Provitamin A carotenoids

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. 

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. 

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. 

During, A, and Harrison, EH, 2007. Mechanisms of provitamin A (carotenoid) and vitamin A (retinol) transport into and out of intestinal Caco-2 cells. J Lipid Res 48, 2283-2294. 

Upregulation of retinoid receptor expression and function by provitamin A carotenoids may play a role in mediating the growth inhibitory effects of retinoids in cancer cells (Lian et al. 2006, Prakash et al. 2004). However, it is unclear if non-provitamin A carotenoids and their metabolites may act... 

Vine, A.L. and Bertram, J.S. 2005. Up-regulation of connexin 43 by retinoids but not by non-provitamin A carotenoids requires RARs. Nutr Cancer 52 105-113. 

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