One type of packaging in food industries is modified atmosphere packaging (MAP) and controlled atmosphere packaging (CAP).
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Modified Atmosphere Packaging (MAP)
MAP is done in two active and non-active forms. In the active form, it is evacuated and then the desired gas composition is injected into the package after placing the product in the package. For example, the packages are completely removed from the air in the packaging of chips, and then nitrogen gas is injected to increase the life of the product not to react with air. In the inactive form, the product is packaged in normal air and the desired modified air is created after a few days due to the product’s breathability and the special permeability of the film. The desired air in MAP packaging is created by examining and creating a dynamic balance of the produced gases inside the package. In this way, the amount of oxygen entering the package should be enough to be completely consumed by the product. Moreover, the flux of carbon dioxide production inside the package and its output must be equal. This gas is exchanged by flexible polymer films of PP, PVC, LDPE, ethylene-vinyl alcohol copolymer, and softened polystyrene. In addition, the permeability of the films for MAP packaging changes with the change of atmospheric composition inside the package and is called smart packaging. In these packages, minimal changes are applied to the fresh food inside these packages by changing the light, relative humidity, temperature, etc.
All types of packaging methods are single, bag, or tray with silicon window.
The influential method for this packaging is such that it reduces the intensity of respiration, material consumption, carbon dioxide production, oxygen consumption, and heat production. As a result, the mechanisms slow down and the life of the product increases. Low concentrations of oxygen can have an insecticidal effect. Therefore, if the quality of the fruit is not affected, low oxygen concentrations may be used instead of insecticides for short periods of storage. However, it should be kept in mind that low oxygen concentrations provide optimal growth conditions for anaerobic microorganisms, and a CO2-rich atmosphere with a small amount of O2 on the microbial flora is a good choice. The metabolism of microorganisms themselves can be effective in changing the closed atmosphere. Therefore, external and effective factors on the modified atmosphere must also be considered. These factors include temperature, relative humidity, and light.
Low temperatures reduce the rate of respiration, control the growth of microorganisms, and delay the metabolic activity of plant tissues. It is important to select and maintain the optimum temperature during production and marketing until the product reaches the end customer. Furthermore, CO2, which must be kept high in the package to preserve fruits and vegetables, is more soluble in water at low temperatures and also reduces the damage caused by lowering the temperature. Therefore, low and optimal temperatures should be selected.
The relative humidity inside the package must be controlled because the presence of humidity makes the product loosen and withered. The relative humidity inside the package is controlled using water-absorbing chemicals such as NaCl, KCl, CaSiO4, xylitol, sorbitol, and anti-fog polymer composition.
Controlled Atmosphere Packaging (CAP)
In the controlled air packaging (CAP) method, the life of the product is increased by replacing the gaseous environment inside and outside the package. This method is mostly used for perishable foods such as meat, chicken, fish, high-moisture pasta, and fruits such as apples, pears, and some vegetables. In this method, different gases are injected into the package, and the air is expelled from it at the same time. Fruits and vegetables consume oxygen and produce carbon dioxide during storage. There are three ways to slow down this breathing and other physiological changes. The first method is to lower the ambient temperature. The second method is to reduce oxygen and the third method is to increase the amount of carbon dioxide. These three things are done in the MAP method as well, but the difference between the CAP and the MAP is the control of changes during the life (durability) of the product. Because it is not possible to control what happens to the product using the MAP method after packaging or the product’s respiration. However, these changes are done by changing 3 gases to have the best combination of retaining gas in the package in the CAP method.
- Oxygen control: Oxygen preserves the red color of meat.
- Control of carbon dioxide: prevents the production and spread of mold and bacteria.
- Nitrogen: It is an inert gas that prevents respiration and enzymatic activities.
For example, this gas produces carbonate acid into the meat tissue and prevents it from spoiling by lowering the pH of the meat by controlling the proper amount of carbon dioxide.
Another type of CAP is maintained under “high humidity and reduced pressure” conditions which are called “Hypobaric Storage”. In this way, the amount of air is reduced, and through this, the amount of oxygen in the warehouse and high humidity prevent the dehumidification of the food product. CAP needs to use strict quality control and storage temperature to ensure the safety and quality of food products. Lack of proper control can have devastating effects on food quality. These changes are influenced by various factors such as growth conditions, animal feeding habits, harvesting or slaughter conditions, health and tissue damage, cold storage temperature, packaging conditions, and other variables.
Advances in CAP technology include faster deployment of optimal space, less fluctuation in O2 and CO2 levels, the ability to change atmospheric composition during storage, if needed, and the ability to clear ethylene from the storage environment.
Advantages of using CAP
- Increasing the natural life of products to 2-4 times more
- Access to target markets with long geographical distances for longer product life
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