At least 600 carotenoids have been identified in natural sources, and they divide into hydrocarbons carotenoids (lycopene and beta-carotene) and their oxygenated derivatives called xanthophylls, which contain hydroxyl or keto groups (astaxanthin, lutein, zeaxanthin).
Carotenoids play a crucial role in human health and are essential to human vision by acting as biological antioxidants that protect cells such as DNA, cell membrane lipids, and proteins from the damaging effects of free radicals. Astaxanthin, a carotenoid naturally found in salmon, shrimp, and other seafoods, is the most abundant carotenoid in the marine world and exhibits potent antioxidant properties.
The most important and abundant carotenoids are composed of a 40-carbon polyene skeleton chain, terminated by six carbon rings with or without keto or hydroxyl groups. This specific structure of alternating single and double bonds in the polyene skeleton of carotenoids is responsible for the absorption of excess energy from other molecules by charge resonance, while the nature of the specific end groups on carotenoids are responsible for their polarity and hence for their solubility in both oil and water environments. These properties are critical factors that might account for the amazing antioxidant properties of carotenoids.
Because carotenoids are fat-soluble (hydrophobic), they are found in fatty tissues in the human body and are transported in blood bounded by lipoproteins. The predominant carotenoids found in human tissues are beta-carotene, alpha-carotene, lycopene, lutein, zeaxanthin, astaxanthin, and beta-cryptoxanthin; their quantities depend on dietary intake.
Carotenoids are powerful antioxidants, protecting the cells of the body from damage caused by free radicals. Valuable and numerous clinical and epidemiological studies show that increased consumption of foods rich in carotenoids is associated with decreased risk of some degenerative diseases, as well as improved immune system function. Carotenoids have also demonstrated the ability to stimulate cell-to-cell communication. Researchers have suggested that poor communication between cells might be one of the main causes of unchecked division of cells, a condition that eventually leads to cancer. By promoting proper communication between cells, carotenoids may play a role in cancer and age related disease prevention, including age-related macular degeneration, cataracts, and other health conditions linked to oxidative or free radical damage.
On the other hand, the results of two double-blind studies suggest that supplementation with synthetic beta-carotene does not reduce the risk of lung cancer and may even increase its risk in smokers. This particular finding suggests that foods that are high in carotenoids may protect against cancer in humans for reasons unrelated to their carotenoid content, and that synthetic beta-carotene may have differing effects from natural beta-carotene, or that found in astaxanthin.
Carotenoids are important to human nutrition as a source of Vitamin A (e.g. from beta-carotene) and as a prevention agent for cancer and heart disease (e.g. lycopene). Carotenoids generally contain a conjugated polyene structure efficient at absorbing light, so they act as light-harvesting complexes (together with proteins) in the photosynthetic process. Carotenoids are also important precursors of many natural flavor and fragrance products extracted from flowers and other plants.
To read more about carotenoids, visit:
The Carotenoids Page
http://dcb-carot.unibe.ch/carotint.htm
The Carotenoid Society
http://www.carotenoidsociety.org/
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