From: Food Packages

To design a packaging in MAP

When you prepare to design a package that uses the protective atmosphere packaging technology, you need to ask yourself a few questions: Which is the most suitable gas mixture? Which are the effects of this gas on the chemical, physics, sensory and microbiologic characteristics of my product? To act with awareness it is essential to know the answers to all these questions that involve the elaboration of many technical issues that will be described hereinafter.

The atmosphere selection
Which atmosphere can I use for increasing the shelf life of my product? The answer cannot be prompt: each product needs a careful experimentation before setting the most suitable atmosphere. Generally we aim to make the best use of the antimicrobic effect of carbon dioxide and good results are generally obtained in the increase of the product preservation. However when we use atmosphere rich in carbonic dioxide possible troubles should be considered: the sensory characteristics can change with high gas concentrations and the product can turn out to be "sour" or "sparkling" with the consequent refusal of the food by the consumer.
Concerning oxygen, its role has been revalued in the last years; For example gaseous mixtures with high content of this gas are used in the packaging of some typologies of fruit, vegetable and of some fish products. Atmosphere entirely composed of nitrogen is the only one that can be considered as really inert: it is used for avoiding the collapse of the packaging material on the product.
An atmosphere of this type can be successfully used in food packaging with low humidity content and with those food products where there is no risk of a microbial growth during their preservation time. Balanced mixtures of these three gases are often used: each mixture must be tested on its product + packaging.
After these premises it should be said that to choose the right mixture it is necessary to know in advance:
the interactions between food and gas: for example the solubility of the carbon dioxide in food to the different temperatures and the organoleptic variations connected to the gas dissolution;
the behaviour of microflora in the selected atmosphere (the risk of proliferation of anaerobic microorganisms or of an undesired selection of the typical microflora);
the permeability of the packaging materials to the used gases, considering the preservation temperature and the total surface;
the packaging airtightness, that is the absence of small holes and/or sealing imperfections;
the deterioration of food in contact with air;
the effectiveness of the packing operation and of the air replacement, or rather the choice of the most suitable packing system, of the gas supply and mixing system, the evaluation of the real composition of the introduced atmosphere and the oxygen residue after the packing operations

The material selection
Before choosing the material different factors should be considered. The first key factor is permeability to gases. The right combination of gases during packing would not have any sense if the material allowed their change; accordingly it's better to use materials with barrier properties. As general rule the materials considered good for MAP technology are those with permeability to oxygen <50 cm3 m-2 day-1 atm-1.
The materials for packaging in protective atmosphere should have barrier properties to steam (WVTR) to prevent the humidity loss from the product. The WVTR values are expressed in g m-2 day-1 indicating to which temperature they were taken and the relative humidity (RH). Concerning the mechanical properties, the materials should have enough resistance to puncturing and should be able to stand the strengths they are subjected to during the transport and the stocking operations. If we deal with thermoformed trays we will have to consider with attention the thickness of the critical points (edges). The sealing reliability is essential to the good conservation of the injected atmosphere.

Kind of packaging
The kind of packaging to choose depends on the food typology and on the commercial destination of the same. There are: rigid and half-rigid trays with lid films; flexible packaging as the pillow packs; bags and so on. The necessity to appear on the shelves of large-scale retail led to design new shapes and typologies of packaging which are in continuous evolution (for instance the stands up pouches) and where the use of protective atmosphere has been successful. In the main it can be said that the are many packaging typologies to design, even if each of them has to meet specific characteristics:

well defined global permeability;
airtightness to the microbial contaminations;
resistance to the mechanical stresses.

Multilayer packaging is often used. In these cases the layer conferring mechanical resistance must be placed on the external side; the layers in the middle are barriers to gases; inside the packaging, instead, there are those sealing the structure. If a barrier layer to water is needed, it will be placed on the external side in case of dry food and inside in case of humid food. In the end the most innovative packaging is that designed to be used in microwaves ovens fit for direct intake without using dishware.