Beta-Carotene: An Indispensable Phytochemical
The Most Biologically and Nutritionally Active Carotenoid
Jun 30, 2009
About 50 carotenoids have been identified in the human diet, 34 have been identified in the human serum, tissues, and breast milk. Of these, alpha-carotene, beta-carotene, and beta-cryptoxanthin serve as precursors of vitamin A. Plant Pigments and their Manipulation: Pigments in Human Health Maintenance (2004) CRC Press by Kevin M. Davies.
Beta-carotene (C40 H56) is an orange pigment found in most fruits and vegetables. It was discovered by Heinrich Wilhelm Ferdinand Wackenroder in 1831 in the roots of carrots and named the substance "carotin." Wackenroder was an analytical chemist at the Pharmaceutical Institute in Jena, Germany. Later in 1907, Richard Willstater assigned the formula C40 H56 to carotin. Handbook of Nutrition and Opthalmology (2007) Humana Press by Richard Semba M.D. MPH.
Characteristics of Beta-Carotene
Like all carotenoids, beta-carotene is:
- the most common form of carotene
- fat soluble - not water-soluble. In a mixed diet, 3-5 grams of fat is enough to ensure its absorption. Carotenoids suspended in oil are more efficiently absorbed than those in water or food.
- manufactured by plants - not animals. In plants, beta-carotene absorbs light, and energy from singlet oxygen - an unstable form of oxygen - and transfers both energies to chlorophyll for photosynthesis. It also acts as a pesticide.
- present in the all-trans configuration in raw fruits and vegetables
- converted to the cis- configuration during cooking. Cis- isomers are shorter in length and are less susceptible to "binding." They are more stable and are more bioavailable.
- released from the food matrix by: chewing, stomach action, and digestive enzymes. The vitamin A activity of beta-carotene in foods is half that of retinol (pre-formed vitamin A).
Biologic Activities of Beta-Carotene
- Beta-carotene is converted to Vitamin A (retinal) in the small intestines of mammals by beta-,carotene 15,15 monooxygenase (an enzyme). In times of plenty, retinal is stored in the liver. It is synthesized into active vitamin A in times of need.
- It quenches singlet oxygen. It also reacts with any radical species present in a biological system. As a powerful antioxidant, it breaks down and converts harmful products to inert substances.
- It prevents the oxidation of fat by breaking down the chain-reaction.
- It facilitates communication between cells by enhancing the expression of a gene that codes for connexin proteins. Connexin proteins forms pores or gap junctions in cell membranes, allowing cells to communicate through the exchange of small molecules.
- It improves immune function by protecting phagocytic cells (white blood cells that protects the body by ingesting harmful bodies, bacteria, dead/dying cells); enhancing the response of T & B cells (immune response cells); by stimulating the effects of T-cell functions, macrophage, and natural killer cell capacities, and by increasing the production of interleukins. Interleukins are signalling molecules on white blood cells. They mediate communication between cells.
- It helps maintain night vision. As vitamin A, beta-carotene maintains the cornea and participates in the conversion of light energy into nerve impulses at the retina. The cells of the retina contain rhodopsin, a pigment molecule. As rhodopsin absorbs light, retinal changes which triggers a nerve impulse that carries information to the brain.
- It protects against sunburn by: quenching radical oxygen species and interferring with several signalling pathways that result in UV-B exposure.
Significant Food Sources
Sweet potatoes tubers and leaves, carrots, cantaloupes, goji berries, palm oil, spinach, chard, egg yolk, liver,pumpkins, squash, mango, turnip greens.
References
Bendich A & Olson TA "Biological Actions of Carotenoids" FASEB Journal June 1989;3(8):1927-32
Davies KM "Carotenoids" in Plant Pigments and their Manipulation: Diverse Roles of Carotenoid Pigments Human Health Maintenance. CRC Press 2004
Sommer A et al. "Xeropthalmia and Keratomalacia" Vitamin A Deficiency: Health, Survival and Vision Oxford University Press, 1996
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