Beta-carotene (β-carotene; BAY-tuh KARE-oh-teen) belongs to a family of organic compounds called the carotenoids. The carotenoids are all brightly pigmented (colored) compounds found in a number of plants, bacteria, algae, and fungi. Beta-carotene is responsible for the yellowish to orange color of pumpkins, apricots, sweet potatoes, nectarines, and, most notably, carrots. The compound also occurs in spinach and broccoli, but in such small concentrations that the green chlorophyl present masks the orange color of beta-carotene. In its pure form, beta-carotene occurs as purple crystals shaped like thin leaflets.
In plants, algae, and photosynthetic bacteria, beta-carotene plays an important role in photosynthesis, the process by which plants convert water and carbon dioxide into carbohydrates and oxygen. In nonphotosynthetic bacteria and fungi, beta-carotene protects the organism against the harmful effects of light and oxygen.
Insoluble in water; slightly soluble in alcohol; soluble in ether, acetone, benzene, and fats
Animals require beta-carotene for normal growth and development, but are unable to manufacture the compound themselves. As a result, they must ingest some beta-carotene from plant sources in order to stay healthy. The compound is a provitamin, a substance that is converted in the body to a vitamin. Beta-carotene is converted into vitamin A, whose role in the body is the maintenance of strong bones and teeth and healthy skin and hair.
Beta-carotene was first isolated by the German chemist Heinrich Wilhelm Ferdinand Wackenroder (1789–1854), who extracted the compound from carrot roots in 1831. The compound was first synthesized in 1950 by the Swiss chemist Paul Karrer (1889–1971).
HOW IT IS MADE
Beta-carotene can be obtained from natural sources by crushing or pulverizing the source (such as carrots) and adding a solvent that will dissolve the organic components of the plant. These components can then be separated from each other by chromatographic techniques. A major commercial source of beta-carotene obtained by this method is the algae Dunaliella salina, which grows in large salt lakes in Australia. The compound can also be prepared synthetically by one of two methods, the BASF and the Roche methods, both named after the pharmaceutical firms where they were developed. Both methods of preparation begin with long-chain hydrocarbons containing about twenty carbon atoms each. These hydrocarbons are then joined to each other to form the 40-carbon beta-carotene compound.
- The name carotene comes from the Latin word for "carrot."
- Scientists have found a way to change the genetic structure of rice so that it contains beta-carotene. The modified rice is designed to help people in countries where vitamin A deficiency is a serious problem.
- At least eight other carotenoids are known. They include α-carotene, β,ψ-carotene, and ψ, ψ-carotene.
COMMON USES AND POTENTIAL HAZARDS
Beta-carotene has two uses: in vitamin supplements and as a food additive. Anyone who eats a healthy diet that includes foods rich in vitamin A, such as fish oil, liver, eggs, butter, and orange or yellow vegetables and fruits, will get adequate amounts of beta-carotene. However, many people take vitamin supplements to ensure that they have enough beta-carotene (as well as other vitamins) in their daily diet. Although some warnings have been issued about taking too much vitamin A, there is no clinical evidence that an overdose of the vitamin does any long-term harm to a person.
Beta-carotene is used as a food additive to increase the color intensity of a product. It is used primarily with yellow and orange foods, such as butter and margarine, although it is sometimes added to ice cream and fruit juices as well. Beta-carotene is used in only very small amounts as a food additive. In these amounts, it poses no health hazard to humans or other animals. The compound has also been used in experiments to test its effectiveness against certain diseases, such as lung cancer. In such cases, it has been found to be more harmful than beneficial, increasing the risk of cancer and death among people participating in the studies.
Words to Know
- A chemical that attacks free radicals, chemical structures that attack cells and may be responsible for the development of cancer.
- A process by which a mixture of substances passes through a column consisting of some material that causes the individual components in the mixture to separate from each other.
- FREE RADICAL
- An atom or group of atoms with a single unpaired electron. Free radicals are very active chemically and tend to attack and destroy other compounds. They are responsible for damage in cells that may lead to a number of health problems, including cancer and ageing.
- A chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants.
FOR FURTHER INFORMATION
"Beta-carotene." University of Bristol School of Chemistry. http://www.chm.bris.ac.uk/motm/carotene/beta-carotene_home.html (accessed on September 22, 2005).
"Beta-carotene." University of Maryland Medical Center. http://www.umm.edu/altmed/ConsSupplements/BetaCarotenecs.html (accessed on September 22, 2005).
Palvetz, Barry A. "A Bowl of Hope, Bucket of Hype?" The Scientist (April 2, 2001): 15.
"Taking Supplements of the Antioxidant." Consumer Reports (September 2003): 49.
Beta-carotene is one of the class of over 600 carbon-based compounds known as carotenoids. Beta-carotene is found in a variety of plants, and provides the color to oranges and carrots. In nature, beta-carotene protects these food sources from the degrading effect of oxygen. Beta-carotene is a fat-soluble chemical, requiring the presence of fatty acids to assist in its absorption into the body. In addition to carrots, beta-carotene is abundant in broccoli and other green vegetables.
Beta-carotene is very similar in its structure to vitamin A (also known as retinol), a chemical essential to human health. Vitamin A is of particular importance to both vision and healthy bone development. Beta-carotene acts as a precursor to vitamin A, where the body will use beta-carotene to manufacture vitamin A if a deficiency in the vitamin is detected. It is for this reason that beta-carotene is also known as a provitamin A.
Beta-carotene has attracted significant attention in the medical community in recent years due to its recognized powers as an antioxidant. Antioxidants are a class of chemicals that are ingested into the body from a variety of food sources. Each has an ability to neutralize the effect of the chemical agents known as free radicals, whose electrochemical composition compels them to seek out molecules within the body from which more electrons can be taken, so as to convert the radical into a stable molecule. The most common and the most potentially destructive of the free radicals are those composed of unstable oxygen molecules, O2. The actions of the free radicals, if unimpeded, will trigger a chain reaction of electron thievery, as each molecule attempts to correct its own electron imbalance. These chain reactions are at the root of the cellular damage caused within the body that potentially leads to the formation of cancers, and is believed to precipitate aging.
Antioxidants such as beta-carotene scavenge the cardiovascular system, neutralizing the O2 radical through a donation of an electron to the radical.
There is considerable debate in the scientific community as to the effect of additional dietary supplements of beta-carotene as antioxidants, as opposed to the ingestion of these chemicals through natural food sources. There is a clear correlation between the increased daily consumption of fruits and vegetables, and the lower risk of cancers and heart disease.
Beta-carotene is the most active of the deeply colored pigments called carotenoids . After consumption, beta-carotene converts to retinol, a readily usable form of vitamin A. Beta-carotene's beneficial effects include protecting the skin from sunlight damage, fighting early cancer cells, boosting immunity, and preventing cataract formation. It also stops the creation of free radicals (oxidants), which are DNA-damaging molecular fragments in the body.
Food sources of beta-carotene include carrots, spinach, kale, and broccoli, as well as animal sources such as liver, whole eggs, and whole milk. Since beta-carotene is fat-soluble, most fat-free milk has been fortified with vitamin A to replace what is lost when the fat is removed.
Vitamin A is stored in the body, and an excess amount can lead to acute symptoms, such as vomiting and muscle weakness, as well as chronic problems such as liver abnormalities, birth defects, and osteoporosis . In addition, beta-carotene supplements have been found in some studies to actually increase the risk of cancer in smokers. (Excess beta-carotene is not stored in the body, however.) Because of these dangers, the Institute of Medicine recommends that beta-carotene supplements are not to be used by the general public. The institute does advocate the use of such supplements for populations with inadequate vitamin A intake.
see also Antioxidants; Carotenoids; Vitamins, Fat-Soluble.
Margen, Sheldon, and the Editors of UC Berkeley Wellness Letter (2002). Wellness Foods A to Z: An Indispensable Guide for Health-Conscious Food Lovers. New York: Rebus.
Wellness Guide to Dietary Supplements. "Beta-Carotene." Available from <http://www.berkeleywellness.com>