Ascorbic acid, antioxidants optimize irradiated beef quality.

Beef is very susceptible to color changes caused by treating the product with irradiation. Irradiated beef has a brown or greenish-brown color, depending on the freshness of the meat. In beef, irradiation produces sulfur volatiles that are responsible for an off-odor.

Antioxidants may be effective in reducing lipid oxidation and retarding the development of off-odors in irradiated meat by scavenging free radicals. However, there is little information available on the effect of such additives on the quality of irradiated beef. In addition, myoglobin is a small, bright red protein. It is very common in muscle cells and gives meat much of its red color. Reducing the activity of ascorbic acid is effective in keeping myoglobin in a ferrous state.

Scientists at Iowa State University wanted to determine the impact of ascorbic acid and selected antioxidants on the color, lipid oxidation and off-odor volatiles of irradiated beef under aerobic storage conditions. They found that the combined use of ascorbic acid and antioxidants improved the quality of irradiated beef.

Beef loins with different aging time after slaughter were used in this research. The loins were ground. To them were added ascorbic acid (0.1%), an antioxidant mix (sesamol and tocopherol at 200 ppm), or ascorbate plus the antioxidant mix. The loins were irradiated at 2.5 kGy using an electron beam irradiator. The product color, TBARS, redox potential and volatile compounds were determined during aerobic storage.

The scientists found that irradiation significantly increased the darkness and decreased the redness of the ground beef at first. The color changes were more drastic in beef that had a longer aging time. Ascorbic acid prevented changes in color that could have been caused by irradiation throughout the product's refrigerated storage period. Ascorbic acid-added beef had a lower oxidation-reduction potential.

Both the ascorbic acid and the sesamol and tocopherol combination reduced lipid oxidation and sulfur-volatiles created by irradiation. However, the antioxidant effect of ascorbic acid was less than that of the antioxidant mix as storage time increased. Ascorbic acid helped in maintaining the product's red color because it provided reducing conditions for heme pigments--the deep red, nonprotein, ferrous component of hemoglobin. The antioxidant mix was important in controlling lipid oxidation and off- odor volatiles in beef.

Further information. Dong Ahn, Department of Animal Science, Iowa State University, 2276 Kildee Hall, Ames, IA 50011; phone: [phone]; fax: [phone]; email: [e-mail].