What, you might ask, does that mean? And why are they packaged that way? Are there any risks? There is a great deal of research on MAP and EMAP, the proper gase mixtures, temperatures, methods and packaging materials. We'll just look at the tip of the proverbial iceberg.
Modfication of the packaged atmosphere attempts to lower the oxygen level and increase the carbon dioxide level to slow bacterial growth and the respiration of fruits and vegetables. Carbon monoxide may also be introduced to keep the red color of fresh meats by binding to the hemoglobin. We'll go back to that in a minute. The atmosphere can be introduced to the package by flushing or by exposure through a permeable membrane (EMAP). For more on the process and MAP systems, click here.
Back in the 1930's, ships transporting fruits pumped high levels CO2 into the storage rooms to increase shelf-life. By the 1970s, modified atmosphere packaging was appearing in your local stores, primarily for meats and fish.
In the years since, the technology and the science has rapidly developed and evolved. MAP is used in numerous circumstances. In each case, the gas mixture and the packaging materials are selected to optimize the conditions for the items being packaged. Foods such as meat, fish and cheese are non-respiring, meaning they do not need breath. For these, a film that does not allow gas exchange is used to hold in the MAP gases that are introduced during packaging.
Items that breath (fruits and vegetables) must be treated differently. They must be given enough oxygen to "breathe" while still extending shelf life. A more permeability packaging film allows an optimal equilbrium of oxygen and carbon dioxide to be created.
There is no direct risk to consumers based on the use of MAP or EMAP. In recent years, there has been debate regarding the use of carbon monoxide (CO) in the packaging of red meat. While no risk was found in the use of low levels of CO, the fact that CO maintains the color of the meat and can, in that way, hide visual evidence of spoilage was raised. The European Food Information Council (EFIC) released a report in 2004 reviewing the data. The report is available here.
The field continues to develop and expand as they attempt to minimize waste and loss in the delivery of food to consumers.