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Modified atmosphere packaging (MAP)

Date 01.15.2014 | Category: Special Topics
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More and more meat and sausage companies are utilising the technology of modified atmosphere packaging throughout Europe. Summed up, MAP (Modified Atmosphere Packaging) can be described as a technology where a gas atmosphere, which deviates from the composition of air, is produced around the product which is being packaged. This then gives rise to a series of advantageous effects for the quality of packaged foodstuffs.

In principle, the key to this technology lies in the variation of the concentration of different gases for different foodstuffs. The technology uses gases which are safe, saleable, inexpensive, easy to obtain and free of any chemical ingredients. The "main gases" which are used are generally carbon dioxide (CO2), nitrogen (N2) and oxygen (02).

The most important conditions of the MAP technology are:
- good "initial quality of the product or the raw material"
- appropriate temperature checks - continuos adherence to a delicate cooling procedure (cooling chain)
- good HACCP concept and the adherence to it (good hygiene)
- appropriate gas mixture
- suitable and dense packaging
- examination by a foodstuffs technologist

The density of the packaging is of particular importance.On the one hand, the packaging must have as little as possible oxygen or gas permeability, and on the other hand, all seal seams must be truly airtight. If this is not, or only partly, guaranteed, MAP can not be used optimally or may even completely fail.
Packaging materials
MAP needs flexible film and/ or plastic or composite dishes in order to maintain the atmosphere and the product. Sufficient quantities of the material must be the material available. The choice of the materials depends on the following criteria: permeability, strength, sealing capability, printability and recyclable nature as well as safety and cost factors. Plastic films, as far as their gas barrier properties are concerned, are very temperature-sensitive. The permeability increases expotentially with the temperature. As the permeability tests are usually made at room temperature and at a lower humidity, it is difficult to predict the barrier properties which will arise with a higher humidity at refrigerator conditions.

Colour of the meat
The actual pigment of fresh meat is myoglobin, which, in dependence on the oxygen status in the surrounding atmosphere, can be present in three forms. The three different derivatives are myoglobin (Mb), oxymyoglobin (MbO2) and metmyoglobin (Mb+). Reduced myoglobin is crimson and is responsible for the colour of the meat shortly after cutting it and for the colour which comes about in the absence of air e.g. in a vacuum packaging. Oxymyoglobin is light red in colour and the typical attractive colour of fully oxygenated meat. Metmyoglobin is brown and is formed by the oxidation of the pigment in the iron form. The actual colour of fresh meat depends on the relative proportion of these three elements on the surface. The fact is that pork is grey to brownish with a high Metmyoglobin content and beef is dark brown. This colouring of the meat is unattractive to the consumer, as he has the impression that the product is old. In reality however, the colour of the meat is not directly connected with its age. This is where one can make use of MAP technology and maintain or lighten the colour by gassing with oxygen and therefore create an optical advantage for the product. The nature of the composition of the gas atmosphere therefore determines the colour of the meat, exactly like the influences of microbiological spoilage. The inside of the packaging is subjected to the dynamic balance of a gas exchange with the atmosphere outside of the packaging, dependent on the permeability of the packaging on the one hand, and as an interaction with the product on the other hand. The gas dissolves to differing extents in the meat fluids, dependent on the solubility compensates and the partial pressure of the atmosphere. The carbon dioxide is easily soluble both in the muscle tissue as well as in the fatty tissue. It is produced by the breathing of the muscle tissue and from the micro-organisms in the packaging. Carbon dioxide and oxygen are the two most important gases. Oxygen forms a light red colouring, especially at higher partial pressures. The concentration of oxygen generally falls during the storage, as the muscles breath, and due to aerobic bacteria. Oxygen can also be completely absent, e.g. in vacuum packaging. The changes and the effects and quality characteristics of the colouring and of the microbial spoilage are principal factors in the consideration of MAP for meat.

MAP with a lower oxygen content can not be used with beef, as the colour is broken down to an unacceptable extent in such an atmosphere. MAP with a higher proportion of oxygen is applied, among others, in order to lighten and maintain the red colouring of the meat.


Pork in MAP packaging with a lower oxygen content is commonly used in wholesale. The myoglobin content in the pork muscle is low, so that the formation of metmyoglobin brings about only a grey or light brownish coloration and not the dark brown coloration which the consumer finds so dreadful in beef and lamb. Now and then MAP is also used with a higher oxygen content in the retail trade.

MAP is used with a lower proportion of oxygen for wholesale. The colour of the product is not broken down with a low concentration of oxygen as the myoglobin content in chicken meat is relatively low.

Meat products
There is a wide range of meat products with various recipes, production procedures, legally determined contents and storage temperatures as well as differing gas compositions.
Initial careful assessments of the inner and outer properties of the products must first be carried out before a suitable packaging method or gas composition can be decided upon.
With raw-preserved meat products like bacon, Parma meat, salami and boiled preserved meat products like ham, corned beef and luncheon meat, the pink colouring is created by the formation of nitrosomyoglobin.During the heating up process the nitrosomyoglobin is transformed into the denatured pink nitrosomyoglobin. The presence of air hinders the formation of the colour. The removal of the air, e.g. by means of vacuum packaging, MAP, can help to improve the colour stability of such products. These pigments are not influenced by a high CO2 rate. Nitrosomyoglobin can be oxidised by means of O2, whereupon green, yellow or colourless oxidised porphyrine is formed when the stickstoffmonoxid splits due to the multitude of components which are created either chemically or microbially. This reaction can further be catalysed by light, whereby the colour can grow pale as a result and the product can then no longer be sold. There is now a possibility of producing an atmosphere of between 40 and 80 % oxygen in order to maintain the colour stability as well as an atmosphere of between 20 and 30 % carbon dioxide in order to delay the microbiological spoilage. Oxygen can however cause bad aromas or lead to the fats becoming rancid. This atmosphere is not suitable for longer periods of preservation. With an atmosphere in the absence of oxygen, the brown coloration of the meat is delayed and the carbon dioxide also helps to impede the spoilage.

MAP for convenience food
This is one of the fastest growing foodstuff sectors and this is where the quality requirements are particularly high. Again, carbon dioxide, nitrogen and a little, if no, oxygen are used for the atmosphere.

Author: ast
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