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Processing Technology
Optimizing CO packaging to extend fresh meat shelf life
By Joseph Sebranek Ph.D on 5/1/2010
In this article:
Using CO for MAP applications
Other applications for CO packaging
Related articles
Comments and insights
The use of carbon monoxide (CO) for modified atmosphere packaging (MAP) of fresh meat is a relatively recent option for the meat industry. Approval of CO for packaging of fresh meat for distribution was first approved by USDA-FSIS in 2002. This was followed in 2004 with approval of CO for retail packaging applications.
This gas is extremely effective as part of a MAP system for fresh meat because CO binds firmly to meat pigment to produce a cherry red color that is visually identical to the red color that results when fresh meat is exposed to air. Fresh meat color "bloom" in air is the result of oxygen binding to the meat pigment, but this is a relatively fragile color even at high oxygen concentrations.
The retail shelf life of fresh meat is often limited by the color loss that typically occurs within a few days of retail display. MAP systems with high oxygen concentrations improve color life over that of a permeable overwrapped package, but the high-oxygen environment is prone to oxidized off-flavors and other oxidation-induced changes. CO-based meat color, on the other hand, is much more stable and will last for weeks instead of days under controlled temperature conditions. Further, the CO atmosphere is typically devoid of oxygen, which achieves a significant shelf-life extension over package atmospheres that include oxygen.
Use of CO for packaging of fresh meat has been the source of considerable controversy, with numerous critics in the news media and elsewhere raising claims of likely product spoilage while color remains attractive. The controversy was initiated by a petition to FDA in 2005 requesting elimination of the use of CO for meat packaging. FDA chose not to act on the petition, and CO as a component of MAP has since established a stellar track record of success for those who have chosen to continue use of this packaging technology.
Using CO for MAP applications
Use of CO as part of MAP is typically done with a gas mixture of 0.4 percent CO, 30 percent carbon dioxide (CO2) and 69.6 percent nitrogen (N2). This mixture offers the advantage of a stable fresh meat color for at least 28 days for ground beef and at least 35 days for steaks and roasts with no oxidized off-flavors or other oxidative changes. The use of CO2 introduces a bacteriostatic agent to the MAP system that slows growth of spoilage and pathogenic bacteria to contribute to the shelf-life extension. At the same time, it is possible for bacterial numbers to reach a high level while the color remains attractive if the product is held for an extended period of time. This is why, in 2008, a statement was added to product labels that reminds consumers, "Color is not an accurate indicator of freshness. Refer to use- or freeze-by date."
While CO in MAP with CO2 is well established as a highly effective means of improving fresh meat color stability and extending shelf life, questions have remained about the most effective use of package headspace to optimize a CO packaging system. Because the concentration of CO is constant at 0.4 percent in commercial applications, changes in headspace volume mean that a differential amount of CO will be available to penetrate the meat surface, depending on the total headspace volume available.
Recent research has suggested that typical meat product packages with MAP have a headspace of about 1.5 liters (L). This study evaluated a variety of headspace volumes and CO concentrations and determined that increased CO concentration in a reduced headspace volume had a greater effect on meat color than the total available quantity of CO in the headspace. The authors of this study concluded that reducing package headspace to 0.4 L with 0.8 percent CO in MAP would result in more color development with less total CO released to the environment when the package is opened, compared with conventional-sized packages with 0.4 percent CO. If the 0.8 percent CO could be used, this would offer additional advantages of smaller packages, less packaging materials used and improved efficiency in packing and shipping.
Other applications for CO packaging
One of the unique advantages of CO in MAP packaging is that the color stability of fresh meat achieved by CO offers the opportunity to combine CO packaging with other technologies that inhibit or destroy bacteria but may have a negative effect on meat color. For example, increasing the concentration of CO2 in MAP will increase the antimicrobial effect of this gas but also may begin to cause discoloration of the product in aerobic atmospheres. Use of CO will provide attractive color with high concentration of CO2. Research on fresh pork sausage reported that a high CO2 atmosphere with CO resulted in about 10 days more shelf life in terms of bacterial spoilage.
However, it is important to remember that CO2 is highly soluble in meat, and a high concentration in the package atmosphere initially can result in package collapse when the gas is absorbed. Most MAP systems limit CO2 to about 30 percent and add N2, which is not soluble in meat, to the gas mixture to avoid package collapse.
Another example of combining technologies, and one that has been commercialized, is the use of CO packaging for pasteurization of fresh meat by irradiation. Irradiation of fresh beef, for example, typically results in a color change if aerobic or vacuum packaging is used, but if CO packaging is used, the bright red color expected of fresh beef is retained. Because irradiation pasteurization greatly reduces the bacteria present in or on the product, shelf life is dramatically improved. Commercially available refrigerated ground beef produced with this combination of technologies had an advertised guaranteed retail shelf life of 38 days. Unfortunately, this product was not a commercial success, probably because of negative consumer perceptions of irradiation processing.
Optimizing CO packaging to extend fresh meat shelf life
By Joseph Sebranek Ph.D on 5/1/2010
In this article:
Using CO for MAP applications
Other applications for CO packaging
Related articles
Comments and insights
The use of carbon monoxide (CO) for modified atmosphere packaging (MAP) of fresh meat is a relatively recent option for the meat industry. Approval of CO for packaging of fresh meat for distribution was first approved by USDA-FSIS in 2002. This was followed in 2004 with approval of CO for retail packaging applications.
This gas is extremely effective as part of a MAP system for fresh meat because CO binds firmly to meat pigment to produce a cherry red color that is visually identical to the red color that results when fresh meat is exposed to air. Fresh meat color "bloom" in air is the result of oxygen binding to the meat pigment, but this is a relatively fragile color even at high oxygen concentrations.
The retail shelf life of fresh meat is often limited by the color loss that typically occurs within a few days of retail display. MAP systems with high oxygen concentrations improve color life over that of a permeable overwrapped package, but the high-oxygen environment is prone to oxidized off-flavors and other oxidation-induced changes. CO-based meat color, on the other hand, is much more stable and will last for weeks instead of days under controlled temperature conditions. Further, the CO atmosphere is typically devoid of oxygen, which achieves a significant shelf-life extension over package atmospheres that include oxygen.
Use of CO for packaging of fresh meat has been the source of considerable controversy, with numerous critics in the news media and elsewhere raising claims of likely product spoilage while color remains attractive. The controversy was initiated by a petition to FDA in 2005 requesting elimination of the use of CO for meat packaging. FDA chose not to act on the petition, and CO as a component of MAP has since established a stellar track record of success for those who have chosen to continue use of this packaging technology.
Using CO for MAP applications
Use of CO as part of MAP is typically done with a gas mixture of 0.4 percent CO, 30 percent carbon dioxide (CO2) and 69.6 percent nitrogen (N2). This mixture offers the advantage of a stable fresh meat color for at least 28 days for ground beef and at least 35 days for steaks and roasts with no oxidized off-flavors or other oxidative changes. The use of CO2 introduces a bacteriostatic agent to the MAP system that slows growth of spoilage and pathogenic bacteria to contribute to the shelf-life extension. At the same time, it is possible for bacterial numbers to reach a high level while the color remains attractive if the product is held for an extended period of time. This is why, in 2008, a statement was added to product labels that reminds consumers, "Color is not an accurate indicator of freshness. Refer to use- or freeze-by date."
While CO in MAP with CO2 is well established as a highly effective means of improving fresh meat color stability and extending shelf life, questions have remained about the most effective use of package headspace to optimize a CO packaging system. Because the concentration of CO is constant at 0.4 percent in commercial applications, changes in headspace volume mean that a differential amount of CO will be available to penetrate the meat surface, depending on the total headspace volume available.
Recent research has suggested that typical meat product packages with MAP have a headspace of about 1.5 liters (L). This study evaluated a variety of headspace volumes and CO concentrations and determined that increased CO concentration in a reduced headspace volume had a greater effect on meat color than the total available quantity of CO in the headspace. The authors of this study concluded that reducing package headspace to 0.4 L with 0.8 percent CO in MAP would result in more color development with less total CO released to the environment when the package is opened, compared with conventional-sized packages with 0.4 percent CO. If the 0.8 percent CO could be used, this would offer additional advantages of smaller packages, less packaging materials used and improved efficiency in packing and shipping.
Other applications for CO packaging
One of the unique advantages of CO in MAP packaging is that the color stability of fresh meat achieved by CO offers the opportunity to combine CO packaging with other technologies that inhibit or destroy bacteria but may have a negative effect on meat color. For example, increasing the concentration of CO2 in MAP will increase the antimicrobial effect of this gas but also may begin to cause discoloration of the product in aerobic atmospheres. Use of CO will provide attractive color with high concentration of CO2. Research on fresh pork sausage reported that a high CO2 atmosphere with CO resulted in about 10 days more shelf life in terms of bacterial spoilage.
However, it is important to remember that CO2 is highly soluble in meat, and a high concentration in the package atmosphere initially can result in package collapse when the gas is absorbed. Most MAP systems limit CO2 to about 30 percent and add N2, which is not soluble in meat, to the gas mixture to avoid package collapse.
Another example of combining technologies, and one that has been commercialized, is the use of CO packaging for pasteurization of fresh meat by irradiation. Irradiation of fresh beef, for example, typically results in a color change if aerobic or vacuum packaging is used, but if CO packaging is used, the bright red color expected of fresh beef is retained. Because irradiation pasteurization greatly reduces the bacteria present in or on the product, shelf life is dramatically improved. Commercially available refrigerated ground beef produced with this combination of technologies had an advertised guaranteed retail shelf life of 38 days. Unfortunately, this product was not a commercial success, probably because of negative consumer perceptions of irradiation processing.
