Low levels of carbon monoxide optimize fresh ground beef quality.

The use of ionizing radiation to reduce or eliminate spoilage bacteria and pathogenic microorganisms in fresh meat is well-established. Irradiation is clearly an effective way to improve both the safety and shelf life of fresh meat products. However, some studies have produced conflicting results about the effects of low-dose irradiation on the quality of fresh meat.

Studies reporting color changes and lipid alterations in fresh meat because it was irradiated suggest that these changes are dependent upon a product's packaging environment and the irradiation dose. Because the lipid alterations reported in irradiated fresh meat are likely induced by the presence of oxygen, many believe that modified atmosphere packaging using a variety of other gases that displace oxygen can minimize a number of changes.

Researchers at Iowa State University wanted to provide new data on the potential for combining irradiation with modified atmosphere packaging containing low levels of carbon monoxide--less than 1%. They wanted to see if this approach would improve the color and lipid stability of fresh ground beef.

The scientists investigated the impact of a packaging atmosphere--aerobic, vacuum or modified atmosphere with carbon monoxide--on ground beef treated with ionizing radiation at doses of 0 kGy, 2.0 kGy and 4.5 kGy. The modified atmosphere was comprised of carbon dioxide, nitrogen and carbon monoxide.

The researchers measured certain ground beef quality attributes, including lipid oxidation (TBA values), surface color (CIE L*, a*, b*) and odor. Researchers made measurements of color and lipid oxidation using instrumental and sensory analysis during 28 days of product storage at refrigerated (0 C to 25 C) temperatures.

Irradiation significantly decreased the amount of color in the product and increased TBA values and off-odor scores. The modified atmosphere and carbon monoxide treatment provided the highest L* and a* values during the 28-day storage period, regardless of irradiation dose.

The TBA values for modified atmosphere and carbon monoxide packaged samples were well below the levels that might be considered rancid. In addition, sensory scores indicated there was a minimal production of irradiation off-odors with the modified atmosphere and carbon monoxide packaging system.

Incorporating low levels of carbon monoxide, less than 1%, into modified atmosphere packaging systems greatly improves the color and odor quality of irradiated fresh ground beef, thus countering potentially negative color effects of irradiation. Carbon monoxide reduced lipid oxidation when compared to other packaging treatments at a 4.5 kGy irradiation dose and provided a very stable, cherry-red product color.

Further information. J. G. Sebranek, 215 Meat Laboratory, Iowa State University, Ames, IA 50011; phone: [phone]; fax: [phone]; email: [e-mail].