Of carotenoids

Carotenoids are natural pigments characterized by a tail to tail linkage between two C20 units and an extended conjugated system of double bonds They are the most widely dis tributed of the substances that give color to our world and occur m flowers fruits plants insects and animals It has been estimated that biosynthesis from acetate produces approximately a hundred million tons of carotenoids per year The most familiar carotenoids are lycopene and (3 carotene pigments found m numerous plants and easily isolable from npe tomatoes and carrots respectively... 

IPP react with each other, releasiag pyrophosphate to form another allyl pyrophosphate containing 10 carbon atoms. The chain can successively build up by five-carbon units to yield polyisoprenes by head-to-tad condensations alternatively, tad-to-tad condensations of two units can yield squalene, a precursor of sterols. Similar condensation of two C2Q units yields phytoene, a precursor of carotenoids. This information is expected to help ia the development of genetic methods to control the hydrocarbon stmctures and yields. 

Bleaching Herbicides. Membrane-based modes of herbicidal action relevant to photosynthesis (37) include those of inhibitors of carotenoid biosynthesis, eg, norflura2on, diftmon, y -phenoxyben2amines inhibitors of chlorophyll biosynthesis, eg, oxadia2on, DTP or... 

Isophorone usually contains 2—5% of the isomer P-isophorone [471-01-2] (3,5,5-trimethyl-3-cyclohexen-l-one). The term a-isophorone is sometimes used ia referring to the a,P-unsaturated ketone, whereas P-isophorone connotes the unconjugated derivative. P-lsophorone (bp 186°C) is lower boiling than isophorone and can be converted to isophorone by distilling at reduced pressure ia the presence of -toluenesulfonic acid (188). Isophorone can be converted to P-isophorone by treatment with adipic acid (189) or H on(Ill) acetylacetoate (190). P-lsophorone can also be prepared from 4-bromoisophorone by reduction with chromous acetate (191). P-lsophorone can be used as an iatermediate ia the synthesis of carotenoids (192). 

Tetraterpenes. Carotenoids make up the most important group of C q terpenes and terpenoids, although not all carotenoids contain 40 carbon atoms. They are widely distributed in plant, marine, and animal life. It has been estimated that nature produces about 100 million t/yr of carotenoids synthetic production amounts to several hundred tons per year (207,208). 

P-Carotene is prescribed in the treatment of the inherited skin disorder erythropoietic protoporphyria (EPP) to reduce the severity of photosensitivity reactions in such patients. The essential theoretical background relevant to the role of carotenoids as photoconductors has been reviewed (211). P-Carotene has also been used as a photoconductor in recording-media film. 

Paul Karrer chemistry research iato constitution of carotenoids, flavins, and vitamins A and B2... 

Fertile sources of carotenoids include carrots and leafy green vegetables such as spinach. Tomatoes contain significant amounts of the red carotenoid, lycopene. Although lycopene has no vitamin A activity, it is a particularly efficient antioxidant (see Antioxidants). Oxidation of carotenoids to biologically inactive xanthophyUs represents an important degradation pathway for these compounds (56). 

In milk approximately 90% of the yellow color is because of the presence of -carotene, a fat-soluble carotenoid extracted from feed by cows. Summer milk is more yellow than winter milk because cows grazing on lush green pastures in the spring and summer months consume much higher levels of carotenoids than do cows ham-fed on hay and grain in the fall and winter. Various breeds of cows and even individual animals differ in the efficiency with which they extract -carotene from feed and in the degree to which they convert it into colorless vitamin A. The differences in the color of milk are more obvious in products made from milk fat, since here the yellow color is concentrated. Thus, unless standardized through the addition of colorant, products like butter and cheese show a wide variation in shade and in many cases appear unsatisfactory to the consumer. 

Walter Haworth and Paul Karrer (W. H.) investigations on carbohydrates, vitamin C and (P. K.) investigation of carotenoids, flavins, and vitamins A and B2... 

Araki, G., and Murai, T., Progr. Theoret. Phys. [Kyoto) 8, 639, Molecular structure and absorption spectra of carotenoids. Application of the Tomonaga theory of Fermions (S. Tomonaga, Progr. Theoret. Phys. [Kyoto) 5, 544 (1950)) for one-dimensional case. 

Montenegro, M.A. Nazareno, M.A Durantini, E.N. Borsarelli, G.D. (2002). Singlet oxygen quenching ability of carotenoids in a reverse micelle membrane mimetic system. Photochemistry and Photobiology, Vol. 75, No. 4, (April 2002), pp.353-361, ISSN 0031-8655... 

Anderson, I.C. Robertson, D.S. (1960). Role of carotenoids in protecting chlorophyll from photodestruction. Plant Physiology, 35, 531-4. 

For syntheses of carotenoids (4), where R is a large group, disconnection (a) achieves the most simplification. How would you make the phosphonium salt (5) needed for this strategy ... 

Krinsky NI Actions of carotenoids in biological systems. Annu Rev Nutr 1993 13 561. 

The antioxidant activities of carotenoids and other phytochemicals in the human body can be measured, or at least estimated, by a variety of techniques, in vitro, in vivo or ex vivo (Krinsky, 2001). Many studies describe the use of ex vivo methods to measure the oxidisability of low-density lipoprotein (LDL) particles after dietary intervention with carotene-rich foods. However, the difficulty with this approach is that complex plant foods usually also contain other carotenoids, ascorbate, flavonoids, and other compounds that have antioxidant activity, and it is difficult to attribute the results to any particular class of compounds. One study, in which subjects were given additional fruits and vegetables, demonstrated an increase in the resistance of LDL to oxidation (Hininger et al., 1997), but two other showed no effect (Chopra et al, 1996 van het Hof et al., 1999). These differing outcomes may have been due to systematic differences in the experimental protocols or in the populations studied (Krinsky, 2001), but the results do indicate the complexity of the problem, and the hazards of generalising too readily about the putative benefits of dietary antioxidants. 

The absorption and transport processes of many of the phytochemicals present in food are complex and not fully understood, and prediction of their bioavailability is problematic. This is particularly true of the lipid-soluble phytochemicals. In this chapter the measurement of carotenoid bioavailability will be discussed. The carotenoids serve as an excellent example of where too little understanding of food structure, the complexity of their behaviour in foods and human tissues, and the nature and cause of widely different individual response to similar intakes, can lead to misinterpretation of study results and confusion in our understanding of the relevance of these (and other) compounds to human health. 

Functional benefits of carotenoids vision, cancer and cardiovascular disease... 

All the actual or putative functional benefits of carotenoids are dependent on their bioavailability amounts consumed, amounts released from the food structure during digestion and extent of absorption and tissue distribution. The following three sections deal with each of these issues in turn. 

Table 7.1 Common dietary sources of carotenoids in regular vegetable foods, xg/100 fresh weight. Data are means derived from literature sources. The normal range of values is the mean at least 85%, and depends upon variety, agronomic conditions, tissue sampled and maturity... 

Table 7.1 shows the common dietary sources of carotenoids in regular vegetable foods, p,g/100 fresh weight. Although the greatest amount of the hydrocarbon carotenoids is present as the all-trans isomer, there is always a proportion of cis isomers present. This table represents only a small number of the fruits and vegetables that contribute carotenoids in the European diet. For more comprehensive information readers are directed to A European Carotenoid Database O Neill et al, 2001, which lists the carotenoid composition of over 100 food items. 

The complex nature of the mass transfer of carotenoids to absorbable lipid species, the diversity of raw and processed foods consumed, and individual variations in the degree of mastication, will lead to differences in the amount of carotenoid that becomes bioaccessible and potentially available for absorption. By understanding the underlying mechanisms of these processes, for a wider range of fruit and vegetable constituents, it will become possible... 

A small but variable proportion of the carotenoids with one or two P-ionone rings (mainly P-carotene) are cleaved in the enterocytes to produce retinol (vitamin A). This process is very tightly controlled, so that too much vitamin A is not produced, although the control mechanism is not clear. Some cleavage of P-carotene can also occur in the liver, but this does not account for the turnover of P-carotene in the body. Small amounts of carotenoids are subject to enterohepatic circulation, but this does not account for losses. 

The measurement of carotenoid absorption is fraught with difficulties and riddled with assumptions, and it is therefore a complex matter. Methods may rely on plasma concentration changes provoked by acute or chronic doses, oral-faecal mass balance method variants and compartmental modelling. 

FURR H c and clark r m (1997) Intestinal absorption and tissue distribution of carotenoids. J Nutr Biochem. 8(7) 364-77. 

GIOVANNUCCI E, ASCHERIO A, RIMM E B, STAMPFER M J, COLDITZ G A and WILLETT W 0 (1995) Intake of carotenoids and retinol in relation to risk of prostate cancer. JNatl Cancer Inst. 87(23) 1767-76. 

HART J D and SCOTT K J (1995) Development and evaluation of an HPLC method for the analysis of carotenoids in foods and the measurement of carotenoid content of vegetables and fruits commonly consumed in the UK. Food Chem. 54(1) 101-111. 

KHACHiK F BEECHER G R and GOLi M B (1992) Separation and identification of carotenoids and their oxidation products in the extracts of human plasma. Anal Chem. 64(18) 2111-22. 

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