Bone and Pigments in Meat

Bone. Bones are used as landmarks for identifying the various meat cuts from carcass. When buying meat, keep in mind that bone weighs more than meat and that the higher the proportion of bone to meat, the less the meat yield and the more the cost of the edible portion. The marrow found within the bone will generally be of two different types: 1) yellow marrow, found in the long bones, and 2) red marrow - red because it is supplied with many blood vessels - in the spongy center of other bones. Marrow is a valued food in many cultures and can provide much of the flavor in soups.

Pigments. Many people evaluate a meat’s color when deciding whether or not to purchase a particular meat cut. The color of meat is derived from pigment-containing proteins, chiefly myoglobin, and to a lesser extent, hemoglobin. The so-called “red meats” - beef, pork, sheep, and lamb - have more of these pigments than poultry or fish. Myoblogin receives oxygen from the blood and stores it in the muscles, while hemoglobin transports oxygen throughout the body and is found primarily in the bloodstream. The higher the concentration of myoglobin in raw meat, the more intense its bright red color. A number of factors influence the concentration of myoglobin. Heavily exercised muscle has a higher demand for oxygen, so it is higher in myoglobin and therefore redder than the less exercised muscles. The red color of meat also increases as the animal ages, which is why beef is redder than veal, and mutton is darker than the pink hue of lamb. Meat color also varies from species to species. Beef is darker than lamb, which, in turn, is darker than pork, a meat that is on the pink side with no visible red.

Exposure of meat to oxygen and heat also changes the color of myoglobin, and therefore the meat. After slaughter, meat undergoes several changes in color over time that are due to modifications in the molecular structure of myoglobin and/or hemoglobin. Myoglobin within the meat is purplish red, but once cut and exposed to oxygen, it changes to become bright red - a color indicating freshness and desired by consumers. After a while, meats left in storage may be exposed to bacteria, less oxygen, and/or kept under flourescent or incandescent lights, all of which turn the meat brownish-red. Using plastic warp that is permeable to oxygen allows meat retailers to maintain the bright red color for a longer period of time, while vacuum wrap, which eliminates the oxygen, causes the meat to appear purplish-red. Cooking meat initially converts the color of well-done meat - grayish brown. Storing cooked meat too long causes the denatured protein to further break down, causing the meat to turn yellow, green, or faded.

The food industry uses several methods to keep meat products from turning brown. One such method is the addition of nitrites to processed meats. Nitrites are responsible for keeping packaged bologna and ham permanently pink, while simultaneously reducing the risk of Clostridium botulinum growth.