why do crustaceans turn pink when cooking?

Answer 1

The red pigment common to all decapod (shrimp, prawn, crab, lobster) exoskeletons (shells) is letons (shells) is astaxanthin, a carotenoid (like b-carotene, the pigment that makes fruits red-orange) found in many organisms from bacteria to birds. In lobsters, as in many decapods, astaxanthin is not a free pigment, but is complexed with a protein called a -crustacyanin, which alters the resonance of astaxanthin such that the complex acts as a blue-green pigment. As mentioned above, astaxanthin is heat stable, while the a-crustacyanin protein is not, so boiling the lobster shell denatures the blue-green a-crustacyanin releasing the red-orange astaxanthin.

Answer 2

From Info Please:

"Why does a lobster turn red when cooked?
The red pigment is the most stable component of the coloring in a lobster shell. The greens and browns which darken the shell in a live lobster are destroyed by cooking."