their breast muscles consist predominantly of
white fibers, while their leg muscles are on
average half white fibers, half red. The breast
muscles of such migratory birds as ducks and
pigeons are predominantly red fibers because
they’re designed to help the birds fly for
hundreds of miles at a time.
Muscle Pigments The principal pigment in
meat is the oxygen-storing protein myoglobin,
which can assume several different forms and
hues depending on its chemical environment.
Myoglobin consists of two connected
structures: a kind of molecular cage with an
iron atom at the center, and an attached
protein. When the iron is holding onto a
molecule of oxygen, myoglobin is bright red.
When the oxygen is pulled away by enzymes
in the muscle cell that need it, the myoglobin
becomes dark purple. (Similarly, hemoglobin
is red in our arteries because it’s fresh from
our lungs, and blue in our veins because it has