Astaxanthin /æstəˈzænθɪn/ is a keto-carotenoid within a group of chemical compounds known as carotenoids, a subclass of the broad group of phytochemicals known as terpenes. Astaxanthin is a metabolite of zeaxanthin and canthaxanthin, containing both hydroxyl and ketone functional groups.
It is a lipid-soluble pigment with red coloring properties, which result from the extended chain of conjugated (alternating double and single) double bonds at the center of the compound. The presence of the hydroxyl functional groups and the hydrophobic hydrocarbons render the molecule amphiphilic.
Astaxanthin is produced naturally in the freshwater microalgae Haematococcus pluvialis, the yeast fungus Xanthophyllomyces dendrorhous (also known as Phaffia rhodozyma) and the bacteria Paracoccus carotinifaciens. When the algae are stressed by lack of nutrients, increased salinity, or excessive sunshine, they create astaxanthin. Animals who feed on the algae, such as salmon, red trout, red sea bream, flamingos, and crustaceans (shrimp, krill, crab, lobster, and crayfish), subsequently reflect the red-orange astaxanthin pigmentation.
Astaxanthin is used as a dietary supplement for human, animal, and aquaculture consumption. Astaxanthin from algae, synthetic and bacterial sources is generally recognized as safe in the United States. The US Food and Drug Administration has approved astaxanthin as a food coloring (or color additive) for specific uses in animal and fish foods. The European Commission considers it as a food dye with E number E161j. The European Food Safety Authority has set an Acceptable Daily Intake of 0.2 mg per kg body weight, as of 2019. As a food color additive, astaxanthin and astaxanthin dimethyldisuccinate are restricted for use in Salmonid fish feed only.