Animal carotenoids, structure

FIGURE 2.2.1 Structures of common carotenoids (I. Main carotenes. II. Xanthophylls. III. Animal carotenoids). 

Figure 3 Selected carotenoid structures from bacteria, algae, plants, and animals, and of precursors and metabolic products with biologic function. The lUPAC numbering is given for lycopene (top right).

New Structures and Stereochemistry.—Carotenoids. Of the few new carotenoid structures that have been reported, all but one are from marine animals. Lac-tucaxanthin, a major xanthophyll in chloroplasts of lettuce (Lactuca sativa) and... 

Carotenoids, precursors of vitamin A, are natural pigments synthesized by plants and some microorganisms. Humans and animals are not able to synthesize and need to acquire them by alimentation. Beyond the health benefits promoted by vitamin A, these compounds have antioxidant capacity which gives protection for cardiovascular and degenerative diseases. The presence of conjugated double bonds in carotenoid structure COTitributes for their pigmentatiOTi, absorption of ultravioletA isible radiation, and antioxidant activity but also is the main reason... 

The carotenoids represent one of the most important and widespread groups of pigments in nature. The structures of some 500 of them are known, and they are responsible for many of the yellow and red colors of flowers, fruits, birds, insects, and other animals. " Carotenoids are synthesized de novo in all organisms except for animals, where the pigments are of dietary origin." Their universal presence in photosynthetic tissues is only noticeable at the onset of leaf senescence, when the chlorophylls disappear. The dramatic changes in color of ripening fruits also reflect the disappearance of chlorophyll and the concomitant, massive increase in carotenoids. 

There is as yet no agreed international list of permitted food colours. Thus a food dye that is permitted in one country may be considered unacceptable in another. The synthetic food colorants permitted in the European Union are listed in Table 1.8 [60]. All were originally introduced as acid dyes for wool many years ago. Furthermore, more than thirty colorants of natural origin are permitted in most countries. The natural carotenoid dyes are of outstanding importance for colouring edible fats and oils. These yellow to red methine dye structures occur in many families of plants and animals, including vegetables, berries,... 

Vitamin Ai (retinol) is derived in mammals by oxidative metabolism of plant-derived dietary carotenoids in the liver, especially -carotene. Green vegetables and rich plant sources such as carrots help to provide us with adequate levels. Oxidative cleavage of the central double bond of -carotene provides two molecules of the aldehyde retinal, which is subsequently reduced to the alcohol retinol. Vitamin Ai is also found in a number of foodstuffs of animal origin, especially eggs and dairy products. Some structurally related compounds, including retinal, are also included in the A group of vitamins. 

Animal tissues have yielded several carotenoids of previously unknown structure. Chiriquixanthins A and B from a yellow frog, Atelopus chiriquiensis, have been found to be epimeric e,e-carotene-3,3 -diols (18) and (19) differing... 

An important function of certain carotenoids is their provitamin A activity. Vitamin A may be considered as having the structure of half of the 3-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 3-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). 

The fat-soluble vitamins comprise vitamins A, D, E, and K, whose biological activities are attributed to a number of structurally related compounds known as vitamers. Also included are those carotenoids that are precursors of vitamin A. Recommended dietary allowances (RDAs) based on human epidemiological and experimental animal studies have been published in the United States for vitamins A, D, E, and K (1). Other countries and international bodies have compiled similar recommendations. In the United States and Canada, fluid milk is supplemented by law with vitamin D to a level of 400 international units per quart (10 /zg/0.95 L) to meet the RDA of 10 p%. Other commodities, such as margarine, milk products, ready-to-eat breakfast cereals, and dietetic foods, are commonly supplemented with vitamins A, D, and E. Except for infant formulas, vitamin K is not added to foods. The addition of vitamins to a particular processed food is intended to provide a specific proportion of the RDA. 

The structure of a number of important xanthophylls as they relate to the structure of P-carotene is given in Figure 6-22. Carotenoids may occur in foods as relatively simple mixtures of only a few compounds or as very complex mixtures of large numbers of carotenoids. The simplest mixtures usually exist in animal products because the animal organism has a limited ability to absorb and deposit carotenoids. Some of the most complex mixtures are found in citrus fruits. 

The surface pigmentation of marine animals is largely due to different caroteno-proteins, which may be yellow, orange, red, purple, blue, or green, depending on the structure of the complexes — the kind of carotenoid, predominantly astaxanthin, cantaxanthin, and (l-carotene, as well as the properties of the proteinaceous compo-... 

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