Hemocyanin
Hemocyanin, not hemoglobin, is present in the blood of shellfish,
that is, crustaceans and mollusks. Hemocyanins are coppercontaining
proteins, as compared with iron-containing proteins
in hemoglobins, and they combine reversely with oxygen. The
contribution of hemocyanins to seafood quality is not very well
understood. It is suspected that the blue discoloration of canned
crabmeat is associated with a high content of hemocyanin. The
average copper content of blue meat (e.g., 2.8 mg%) is higher
than meat of normal color (e.g., 0.5 mg%) (Ghiretti 1956).
Myoglobin
Myoglobin in fish muscle is retained in the intracellular structure.
In fish muscle, the red, white, and intermediate fibers tend to be
more distinctively segregated than they are in muscle from land
animals. The myoglobin content in muscle of yellowfin tuna
was found to range from 37 to 128 mg% in the light-colored
muscle and from 530 to 22,400 mg% in the dark-colored muscle
(Wolfe et al. 1978). In cod, the deep-seated, dark-colored muscle
is richer in myoglobin than superficial dark-colored muscle
(Brown 1962, Love et al. 1977).
Myoglobin in fish is easily oxidized to a brown-colored metmyoglobin.
The discoloration of tuna during frozen storage is
associated with the formation of metmyoglobin, depending on
temperature and location (Tichivangana and Morrissey 1985).
Greening is a discoloration problem associated with cooking
various tunas. The problem arises from the formation of a
sulfhydryl adduct of myoglobin in the presence of an oxidizing