Carotenoids, definition

Carotenoids can be converted into mixtures of geometrical isomers under appropriate conditions, the most common being iodine catalyzed photoisomerization. This produces an equilibrium mixture of isomers, in general the all-trans isomers predominates. These isomers in an isomeric mixture cannot be measured separately by simple spectrophotometric determination. The usual method of subsequent measurement would be chromatographic separation, diode-array detection, and spectral analysis. In the absence of any definitive data on extinction coefficients for cfv-isomcrs, they are quantified against the all-trans isomer. Modem procedures involve the direct synthesis of c/.v-carotcnoids. 

It must be stressed that the value obtained in this way for mixtures of carotenoids is only an approximation. For more definitive analysis column chromatography (unit F2.3) should be used. 

He defines the carotenoids as natural compounds and the polymethines as synthetic. He also makes a distinction between polymethine dyes and carbonyl dyes. The Rhodonines appear to satisfy both his definitions. 

The term lipid can be defined as fatty acids, their derivatives, and substances related biosynthetically or functionally to these compounds. This definition encompasses cholesterol and bile acids, but does not include other steroids, fat-soluble vitamins, carotenoids, or terpenes (Christie, 1987, p. 42). 

Figure 29-3. Chemical structures of important vitamin A species and the provitamin A carotenoid i-carotene. All-fra/w-fi-carolene (T) is the most important provitamin A carotenoid, which can be converted to all-fraws-retinal and then all-tram-retinol (If), which by definition is vitamin A. All-tram-retinol can be esterified with long-chain fatty acids to form retinyl ester (III), the storage form of vitaminA in the body.The active form of vitamin A in vision is 11-cts-retinal (TV).The transcriptionally active forms of vitaminA are all-tram-retinoic acid (V) and 9-cts-retinoic acid (VI). 13-cA-Retinoic acid (VII) has poor transcriptional regulatory activity but is used clinically as isotretinoin to treat skin diseases.

The vitamin A content of foods is often given in terms of the international unit (IU). One IU of vitamin A is defined as 0.3 tg of all-trans-retinol. The term retinol equivalent (RE) is used to convert all sources of vitamin A and carotenoids in the diet to a single unit. One RE is by definition 1 pg of all-trans retinol, 12 pg of P-carotene, or 24 pg of other (mixed) provitamin A carotenoids. The recommended dietary allowance for vitamin A ranges from 375 pg RE/day for infants to 1,000 RE/day for adults. 

An important event this year is the publication of Carotenoids . This volume should be a definitive reference work on carotenoids for many years, and the scope of the book can be judged from its contents. To a large extent this volume replaces the standard work by the late Professor P. Karrer, and a review of the significance of his pioneering studies and recent developments has appeared. Other reviews have covered aspects of ionone chemistry, polyprenol quinones and related compounds,and theoretical calculations on the u.v. spectra of polyenes. ... 

International Union of Pure and Applied Chemistry, /. Am. Chem. Soc. 82, 5575-84 (I960) Definitive rules for the nomenclature of amino acids, steroids, vitamins, and carotenoids (lUPAC). 

Vesely and Jakes (13) pointed out that the definition for lipides adopted in 1923 was not sufficiently precise. It included, among lipides, the fats formed of mixtures of esters and nonlipidic substances (free fatty acids, steroids, carotenoids, hydrocarbons) on the other hand, certain essential oils formed mainly of esters might be considered lipides. Vesely and Jakes advocated a more precise and concise definition for lipides natural esters nonvolatile with steam and possessing no aromatic ring in their molecule. ... 

Capsaicin was prepared and being evaluated by the military as early as the 1920s in the United States. Interest in its development waned when CS was synthesized, and research efforts were redirected to the development of CS as an RCA. Unlike the other RCAs such as CS, CR and CN, which have definite chemical compositions, OC is a mixture of compounds containing capsaicinoids, various acids and esters, alcohols, aldehydes, ketones, and carotenoid pigments. Capsaicin as the major component is considered to be the active ingredient without consideration as to the activity or interactions of the other capsaicinoids or components. Although the activity of the other capsaicinoids is similar, they differ in potency. 

It was observed that people with low carotenoid intake or low blood levels have an increased risk of degenerative diseases. In a number of these diseases free radical damage plays a role in the pathophysiology of the disease. Earlier studies were focused mainly on p-carotene and the lycopene protective effect against prostate and lung cancer, but there is as yet no definitive proof for a causal relationship or for a beneficial antioxidant effect of carotenoids. 

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