Modified atmosphere is the practice of modifying the composition of the internal atmosphere of a package (commonly food packages, drugs, etc.) in order to improve the shelf life. The modification process often tries to lower the amount of oxygen (O2), moving it from 20.9% to 0%, in order to slow down the growth of aerobic organisms and the speed of oxidation reactions.
The removed oxygen can be replaced with nitrogen (N2), commonly acknowledged as an inert gas, or carbon dioxide (CO2), which can lower the pH or inhibit the growth of bacteria. Carbon monoxide can be used for preserving the red color of meat.
Re-balancing of gases inside the packaging can be achieved using active techniques such as gas flushing and compensated vacuum or passively by designing “breathable” films known as equilibrium modified atmosphere packaging (EMAP).
Packets containing scavengers may be used. Controlled Atmosphere Storage (CAS) was used from the 1930s when ships transporting fruits had high levels of CO2 in their holding rooms, thus increasing the shelf-life of the product.
In the 1970s MA packages reached the stores when bacon and fish were sold in retail packs in Mexico.
Since then development has been continuous and interest in MAP has grown due to consumer demand.
This has led to advances, for example in the design and manufacturing of Bacon films.
New techniques have been designed, such as the use of anti-fogging layer to improve product visibility.
From MAP a new packaging technique, EMAP, has been developed. The three major commodity types are fruits and vegetables, meat and meat products, and seafood.
Many products such as red meat, seafood, minimally processed fruits and vegetables, pasta, cheese, bakery goods, poultry, cooked and cured meats, ready meals and dried foods are packaged under MA.
It has been estimated that 25-40% of all fresh produce harvested will not reach the consumers table, due to spoilage and mishandling that occurs during distribution.
Modified Atmosphere Packaging (MAP) is a technique used for prolonging the shelf-life of fresh or minimally processed foods.
In this preservation technique the air surrounding the food in the package is changed to another composition.
This way the initial fresh state of the product may be prolonged. It is the shelf-life of perishable products like meat, fish, fruits and vegetables that will be prolonged with MAP since it slows the natural deterioration of the product. MAP is used with various types of products.
The mixture of gases in the package depends on the type of product, packaging materials and storage temperature.
Meat, fish and cheese are non-respiring products needing very low gas permeability films and so-called high barrier films are used. The initial flushed gas-mixture will be maintained inside the MA package.
Conversely, fruits and vegetables are respiring products where the interaction of the packaging material with the product is important and so low barrier or so-called high permeability films are used for these.
So long as the permeability (for O2 and CO2) of the packaging film is adapted to the product's level of respiration, an equilibrium modified atmosphere will be established in the package and the shelf-life of the product will increase.
Among fresh-cut produce Equilibrium Modified Atmosphere Packaging (EMAP) is the most commonly used packaging technology.
When packaging vegetables and fruits the gas atmosphere of package is not air (O2 21%; CO2 0.038%; N2 78%) but consists usually of a lowered level of O2 and a heightened level of CO2.
This kind of package slows down the normal respiration of the product to prolong its shelf-life. Of course there are other factors, like the size of the product, severity of preparation, maturity of the product and type of tissue that have an effect to the shelf-life of EMA packaged produce.
Two techniques are used in the industry to pack vegetables. Namely gas-flushing and compensated vacuum.
In gas-flushing the desired gas mixture is instilled in quantity into the packaging, pushing out the air, whereas in compensated vacuum the air is removed and the desired gas mixture then instilled. The label "packaged in a protective atmosphere" can refer to either of these.
An example of a gas mixture used for non-vegetable packaged food (such as crisps) is 99.9% nitrogen gas, which is inert at the temperatures and pressures to which the packaging is subjected.