The growing world demand for food has highlighted the necessity of both reducing food waste during distribution and consumption (in countries with advanced economies, it is estimated that about 30% of food is lost at this stage) and improving preservation techniques to maintain the nutritional characteristics of foodstuffs. These requests, together with the changes in life styles and consumption models, have promoted the development of specific preservation techniques including the packaging of food in modified or protective atmosphere (MAP).
MAP is based on the principle of replacing the air in the packaging with a pre-determined gas mixture. MAP technology can be applied to various types of fresh and processed foods. In addition, depending on the nature of the food matrix and the duration of the shelf-life to be attained, it is possible to take action on the following factors:
• the type and proportions of gases in the mixes,
• storage temperature,
• packaging types and materials, and
• the treatments provided by the transformation process.
As packaging gases are food additives according to art.20 paragraph b of the EU regulations no. 1169/2011, they are not to be considered as ingredients of the packaged food and, consequently, they are not required to be listed among the ingredients. The only information required is that the packages are marked with "packaged in a protective atmosphere”, according to attachment III, paragraph 1 of the regulations mentioned above.
The gases most commonly used for MAP are oxygen (O2), nitrogen (N2), carbon dioxide (CO2) and argon (Ar). In the gas mixtures used for MAP, the O2 level is often in lower concentrations in comparison to the amount normally present in the air. The exception is in the case of red meat, cold cuts and some types of fish, for which MAP uses very oxygen-rich formulas so as to keep the food a bright shade of red. The other gas naturally present in the air is CO2, whose concentration is often varied in MAP mixes. Carbon dioxide is one of the gases most frequently used because of its bacteriostatic and fungistatic properties. It dissolves easily in water and packaged food fats to form carbonic acid, which creates a low pH environment.
In general, MAP use for fresh foods (fruits and vegetables, cheeses, dairy products, meat, fish and processed fish products, bakery products, etc.) commonly permits foodstuffs to be stored at the same temperature and storage times to be doubled, in comparison to packaging systems using the normal composition of the air. The type of gas mixture, its production, and the type of packaging used are all important factors in modifying shelf-life duration and, in some cases, also some of the qualitative characteristics of the food itself.
For example, in the specific case of meat, the two main mechanisms compromising shelf-life are microbial proliferation and color change caused by the oxidation of the myoglobin’s red pigment. This aspect has considerable commercial importance, as the consumer, when buying meat, attaches much more importance to its color than to other qualitative factors. The use of high-pressure oxygen contributes to the meat’s bright red color. However, this technique has side-effects, including an acceleration of the lipid oxidation process. The lipid oxidation products resulting from cholesterol oxidation, are particularly important. In fact, cholesterol oxidation products (COPs) are atherogenic and cytotoxic compounds, and are potentially harmful to human health. It is therefore clear that, in the case of red meats and cold cuts, extending a product’s shelf-life and, in particular, maintaining a specific qualitative aspect, like color, involve a modification of the product’s nutritional and health properties that should be more carefully considered.
After choosing the best composition of gases to achieve the intended purpose, it is important to use this mixture within the package using high-precision techniques that ensure minimal error in the production of the mix itself. Although there are few specific studies in the literature in this regard, the use of new-generation gas mixers guarantees greater accuracy than the use of pre-mixed bottles. Finally, the quality of the packaging material and the packaging methods themselves must ensure that the desired mixture is maintained for as long as possible or, in the case of food respiration (as in the case of fruit and vegetables), evolves in a controlled manner. To this end, numerous types of packaging materials are available that differ in barrier and physical malleability properties, strength, transparency and film durability; the ability to preserve the integrity of the heat-sealed closure; the degree of film fogging as a result of product respiration; water vapor transmission speeds, resistance to chemical degradation, absence of toxicity as well as chemical inertness and, finally, the ease with which they can be formed and their cost.
The use of MAP presents a very interesting opportunity for the conservation of many fresh foods. However, there are some application aspects of this technology that should be very carefully considered to make it more effective, as well as other aspects that, nevertheless, deserve further study, including research. It is worth pointing out that the label indicating either the composition of the gas mixture used, or the proportion of the same has not yet been provided at a regulatory level. Moreover, in producing the mix, food processors are not required to guarantee a minimum degree of necessary accuracy to achieve maximum effectiveness. This aspect is an important limit, as the shelf-life duration guaranteed on the label may be compromised. Increased transparency, therefore, would be useful, especially considering that some interactions between O2 and lipids can produce COPs that are particularly insidious as oxidation levels below the perceptible level of rancidity may be present and there may be no perceptible smell.