Modified atmosphere is a common technical definition that describes the practice of modifying the composition of the internal atmosphere of a package, most commonly food packages, in order to improve the shelf life.

The modification process often tries to lower the amount of oxygen in order to slow down the growth of aerobic lifeforms 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.

Modified-atmosphere packaging or MAP, as the term implies, is to change the mix of gases inside a package. Its primary benefit to meat and poultry is to extend the shelf life, but it has other effects, such as preserving or enhancing color, texture and flavor, depending on the gas mix and product.

As commonly known in our industry, meat and meat products are particularly susceptible to bacterial growth due to their high water activity. When cut, meat surfaces exposed to ambient air provide excellent breeding grounds for most bacteria.

That said, poultry is also very susceptible to bacterial spoilage, evaporation loss, off-odor, discoloration and biochemical deterioration. The sterile poultry tissue becomes contaminated during the evisceration process. According to Germany-based engineering firm, The Linde Group, the practical shelf-life of gas-packed poultry is somewhere between 16 and 21 days. In contrast to red meats, poultry does not undergo irreversible discoloration of the meat’s surface in the presence of O2. The spoilage of raw poultry is mainly caused by microbial growth, fuelled by the pseudomonas and achromobacter genera in particular, the company says. These aerobic bacteria are effectively inhibited by CO2 in MAP.

MAP is a technique in which modified-atmosphere is put into the package upon filling, and designed to extend the shelf life and/or quality of the product by reducing oxidation with less oxygen, adding bacteriostatic properties with carbon dioxide or ethanol, enhancing color, etc., explains Kenneth S. Marsh, Ph.D., and president of Central, S.C.-based Kenneth S. Marsh & Associates Ltd., consultants to the food, pharmaceutical and packaging industries.

“MAP can extend quality and shelf life,” he says. “By choosing the correct atmosphere, benefits accrue for a variety of products.”

Food safety is the No. 1 concern of the meat industry, and it is one of the best reasons for purchasing case-ready MAP products, says Randy Huffman, Ph.D., and president of the American Meat Institute Foundation (AMIF).

“Because this product is prepared under the watchful eye of the USDA and there are few chances of cross-contamination after the meat leaves the processor, these products enjoy a higher food-safety profile,” he says. “Also, certain MAP formats use gas combinations that have been shown to provide antimicrobial properties. Other benefits include the opportunity to improve inventory control and reduce ‘out-of-stocks,’ as well as the leak-proof nature of the package which can improve the consumer appeal.”

Case-ready MAP provides a higher margin of safety for fresh meat products because it is produced and packaged under USDA inspection, says Huffman.

“Additionally, since it is packaged at the plant, there are fewer hands touching the product and less opportunity for cross-contamination before it reaches the consumer,” he says. “Case-ready MAP for ground beef also provides the retailer with the benefit of not having to store generated trimmings on hand at each store, which can create significant logistical and safety challenges.”

Modified-atmosphere packages are innovative formats that improve the quality and safety of fresh meat products, says Huffman.

“The tamper-proof packages leave a space between the meat on the tray and the top of the package,” he says. “Various combinations of gases can be added to this space, including oxygen, nitrogen, carbon monoxide and carbon dioxide. These are flushed into the package at very specific ratios in order to achieve a desired effect.”

Consumers have reacted very favorably to this format of packaging because it’s leak-proof and it prevents premature browning of the meat, says Huffman. He adds that new research has shown that low-oxygen formats of MAP can improve the overall food-safety profile over traditionally packaged fresh-meat products. MAP does so by deterring the growth of E. coli O157:H7 during refrigerated and even temperature abuse storage.

Indeed, acceptance of change at the retail meat case continues to be a challenge, but times are changing.

“There continues to be an incremental increase in the availability of case-ready MAP products in the retail meat case as more consumers, retailers and processors recognize the potential benefits,” Huffman says.

The biggest challenge Marsh has observed with this packaging method is a misunderstanding of what MAP truly is.

“I have seen situations in which packaging people expected the product people to assess safety, and vice versa, with potentially hazardous results. MAP can extend quality, but it is not a processing technique,” he says. “One company that I consulted with utilized low oxygen to reduce oxidation and wanted me to model how long it would take for the oxygen level to increase to 3 percent — their maximum oxygen content.

“What they missed was oxygen could be used within the package and make the package atmosphere anaerobic, and thereby allow growth of pathogens that could kill people. Neither packaging nor product development had considered this possibility. The company dropped the MAP packaging idea for this product because of this potential hazard.”

There has been true expansion of benefits and products in the MAP arena, explains Huston Keith, market research and product development expert and the principal and founder of Marietta, Ga.-based Keymark Associates.

“Two recent trends are the increased use of MAP for deli-sliced pre-packaged lunch meats and carbon monoxide (CO) for fresh red meats,” Keith says. “While deli-sliced meats could be preserved as long, and less expensively, with vacuum packaging, vacuum often compresses the thin slices so that they cannot be pulled apart.”

Trace amounts of CO keep fresh meat red far longer than high levels (60 to 80 percent) of oxygen, which ultimately leads to meat deterioration, Keith adds.

“CO has been controversial because meat can stay red past a safe period of consumption, possibly confusing consumers who rely on the red color as an indicator of freshness,” he explains. “However, there is no evidence that this is a problem, and it was publicized by an anti-oxidant maker who feared a loss of sales [in the wake of the use of CO in MAP applications].”

The National Meat Case Study found that case-ready products have grown to 60 percent of the meat case, says Huffman.

“This is up from 49 percent in 2002, and includes products from every red meat and poultry species commercially consumed,” he says. The industry will continue to look for new packaging materials and methods that reduce packaging waste and improve the shelf life and appearance of these products, while at the same time, finding ways to make the systems more cost-effective, he adds.

“As consumers spend more time out of the home and have less time to prepare meals, the opportunity to add value to these products exists by enhancing the products with added flavors, marinades, or rubs,” Huffman says. “This allows consumers to purchase an appealing, safe product that is easy to handle and ready to cook with little preparation time necessary.”