|Jmol-3D images||Image 1|
|Molar mass||596.84 g mol−1|
|Appearance||red solid powder|
|Density||1.071 g/mL |
216 °C, 489 K, 421 °F ()
774 °C, 1047 K, 1425 °F ()
|Solubility||30 g/L in DCM; 10 g/L in CHCl3; 0.5 g/L in DMSO; 0.2 g/L in acetone |
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Astaxanthin (//) is a carotenoid. It belongs to a larger class of phytochemicals known as terpenes, which are built from five carbon precursors; isopentenyl diphosphate (or IPP) and dimethylallyl diphosphate (or DMAPP). 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 moities, hydroxyl (OH) or ketone (=0), 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 colorful, lipid-soluble pigment. This colour is due to the extended chain of conjugated (alternating double and single) double bonds at the centre of the compound. This chain of conjugated double bonds is also responsible for the antioxidant function of astaxanthin (as well as other carotenoids) as it results in a region of decentralized electrons that can be donated to reduce a reactive oxidizing molecule.
Astaxanthin is found in microalgae, yeast, salmon, trout, krill, shrimp, crayfish, crustaceans, and the feathers of some birds. It provides the red color of salmon meat and the red color of cooked shellfish. Professor Basil Weedon's group was the first to prove the structure of astaxanthin by synthesis, in 1975.
Astaxanthin, unlike several carotenes and one other known carotenoid, is not converted to vitamin A (retinol) in the human body. Like other carotenoids, astaxanthin has self-limited absorption orally and such low toxicity by mouth that no toxic syndrome is known. It is an antioxidant with a slightly lower antioxidant activity in some model systems than other carotenoids. However, in living organisms the free-radical terminating effectiveness of each carotenoid is heavily modified by its lipid solubility, and thus varies with the type of system being protected.
While astaxanthin is a natural nutritional component, it can also be used as a food supplement. The supplement is intended for human, animal, and aquaculture consumption. The commercial production of astaxanthin comes from both natural and synthetic sources.
The U.S. Food and Drug Administration (FDA) 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. Natural astaxanthin is considered generally recognized as safe (GRAS) by the FDA, but as a food coloring in the United States it is restricted to use in animal food.
Natural sources 
The following sources are used for the commercial production of astaxanthin:
- Euphausia pacifica (Pacific krill)
- Euphausia superba (Antarctic krill)
- Haematococcus pluvialis (MicroAlgae)
- Pandalus borealis (Arctic shrimp)
- Xanthophyllomyces dendrorhous, formerly Phaffia rhodozyma (yeast)
As a natural source, the following can be found in nature (or a production facility) with the approximate astaxanthin concentrations:
|Source||Astaxanthin concentration (ppm)|
|Arctic shrimp (P borealis)||~ 1,200|
|Phaffia yeast||~ 10,000|
|Haematococcus pluvialis||~ 40,000|
Currently, the primary natural source for astaxanthin is the microalgae Haematococcus pluvialis. It seems to accumulate the highest levels of astaxanthin in nature; Commercially more than 40 g of astaxanthin can be obtained from one kg of dry biomass. It has the advantage of the population doubling every week, which means scaling up is not an issue. However, it does require some expertise to grow the algae with a high astaxanthin content. Specifically, the microalgae is grown in two phases. 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 virtually all in 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. This contributes to greater efficacy because the all-E (trans) isomer has greater bio-availability than the cis isomer.
The Krill fishing operation is complex. It is done in Antarctic waters, under extreme weather conditions and far away from ports with substantial operational complexities. Krill's fishing location and the difficult weather conditions in the main fishing area, together with the costs involved in the operation, have contributed to a slow development of the industry. Krill fishing is by far different than any other fishing operation today known. The knowledge to work with it belongs to very few people in the world.
Astaxanthin is commercially collected from shrimp processing waste. 12,000 pounds of wet shrimp shells can yield a 6–8 gallon astaxanthin/triglyceride oil mixture.
Synthetic sources 
Nearly all commercial astaxanthin for aquaculture is produced synthetically, with an annual turnover of over $200 million and a selling price of roughly $5000–6000 per kilo as of July 2012. However, synthetic production of astaxanthin is not preferred in some cases because synthetic astaxanthin contains a mixture of stereoisomers. Astaxanthin is fairly abundant and obtainable from natural sources, and some consumers prefer natural products over synthetic ones.
An efficient synthesis from isophorone, cis-3-methyl-2-penten-4-yn-1-ol and a symmetrical C10-dialdehyde has been discovered and is used commercially. It combines these chemicals together with an ethynylation and then a Wittig reaction. Two equivalents of the proper ylide combined with the proper dialdehyde in a solvent of methanol, ethanol, or a mixture of the two, yields astaxanthin in up to 88% yields.
Metabolic engineering 
The cost of astaxanthin production, high commercial price and lack of a leading fermentation production systems, combined with the shortfalls of chemical synthesis mean that research into alternative fermentation production methods has been carried out. Metabolic engineering offers the opportunity to create biological systems for the production of a specific target compound. The metabolic engineering of bacteria (Escherichia coli) recently allowed production of astaxanthin at >90% of the total carotenoids, providing the first engineered production system capable of efficient astaxanthin production. Astaxanthin biosynthesis proceeds from beta-carotene via either zeaxanthin or canthaxanthin. Historically, it has been assumed that astaxanthin biosynthesis proceeds along both routes. However, recent work has suggested that efficient biosynthesis may, in fact, proceed from beta-carotene to astaxanthin via zeaxanthin. The production of astaxanthin by metabolic engineering, in isolation, will not provide a suitable alternative to current commercial methods. Rather, a bioprocess approach should be adopted. Such an approach would consider fermentation conditions and economics, as well as downstream processing (extraction). Carotenoid extraction has been studied extensively, for example, the extraction of canthaxanthin (a precursor to astaxanthin) was studied within an E. coli production process demonstrating that extraction efficiency was increased substantially when two solvents; acetone and methanol, were used sequentially rather than as a combined solution. 
Difference between natural and synthetic forms 
Astaxanthin has two chiral centers, at the 3- and 3′-positions. Therefore, there are three stereoisomers; (3R,3′R), (3R,3′S) (meso), and (3S,3′S). Synthetic astaxanthin contains a mixture of the three, in approximately 1:2:1 proportions. Naturally occurring astaxanthin varies considerably from one organism to another. The astaxanthin in fish is of whatever stereoisomer the fish ingested. The astaxanthin produced by haematococcus pluvialis, which is commonly used in the feed of animals that are in turn consumed by humans, is the (3S,3′S) stereoisomer.
Astaxanthin is used as a feed supplement for salmon, crabs, shrimp, chickens and egg production. Regardless of the source, astaxanthin provides some important benefits beyond coloration. It also has been found to be essential for proper growth and survival.
For seafood and animals 
The primary use of synthetic astaxanthin today is as an animal feed additive to impart coloration, including farm-raised salmon and egg yolks. Synthetic carotenoid pigments colored yellow, red or orange represent about 15–25% of the cost of production of commercial salmon feed. Today, almost all commercial astaxanthin for aquaculture is produced synthetically from petrochemical sources. While it constitutes a tiny portion of salmon feed (50 to 100 parts per million), astaxanthin represents a major share of the cost, up to 20%.
Class action lawsuits have been filed against some major grocery store chains for not clearly labeling the salmon "color added". The chains followed up quickly by labeling all such salmon as "color added". "...law-firm Smith & Lowney persisted with the suit for damages, but a Seattle judge dismissed [the case], ruling that enforcement of the applicable food laws was up to government and not individuals."
For humans 
The primary use for humans is as a food supplement. Research shows that, due to astaxanthin's potent antioxidant activity, it may be beneficial in cardiovascular, immune, inflammatory and neurodegenerative diseases. Some research supports the assumption that it may protect body tissues from oxidative and ultraviolet damage through its suppression of NF-κB activation. 
Role in the food chain 
It has been speculated that gulls are "flushed" pink when molting, especially in areas with farm-raised salmon. However, not enough is known about the relationship between astaxanthin and plumage. For example, cardinals seem to produce astaxanthin from carotenoids when molting, even when fed primarily seed with natural yellow dye.
Lobsters, shrimp, and some crabs turn red when cooked because the astaxanthin, which was bound to the protein in the shell, becomes free as the protein denatures and unwinds. The freed pigment is thus available to absorb light and produce the red color. 
In April 2009, the US FDA approved astaxanthin as an additive for fish feed only as a component of a stabilized color additive mixture. Color additive mixtures for fish feed made with astaxanthin may contain only those diluents that are suitable. The color additives astaxanthin, ultramarine blue, canthaxanthin, synthetic iron oxide, dried algae meal, Tagetes meal and extract, and corn endosperm oil are approved for specific uses in animal foods. Haematococcus algae meal (21 CFR 73.185) and Phaffia yeast (21 CFR 73.355) for use in fish feed to color salmonoids were added in 2000. In the European Union, astaxanthin-containing food supplements derived from sources that have no history of use as a source of food in Europe, fall under the remit of the Novel Food legislation, EC (No.) 258/97. Since 1997, there have been five novel food applications concerning products that contain astaxanthin extracted from these novel sources. In each case, these applications have been simplified or substantial equivalence applications, because astaxanthin itself is recognised as a food component in the EU diet.
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