Carotenoids occurence

Typically several different carotenoids occur in plant tissues containing this class of pigments. Carotenoids are accumulated in chloroplasts of all green plants as mixtures of a- and P-carotene, P-cryptoxanthin, lutein, zeaxanthin, violaxanthin, and neoxanthin. These pigments are found as complexes formed by noncovalent bonding with proteins. In green leaves, carotenoids are free, nonesterified, and their compositions depend on the plant and developmental conditions. In reproductive... 

Both chlorophylls and carotenoids occur in all green leaves, but their color is masked by chlorophyll in photosynthetic tissues. When the chlorophylls break down as leaves senesce (mature), the yellow and orange carotenoids persist and the leaves turn yellow. Carotenoids are responsible for the colors of familiar animals such as lobsters, flamingos, and fish. Often people are unaware of the chemical nature of food colorants. ... 

In dark conditions, the spontaneous isomerization of carotenoids occurs in solution the rate is dependent on temperature, solvent, and carotenoid structure. In the case of P-carotene, 13-di-P-carotene was formed approximately three times faster than the 9-cis- isomer at room temperature and at 150°C. ... 

To measure distances in the wider temperature range, this procedure was modified. Relaxation of the carotenoid occurs through several different mechanisms including the dipolar-dipolar interaction. Assuming that kAA is the rate constant of the dipolar-dipolar interaction and K=(k,l + k2 + k3 +. ..) is the sum of the rate constants of all other relaxation pathways, we can extract kAA from the following equation ... 

In the eye, carotenoids occur mainly in the retina, but the xanthophylls, lutein and zeaxanthin, can also be detected in the lens and the ciliary body. The human lens contains lutein and zeaxanthin... 

Lycopene, a carotenoid occurring mainly in tomatoes, is extensively applied as a natural colouring agent in food and food products. 

The characteristic absorption spectrum of each carotenoid is determined by a series of conjugated double bounds, the so-called chromophore. Usually the spectrum shows three absorption bands, which are affected by the length of the chromophore, the nature of the double bound, and the taking out of conjunction of one double bond. Several absorption spectra of some common carotenoids are shown in Fig. 2. A change of solvent may, however, cause a shift of the absorption bands. Owing to the extensive double-bond system, carotenoids exist in many geometrical isomeric forms (Z or E isomers). In nature most carotenoids occur in the all-trans form (E isomers) cis isomers (Z isomers) are frequently present in small amounts (6). Cis isomers can be distinguished from trans isomers by a characteristic absorption band ( cis peak ) that appears at 300-360 nm (7). 

Due to their antioxidant status, carotenoids are extremely sensitive to UV light, as well as air and temperature [16]. In nature, each carotenoid occurs with several geometrical ZIE stereoisomers, which can isomerise or oxidise easily [17]. These carotenoid stereoisomers can differ considerably in their biological effectiveness, for instance in bioavailability [18,19], in quenching free radicals, or in the prevention of diseases [20]. Therefore, the unambiguous and quantitative analysis of the pattern of carotenoid stereoisomers from biological matrices is indispensable, especially with regard to dietary supplementation. 

It is conceivable that the different carotenoids have specialized functions in different tissues as has been shown for the xanthophylls lutein and zeaxanthin, which are virtually the only carotenoids occurring in the macular area of the retina. The distribution of lycopene in human tissues is shown in Table 63.2 and Table 63.3. 

One of the highest known concentrations of carotenoids occurs in crude palm oil. It contains about 15 to 300 times more retinol equivalent than carrots, green leafy vegetables, and tomatoes. All of the carotenoids in crude palm oil are destroyed by the normal processing and refining operations. Recently, improved gentler processes have been developed that result in a red palm oil that retains most of the carotenoids. The composition of the carotenes in crude palm oil with a total carotene concentration of 673 mg/kg is shown in Table 6-5. 

Carotenoids occur in essentially all green plants, algae, and photosynthetic bacteria, with over 600 types occurring in nature (150 types may be involved in photosynthesis). The dominant pigments for plant leaves are the... 

Carotenoids involved in photosynthesis are bound to and help stabilize chlorophyll-protein complexes, of which various types occur in the lamellar membranes of chloroplasts (Fig. 1-10). Carotenoids also are found in organelles known as chromoplasts, which are about the size of chloroplasts and are often derived from them. For instance, lycopene (red) is in tomato fruit chromoplasts, and a- and pi-carotenes (orange) occur in carrot root chromoplasts. A great diversity of carotenoids occurs in the chromoplasts of flower petals, which is important for attracting pollinators, and fruits, which aids in seed dispersal by attracting other animals. 

IMS is a relatively new technique in which ions are separated based on size and shape using an electric field. IMS was utilized by Dong et ah (2010) to separate all-trans -lycopene from cw-lycopene and all-irans -(3-carotene from cw-(3-carotene. Unfortunately, the various cis isomers could not be separated from each other using IMS alone. The authors provided evidence to suggest that cis/trans isomerization of carotenoids occur in-source (ESI positive mode was used in these experiments). Because of this isomerization, it does not appear likely that IMS will replace HPLC as a means of separating geometrical isomers of carotenoids in the near future (Dong et ah, 2010). 

Properties Yellow pigment. An oxygenated carotenoid occurring in green vegetation and in some animal products, notably egg yolk. Mp 190-3C. Insoluble in water slightly soluble in alcohol and ether. 

Carotenoids are susceptible to oxidative changes during dehydration due to the high degree of unsaturation in their chemical structure. The major carotenoids occurring in food are carotenes and oxycarotenoids (xanthophylls). 

Carotenoids occur in the leaves, shoots and roots of all higher plants (content up to... 

Fruits with low content of carotenoids (occurring mostly in chloroplasts) such as P-carotene, lutein, violaxanthin, neoxanthin (e. g., pineapples, bananas, figs and grapes). 

Table 18.11. Carotenoids occurring in fruit (Roman numerals refer to their structures shown in 3.8.4)...

The reaction products of singlet oxygen with carotenoids occurring in the natural singlet state ( carotenoids) are triplet oxygen and carotenoids in the excited triplet state ( carotenoids). Other reaction sequences of carotenoids are described in Section 5.2.6.2.I. 

Qualitative and quantitative composition of carotenoids depends on many factors, such as the species and varieties of plants, season, maturity stage, method of processing and other factors. In some fruits and also in potatoes, carotenoids occur in units of mg/kg, but in most fruits and vegetables they are present in dozens of mg/kg, and in carrots, tomatoes and peppers there are hundreds of mg/kg of carotenoids. 

Czeczuga B, Moberg R, Alstrup V (1992) Investigations on Carotenoids in Lichens XXXll. Carotenoids Occurring in the Thalli of Lichens from Kenya (Equatorial... 

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