Basics of Modified Atmosphere Packaging
Modified atmosphere packaging (MAP) is well established in the food industry and continues to gain in importance. MAP means, simply put, that the natural ambient air in the package is replaced by a gas or gas mixture, often nitrogen and carbon dioxide. This packaging under a protective atmosphere preserves the quality of fresh produce over a longer period of time, prolongs shelf life, and gives food producers access to a geographically larger market for perishable products. This is suitable for meat and sausage products, fish, dairy products, bread, fruit and vegetables, and convenience products.
Modified atmospheres are not limited to the packaging process. They can also feature as part of the production process, for example, in the storage and transport of fruit and vegetables in halls or containers.
The standards required by modified atmosphere packaging are comparatively high and must be controlled and monitored to ensure safety. Therefore, food manufacturers rely on modern MAP gas technology and various levels of quality assurance for maximum process safety.
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Benefits of modified atmospheres
• Longer shelf life / higher quality
Food packaged under a protective atmosphere spoils at a much slower rate. Combined with continuous cooling, modified atmosphere packaging can significantly extend the freshness and shelf life. This effect varies depending on the product type. However, a doubling of the shelf life is usually possible. In general, MAP products keep a high quality over a longer period of time and arrive at the consumer in the best possible condition.
• Less waste
Longer durability is often associated with fewer problems during long distance shipment – and a longer shelf life. As a result, waste disposal due to spoiled food can often be reduced.
• More sales opportunities
Because of the longer shelf life, modified atmosphere packaging typically opens up new geographic markets to manufacturers. Particularly with perishable goods, longer shipment distances can be achieved, and a global market can become a reality.
• Fewer preservatives
As packaging under a protective atmosphere extends the shelf life of food, the use of preservatives can be reduced or even completely eliminated in many cases. Consumers get products that do not contain artificial additives.
• Appealing package design
Next to functional aspects, the design of the packaging plays a significant role in the competition for consumers. The look and feel, in addition to the quality impression, influence the purchasing behavior. Modified atmosphere packaging is very well suited for the most appealing package design and presentation of the food product.
Limitations of modified atmospheres
• Comparatively high complexity
The modified atmosphere packaging process involves comparatively high requirements. Possible failures include incorrect gas composition, leaks due to faulty temperature or pressure distribution, contaminated or worn tools, seal contamination, or defective material. However, with modern MAP technology and comprehensive quality assurance, the risks can be mastered.
• Cost
High-quality packaging films, the consumption of gas and the personnel costs for quality control all into the cost of modified atmosphere packaging. However, these costs can be minimized with the efficient use of resources.
• Influence on product quality
Unlike using preservatives, in most cases, the protective gases are not absorbed by the food and, thus, do not alter the nature or taste of the product. However, there are exceptions to this rule. For example, an excessively high concentration of CO2 can be absorbed by the food and make it sour. Fortunately, these effects can be avoided with adapted gas mixtures. There are also issues specific to meat. The influence of a very high oxygen concentration on the color and quality of meat is controversial, and modified atmospheres are supposed to make the meat tastier, but data to support this is sparse.
Factors influencing the shelf life of food, and the influence of modified atmospheres
From the time that fruits and vegetables are harvested or animals are slaughtered, the spoilage process begins. This process is often accelerated the more the products are processed, e.g., in the case of cut fruit or minced meat. How long foods remain suitable for consumption varies greatly and depends on various factors, including the content of water and salt, pH value, hygiene conditions during production, storage conditions, such as temperature or humidity, and packaging. Depending on the characteristics and combinations of these factors, food products vary in their sensitivity to microbial or chemical / biochemical spoilage.
Chemical and biochemical spoilage
Directly after harvest or slaughter, chemical processes begin to change the structure or quality. Sometimes this is useful, e.g., dry-aging of meat, which can be seen as a maturation to improve quality. In principle, however, the quality of organic material decreases. For example, the oxidation of fats quickly leads to rancidity.
Microbial spoilage
Microorganisms are a major threat to the shelf life and quality of food. On the one hand, they influence color and smell, but they can also lead to health hazards and make the products inedible. The source of the microorganisms is either the food itself or an impurity that cannot be completely excluded in the production and packaging process.
The changes due to chemical / biochemical and microbial spoilage can be significantly slowed by MAP techniques, combined with cooling. Various gases and mixtures with different properties are used to slow the process of spoilage as much as possible.
Typical gases for Modified Atmosphere Packaging
Carbon dioxide (CO2) and nitrogen (N2) are the main protective gases used in food packaging. Carbon monoxide (CO) and argon (Ar) are also common in some countries, for example, in the US. And oxygen (O2) is also used in some cases.
Oxygen (O2) causes food to spoil due to oxidation and forms the ideal preconditions for aerobic microorganisms to grow. As a result, oxygen is frequently excluded from modified atmosphere packaging. However, in some cases processing is deliberately carried out with high oxygen concentrations, for example, with red meat. Oxygen prevents the red color from becoming pale, and it inhibits the growth of anaerobic organisms.
Carbon dioxide (CO2) is colorless, odorless and tasteless. Due to its oxidation-inhibiting and growth-inhibiting effects on most aerobic bacteria and molds, the gas is frequently used to increase the shelf life of food. As the shelf life of packaged or stored food is normally longer, the CO2 concentration is higher. Nevertheless, many products can become sour if the CO2 concentration is too high. In addition, the gas can diffuse out of the packaging or be absorbed by the product, causing the packaging to collapse. The use of supporting or filling gases can slow down this effect.
Nitrogen (N2) is an inert gas and, owing to its production process, is typically of relatively high purity. It is usually used for displacing air, especially atmospheric oxygen, in food packaging. This prevents the oxidation of food and inhibits the growth of aerobic microorganisms. It is frequently used as a supporting or filling gas as it diffuses very slowly through plastic films and, therefore, remains longer in the packaging.
Carbon monoxide (CO) is colorless, odorless and tasteless. Similar to oxygen, carbon monoxide is sometimes used to retain the red color of meat. The required concentrations are very low, in the ppm range.
Argon (Ar) is inert, colorless, odorless and tasteless. Owing to the similarity of its properties to those of nitrogen, argon can replace nitrogen in many applications. It is believed that certain enzyme activities are inhibited and argon slows metabolic reactions in some types of vegetables. Due to the marginal effects and the higher price compared to nitrogen, its use is rather rare.
Hydrogen (H2) and helium (He) feature in modified atmospheres in some applications. However, these gases are not used to extend the shelf life. They are used as trace gases for some leak detection systems available on the market. The relatively small molecular size of the gases allows rapid escape through packaging leaks. Since these gases otherwise have no positive properties in regard to the food products and are expensive and difficult to handle, their use is rare. The most common method for leak testing is the detection of CO2 which is the core component in many MAP processes.
If food is packaged under a protective atmosphere, gases must meet the FDA Food Code : Annex 6 - Food Processing Criteria.
Foods suited to Modified Atmosphere Packaging
Modified atmosphere packaging is suitable for a wide range of food products. While traditionally mainly dairy products, meat products and bread were packaged under a protective atmosphere, now MAP is increasingly used for other foods, such as fish, coffee, fruit and vegetables. In addition, modified atmosphere packaging is driven by the growing popularity of ready-made meals and convenience products.
Meat and sausage products
Meat and sausage products are highly susceptible to spoilage from microbial growth. As this growth is enhanced by high moisture and nutrient content, raw meat is especially prone to spoilage. No matter whether beef, pork or poultry, spoilage begins from the moment of slaughter and continues throughout the butchering process. Besides stringent hygiene standards and continuous cooling, modified atmospheres can significantly extend the shelf life of meat and sausage products – with CO2 as the most important among the protective gases. At concentrations above 20%, CO2 can considerably reduce microbial growth. In the case of red meat, there is also the risk of oxidation of the red pigments. The meat will lose its color, becoming gray and unappetizing in appearance. This is especially true with beef. To combat this problem, a high oxygen concentration in protective gas packaging can prevent oxidation. In addition, a very low carbon monoxide concentration (approx. 0.4% or ppm) can further help to retain the red color.
Poultry is particularly sensitive to rapid spoilage and, therefore, subject to stricter cooling requirements. Here, too, a modified atmosphere with CO2 will extend the shelf life. A high oxygen concentration is also used for poultry without skin in order to retain the color of the meat. As CO2 can be partially absorbed by food, nitrogen is added as a supporting gas to prevent the packaging from collapsing.
Sausage and meat products, e.g., marinated or smoked meat, react differently depending on the preparation. While shelf life is inherently longer than that of raw meat, it can also be positively influenced with protective gases. The CO2 concentration should not exceed recommended limits with these products, however, or a sour taste may occur.
Fish and Seafood products
Fish and seafood are some of the most sensitive foods. They are at risk of rapidly declining in quality and spoiling, even shortly after the catch. The reason for this lies in seafood’s neutral PH value – an ideal precondition for microorganisms, as well as special enzymes that negatively affect taste and odor. Fish, which is rich in fatty acids, also becomes rancid quickly. The most important element for a longer shelf life is cooling close to 32°F, but modified atmospheres with at least 20% CO2 also slow the growth of bacteria, and CO2 concentrations around 50% are frequently used. As with other foods, higher levels of CO2 can lead to undesirable side effects, such as liquid loss or a sour taste. In the case of low-fat fish and shellfish, oxygen is also used in the packaging. This prevents a fading or loss of color, while simultaneously serving as a growth inhibitor for some types of bacteria. When dealing with shellfish and crustaceans, special attention should be paid to ensuring a CO2 concentration that is not too high. As these products absorb the most CO2, there’s a greater risk of sour taste. In addition, there’s a greater risk of package collapse. However, using nitrogen as an inert supporting gas prevents this effect.
Dairy products
Cheese is predominantly spoiled by microbial growth or rancidness. While a continuous cooling chain extends the shelf life, in the case of hard cheese, there is a risk of mold formation upon contact with oxygen. As a result, vacuum packaging was frequently used in the past, even though this type of packaging is awkward to open and can leave unattractive marks on the product. Modified atmosphere packaging with CO2, on the other hand, effectively prevents mold formation – without the undesirable effects of vacuum packaging – but does not otherwise affect the maturation of the cheese.
Soft cheese can quickly become rancid. While this problem can also be tackled with CO2, soft cheese absorbs this gas at a greater rate than other types of cheese, resulting in a risk of sour taste and package collapse. Therefore, a lower CO2 and higher nitrogen concentration should be used. Likewise, dairy products such as yogurt and cream can absorb too much CO2 and become sour; these products should be packaged with an even lower concentration of CO2.
Powdered milk, frequently used in baby formula, is a highly sensitive product. It is especially important to ensure that oxygen is displaced from the packaging in order to extend the shelf life. In practice, packaging is carried out in pure nitrogen with as low a residual oxygen content as possible.
Bread and Cake
The shelf life of bread, cake and cookies is primarily affected by mold formation. Although a high standard of hygiene during production and packaging can significantly minimize this risk, using a modified atmosphere with CO2 (and without oxygen) minimizes the risk considerably further, greatly extending the shelf life. Because these products may absorb CO2, nitrogen is often included as a supporting gas to prevent package collapse.
Fruit and Vegetables
Modified atmosphere packaging makes it possible to offer consumers fresh and untreated products – in other words, succulent fruit and vegetables – with a long shelf life. At the same time, fruit and vegetables are subject to unique requirements regarding the nature of the packaging and atmosphere. In contrast to other types of food, fruit and vegetables continue breathing after the harvest and, consequently, require an oxygen concentration in the packaging. Furthermore, the packaging film doesn’t have to be airtight. By taking the product’s respiration and the permeability of the film (typically via micro-perforation) into account, the ideal composition of CO2, nitrogen and low amounts of oxygen can be maintained. The term used here is EMA – equilibrium modified atmosphere. The gas composition is individually adapted to the corresponding product.
Thorough cleaning and hygienic processing are the fundamental preconditions for long-lasting freshness. Modified atmospheres, in conjunction with cooling, can be used to extend the shelf life of fresh produce while achieving an attractive packaging design at the point of sale.
Pasta and ready-made meals
The nature and composition of fresh pasta and, in particular, ready-made meals vary greatly. Products such as ready-made pizzas or sandwiches contain many different ingredients with a variety of shelf lives and spoilage properties. In the majority of cases, modified atmospheres can significantly extend the shelf life without using oxygen. Mixtures of CO2 and nitrogen are used with the concentration of gases adjusted to the content of the product. If, for example, there is a risk that large volumes of CO2 will be absorbed by the product, the nitrogen concentration should be increased to prevent the packaging from collapsing.
Snacks and Nuts
Snack products containing fats, for example, potato chips or peanuts, are at increased risk of oxidation, whereby the products can quickly become rancid if the packaging is not optimal. To extend the shelf life, it is critical that contact with oxygen is minimized. In this case, modified atmospheres with 100% nitrogen are frequently used. Not only does this prevent premature spoilage, the nitrogen atmosphere also provides protection from mechanical damage to sensitive products, such as potato chips in conventional packets.
Wine
Gases or gas mixtures are often used to protect wine in the different phases of its production process and to retain the quality of the product. They are mainly used to avoid contact with oxygen and prevent microbial deterioration. The tank headspace is replaced with an inert gas or a gas mixture, for example, of CO2, N2 or Ar. The composition of the gases is chosen according to the type of wine.
Coffee
As a dried product, coffee is relatively immune to spoilage by microorganisms. However, due to its fatty acid content, the product may turn rancid as a result of oxidation. To prevent this, coffee is packaged to exclude oxygen. Instead, a modified atmosphere comprising pure nitrogen is frequently used in coffee bags or capsules.
