Most of the people believe that red meat’s red juice is blood. But they are wrong. When you buy raw meat from a store, it will contain almost no blood. The red juice is a mixture of a protein called myoglobin and water.
The myoglobin can be found in muscle cells. It has the ability to store oxygen. Myoglobin contains high level of red pigments. This is why raw meat is red. The more myoglobin it contains, the redder it will be. The main difference between red meat and white meat is that the former contains myoglobins, while the latter does not. In most mammals myoglobin levels are high and that is why the meat is redder, as compared to poultry.
The protein reacts to the heating process. iron atoms of the myoglobin lose electrons and they move up to a higher oxidation level. This causes meat to turn from pinkish-red to brown.