process, namely aerobic bacteria and oxidation reactions, both of which require O2. Therefore, to extend the shelf life or maintain the quality of fruits and vegetables, you need to reduce the environmental O2 content. Tests have shown that the O2 content in the package is <1%. As a result, the growth of various bacteria decreased rapidly, and when it decreased to 0.5%, its growth was inhibited and reproduction ceased. However, the deterioration of some fruits and vegetables is due to anaerobic/micro-aerobic microorganisms and non-oxidation reactions. It is difficult to effectively use vacuum packaging alone, and the product is inevitably shrunk and not suitable for many foods. The MAP technology is specifically designed for the problems that exist in vacuum packaging and can further inhibit microbial spoilage and product shrinkage. MAP, like vacuum packaging, is usually combined with refrigeration. Its core is to regulate the gas around the fruits and vegetables into a gas containing low oxygen and high carbon dioxide compared with the normal atmosphere, with appropriate temperature conditions to extend the shelf life of fresh products. The MAP technology regulates oxygen, nitrogen, and carbon dioxide.
(a) The ideal condition for the preservation of oxygen fruits and vegetables is to exclude O2. However, when packaging fresh fruits and vegetables, O2 is essential. Because fruits and vegetables must be respired after harvesting (eg, O2 consumption and CO2 production), and if O2 is absent, anaerobic respiration will occur, which will accelerate sensory quality changes and decay.
(B) Carbon dioxide CO2 can inhibit the growth and growth of bacteria and fungi, but the specific mechanism of action is not very clear. To be sure, this depends on the diffusion of gas within the package for the following reasons:
(1) The inhibitory effect is directly related to the presence of CO2. Gill and Tan (1980) pointed out that the inhibitory effect is linear with the CO2 concentration until its concentration reaches 50% to 60% (atmospheric volume ratio), and further increasing the concentration is not obvious for most microorganisms. Shay and Egan (1987) and Gill and Penney (1988) both believe that more than 50% to 60% will diffuse into the product, so that the best results can be achieved. Therefore, the packaging volume and the air permeability and surface area of ​​the packaging material should be considered.
(2) The solubility of CO2 is inversely proportional to the storage temperature, so low temperature has a synergistic effect.
(3) When the CO2 concentration is high, if there is some dissolved gas containing carbonic acid, sourness will be produced.
(4) Absorption of gas by the product will reduce the volume of the gas, so this will cause the product to collapse, which will cause slight changes in appearance, and sometimes it will lead people to mistaken for lax packaging and packaging material defects.
In addition, the bacteriostatic effect of CO2 also depends on the growth stage of the microorganisms that are present. CO2 can increase the delay period and reduce reproductive efficiency in logarithmic growth phase; however, the former has more obvious effects, so the inhibitory effect will decrease when the bacteria transitions from the delayed phase to the logarithmic phase. In this way, CO2 will be more effective in the early stages of inflatable packaging. (To be continued)