Generally, beef and lamb have more myoglobin in their muscles than pork, veal, fish, and poultry. Intact males such as breeding bulls have muscle that contains more myoglobin than females (heifers) or steers (castrated males) at a comparable age. However once a calf is weaned and begins to eat grass, its flesh begins to darken. Young cattle are fed primarily milk products to keep their flesh light in colour. The pale muscles of veal carcasses indicate an immature animal, which has a lower myoglobin count than those of more mature animals. This condition does not alter the quality of the meat however, it is generally less attractive to consumers. The condition will remain after the product is cooked and can often be seen on sliced roast beef used in sandwich making. This can often occur during the processing of round steak from the hip primal and can be identified by the rainbow-like colours that appear from the reflection of light off the meat surface. Oxidation can also occur when iron in the meat binds with oxygen in the muscle. This will continue to develop until the iron in the myoglobin oxidizes to the point of the metmyoglobin stage. As soon as meat is cut, oxygen reacts with the myoglobin and creates the bright red colour associated with oxymyoglobin. Oxygen plays two important roles, which affect the colour in opposite ways. The brown colour doesn’t mean there is anything wrong with the product in fact, purchasing meat at this stage is a great way to stock up on cheaper steaks for the freezer.) (You may see steaks with this colour in the discount bin at a supermarket. Brown (metmyoglobin): occurs when the iron in the myoglobin is oxidized, which usually takes about three days after cutting.Cherry red (oxymyoglobin): occurs several minutes after cutting and after exposure to oxygen.Purplish red (myoglobin): occurs immediately after a steak is sliced.As this process happens, the meat colour goes through three stages and three colours that are easy to see, especially on freshly cut beef meats. When animals are no longer alive and air comes in contact with the meat, myoglobin reacts with oxygen in an attempt to reach a state of equilibrium, at which point no further changes occur. Meat colour is associated with two proteins: myoglobin(in the muscle) and hemoglobin(in the blood). This is normal however, inexperienced customers may interpret this as a sign of not being cooked properly. Note: Chicken thighs, even when fully cooked, may have a reddish tinge and blood seepage from the thigh bone. In domestic poultry (chickens and turkeys), there is a difference between breasts (white meat) and thighs and drumsticks (dark meat). In contrast, ducks and geese and most other game birds that fly long distances have exclusively dark meat. Upland game birds, such as partridge and grouse, that fly only for short bursts have white breast meat. The colour of the meat is determined by how the muscle is used.
Meat cutters and cooks may often be asked why different parts of a chicken have white meat and other parts have dark meat, or why duck or game birds have mostly dark meat. Poultry provides a good opportunity to see and learn about the differences in meat colour.
Mutton (sheep over 12 months of age with darker flesh) appeals to an even smaller range of customers. Dark meats such as horse are more popular in Quebec and European countries. The bright red colour of good quality beef, sockeye salmon, and young lamb are naturally appealing, whereas the paler colours of veal and other fish species are less appealing to many (although more sought after by some ethnic groups). Meat colour is significant to consumer acceptance of products. Pure white to grey-white or pink to dark red Table 3 Typical colour of meat from different species Species Typical meat colour for different species is shown in Table 3. Beef shows a range of colour from first being cut to the end of its shelf life (about three days). The post mortem colour development of meat varies greatly from one species to another, with variations in fresh beef being very prominent.
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