beta-Carotene
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| β-Carotene | |
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| CAS number | [] |
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| Properties | |
| Molecular formula | C40H56 |
| Molar mass | 536.87 g mol−1 |
| Appearance | red-purple solid |
| Density | 0.941 ± 0.06 g/cm3 |
| Melting point |
180-182 °C |
| Solubility in water | Insoluble in cold water or hot water. Soluble in diethyl ether, acetone, benzene, chloroform, carbon disulfide. Moderately soluble in petroleium ether, oils.Very slightly soluble in methanol.
Soluble in fat solvents |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
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β-Carotene is an organic compound - a terpenoid, a red-orange pigment abundant in plants and fruits. As a carotene with β-rings at both ends, it is the most common form of carotene. It is a precursor (inactive form) of vitamin A.[1] Being highly conjugated, it is deeply colored, and as a hydrocarbon lacking functional groups, it is very lipophilic.
The structure was deduced by Karrer et al.[2] In nature, β-carotene is a precursor to vitamin A via the action of beta-carotene 15,15'-monooxygenase. β-Carotene is also the substance in carrots that colours them orange. β-Carotenoid is biosynthesized from geranylgeranyl pyrophosphate.[1]
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[edit] Pro-vitamin A activity and sources in the diet
Plant carotenoids are the primary dietary source of pro-vitamin A worldwide, with β-carotene as the most well-known pro-vitamin A carotenoid. Carotenoids are absorbed into the small intestine by passive diffusion. One molecule of beta-carotene can be cleaved by a specific intestinal enzyme into two molecules of vitamin A.
Until recently, vitamin A activity in foods was expressed as international units (IU). This is still the measurement generally used on food and supplement labels. However, it is difficult to calculate the total vitamin A activity in the diet in terms of IU, because both the absorption and conversion of carotenoids, as compared with retinol, are variable. Absorption efficiency is estimated to be between 9-22%. The absorption and conversion of carotenoids may depend on the form that the beta-carotene is in (cooked vs. raw vegetables, in a supplement), intake of fats and oils at the same time, and the current levels of vitamin A and beta-carotene.
One retinol equivalent is equal to:
1 RE = 1 µg retinol
1 RE = 6 µg beta-carotene
1 RE = 12 µg other provitamin A carotenoids
1 RE = 3.33 IU vitamin A activity from retinol
1 RE = 10 IU vitamin A activity from beta-carotene
Beta-carotene is abundant in Vietnamese gac (Momordica Cochinchinensis Spreng), crude palm oil, yellow and orange fruits, such as mangoes and papayas, orange root vegetables such as carrots and yams and in green leafy vegetables such as spinach, kale, sweet potato leaves, and sweet gourd leaves. Vietnam gac and crude palm oil have by far the highest content of β-carotene of any known fruit or vegetable, 10 times higher than carrots for example. However, Gac is quite rare and unknown outside its native region of SE Asia, and crude palm oil is typically processed to remove the cartenoids before sale to improve the color and clarity.
[edit] Side effects
The most common side effect of excessive β-carotene consumption is carotenodermia, a harmless condition that presents as a conspicuous orange skin tint arising from deposition of the carotenoid in the outermost layer of the epidermis[3]. Chronic, high doses of β-carotene have been associated with increased rate of lung cancer among those who smoke.[4]
[edit] See also
[edit] References
- ^ a b Susan D. Van Arnum (1998). Vitamin A in Kirk-Othmer Encyclopedia of Chemical Technology. New York: John Wiley. pp. 99–107. doi:.
- ^ P. Karrer, A. Helfenstein, H. Wehrli, A. Wettstein (1930). "Pflanzenfarbstoffe XXV. Über die Konstitution des Lycopins und Carotins". Helvetica Chimica Acta 13: 1084–1099. doi:.
- ^ Stahl W, Heinrich U, Jungmann H, et al. (1998). "Increased Dermal Carotenoid Levels Assessed by Noninvasive Reflection Spectrophotometry Correlate with Serum Levels in Women Ingesting Betatene". Journal of Nutrition 128 (5): 903-7. PMID 9567001.
- ^ Tanvetyanon T, Bepler G (July 2008). "Beta-carotene in multivitamins and the possible risk of lung cancer among smokers versus former smokers: a meta-analysis and evaluation of national brands". Cancer 113 (1): 150–7. doi:. PMID 18429004.
[edit] External links
- A11
- USDA Webpage on β-carotene Content of Gac - Fatty Acids and Carotenoids in Gac (Momordica Cochinchinensis Spreng) Fruit.
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