This article introduces basic knowledge of MAP modified atmosphere packaging and related packaging machines. For the gas mixing ratio of different food products, please go to MAP Modified Atmosphere Packaging Food Products. For modified atmosphere packaging machines details, please go to the MAP machine page.
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ToggleThe normal air composition is nitrogen (N2) 78.08%, oxygen (O2) 20.96% and carbon dioxide (CO2) 0.03%, and various concentrations of water vapor, inert or rare gas. With the loss or absorption of water, the reaction with oxygen, and the growth of aerobic microorganisms such as bacteria and molds, many foods deteriorate rapidly in the air. These changes can make food uncomfortable and may be harmful to human consumption. By slowing down chemical and biochemical spoilage reactions and slowing down (or in some cases preventing) the growth of perishable microorganisms, storing food in a modified gas environment can maintain product quality and extend its shelf life.
Modified atmosphere packaging (MAP) is to package perishable products in an atmosphere that has been modified to be able to extend the shelf life of packaged products. Although controlled atmosphere storage (CAS) involves careful control and addition of gas to maintain a fixed concentration of gas around the product, the gas composition of fresh MAP products is constantly changing due to chemical reactions and microbial activity. The external environment may also be generated by the penetration of packaging materials.
Modified atmosphere packaging of food can provide a longer shelf life and improved product display in a convenient container, making the product more attractive to retail shoppers. MAP modified atmosphere packaging would not improve the quality of poor-quality food, it is very important to ensure that the product is of the highest quality before packaging to optimize the benefits of MAP packaging. MAP modified atmosphere packaging also requres perfect hygiene practices and temperature control throughout the packaging and storage process.
The first commercial application of MAP modified atmosphere packaging was for CAS of fruits and vegetables. In the early s, fresh carcasses were exported from New Zealand and Australia under the CAS. The initial development mainly involved the storage and transportation of bulk food. In the s, studies on the effect of gas on extending the shelf life of food were carried out on fresh meat. Killefer () reported that when meat is stored in a 100% CO2 atmosphere, the shelf life of frozen pork and lamb doubles. The first published research on poultry products was carried out in the s; fresh poultry is stored in a 100% carbon dioxide atmosphere, which significantly extends the shelf life.
The shelf life of the chicken portion was reported that as the CO2 concentration in the storage environment rises to 25% CO2, the impact on shelf life becomes greater.
MAP modified atmosphere packaging of fresh meat for retailing market was introduced in the early s. Meat processing and packaging in Europe developed in the s, mainly producing MAP meat in consumer packaging for distribution at the point of sale. In recent years, in the ever-changing retail environment, the supply of packaged foods including meat has increased significantly. , Poultry, fish, bacon, bread, cake, potato chips, cheese, and lettuce. The retail sales of MAP packaging products in the UK increased from approximately 2 billion packages in the mid-s to 2.8 billion packages in . Meat products accounted for 29% and 15% of MAP’s total food retail sales respectively (Anon, ).
The three main gases used in MAP modified atmosphere packaging are O2, CO2, and N2. The choice of gas depends entirely on the food to be packaged. These gases are used alone or in combination and are usually used to balance the safety shelf life and the best sensory properties. Rare or inert gases (such as argon) are used commercially in products such as coffee and snacks, but there is limited literature on their uses and benefits. Experimental uses of carbon monoxide (CO) and sulfur dioxide (SO2) have also been reported.
Carbon dioxide (CO2) is a colorless gas with a slightly pungent odor at very high concentrations. It will suffocate when exposed to moisture and is slightly corrosive. CO2 is easily soluble in water (1.57 g/kg at 100 kPa, 20°C) to form carbonic acid (H2CO3), which increases the acidity of the solution and lowers the pH value. This gas is also soluble in lipids and other organic compounds. The solubility of CO2 increases with decreasing temperature. For this reason, the antibacterial activity of CO2 is significantly higher at temperatures below 10°C than at 15°C or higher. This has important implications for the food MAP discussed later. Due to the reduced air space, the high solubility of CO2 will cause the packaging to deteriorate. In some MAP applications, compressed packaging is preferred, such as cheese in retail packaging.
Oxygen (O2) is a highly reactive, odorless, and colorless gas that promotes combustion. Its solubility in water is very low (0.040 g/kg at 100 kPa, 20 °C). Oxygen can cause many types of food spoilage reactions, including fat. Oxidation, blackening reaction, and pigment oxidation. The most common perishable bacteria and fungi require oxygen to grow. In order to extend the shelf life of food, the atmosphere of the package must therefore contain low concentrations of residual O2. Foods with low O2 concentrations can cause quality and safety issues (such as poor discoloration of red meat pigments, aging of fruits and vegetables, and growth of food-borne bacteria), which should be considered when selecting gaseous formulations for prepackaged foods.
Nitrogen (N2) is a relatively inert gas, odorless, tasteless or colorless, has a lower density than air, is non-flammable, and has low solubility in water (0.018 g kg-1 to 100 kPa, 20°C) and other food ingredients Nitrogen does not support the growth of aerobic microorganisms, so it inhibits the growth of aerobic spoilage, but cannot prevent the growth of anaerobic bacteria. The N2 in the gas mixture compensates for the decrease in volume caused by the dissolution of CO2.
Carbon monoxide (CO) is a colorless, odorless, and odorless gas that is highly reactive and flammable. Its water solubility is poor, but it is relatively soluble in some organic solvents. The CO was investigated and approved in the meat MAP. Used to prevent browning of packaged lettuce in the United States. Commercial use is restricted due to its toxicity and the formation of potentially explosive mixtures with air.
Noble gases are a class of non-reactive elements, including helium (He), argon (Ar), xenon (Xe) and neon (Ne). These gases are now used in many foods, such as potato snacks. Although it is scientifically difficult to understand how the use of inert gases provides savings over N2, they are still in use, indicating that there may be benefits that have not yet been announced. For you to use.
Food may contain many kinds of microorganisms, including bacteria and their spores, yeasts, molds, protozoa, and viruses. Although packaging experts are most concerned about preventing the growth of bacteria, yeasts, and molds in food, it should be noted that even if some pathogens do not grow in food, they will exceed the shelf life and cause food poisoning. Or consumer disease. This section discusses the main microbial groups that MAP modified atmosphere packaging can control or affect.
Bacteria, yeasts, and molds have different respiratory and metabolic requirements and can be grouped according to their oxygen requirements.
Aerobes: They require O2 to grow and include the ubiquitous Pseudomonas gram-negative spoilage bacteria. This group also includes some pathogenic bacteria, such as Vibrio parahaemolyticus. Note that some other Vibrio species are classified as facultative aerobes.
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Microaerophiles: They grow at low O2 concentrations. Therefore, the hypoxic environment is selective for some major pathogens (such as Campylobacter jejuni and Listeria monocytogenes). Certain microaerobic bacteria, such as Lactobacillus. Even under conditions of low oxygen levels, higher CO2 levels may be required to achieve optimal growth.
Facultative anaerobes: They usually grow best under O2, but they can grow without it. These include several important genera of the Enterobacteriaceae, including pathogens such as Escherichia coli, Salmonella and Shigella, Staphylococcus aureus, Listeria monocytogenes, Brucella, Vibrio, enzymatic Yeast. And some Bacillus species. Aeromonas hydrophila is an emerging pathogen, especially related to fish and fish products. Many strains are psychrophilic, and some can grow at a temperature of 3 to 5°C.
Anaerobes: They are inhibited or eliminated by the presence of O2, for example by the pathogenic bacterium Clostridium botulinum. Removal of oxygen, such as in vacuum packaging, limits the growth of aerobic spoilage and pathogenic bacteria, thereby extending the shelf life. The above are other microorganisms that can grow under these conditions, including the pathogens Escherichia coli and hydrophile.
The antibacterial properties of CO2 have long been known (Valley & Rettger, ). Recent studies have shown that CO2 is effective against psychrotrophic bacteria (King & Nagel, ) and can extend the shelf life of foods stored at low temperatures.
There are several theories about the actual mechanism behind the carbon dioxide effect. Generally speaking, CO2 will increase the lag period and generation time of microorganisms, and this effect is expected to increase at lower temperatures. Antibacterial mechanisms, including lowering CO2 pH, inhibiting succinate oxidase when CO2 concentration is higher than 10%, inhibiting certain decarboxylase and cell membrane changes (Valley & Rettger, ; King & Nagel, ; Gill & Tan, ; En Foss and Morin, ). Various researchers including Daniels and others have also studied the area. (). The susceptibility of some pathogenic bacteria and perishable bacteria to CO2 is shown in Table 10. As mentioned in Section 10, Gram-negative bacteria are more inhibited than Gram-positive bacteria. CO2 exposure is highly dependent on temperature. Therefore, in order to protect the health of consumers, the integrity of temperature control must be maintained throughout the supply chain. CO2 can stimulate Clostridium botulinum (Eklund, ).
CO2 is easily soluble in water and lipids, especially at low temperatures, so adsorption adjustment is required. In fresh meat, until the container is destroyed. The latter occurs when CO2 is the main gas and the gas is dissolved in the water and fat phases of the product. To counteract this effect, an insoluble gas such as nitrogen can be used. If CO2 is needed to control the growth of bacteria and mold, usually at least 20% is used.
Nitrogen is a relatively inert gas. It is used to replace the air in MAP, especially O2. By removing air and O2, the growth of aerobic decomposition organisms is inhibited or stopped. Put pressure on the packaging to avoid tearing the packaging of foods with high moisture and fat content. For example, due to the solubility of CO2 in water and fat, these products tend to absorb CO2 from the packaging environment.
Choosing the most suitable packaging materials is critical to maintaining food quality and safety in MAP modified atmosphere packaging. Flexible and semi-rigid plastics and plastic laminates are the most commonly used materials for MAP Foods. Plastic materials account for about one-third of all food packaging needs, and their use is expected to increase.
Relatively easy to shape, lightweight, good transparency, heat sealing and strength are some of the characteristics of plastics, making them suitable as food packaging materials. Promote the development of plastics that are more suitable for specific applications in food packaging.
However, none of the plastics has properties suitable for all food packaging applications. Plastic packaging materials can be composed of a single layer of a single plastic, but most (if not all) MAP films are multi-layer structures composed of multiple layers of different plastics. National technology or coating technology, different types of plastics can be combined to form rigid films, sheets or bags. By carefully selecting each plastic component, a material that has important packaging characteristics and best meets the requirements can be developed.
MAP’s plastic containers are most commonly used as flexible films for bags, pouches, pillows, and top straps, or as rigid and semi-rigid structures for bottom trays, plates, glasses, and cups. Commonly used flexible plastic laminates are made of polyethylene (PE), polypropylene (PP), polyamide (nylon), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyvinylidene chloride (PVdC) and ethylene vinyl alcohol (EVOH). Semi-rigid structures are usually made of PP, PET, PVC-U and expanded polystyrene.
The following content is a brief overview of the commonly used plastics for MAP modified atmosphere packaging applications.
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