Track carbon dioxide concentrations in MAP systems.

Modified atmosphere packaging (MAP) systems have been used with meat and meat products for nearly two decades. Generally, MAP offers quality protection. It can extend the shelf life of products by up to four times, compared with storage under air. The use of MAP with vacuum packaging or gas packaging in various mixtures of nitrogen and carbon dioxide inhibits the growth of aerobic microorganisms and slows food deterioration caused by oxidation.

A product packaged in a MAP system keeps its fresh appearance. With MAP for instance, the pink color of meat products is more stable without gray shades, and the flavor is not influenced by rancid products. But MAP must be used properly, such as in combination with antimicrobial hurdles like salt, water activity, smoking, chilling storage and bacteriocins.

But variations in carbon dioxide levels can impact the MAP system. It is important to keep an eye on these changes, as they affect the quality of the end product. Changes in levels of carbon dioxide are caused mainly by the absorption activities of the product.

With this in mind, scientists at the Prague Institute of Chemical Technology (Department of Food Preservation and Meat Technology, 166 28 Prague 6, Technicka 3, Czech Republic) studied the changes in MAP systems during the storage of packaged sliced Lyoner sausage. Samples of the sausage (200 g) were packaged in round thermoformed trays sealed by plastic film using a MA of pure nitrogen, carbon dioxide or their mixtures containing 25% and 50% carbon dioxide.

Empty packages without meat product were used as the controls. The samples were stored for eight weeks at 4 C. Carbon dioxide concentrations in MA during storage changed in a different way, depending on the initial content in the inner atmosphere. The changes were caused mainly by absorption or desorption of this gas in water or the fat phase of sausage and by microbial, or enzymatic, production of carbon dioxide. The influence of gas diffusion through the packaging film was less important.

In packages with an initial carbon dioxide level of 100% and sometimes with that of 50%, a considerable pressure decrease occurred, known as the pseudovacuum effect. The changes in the oxygen level were caused by the oxidation of the meat and by diffusion through the packaging film. When the pseudovacuum effect occurred, levels of residual oxygen increased in the small head space to the level close to its concentration in air.

Nitrogen as an inert gas neither dissolved considerably in meat products, nor reacted with the meat product compounds. Changes in its concentration in MAP systems were influenced by its diffusion through the plastic film and by variations of the total volume of the head space in the packages.

Further information. Petr Pipek; phone: [phone]; fax: [phone]; email: [e-mail].