In general, carbon dioxide has a strongly inhibiting effect on the growth of bacteria in meat and fowl. The aerobic bacteria genus Pseudomonas forms the biggest threat to fresh meat.
The discolouration of meat due to oxidation of the red pigment is a particular challenge. In order to maintain the red colour, the packaging atmosphere for red meat must have a high level of oxygen content (60-80%). This keeps oxygen levels in the myoglobin of the meat high. Meat with lots of pigment, such as beef, requires higher concentrations of oxygen compared to meat with less pigment, such as pork.
With the correct MAPAX mixtures, the practical shelf life for meat intended for the consumer market can be extended from 2-4 days to 5-8 days at 4˚C. In the event of packaging for the wholesale trade, shelf life can be extended further by means of a higher CO2 content.
Fowl is very sensitive to bacterial growth, loss of weight due to evaporation, development of unpleasant smells, discolouration and biochemical decay. The tissue of fowl can easily become contaminated whilst gutting the fowl.
The practical shelf life of fowl packed under gas conditions ranges from 16 to 21 days. The volume of the surplus space in the packaging must preferably match that of the product volume. Fowl, contrary to red meat, is not sensitive to the irreversible discolouration of the meat surface due to the absence of oxygen.
The decay of fowl is mainly caused by bacterial growth, more in particular by the Pseudomonas and Achromobacter genera. The growth of these aerobic bacterial types is effectively inhibited by protective atmospheres containing CO2. Substantially extending the shelf life of fowl requires CO2 levels in excess of 20%.
In order to prevent issues with squeezed packaging and too much loss of moist in raw fowl, the gas/product proportion must be increased when using higher concentrations of CO2 content. If the packaging is not squeezed (e.g. in the event of bulk or wholesale-size packaging), it is recommended to use 100% CO2. Nitrogen is used as inert filling gas in both packaging for the retail trade and in bulk packaging with protective atmosphere.