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Carotenoid

Chemical structure of β-carotene, a common natural pigment.

Carotenoids (/kəˈrɒtɪnɔɪd/) are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi.[1] Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, canaries, flamingos, salmon, lobster, shrimp, and daffodils. Over 1,100 identified carotenoids can be further categorized into two classes – xanthophylls (which contain oxygen) and carotenes (which are purely hydrocarbons and contain no oxygen).[2]

All are derivatives of tetraterpenes, meaning that they are produced from 8 isoprene units and contain 40 carbon atoms. In general, carotenoids absorb wavelengths ranging from 400 to 550 nanometers (violet to green light). This causes the compounds to be deeply colored yellow, orange, or red. Carotenoids are the dominant pigment in autumn leaf coloration of about 15-30% of tree species,[3] but many plant colors, especially reds and purples, are due to polyphenols.

Macular pigments of the human eye

Carotenoids serve two key roles in plants and algae: they absorb light energy for use in photosynthesis, and they provide photoprotection via non-photochemical quenching.[4] Carotenoids that contain unsubstituted beta-ionone rings (including β-carotene, α-carotene, β-cryptoxanthin, and γ-carotene) have vitamin A activity (meaning that they can be converted to retinol). In the eye, lutein, meso-zeaxanthin, and zeaxanthin are present as macular pigments whose importance in visual function, as of 2016, remains under clinical research.[3][5]

  1. ^ Nelson, David L.; Cox, Michael M. (2005). Principles of Biochemistry (4th ed.). New York: W. H. Freeman. ISBN 0-7167-4339-6.
  2. ^ Yabuzaki, Junko (2017-01-01). "Carotenoids Database: structures, chemical fingerprints and distribution among organisms". Database. 2017 (1). doi:10.1093/database/bax004. PMC 5574413. PMID 28365725.
  3. ^ a b Cite error: The named reference lpi was invoked but never defined (see the help page).
  4. ^ Armstrong GA, Hearst JE (1996). "Carotenoids 2: Genetics and molecular biology of carotenoid pigment biosynthesis". FASEB J. 10 (2): 228–37. doi:10.1096/fasebj.10.2.8641556. PMID 8641556. S2CID 22385652.
  5. ^ Bernstein, P. S.; Li, B; Vachali, P. P.; Gorusupudi, A; Shyam, R; Henriksen, B. S.; Nolan, J. M. (2015). "Lutein, Zeaxanthin, and meso-Zeaxanthin: The Basic and Clinical Science Underlying Carotenoid-based Nutritional Interventions against Ocular Disease". Progress in Retinal and Eye Research. 50: 34–66. doi:10.1016/j.preteyeres.2015.10.003. PMC 4698241. PMID 26541886.
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