From Wikipedia, the free encyclopedia
Carotenoids are organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants
and some other photosynthetic organisms like algae, some types of fungus and some bacteria.
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.[1] 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.
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.[2]
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,[3]
although this conclusion may be due to the inclusion of studies
involving smokers.[4] 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).[5]
Properties
Carotenoids belong to the category of tetraterpenoids
(i.e. they contain 40 carbon atoms). Structurally they are in the
form of a polyene chain
which is sometimes terminated by rings.
Probably the most well-known carotenoid is the one that gives
this second group its name, carotene, found in carrots (also apricots) and
are responsible for their bright orange colour. Crude palm oil,
however, is the richest source of carotenoids in nature in terms of
retinol (provitamin A) equivalent[6].
Vietnamese Gac fruit contains the
highest known concentration of the carotenoid lycopene.
Their colour, ranging from pale yellow through bright orange to
deep red, is directly linked to their structure. Xanthophylls are
often yellow, hence their class name. The double carbon-carbon
bonds interact with each other in a process called conjugation, which allows electrons
in the molecule to move freely across these areas of the molecule.
As the number of double bonds increases, electrons associated with
conjugated systems have more room to move, and require less energy
to change states. This causes the range of energies of light
absorbed by the molecule to decrease. As more frequencies of light
are absorbed from the short end of the visible spectrum, the
compounds acquire an increasingly red appearance.
Physiological effects
In 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 humans,
carotenoids have been linked to oxidation-preventing
mechanisms.
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.[7] 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 vitamin A and worsen the lung cell proliferation
induced by smoke[8]).
Similar results have been found in other animals. Not all
carotenoids are helpful, e.g. etretinate is a teratogen.
Humans and animals are
incapable of synthesizing carotenoids, and must obtain them through
their diet, yet they are common and often in ornamental features.
For example, the pink colour of flamingos and salmon, and the red colouring of lobsters 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.
Simplified carotenoid synthesis
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
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
Despite being important in nutrition, some carotenoids are
produced by bacteria to protect themselves from immune attack, such
as MRSA. The
golden pigment of S. aureus allows it to
survive competitive attack by Lactobaccillus
as well as the human immune system.[9]
List of naturally
occurring carotenoids
- Hydrocarbons
- Lycopersene
7,8,11,12,15,7',8',11',12',15'-Decahydro-γ,γ-carotene
- Phytofluene
- Hexahydrolycopene
15-cis-7,8,11,12,7',8'-Hexahydro-γ,γ-carotene
- Torulene 3',4'-Didehydro-β,γ-carotene
- α-Zeacarotene 7',8'-Dihydro-ε,γ-carotene
- Alcohols
- Alloxanthin
- Cynthiaxanthin
- Pectenoxanthin
- Cryptomonaxanthin
(3R,3'R)-7,8,7',8'-Tetradehydro-β,β-carotene-3,3'-diol
- Crustaxanthin β,-Carotene-3,4,3',4'-tetrol
- Gazaniaxanthin (3R)-5'-cis-β,γ-Caroten-3-ol
- OH-Chlorobactene 1',2'-Dihydro-f,γ-caroten-1'-ol
- Loroxanthin β,ε-Carotene-3,19,3'-triol
- Lycoxanthin γ,γ-Caroten-16-ol
- Rhodopin 1,2-Dihydro-γ,γ-caroten-l-ol
- Rhodopinol aka Warmingol
13-cis-1,2-Dihydro-γ,γ-carotene-1,20-diol
- Saproxanthin
3',4'-Didehydro-1',2'-dihydro-β,γ-carotene-3,1'-diol
- 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
- Epoxides
- Diadinoxanthin
5,6-Epoxy-7',8'-didehydro-5,6-dihydro—carotene-3,3-diol
- Luteoxanthin 5,6:
5',8'-Diepoxy-5,6,5',8'-tetrahydro-β,β-carotene-3,3'-diol
- Mutatoxanthin
- Citroxanthin
- Zeaxanthin
furanoxide 5,8-Epoxy-5,8-dihydro-β,β-carotene-3,3'-diol
- Neochrome
5',8'-Epoxy-6,7-didehydro-5,6,5',8'-tetrahydro-β,β-carotene-3,5,3'-triol
- Foliachrome
- Trollichrome
- Vaucheriaxanthin
5',6'-Epoxy-6,7-didehydro-5,6,5',6'-tetrahydro-β,β-carotene-3,5,19,3'-tetrol
- Aldehydes
- Rhodopinal
- Wamingone 13-cis-1-Hydroxy-1,2-dihydro-γ,γ-caroten-20-al
- Torularhodinaldehyde 3',4'-Didehydro-β,γ-caroten-16'-al
- Acids and Acid Esters
- Torularhodin 3',4'-Didehydro-β,γ-caroten-16'-oic acid
- Torularhodin methyl ester Methyl
3',4'-didehydro-β,γ-caroten-16'-oate
- Ketones
- Canthaxanthin aka Aphanicin,
Chlorellaxanthin β,β-Carotene-4,4'-dione
- Capsanthin
(3R,3'S,5'R)-3,3'-Dihydroxy-β,κ-caroten-6'-one
- Capsorubin
(3S,5R,3'S,5'R)-3,3'-Dihydroxy-κ,κ-carotene-6,6'-dione
- Cryptocapsin (3'R,5'R)-3'-Hydroxy-β,κ-caroten-6'-one
- 2,2'-Diketospirilloxanthin
1,1'-Dimethoxy-3,4,3',4'-tetradehydro-1,2,1',2'-tetrahydro-γ,γ-carotene-2,2'-dione
- Flexixanthin
3,1'-Dihydroxy-3',4'-didehydro-1',2'-dihydro-β,γ-caroten-4-one
- 3-OH-Canthaxanthin aka Adonirubin aka Phoenicoxanthin
3-Hydroxy-β,β-carotene-4,4'-dione
- Hydroxyspheriodenone
1'-Hydroxy-1-methoxy-3,4-didehydro-1,2,1',2',7',8'-hexahydro-γ,γ-caroten-2-one
- Okenone 1'-Methoxy-1',2'-dihydro-c,γ-caroten-4'-one
- Pectenolone
3,3'-Dihydroxy-7',8'-didehydro-β,β-caroten-4-one
- Phoeniconone aka Dehydroadonirubin
3-Hydroxy-2,3-didehydro-β,β-carotene-4,4'-dione
- Phoenicopterone β,ε-caroten-4-one
- Rubixanthone 3-Hydroxy-β,γ-caroten-4'-one
- Siphonaxanthin
3,19,3'-Trihydroxy-7,8-dihydro-β,ε-caroten-8-one
- 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
- Nonaprenoxanthin
2-(4-Hydroxy-3-methyl-2-butenyl)-7',8',11',12'-tetrahydro-e,y-carotene
- Decaprenoxanthin
2,2'-Bis(4-hydroxy-3-methyl-2-butenyl)-e,e-carotene
- 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
- ^
Armstrong GA, Hearst JE (1996). "Carotenoids 2: Genetics and
molecular biology of carotenoid pigment biosynthesis".
Faseb J. 10 (2): 228–37. PMID 8641556. http://www.fasebj.org/cgi/pmidlookup?view=long&pmid=8641556.
- ^
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
- ^
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.
- ^
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.
- ^
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. http://jn.nutrition.org/cgi/pmidlookup?view=long&pmid=15735074.
- ^
Choo Yuen May Palm oil
carotenoids
- ^
β-Carotene and other
carotenoids as antioxidants. From U.S. National Library of
Medicine. November, 2008.
- ^
Alija AJ, Bresgen N, Sommerburg O,
Siems W, Eckl PM (2004). "Cytotoxic and genotoxic
effects of β-carotene breakdown products on primary rat
hepatocytes". Carcinogenesis 25 (5):
827–31. doi:10.1093/carcin/bgh056. PMID 14688018. http://carcin.oxfordjournals.org/cgi/content/full/25/5/827.
- ^
Liu GY, Essex A, Buchanan JT, et
al. (2005). "Staphylococcus aureus golden
pigment impairs neutrophil killing and promotes virulence through
its antioxidant activity". J. Exp. Med.
202 (2): 209–15. doi:10.1084/jem.20050846. PMID 16009720. PMC 2213009. http://www.jem.org/cgi/content/full/202/2/209.
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.
External
links