What is MAP (Modified Atmosphere Packaging)?

Modified Atmosphere Packaging (MAP) is also named as Replaced Gas Packaging literally, which is one type of packaging to keep food fresh and longer shelf life, developing upon vacuuming packing and nitrogen filled packaging basis, mainly applied to maintain food freshness.

The principal of Modified Atmosphere Packaging is built to replace inner gas of packaging boxes or bags by filling two to four mixed gases that each is proportioning by food property, driving to restrain bacteria growth by changing inner ambient of packaging boxes (bags) that takes advantage of slowing down the pace of which fresh vegetables and fruits get metabolized to keep food freshness longer or enhance shelf life.

In case of preserving vegetables and fruits fresh, this kind of food after picking still conducts respiration as burning out O2 and exhaling CO2, where ambient is filled with concentration of CO2 by increasing gradually and O2 by decreasing. Applying high oxygen permeability packaging film can exchange gas with atmosphere by refilling O2 in and releasing CO2 out. Once the oxygen permeability and vegetables (fruits) respiration are in consistently same pace, the inner ambient of packaging boxes (bags) reaches certain balance of gas concentration which helps vegetables and fruits keep in slight respiration pace, not like anaerobic respiration, to maintain food freshness by prolonging the ripeness of vegetables and fruits. Modified Atmosphere Packaging carries out to ensure food texture, nutrition and shelf life without adding preservatives and additives.

Modified Atmosphere generally consisted of CO2, N2, O2 and few of rare gases such as NO2, SO2, Ar and etc applying for maintain food freshness. Each gas follows specific function as below:

CO2: Restrain growth and reproduction of the mostly rotten bacterium and mould. This is the major bacteriostatic agent among above mentioned gases.

O2: Restrain growth and reproduction of the most major of anaerobic rotten bacterium and preserve fresh vegetables and fruits respire.

N2: This inert gas in general doesn’t have chemical reaction with food neither has been absorbed by food. It is used to fill in packaging to prevent boxes/bags from caving in after CO2 leaks out.

What types of gas with each proportion is differently adjusted by food type. For crops packaging case the most important is to maintain oxygen permeability and food product respiration pace consistently.

The application of Modified Atmosphere Packaging on some product is relatively mature, such as packaging for small food, coffee and processed meat. Now it is used to pack more and more products covering refrigerated food, ready-to-serve food, particularly pre-sliced fresh farm food, cheeses and sandwiches use a lot of Modified Atmosphere package.

Different type of gas performs different permeability

The design with Modified Atmosphere Packaging System should consider a variety of factors. The most critical factor is relatively concentrations of CO2 and O2. This is mainly determined by the gas concentration in the package and the gas permeability of the packaging material, that is, the proportional control precision of modified atmosphere gas and the gas replacement rate of the packaging material. Modified Atmosphere Packaging material is mostly made by low barrier type that contains high oxygen permeability, differently from vacuum packaging and nitrogen filling package material.

The difference in permeability of material is related to factors such as the aggregation state of the polymer (crystallinity), the gas diffusion and gas solubility created by the polymer structure, and the influence of the additive. The different types of gas applying in the same material have different permeability. In case of the same material, generally gas permeability from high to low is ranked as CO2, O2 and N2, this is in association with dimension (dynamic diameter) and shape of gas molecule. The shorter dynamic diameter of molecule is, the easier diffusion goes. The diffusion rate is also greater. However, diameter is not the only one factor basis to judge permeability, because this is also involved in gas solubility to polymer. In addition, the shape of molecule can also influence permeability. There is a study carrying out a report that rectangular shaped molecule brings high diffusion as well as permeability. The slight change of shape can cause extremely different permeability.

How to make a right choice of Modified Atmosphere Packaging Material

No doubts, the application of Modified Atmosphere Packaging to product is certainly based on property of product to make a proper choice of packaging material permeability. Modified Atmosphere Packaging generally fills with gases mixed by O2, CO2 and N2 or the other mixed combination of O2 and CO2. Therefore, doing precisely test of permeability in O2, CO2 and N2 to the material is necessary while choosing Modified Atmosphere Packaging material. The test of each gas permeability is equally important. Never simply doing detection of O2 permeability to the material and then convert it according to the empirical ration. A fully test of each gas permeability needs to be completed. It can be imagined that if choosing modified atmosphere packaging material by mistake because detection indicator failed or fully test never done, it will not only cause huge economic losses, but also cause a serious waste of resources.