Epithelial Discoloration
The market value of squid is related to the contraction state of
its epidermal chromatophores, called ommochromes. In recently
harvested, prerigor squid, the pigment is dispersed throughout
the chromatophores; hence, the dark red-brown appearance of
the epithelial tissue. Following rigor mortis, the pigment cells
contract, giving the skin a pale, light coloration dotted with dark
flecks. The continued storage of squid results in a structural deterioration
of the ommochrome membrane, leading to bleeding
of pigment and downgrading of quality. The dark brown coloration
characteristic of very fresh squid can be retained during
processing, for example, by freezing or dehydration. However,
improper storage of frozen or dried squid will result in chromatophore
disruption and red discoloration of the meat (Hink
and Stanley 1985).
The frozen storage of some fish may result in subcutaneous
yellowing of flesh below the pigmented skin (Thompson and
Thompson 1972). Apparently, freezing or other processes that
disrupt chromatophores can lead to the release of carotenoids
and their migration to the subcutaneous fat layer. Subcutaneous
yellowing that occurs during the prolonged storage of frozen fish
can originate from other causes, that is, yellowing associated
with lipid oxidation and carbonyl-amine reactions