What gives red meat its color?
Monika Gibis researches and teaches at the University of Hohenheim in the field of food material science, which she heads as deputy head. The professor's research focuses on meat consumption and the discoloration of packaged beef, among other things.
»After slaughter and bleeding the carcass, there is no blood left in the meat. The red coloring does not come from the blood, but from the muscle proteins. Myoglobin, the name of the red protein pigment, stores oxygen in the muscles. Like the blood pigment hemoglobin, myoglobin contains iron. However, the substances differ on a molecular level. While hemoglobin has four iron atoms in its structure, myoglobin only has one. The iron atoms can be in different states of oxidation, which influences the color of the meat. Freshly cut meat has a red-violet color. This is because the myoglobin has not yet come into contact with oxygen. As soon as the meat is cut, however, the myoglobin binds the oxygen and becomes oxymyoglobin, which gives it the bright red color. Consumers associate this color with the meat being fresh.
However, if it is exposed to air for a long time, the iron in the myoglobin can oxidize with oxygen. This causes the meat to turn brown. This condition is known as metmyoglobin. The brown spots in the meat are not necessarily a sign of spoilage, but rather of iron oxidation. In some cases, the brown color can also be seen in vacuum-packed meat. We cannot yet explain clearly why this is the case. It is an ongoing research project.
The oxidation that turns red to brown can be accelerated by heating. When meat is cooked, the color changes quickly because the high temperatures cause an irreversible change in the meat proteins. The red myoglobin oxidizes to brown metmyoglobin. The red color also changes when the meat spoils, which is another complex chemical process triggered by microorganisms. As long as the meat does not have a bad smell, brown discoloration does not necessarily mean that it is no longer edible, but is often a normal process triggered by brief contact with air, type of packaging or temperature change."
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