Carotenoid
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Carotenoids are organic pigments naturally occurring in plants and some other photosynthetic organisms like algae, some types of fungus and some bacteria.
Carotenoids are characterized by a large (35-40 carbon atoms) polyene chain, sometimes terminated by rings. Carotenoids where some of the double bonds have been oxidized are known as xanthophylls, the un-oxidized carotenoids are known as carotenes.
Their color, ranging from pale yellow, through bright orange, to deep red, is directly linked to their structure: The double carbon-carbon bonds interact with each other in a process called conjugation. As the number of double bonds increases, the wavelength of the absorbed light increases, giving the compound an increasingly red appearance. The pink colour of flamingos and salmon, and the red colouring of lobsters are caused by carotenoids.
In photosynthetic organisms, 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-photosynthetic organisms, carotenoids have been linked to oxidation-preventing mechanisms.
Animals are incapable of synthesizing carotenoids, and must obtain them through their diet.
Probably the most well-known carotenoid is the one that gives this group its name, carotene, found in carrots and responsible for their bright orange colour. Epidemiological studies have shown that people with high beta-carotene intake and high plasma levels of beta-carotene have a significantly reduced risk of lung cancer. But studies of supplementation with large doses of beta-carotene in smokers have shown an increase in cancer risk (possibly because excessive beta-carotene results in breakdown products that reduce plasma Vitamin A and worsen the lung cell proliferation induced by smoke).
External links
- http://www.carotenoidsociety.org/ (http://www.carotenoidsociety.org/)
- Carotenoid Terpenoids (http://www.benbest.com/nutrceut/phytochemicals.html#carotenoids)