Carbon monoxide is approved for use in MAP for meat systems (USDA FSIS, 2013) at levels of 0.4% in combination with 20 to 30% CO2. Carboxymyoglobin is much more stable toward oxidation than oxymyoglobin due to the stronger affinity of CO for the iron porphyrin site on the myoglobin molecule. It is believed that this stable red color may conceal spoilage and place consumers at risk (Pattron, 2007). Cornforth and Hunt (2008) reported that the two major disadvantages of CO-MAP included a negative image of CO by consumers because it is a potentially hazardous gas, and concern that products might look fresh even though bacterial levels are high and the product is spoiled. However,Watts, Wolfe, and Brown (1978) found that CO-treated ground beef did not remain red indefinitely. When ground beef was treated with 1% CO and then exposed to air, CO was slowly lost (T1/2 = 3 days), and there was an 85% loss of CO after cooking. CO is also considered a processing aid and therefore, is not required to appear on the product label to inform consumers of its use in the product.