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|Section2= |Section3= }} Astaxanthin is a keto-carotenoid.〔Production of ketocarotenoids by microalgae. Margalith PZ, Appl Microbiol Biotechnol., Apr 1999, volume 51, issue 4, pages 431-438, 〕〔Efficient Syntheses of the Keto-carotenoids Canthaxanthin, Astaxanthin, and Astacene. Seyoung Choi and Sangho Koo, J. Org. Chem., 2005, 70 (8), pages 3328–3331, 〕 It belongs to a larger class of chemical compounds 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 (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 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 dietary 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.〔 See Note 1.〕 The European Commission considers it food dye and it is given the E number E161j.〔(E-numbers : E100- E200 Food Colours ). Food-Info.net. Retrieved on 2013-04-25.〕 Natural astaxanthin is generally recognized as safe (GRAS) by the FDA,〔(Astaxanthin wins full GRAS status ). Nutraingredients-usa.com. Retrieved on 2013-04-25.〕〔(Algatechnologies gets GRAS for AstaPure astaxanthin ). Foodnavigator-usa.com. Retrieved on 2013-04-25.〕 but as a food coloring in the United States it is restricted to use in animal food.〔(Summary of Color Additives for Use in the United States in Foods, Drugs, Cosmetics, and Medical Devices ). Fda.gov. Retrieved on 2013-04-25.〕 ==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: Currently, the primary natural source for astaxanthin is the microalgae ''Haematococcus pluvialis''. ''Haematococcus pluvialis'' 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.〔(Astaxanthin – a superb natural antioxidant ). algatech.com〕 ''Haematococcus pluvialis'' 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 are 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.〔Boussiba; Sammy, V.; Avigad, C.; et al. (2000) Procedure for large-scale production of astaxanthin from haematococcus. (U. S. Patent 6,022,701 ).〕 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 (3''R'', 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.〔(Natural vs. Synthetic Astaxanthin Sources ). naturxan.com〕 For obtaining astaxanthin from ''Euphausia superba'' (Antarctic krill), there are a number of issues:〔Katevas, Dimitri Sclabos (6 October 2003). (The Krill ). aquafeed.com〕 Astaxanthin is also commercially collected from shrimp processing waste. 12,000 pounds of wet shrimp shells can yield a 6–8 gallon astaxanthin/triglyceride oil mixture.〔Anderson, Lyle K. Extraction of Carotenoid Pigment from Shrimp Processing Waste. (U.S. Patent 3906112 ). Sep 16, 1975〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Astaxanthin」の詳細全文を読む スポンサード リンク
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