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By Harold McGee
Published 2004
Meat pigments. Left: The heme group, a carbon-ring structure at the center of both hemoglobin and myoglobin molecules that holds oxygen for use by the animal body’s cells. The protein portion of these molecules, the globin, is a long, folded chain of amino acids, and is not shown here. Right: Three different states of the heme group in uncooked meat. In the absence of oxygen, myoglobin is purple. Myoglobin that has bound a molecule of oxygen gas is red. When little oxygen is available for some time, the iron atom in the heme group is readily oxidized—robbed of an electron—and the resulting pigment molecule is brownish (right).