The color of meat is caused by myoglobin, depending on which state it is in. Myoglobin is the pigment in meat that transports oxygen from hemoglobin in the blood to the muscles where they are needed. When myoglobin is oxygenated, it turns to oxymyoglobin which has a bright reddish-pink color. This is the color that is usually seen by customers as depicting “freshness”. Oxymyoglobin can become oxidized by losing an electron from its iron atom, thus changing from Fe2+ to Fe3+. This changes it to metmyoglobin which has a brown color. In order to maintain this fresh appearance, meats cuts in retail are packaged using oxygen permeable films. Nitrates and nitrites in meat cures convert myoglobin to nitrosomyoglobin which has a dark red color. After cooking, nitrosomyoglobin is converted to nitrosohemochrome which is a stable light-pink color.
