Experiments have shown that when the oxygen content in the package is less than 1%, the growth of various bacteria rapidly decreases, and when it is reduced to 0.5%, its growth is inhibited and the breeding stops. However, the decay 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 use of vacuum-packed products will inevitably occur shrinkage. Many aspects are not suitable.
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.
1. Oxygen The ideal condition for the preservation of fruits and vegetables is to exclude oxygen. However, when packaging fresh fruits and vegetables, oxygen is essential.
2. carbon dioxide
Carbon dioxide 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 carbon dioxide. The inhibitory effect is linearly related to the concentration of carbon dioxide until its concentration reaches 50% to 60% (atmospheric volume ratio). If it exceeds 50% to 60%, it will diffuse into the product, so that the best effect 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 carbon dioxide is inversely proportional to the storage temperature, so low temperatures have a synergistic effect.
3) When the concentration of carbon dioxide 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 a slight change in appearance, and sometimes it will be mistaken for lax packaging and packaging material defects.
In addition, the bacteriostatic effect of carbon dioxide also depends on the growth stage of the microorganisms that are present. Carbon dioxide can increase the delay period and reduce the reproductive efficiency of the 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, carbon dioxide will be more effective in the early stages of inflatable packaging.
3. Nitrogen
Nitrogen is an inert, odorless gas that controls chemical reactions. Neutral in contact with food, can be used for food preservation. Compared with other commonly used gases, nitrogen does not easily penetrate the packaging film, and is mainly used as a filling gas in the modified atmosphere packaging system.
In summary, the design of the modified atmosphere packaging system should take into consideration various factors. The most important factor is the relative content of carbon dioxide and oxygen in the packaging, which is mainly determined by the gas concentration in the packaging and the permeability of the packaging material.