Carotenoid, provitamin

Among the several vitamins in this classification, only vitamin A is present in appreciable quantity as carotenoid provitamin A in citrus (38). No vitamin D has ever been reported in citrus nor any plant vitamin D precursors, such as ergosterol. Several of the sterols present in citrus fruits are reported (39, 40, 41), but they are not related to vitamin D. 

Vitamin A is used to fortify margarine and skim milk. It is added to margarine at a level of 3,525 IU per 100 g. Some of the carotenoids (provitamin A) are used as food colors. 

DIETARY REFERENCE INTAKE FOR VITAMIN A ILaHI The current DRI is 700 (women) to 900 (men) meg, which is the equivalent of 2,333 to 3,000 international units (IU). For packaged goods, look on the Nutrition Facts panel for vitamin A content higher than 10 percent DV (daily value), and look on the ingredients list as well for a carotenoid provitamin A source—such as one of the superfruits. 

In a previous work, Di Scala and Crapiste (2005) studied the effect of temperature on some of the most important quality characteristics of individual pieces of red sweet pepper Capsicum annuum. L) during drying. Color and antioxidant content are among the main quality attributes of these vegetables besides textural and flavor attributes. Both carotenoids (provitamin A) pigments and ascorbic acid contents are related to pepper variety (Roura et al., 2001) and technological factors. 

The following sections focus on the antioxidant potential of several natural vitamins, such as carotenoids (provitamin-A), tocophaols (vitamin-E), and ascorbic acid (vitamin-C) against the oxidative deterioration of oil based systems. For each specific compound, the mechanisms of action... 

An important function of certain carotenoids is their provitamin A activity. Vitamin A may be considered as having the stmcture of half of the P-carotene molecule with a molecule of water added at the end position. In general, all carotenoids containing a single unsubstituted P carotene half have provitamin A activity, but only about half the activity of P carotene. Provitamin A compounds are converted to Vitamin A by an oxidative enzyme system present in the intestinal mucosa of animals and humans. This conversion apparendy does not occur in plants (see Vitamins, VITAMIN a). 

Vitamin A constitutes the most significant sector of the commercial retinoid market and is used primarily in the feed area. In the pharmaceutical area, there are several important therapeutic dermatologic agents which stmcturaHy resemble vitamin A and they are depicted in Figure 2 (see Pharmaceuticals). The carotenoids as provitamin A compounds also represent an important commercial class of compounds with P-carotene [7235-40-7] (10) occupying the central role (Fig. 3) (9). 

Biological, spectroscopic, and chromatographic methods have been used to assay vitamin A and the carotenoids. Biological methods have traditionally been based on the growth response of vitamin A—deficient rats. The utiUty and shortcomings of this test have been reviewed (52,53). This test has found apphcabiUty for analogues of retinol (54,55). Carotenoids that function as provitamin A precursors can also be assayed by this test (56). 

Many carotenoids function in humans as vitamin A precursors however, not all carotenoids have provitamin A activity (Table 3). Of the biologically active carotenoids, -carotene has the greatest activity. Despite the fact that theoretically one molecule of -carotene is a biological source of two molecules of vitamin A, this relationship is not observed and 6 p.g -carotene is equivalent to 1 p. vitamin A. Although -carotene and vitamin A have complementary activities, they caimot totally replace each other. Because the conversion of -carotene to vitamin A is highly regulated, toxic quantities of vitamin A cannot accumulate and -carotene can be considered as a safe form of vitamin A (8). 

Animals cannot synthesize vitamin A-active compounds and necessary quantities are obtained by ingestion of vitamin A or by consumption of appropriate provitamin A compounds such as P-carotene. Carotenoids are manufactured exclusively by plants and photosynthetic bacteria. Until the discovery of vitamin A in the purple bacterium Halobacterium halobium in the 1970s, vitamin A was thought to be confined to only the animal kingdom (56). Table 4 Hsts RDA and U.S. RDA for vitamin A (67). 

D. Bhatia, ed., "Vitamius, Part III Vitamin A and Provitamin Carotenoids," iu the Emyc/opedia of Food Science and Techno/og, ]olm. Wiley Sons, Inc., New York, 1991. 

PApo-8 -carotenal. The specifications of this colorant. (38) were discussed earlier. P-Apo-8 -carotenal has provitamin activity with 1 g of the colorant equal to 1,200,000 lU of vitamin A. Like all crystalline carotenoids, it slowly decomposes ia air through oxidatioa of its coajugated double boads and thus must be stored ia sealed coataiaers uader an atmosphere of iaert gas, preferably under refrigeration. Also like other carotenoids P-apo-8 -carotenal readily isomerizes to a mixture of its cis and trans stereoisomers when its solutions are heated to about 60°C or exposed to ultraviolet... 

YE X, AL-BABILI s, KLOTZ A, ZHANG J, LUCCA p, BEYER p and POTRYKUS I (2000) Engineering provitamin A ( 3-carotene) biosynthesis pathway into (carotenoid-free) rice endosperm . Science, 287, 303-5. 

In animals, the major function of carotenoids is as a precursor to the formation of vitamin A. Carotenoids with provitamin A activity are essential components of the human diet, and there is considerable evidence that they are absorbed through the diet and often metabohzed into other compounds. Beyond their important role as a source of vitamin A for humans, dietary carotenoids, including those that are not provitamin A carotenoids, have been implicated as protecting against certain forms of cancer and cardiovascular disease. ... 

Rodriguez-Amaya, D.B., Carotenoids and Food Preparation The Retention of Provitamin A Carotenoids in Prepared, Processed, and Stored Foods, USAID/OMNI, Washington, D.C., 1997. 

Fruifs and vegetables also contain ofher bioactive substances such as polyphenols (including well-known pigments anthocyanins, flavonols) and non-provitamin A carotenoids (mainly lycopene, lutein, and zeaxanthin) that may have protective effects on chronic diseases. Polyphenols and carotenoids are known to display antioxidant activities, counteracting oxidative alterations in cells. Besides these antioxidant properties, these colored bioactive substances may exert other actions on cell signaling and gene expression. 

In order to exhibit provitamin A activity, the carotenoid molecule must have at least one unsubstituted p-ionone ring and the correct number and position of methyl groups in the polyene chain. Compared to aU-trans P-carotene (100% provitamin A activity), a-carotene, P-cryptoxanthin, and y-carotene show 30 to 50% activity and cis isomers of P-carotene less than 10%. Vitamin A equivalence values of carotenoids from foods have been recently revised to higher ratio numbers (see Table 3.2.2) due to poorer bioavailability of provitamin A carotenoids from foods than previously thought when assessed with more recent and appropriate methods. 

The underlying mechanisms involved in the activities of carotenoid oxidation products are due either to a possible role as precursors of retinoids that would be the active species for positive effects or to their own specific activities. This latter case is illustrated by the activity of non-provitamin A carotenoid oxidation products such as those derived from lycopene. However, biological effects of carotenoid oxidation products other than retinoids are only hypothesized in vivo in humans, which hypothesis has been used as the basic principle to justify in vitro studies of these compounds. 

Tables 4.2.1 and 4.2.2 show, respectively, major sources of P-carotene and other provitamin A carotenoids, especially a-carotene and P-cryptoxanthin. Since cis isomers have different biological and physical-chemical properties than their corresponding dll-trans carotenoids, whenever available, their distribution was included in the tables. The structures of P-carotene cis isomers are shown in Figure 4.2.1, whereas the structures of the other provitamin A carotenoids are presented in Figure...

Rich Food Sources of Other Provitamin A Carotenoids... 

Among thermal processes, canning caused the largest trans-to-cis isomerization of provitamin A carotenoids, increasing the total cis isomers by 39% for sweet potatoes, 33% for carrots, 19% for collards, 18% for tomatoes, and 10% for peaches 13-di-P-carotene was the isomer formed in highest amonnts. ... 

Losses of 45 to 48% in the P-carotene contents and formation of cis isomers were also verified by pasteurization of carrot juice at 110 and 120°C for 30 sec. No significant effects on trans-to-cis isomerization of a- and P-carotene isomers were observed after acidification and heating of carrot juice at 105°C for 25 sec. In addition, an increase of only 3% in the cis isomers of provitamin A carotenoids was observed after orange juice pasteurization. " ... 

Nyambaka, H. and Ryley, J., An isocratic reversed-phase HPLC separation of the stereoisomers of the provitamin A carotenoids (a- and (3-carotene) in dark green vegetables, Food Chem., 55, 63, 1996. 

Lessin, W.J., Catigani, G.L., and Schwartz, S.J., Quantification of ds-trans isomers of provitamin A carotenoids in fresh and processed fruits and vegetables, J. Agric. Food Chem., 45, 3728, 1997. 

Heinonen, M.I., Carotenoids and provitamin A activity of carrot (Daucus carota L.) cultivars, J. Agric. Food Chem., 38, 609,1990. 

Ahneida, L.B. and Penteado, M.V.C., Carotenoids with provitamin A activity of carrots Daucus carota L.) consumed in Sao Paulo, Brazil, Rev. Farm. Bioquim. Univ. S. Paulo, 23, 133, 1987. 

Englberger, L. et al.. Further analyses on Micronesian banana, taro, breadfruit and other foods for provitamin A carotenoids and minerals, J. Food Compos. Anal, 16, 219, 2003. 

Ye, X. et al.. Engineering the provitamin A (beta-carotene) biosynthetic pathway into (carotenoid-free) rice endosperm. Science 287, 303, 2000. 

Mercadante, A.Z. and Rodriguez-Amaya, D.B., Confirmation of the identity of a-cryptoxanthin and incidence of minor provitamin A carotenoids in green leafy vegetables, Cienc. Tecnol. Alim., 21, 216, 2001. 

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