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The term carotene (also carotin, from the Latin carota, "carrot"Mosby's Medical, Nursing and Allied Health Dictionary, Fourth Edition, Mosby-Year Book 1994, p. 273) is used for many related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but in general cannot be made by animals (with the exception of some and which acquired the synthesizing genes from fungi). (2025). 9780471238966 ISBN 9780471238966 Carotenes are photosynthetic pigments important for photosynthesis.
Carotenes contain no oxygen atoms. They absorb ultraviolet, violet, and blue light and scatter orange or red light, and yellow light(in low concentrations).
Carotenes are responsible for the orange colour of the carrot, after which this class of chemicals is named, and for the colours of many other fruits, vegetables and fungi (for example, , chanterelle and orange cantaloupe melon). Carotenes are also responsible for the orange (but not all of the yellow) colours in dry foliage. They also (in lower concentrations) impart the yellow coloration to milk-fat and butter. Omnivorous animal species which are relatively poor converters of coloured dietary carotenoids to colourless retinoids, such as humans and , have yellow-coloured adipose tissue, as a result of the carotenoid retention from the vegetable portion of their diet.
Carotenes contribute to photosynthesis by transmitting the light energy they absorb to chlorophyll. They also protect plant tissues by helping to absorb the energy from singlet oxygen, an excited form of the oxygen molecule O2 which is formed during photosynthesis.
Beta-Carotene is composed of two retinol groups, and is broken down in the mucosa of the human small intestine by β-carotene 15,15'-monooxygenase to retinal, a form of vitamin A. β-Carotene can be stored in the liver and body fat and converted to retinal as needed, thus making it a form of vitamin A for humans and some other mammals. The carotenes alpha-Carotene and gamma-Carotene, due to their single retinyl group (β-ionone ring), also have some vitamin A activity (though less than β-carotene), as does the xanthophyll carotenoid β-cryptoxanthin. All other carotenoids, including lycopene, have no beta-ring and thus no vitamin A activity (although they may have antioxidant activity and thus biological activity in other ways).
Animal species differ greatly in their ability to convert retinyl (beta-ionone) containing carotenoids to retinals. Carnivores in general are poor converters of dietary ionone-containing carotenoids. Pure carnivores such as lack β-carotene 15,15'-monooxygenase and cannot convert any carotenoids to retinals at all (resulting in carotenes not being a form of vitamin A for this species); while cats can convert a trace of β-carotene to retinol, although the amount is totally insufficient for meeting their daily retinol needs.
Carotenes are found in plants in two primary forms designated by characters from the Greek alphabet: alpha-Carotene (α-carotene) and beta-Carotene (β-carotene). gamma-Carotene, delta-Carotene, epsilon-Carotene, and zeta-Carotene (γ, δ, ε, and ζ-carotene) also exist. Since they are hydrocarbons, and therefore contain no oxygen, carotenes are fat-soluble and insoluble in water (in contrast with other , the , which contain oxygen and thus are less chemically hydrophobic).
Absorption from these foods is enhanced if eaten with fats, as carotenes are fat soluble, and if the food is cooked for a few minutes until the plant cell wall splits and the color is released into any liquid. 12 μg of dietary β-carotene supplies the equivalent of 1 μg of retinol, and 24 μg of α-carotene or β-cryptoxanthin provides the equivalent of 1 μg of retinol.
beta-Carotene is the more common form and can be found in yellow, orange, and green leafy and . As a rule of thumb, the greater the intensity of the orange colour of the fruit or vegetable, the more β-carotene it contains.
Carotene protects plant cells against the destructive effects of ultraviolet light so β-carotene is an antioxidant.
The New England Journal of Medicine published an article in 1994 about a trial which examined the relationship between daily supplementation of β-carotene and vitamin E (α-tocopherol) and the incidence of lung cancer. The study was done using supplements and researchers were aware of the epidemiological correlation between carotenoid-rich fruits and vegetables and lower lung cancer rates. The research concluded that no reduction in lung cancer was found in the participants using these supplements, and furthermore, these supplements may, in fact, have harmful effects.
The Journal of the National Cancer Institute and The New England Journal of Medicine published articles in 1996 about a trial with a goal to determine if vitamin A (in the form of retinyl palmitate) and β-carotene (at about 30 mg/day, which is 10 times the Reference Daily Intake) supplements had any beneficial effects to prevent cancer. The results indicated an increased risk of lung and prostate cancers for the participants who consumed the β-carotene supplement and who had lung irritation from tobacco smoking or asbestos exposure, causing the trial to be stopped early.
A review of all randomized controlled trials in the scientific literature by the Cochrane Collaboration published in JAMA in 2007 found that synthetic β-carotene increased mortality by 1–8% (Relative Risk 1.05, 95% confidence interval 1.01–1.08).
However, this meta-analysis included two large studies of smokers, so it is not clear that the results apply to the general population.
See the letter to JAMA by Philip Taylor and Sanford Dawsey and the reply by the authors of the original paper.
The review only studied the influence of synthetic antioxidants and the results should not be translated to potential effects of fruits and vegetables.
Most of the world's synthetic supply of carotene comes from a manufacturing complex located in Freeport, Texas and owned by DSM. The other major supplier BASF also uses a chemical process to produce β-carotene. Together these suppliers account for about 85% of the β-carotene on the market. In Spain Vitatene produces natural β-carotene from fungus Blakeslea trispora, as does DSM but at much lower amount when compared to its synthetic β-carotene operation. In Australia, organic β-carotene is produced by Aquacarotene Limited from dried marine algae Dunaliella salina grown in harvesting ponds situated in Karratha, Western Australia. BASF Australia is also producing β-carotene from microalgae grown in two sites in Australia that are the world's largest algae farms. In Portugal, the industrial biotechnology company Biotrend is producing natural all- trans-β-carotene from a non-genetically modified bacteria of the genus Sphingomonas isolated from soil.
Carotenes are also found in palm oil, corn, and in the milk of dairy cows, causing cow's milk to be light yellow, depending on the feed of the cattle, and the amount of fat in the milk (high-fat milks, such as those produced by Guernsey cattle cows, tend to be yellower because their fat content causes them to contain more carotene).
Carotenes are also found in some species of termites, where they apparently have been picked up from the diet of the insects.
The second is a Grignard reaction, elaborated by Hoffman-La Roche from the original synthesis of Inhoffen et al. They are both symmetrical; the BASF synthesis is C20 + C20, and the Hoffman-La Roche synthesis is C19 + C2 + C19.
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 is no such thing as an "α-ring".
These and similar names for the ends of the carotenoid molecules form the basis of a systematic naming scheme, according to which:
ζ-Carotene is the biosynthesis precursor of neurosporene, which is the precursor of lycopene, which, in turn, is the precursor of the carotenes α through ε.
Forms of carotene
The two primary of carotene, α-carotene and β-carotene, differ in the position of a double bond (and thus a hydrogen) in the cyclic group at one end (the right end in the diagram at right).
β-Carotene and physiology
β-Carotene and cancer
An article on the American Cancer Society says that The Cancer Research Campaign has called for warning labels on β-carotene supplements to caution smokers that such supplements may increase the risk of lung cancer.
β-Carotene and photosensitivity
Oral β-carotene is prescribed to people suffering from erythropoietic protoporphyria. It provides them some relief from photosensitivity.
Carotenemia
Carotenemia or hypercarotenemia is excess carotene, but unlike excess vitamin A, carotene is non-toxic. Although hypercarotenemia is not particularly dangerous, it can lead to an oranging of the skin (carotenodermia), but not the conjunctiva of eyes (thus easily distinguishing it visually from jaundice). It is most commonly associated with consumption of an abundance of , but it also can be a medical sign of more dangerous conditions.
Production
Carotenes are produced in a general manner for other terpenoids and terpenes, i.e. by coupling, cyclization, and oxygenation reactions of isoprene derivatives. Lycopene is the key precursor to carotenoids. It is formed by coupling of geranylgeranyl pyrophosphate and geranyllinally pyrophosphate. (2025). 9780471238966 ISBN 9780471238966
Synthesis
There are currently two commonly used methods of total synthesis of β-carotene. The first was developed by BASF and is based on the Wittig reaction with Wittig himself as patent holder:Wittig G.; Pommer H.: DBP 954247, 1956Wittig G.; Pommer H. (1959). Chem. Abstr''. 53: 2279
Nomenclature
Carotenes are containing no oxygen. Carotenoids containing some oxygen are known as .
Food additive
Carotene is used to colour products such as juice, cakes, desserts, butter and margarine. It is approved for use as a food additive in the EU (listed as additive E160a)UK Food Standards Agency: Australia and New Zealand (listed as 160a)Australia New Zealand Food Standards Code and the US.US FDA:
See also
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