|MadSci Network: General Biology|
Because myoglobin is used for oxygen storage, the amount of usage a muscle gets will determine the amount of myoglobin in the fibers. Muscles are composed of two different types of muscle fibers which vary in proportions between muscles. Fast-twitch, or white fibers, have a low myoglobin content, since they depend on anaerobic Glycolysis for energy production. Slow-twitch, or red fibers have a high myoglobin content, since they depend on the aerobic TCA or Krebs' Cycle for energy production. So dark meat color is a result of a relatively high concentration of slow-twitch fibers in the muscle of the animal. Muscles that are used constantly, like legs, have more slow-twitch fibers, so their meat is much darker, than muscles that get little use, like the wings on a chicken. In fact, if you look at the wings of a birds that flies alot, like a duck, the meat is very red.
Other factors contribute to the myoglobin content of a muscle like the age and size of the animal. Beef is darker than veal because muscles from older animals often have higher myoglobin concentrations. Likewise, smaller animals, like rabbits (0.02 percent myoglobin), typically have a lower myoglobin concentration and lighter colored meat than larger animals, like horses (0.7 percent myoglobin), which have very high concentrations of myoglobin and dark colored meat. This is due to differences in basal metabolic rates, since larger animals have a lower metabolism. Also, deep-diving animals, like whales (7 percent myoglobin), rely on their muscles' ability to store oxygen between trips to the surface to refill their lungs, and so have very dark purple meat.
To summarize: chickens are small, flightless animals, so wing and breast meat are light in color (low myoglobin); deer are large, active animals, so venison is very dark in color (high myoglobin).
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