A naturally occurring carotenoid (yellow, orange, or red pigment), originally isolated from lobsters, but also found in other crustaceans and certain fish, like salmon. Studies have shown that long-term supplementation with astaxanthin may help slow skin aging via its anti-inflammatory and antioxidant effects. Astaxanthin /æstəˈzænθɪn/ is a keto-carotenoid with various uses including dietary supplement and food dye. It belongs to a larger class of chemical compounds known as terpenes (as a tetraterpenoid). Astaxanthin is classified as a xanthophyll (originally derived from a word meaning "yellow leaves" since yellow plant leaf pigments were the first recognized of the xanthophyll family of carotenoids), but currently employed to describe carotenoid compounds that have oxygen-containing components, hydroxyl (-OH) or ketone (C=O), such as zeaxanthin and canthaxanthin. Indeed, astaxanthin is a metabolite of zeaxanthin and/or canthaxanthin, containing both hydroxyl and ketone functional groups. Like many carotenoids, astaxanthin is a lipid-soluble pigment. Its reddish colour is due to the extended chain of conjugated (alternating double and single) double bonds at the centre of the compound.

Astaxanthin is a blood-red pigment and is produced naturally in the freshwater microalgae Haematococcus pluvialis and the yeast fungus Xanthophyllomyces dendrorhous (also known as Phaffia rhodozyma[5]). When the algae is stressed by lack of nutrients, increased salinity, or excessive sunshine, it creates astaxanthin. Animals who feed on the algae, such as salmon, red trout, red sea bream, flamingos, and crustaceans (i.e. shrimp, krill, crab, lobster, and crayfish), subsequently reflect the red-orange astaxanthin pigmentation to various degrees.

Astaxanthin can also be used as a dietary supplement intended for human, animal, and aquaculture consumption. The industrial production of astaxanthin comes from plant- or animal-based and synthetic sources. The U.S. 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 food dye and it is given the E number E161j. Astaxanthin from algae, synthetic and bacterial sources, is generally recognized as safe (GRAS) by the FDA. The European Food Safety Authority has set an Acceptable Daily Intake of 0.2 mg per kg body weight in 2019. As a food color additive astaxanthin and astaxanthin dimethyldisuccinate are restricted for use in Salmonid fish feed only. Astaxanthin is present in most red-coloured aquatic organisms. The content varies from species to species, but also from individual to individual as it is highly dependent on diet and living conditions. Astaxanthin, and other chemically related asta-carotenoids, has also been found in a number of lichen species of the arctic zone. Algae are the primary natural source of astaxanthin in the aquatic food chain. The microalgae Haematococcus pluvialis seems to accumulate the highest levels of astaxanthin in nature and is currently, the primary industrial source for natural astaxanthin production where more than 40 g of astaxanthin can be obtained from one kg of dry biomass.[citation needed] Haematococcus pluvialis has the productional advantage of the population doubling every week, which means scaling up is not an issue. Specifically, the microalgae are grown in two phases.[citation needed] First, in the green phase, the cells are given an abundance of nutrients to promote proliferation of the cells. In the subsequent red phase, the cells are deprived of nutrients and subjected to intense sunlight to induce encystment (carotogenesis), during which the cells produce high levels of astaxanthin as a protective mechanism against the environmental stress. The cells, with their high concentrations of astaxanthin, are then harvested.

Phaffia yeast Xanthophyllomyces dendrorhous exhibits 100% free, non-esterified astaxanthin, which is considered advantageous because it is readily absorbable and need not be hydrolysed in the digestive tract of the fish. In contrast to synthetic and bacteria sources of astaxanthin, yeast sources of astaxanthin consist mainly of the (3R, 3'R)-form, an important astaxanthin source in nature. Finally, the geometrical isomer, all-E, is higher in yeast sources of astaxanthin, as compared to synthetic sources.

In shellfish, astaxanthin is almost exclusively concentrated in the shells, with only low amounts in the flesh itself, and most of it only becomes visible during cooking as the pigment separates from the denatured proteins that otherwise bind it. Astaxanthin is extracted from Euphausia superba (Antarctic krill) and from shrimp processing waste. 12,000 pounds of wet shrimp shells can yield a 6–8 gallon astaxanthin/triglyceride oil mixture.

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