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==Physiological effects==
==Physiological effects==
Elijah Dunston
In [[photosynthesis|photosynthetic]] organisms, specifically [[flora]], carotenoids play a vital role in the photosynthetic reaction centre. They either participate in the energy-transfer process, or protect the reaction center from [[auto-oxidation]]. In non-photosynthesizing organisms, specifically [[human]]s, carotenoids have been linked to oxidation-preventing mechanisms.

[[Image:Carotenoids disposition in proteins.png|thumb|330px|left|Carotenoids disposition in proteins. Left: in [[cyanobacterium]] photosystem I carotenoids are outside (orange) {{PDB|1jb0}}. Right: in [[rhodopsin]] retinal is deep inside (pink) {{PDB|1f88}}.]]
Carotenoids have many physiological functions. Given their structure (above), carotenoids are efficient free-radical scavengers, and they enhance the vertebrate immune system. There are several dozen carotenoids in foods people consume, and most carotenoids have antioxidant activity.<ref>[http://www.ncbi.nlm.nih.gov/pubmed/10511324 β-Carotene and other carotenoids as antioxidants.] From [http://www.ncbi.nlm.nih.gov/sites/entrez/ U.S. National Library of Medicine]. November, 2008.</ref> [[epidemiology|Epidemiological]] studies have shown that people with high β-carotene intake and high plasma levels of β-carotene have a significantly reduced risk of lung [[cancer]]. However, studies of supplementation with large doses of β-carotene in smokers have shown an increase in [[cancer]] risk (possibly because excessive β-carotene results in breakdown products that reduce plasma [[retinol|vitamin A]] and worsen the lung [[cell growth|cell proliferation]] induced by smoke<ref>{{cite journal |author=Alija AJ, Bresgen N, Sommerburg O, Siems W, Eckl PM |title=Cytotoxic and genotoxic effects of β-carotene breakdown products on primary rat hepatocytes |journal=Carcinogenesis |volume=25 |issue=5 |pages=827–31 |year=2004 |pmid=14688018 |doi=10.1093/carcin/bgh056 |url=http://carcin.oxfordjournals.org/cgi/content/full/25/5/827}}</ref>). Similar results have been found in other animals. Not all carotenoids are helpful, e.g. [[etretinate]] is a [[teratogen]].

Humans and [[animal]]s are mostly incapable of synthesizing carotenoids, and must obtain them through their diet. The notable exception is the red pea aphid, which has the [[genes]] necessary for synthesizing carotenoids, thought to have been acquired from [[fungi]] via [[horizontal gene transfer]].<ref name="moran2010"/> Carotenoids are a common and often ornamental feature in animals. For example, the pink colour of [[flamingo]]s and [[salmon]], and the red colouring of cooked [[lobster]]s are due to carotenoids. It has been proposed that carotenoids are used in ornamental traits (for extreme examples see [[puffin]] birds) because, given their physiological and chemical properties, they can be used as honest indicators of individual health, and hence they can be used by animals when selecting potential mates.

In the [[macula lutea]] of the human eye, certain carotenoids are actively concentrated to the point that they cause a yellow coloring, and this may help to protect the retina from blue and [[actinic]] light, in the same way that carotenoids protect the photosystems of plants. Carotenoids are also actively concentrated in the [[corpus luteum]] of the ovaries, where they impart the characteristic color, and may act as general antioxidants.

[[Image:Carotenoid.svg|thumb|250px|Simplified carotenoid synthesis [[metabolic pathway|pathway]].]]
The most common carotenoids include lycopene and the vitamin A precursor β-carotene. In plants, the xanthophyll [[lutein]] is the most abundant carotenoid and its role in preventing age-related eye disease is currently under investigation. Lutein and the other carotenoid pigments found in mature leaves are often not obvious because of the presence of [[chlorophyll]]. However, when chlorophyll is not present, as in young foliage and also dying [[deciduous]] foliage (such as autumn leaves), the yellows, reds, and oranges of the carotenoids are predominant. For the same reason, carotenoid colours often predominate in ripe fruit (e.g., oranges, tomatoes, bananas), after being unmasked by the disappearance of chlorophyll.


==Aroma chemicals==
==Aroma chemicals==

Revision as of 18:00, 6 October 2010

The orange ring surrounding Grand Prismatic Spring is due to carotenoid molecules, produced by huge mats of algae and bacteria.

Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some types of fungus some bacteria and at least one species of aphid. Carotenoids are generally not manufactured by species in the animal kingdom, although one species of aphid is known to have acquired the genes for carotenoid synthesis from fungi, by the known phenomenon of horizontal gene transfer.[1]

There are over 600 known carotenoids; they are split into two classes, xanthophylls (which contain oxygen) and carotenes (which are purely hydrocarbons, and contain no oxygen). Carotenoids in general absorb blue light. They serve two key roles in plants and algae: they absorb light energy for use in photosynthesis, and they protect chlorophyll from photodamage.[2] In humans, four carotenoids (beta-carotene, alpha-carotene, gamma-carotene, and beta-cryptoxanthin) have vitamin A activity (meaning they can be converted to retinal), and these and other carotenoids can also act as antioxidants. In the eye, certain other carotenoids (lutein and zeaxanthin) apparently act directly to absorb damaging blue and near-ultraviolet light, in order to protect the macula lutea.

People consuming diets rich in carotenoids from natural foods, such as fruits and vegetables, are healthier and have lower mortality from a number of chronic illnesses.[3] However, a recent meta-analysis of 68 reliable antioxidant supplementation experiments involving a total of 232,606 individuals concluded that consuming additional β-carotene from supplements is unlikely to be beneficial and may actually be harmful,[4] although this conclusion may be due to the inclusion of studies involving smokers.[5] With the notable exception of Vietnam Gac and crude palm oil, most carotenoid-rich fruits and vegetables are low in lipids. Since dietary lipids have been hypothesized to be an important factor for carotenoid bioavailability, a 2005 study investigated whether addition of avocado fruit or oil, as lipid sources, would enhance carotenoid absorption in humans. The study found that the addition of both avocado fruit and oil significantly enhanced the subjects' absorption of all carotenoids tested (α-carotene, β-carotene, lycopene, and lutein).[6]

Properties

Elijah Dunston

Physiological effects

Elijah Dunston

Aroma chemicals

Products of carotenoid degradation such as ionones, damascones and damascenones are also important fragrance chemicals that are used extensively in the perfumes and fragrance industry. Both β-damascenone and β-ionone although low in concentration in rose distillates are the key odour-contributing compounds in flowers. In fact, the sweet floral smells present in black tea, aged tobacco, grape, and many fruits are due to the aromatic compounds resulting from carotenoid breakdown.

Disease

penis in the pusy

Question of synthesis the in corpus luteum

Following a 1968 report that beta-carotene was synthesized in laboratory conditions in slices of corpus luteum from cows, an organ known to concentrates beta-carotene (hence its color and name), attempts have been made to replicate these findings, but have not succeeded. The idea is not presently accepted by the scientific community. [7] Rather, the mammalian corpus luteum, like the macula lutea in the retina of the mammalian eye, merely concentrates carotenoids from the diet.

List of naturally occurring carotenoids

  • Glycosides
    • Oscillaxanthin 2,2'-Bis(β-L-rhamnopyranosyloxy)-3,4,3',4'-tetradehydro-1,2,1',2'-tetrahydro-γ,γ-carotene-1,1'-diol
    • Phleixanthophyll 1'-(β-D-Glucopyranosyloxy)-3',4'-didehydro-1',2'-dihydro-β,γ-caroten-2'-ol
  • Ethers
    • Rhodovibrin 1'-Methoxy-3',4'-didehydro-1,2,1',2'-tetrahydro-γ,γ-caroten-1-ol
    • Spheroidene 1-Methoxy-3,4-didehydro-1,2,7',8'-tetrahydro-γ,γ-carotene
  • Esters of Alcohols
    • Astacein 3,3'-Bispalmitoyloxy-2,3,2',3'-tetradehydro-β,β-carotene-4,4'-dione or 3,3'-dihydroxy-2,3,2',3'-tetradehydro-β,β-carotene-4,4'-dione dipalmitate
    • Fucoxanthin 3'-Acetoxy-5,6-epoxy-3,5'-dihydroxy-6',7'-didehydro-5,6,7,8,5',6'-hexahydro-β,β-caroten-8-one
    • Isofucoxanthin 3'-Acetoxy-3,5,5'-trihydroxy-6',7'-didehydro-5,8,5',6'-tetrahydro-β,β-caroten-8-one
    • Physalien
    • Zeaxanthin dipalmitate (3R,3'R)-3,3'-Bispalmitoyloxy-β,β-carotene or (3R,3'R)-β,β-carotene-3,3'-diol dipalmitate
    • Siphonein 3,3'-Dihydroxy-19-lauroyloxy-7,8-dihydro-β,ε-caroten-8-one or 3,19,3'-trihydroxy-7,8-dihydro-β,ε-caroten-8-one 19-laurate
  • Apo Carotenoids
    • β-Apo-2'-carotenal 3',4'-Didehydro-2'-apo-b-caroten-2'-al
    • Apo-2-lycopenal
    • Apo-6'-lycopenal 6'-Apo-y-caroten-6'-al
    • Azafrinaldehyde 5,6-Dihydroxy-5,6-dihydro-10'-apo-β-caroten-10'-al
    • Bixin 6'-Methyl hydrogen 9'-cis-6,6'-diapocarotene-6,6'-dioate
    • Citranaxanthin 5',6'-Dihydro-5'-apo-β-caroten-6'-one or 5',6'-dihydro-5'-apo-18'-nor-β-caroten-6'-one or 6'-methyl-6'-apo-β-caroten-6'-one
    • Crocetin 8,8'-Diapo-8,8'-carotenedioic acid
    • Crocetinsemialdehyde 8'-Oxo-8,8'-diapo-8-carotenoic acid
    • Crocin Digentiobiosyl 8,8'-diapo-8,8'-carotenedioate
    • Hopkinsiaxanthin 3-Hydroxy-7,8-didehydro-7',8'-dihydro-7'-apo-b-carotene-4,8'-dione or 3-hydroxy-8'-methyl-7,8-didehydro-8'-apo-b-carotene-4,8'-dione
    • Methyl apo-6'-lycopenoate Methyl 6'-apo-y-caroten-6'-oate
    • Paracentrone 3,5-Dihydroxy-6,7-didehydro-5,6,7',8'-tetrahydro-7'-apo-b-caroten-8'-one or 3,5-dihydroxy-8'-methyl-6,7-didehydro-5,6-dihydro-8'-apo-b-caroten-8'-one
    • Sintaxanthin 7',8'-Dihydro-7'-apo-b-caroten-8'-one or 8'-methyl-8'-apo-b-caroten-8'-one
  • Nor and Seco Carotenoids
    • Actinioerythrin 3,3'-Bisacyloxy-2,2'-dinor-b,b-carotene-4,4'-dione
    • β-Carotenone 5,6:5',6'-Diseco-b,b-carotene-5,6,5',6'-tetrone
    • Peridinin 3'-Acetoxy-5,6-epoxy-3,5'-dihydroxy-6',7'-didehydro-5,6,5',6'-tetrahydro-12',13',20'-trinor-b,b-caroten-19,11-olide
    • Pyrrhoxanthininol 5,6-epoxy-3,3'-dihydroxy-7',8'-didehydro-5,6-dihydro-12',13',20'-trinor-b,b-caroten-19,11-olide
    • Semi-α-carotenone 5,6-Seco-b,e-carotene-5,6-dione
    • Semi-β-carotenone 5,6-seco-b,b-carotene-5,6-dione or 5',6'-seco-b,b-carotene-5',6'-dione
    • Triphasiaxanthin 3-Hydroxysemi-b-carotenone 3'-Hydroxy-5,6-seco-b,b-carotene-5,6-dione or 3-hydroxy-5',6'-seco-b,b-carotene-5',6'-dione
  • retro Carotenoids and retro Apo Carotenoids
    • Eschscholtzxanthin 4',5'-Didehydro-4,5'-retro-b,b-carotene-3,3'-diol
    • Eschscholtzxanthone 3'-Hydroxy-4',5'-didehydro-4,5'-retro-b,b-caroten-3-one
    • Rhodoxanthin 4',5'-Didehydro-4,5'-retro-b,b-carotene-3,3'-dione
    • Tangeraxanthin 3-Hydroxy-5'-methyl-4,5'-retro-5'-apo-b-caroten-5'-one or 3-hydroxy-4,5'-retro-5'-apo-b-caroten-5'-one
  • Higher Carotenoids
  • C.p. 450 2-[4-Hydroxy-3-(hydroxymethyl)-2-butenyl]-2'-(3-methyl-2-butenyl)-b,b-carotene
    • C.p. 473 2'-(4-Hydroxy-3-methyl-2-butenyl)-2-(3-methyl-2-butenyl)-3',4'-didehydro-l',2'-dihydro-b,y-caroten-1'-ol
    • Bacterioruberin 2,2'-Bis(3-hydroxy-3-methylbutyl)-3,4,3',4'-tetradehydro-1,2,1',2'-tetrahydro-y,y-carotene-1,1'-dio

See also

References

  1. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1126/science.1187113, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1126/science.1187113 instead.
  2. ^ Armstrong GA, Hearst JE (1996). "Carotenoids 2: Genetics and molecular biology of carotenoid pigment biosynthesis". Faseb J. 10 (2): 228–37. PMID 8641556.
  3. ^ A. T. Diplock1, J.-L. Charleux, G. Crozier-Willi, F. J. Kok, C. Rice-Evans, M. Roberfroid, W. Stahl, J. Vina-Ribes. Functional food science and defence against reactive oxidative species, British Journal of Nutrition 1998, 80, Suppl. 1, S77–S112
  4. ^ Bjelakovic G; et al. (2007). "Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis". JAMA. 297 (8): 842–57. doi:10.1001/jama.297.8.842. PMID 17327526. {{cite journal}}: Explicit use of et al. in: |author= (help)
  5. ^ It is known that taking β-carotene supplements is harmful for smokers, and the meta-analysis of Bjelakovic et al. was influenced by inclusion of these studies. See the letter to JAMA by Philip Taylor and Sanford Dawsey and the reply by the authors of the original paper.
  6. ^ Unlu N; et al. (1 March 2005). "Carotenoid Absorption from Salad and Salsa by Humans Is Enhanced by the Addition of Avocado or Avocado Oil". Human Nutrition and Metabolism. 135 (3): 431–6. PMID 15735074. {{cite journal}}: Explicit use of et al. in: |author= (help)
  7. ^ Brian Davis. Carotenoid metabolism as a preparation for function. Pure & Applied Chemistry, Vol. 63, No. 1, pp. 131-140, 1991. available online. Accessed April 30, 2010.

Classifications

Carotenoids can have many classifications. Some are alcohols, hydrocarbons, ethers, epoxides, ketones, acids, etc. They can be classified also into apo Carotenoids, nor and seco Carotenoids, retro Carotenoids, retro apo carotenoids and "Higher Carotenoids."

Wikimedia Commons has media related to Carotenoids.
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