Why lobsters turn red in the pot and farmed salmon flesh looks pink
A live lobster is dull because its red pigment, astaxanthin, is locked onto shell proteins. Heat unravels those proteins, the pigment breaks free, and the shell blushes. The same molecule, made by stressed algae and passed up the food chain, colours flamingos, shrimp and wild salmon, and is added to feed for farmed ones.
Astaxanthin belongs to the carotenoids, the family of pigments that includes beta-carotene. Its red comes from a long central chain of alternating single and double bonds, and hydroxyl and ketone groups at each end make it part water-friendly and part oily. Freshwater microalgae called Haematococcus pluvialis produce it when starved of nutrients, exposed to extra salt or blasted by sunlight, reaching about 3.8 percent of their dry weight. A yeast and a bacterium make it too.
Animals cannot build it themselves, so they collect it through diet. Salmon, red sea bream, flamingos, krill, crabs and crayfish all owe their red or orange hues to it, and levels vary between individuals depending on what they eat. In shellfish it sits almost entirely in the shell rather than the flesh. The molecule is also a strong antioxidant, shielding cell membranes from damage by free radicals, a benefit shared with the creatures that eat it.
Its structure was confirmed by synthesis in 1975, and today nearly all astaxanthin used in fish farming is made chemically, a market worth about 1 billion dollars in 2019. Synthetic versions contain its three mirror-image forms in roughly 1:2:1 proportions, whereas natural sources vary. Coloured pigments account for some 15 to 25 percent of the cost of commercial salmon feed, and they also deepen the colour of egg yolks.
That practice reached the courts in the United States, where class actions accused grocery chains of failing to label treated salmon as colour added. The chains quickly relabelled, and a Seattle judge later dismissed the damages suit, ruling that enforcing food law was the government's job. In Europe the pigment is listed as food dye E161j.
Source: Astaxanthin
