Mechanisms of color change and the prevention of off-color and off-flavor in irradiated meat

To determine the effect of irradiation on the oxidative quality changes during the storage, pork loin and turkey breast muscles were irradiated using an electron beam. Irradiation accelerated lipid oxidation, increased redness, and produced several sulfur (S)-volatiles that were responsible for the characteristic irradiation off-odor. This quality deterioration by irradiation was dependent on packaging conditions. Lipid oxidation was more problematic when meat was aerobically stored, whereas the production of S-volatiles was greater in vacuum-packaged irradiated raw meats. But when meat was freezer-stored, aerobic packaging was more susceptible to the production of both oxidation-dependent and S-volatiles. Irradiation made the color of meats redder and the redness was more distinct and stable under vacuum conditions. In irradiated meat, the production of carbon monoxide (CO), which can bind to myoglobin as a sixth ligand, was proportional to the irradiation dose. Oxidation-reduction potential was also decreased by irradiation indicating that more reducing conditions were supplied to heme pigments. Thus, it can be concluded that the increased a*-values in irradiated meat was caused by heme pigment-CO ligand formation. The absorption spectra of meat drip also showed that the peak wavelengths of irradiated meat were similar to those of the CO-myoglobin. Therefore, we suggest that CO-myoglobin be a major heme pigment responsible for the red or pink color in irradiated meats. These color changes and the mechanisms in irradiated raw meat were similar in irradiated precooked meat. A few strategies to reduce the oxidative quality deterioration of irradiated meats were studied. Addition of an antioxidant (sesamol, gallate, Trolox, or α-tocopherol) or their combination was effective in reducing the S-volatiles in vacuum-packaged irradiated meats or in controlling lipid oxidation in aerobically packaged irradiated ones. A modified packaging concept (double-packaging; combined use of vacuum and aerobic packaging) was also effective in eliminating S-volatiles and minimizing lipid oxidation during the storage. Especially, gallate + α-tocopherol along with double-packaging reduced effectively the red color of irradiated raw and cooked meats. These beneficial effects of double-packaging and antioxidant were more critical in irradiated cooked meat, and it was a very effective method to control the oxidative quality changes of irradiated meats.