Carotene
From Wikipedia, the free encyclopedia
Carotene is an orange photosynthetic pigment important for photosynthesis. It is responsible for the orange colour of the carrot and many other fruits and vegetables. It contributes to photosynthesis by transmitting the light energy it absorbs to chlorophyll.
Chemically, carotene is a terpene. It is the dimer of retinol (vitamin A) and comes in two primary forms designated by characters from the Greek alphabet: alpha-carotene (α-carotene) and beta-carotene (β-carotene). Gamma, delta and epsilon (γ, δ and ε-carotene) also exist. Carotene can be stored in the liver and converted to vitamin A as needed, thus making it a provitamin.
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[edit] Carotenemia
Carotenemia or hypercarotenemia is excess carotene, and unlike excess Vitamin A is non-toxic. Although hypercarotenemia is not particularly dangerous, it can lead to a yellowing of the skin (carotenodermia). It is most commonly associated with consumption of an abundance of carrots, but it also can be a medical sign of more dangerous conditions. A randomised trial into the use of β-carotene and Vitamin A for prevention of lung cancer had to be stopped early due to the apparent increase in the incidence of lung cancer in those with lung irritation from smoking or asbestos exposure.[1].
[edit] The two forms
The two primary isomers of carotene, α-carotene and β-carotene, differ in the position of double bonds in the cyclic group at the end.
β-carotene is the more common form and can be found in yellow, orange, and green leafy fruits and vegetables. These can be carrots, spinach, lettuce, tomatoes, sweet potatoes, broccoli, cantaloupe, orange, and winter squash. As a rule of thumb, the greater the intensity of the color of the fruit or vegetable, the more β-carotene it contains.
β-carotene is an anti-oxidant and as such can be useful for curbing the excess of damaging free radicals in the body. However, the usefulness of β-carotene as a dietary supplement (i.e. taken as a pill) is still subject to debate[1]. β-carotene is fat-soluble.
[edit] Carotenoids
Carotenes are un-oxidized carotenoids. Carotenoids in which some of the double bonds have been oxidized are known as xanthophylls.
[edit] Beta Carotene and Cancer
It has been shown in trials that the use of synthetically-produced beta carotene (that is, beta carotene in supplement form such as the pills typically sold in stores) increases the rate of lung cancer and prostate cancer, and increases mortality in smokers. These results have been observed in beta carotene supplements and not in foods with naturally occurring beta carotene. [1]
An article on the American Cancer Society says that The Cancer Research Campaign has called for warning labels on beta carotene supplements to caution smokers that such supplements may increase the risk of lung cancer. [2]
The New England Journal of Medicine published an article (Vol. 330, No. 15) in 1994 about a trial which examines the relationship between daily supplementation of beta carotene and vitamin E (alpha-tocopherol) and the incidence of lung cancer. The study was done using supplements and researchers were aware of the relationship between carotenoid-rich fruits and vegetables and lower lung cancer rates. The research concludes that no reduction in lung cancer was found in the participants using these supplements (beta carotene), and furthermore, these supplements may, in fact, have harmful effects. [3]
The Journal of the National Cancer Institute published an article (Vol. 88, No. 21) in 1996 about a trial that was conducted to determine if vitamin A (retinyl palmitate) and beta carotene had any beneficial effects to prevent cancer. The results indicate an increased risk of lung cancer for the participants who consumed the beta carotene supplement.[4] The home page of The Journal of the National Cancer Institute is http://www.jncicancerspectrum.oupjournals.org
[edit] Production
Most of the world's synthetic supply comes from a manufacturing complex located in Freeport, Texas and owned by DSM. This site uses Blakeslea trispora in a fermentation process for the production of beta-carotene. In Australia, organic beta carotene is farmed by Aquacarotene Limited from dried marine algae Dunaliella salina grown in harvesting ponds situated in Karratha, Western Australia.
[edit] Total Synthesis
There are currently 2 commonly used methods of total synthesis of β-carotene. The first was developed by the Badische Anilin- & Soda-Fabrik (BASF) and is based on the Wittig reaction. The second is a Grignard reaction, elaborated by F. Hoffman-La Roche & Co. Ltd (Roche) from the original synthesis of Inhoffen et al. They are both symmetrical; the BASF synthesis is C20 + C20 , and the Roche synthesis is C19 + C2 + C19
[edit] Nomenclature
The two ends of the β-carotene molecule are structurally identical, and are called β-rings. Specifically, the group of nine carbon atoms at each end form a β-ring.
The α-carotene molecule has a β-ring at one end; the other end is called an ε-ring. There are no "α-rings".
These and similar names for the ends of the carotenoid molecules form the basis of a systematic naming scheme, according to which:
- α-carotene is β,ε-carotene;
- β-carotene is β,β-carotene;
- γ-carotene (with one β ring and one uncyclized end that is labelled psi) is β,ψ-carotene;
- δ-carotene (with one ε ring and one uncyclized end) is ε,ψ-carotene;
- ε-carotene is ε,ε-carotene,
[edit] References
- ^ a b Effects of a Combination of Beta Carotene and Vitamin A on Lung Cancer and Cardiovascular Disease
