Color of carotenoids

The color of carotenoids is the result of the presence of a conjugated double bond system in the molecules. The electron excitation spectra of such systems are of interest for elucidation of their structure and for qualitative and quantitative analyses. 

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... 

Not all carotenoids are hydrocarbons Oxygen containing carotenes called xantho phylls which are often the pigments responsible for the yellow color of flowers are espe cially abundant... 

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. 

An excellent case in point is the coloration of the American lobster, Homarus americanus. The pigment associated with the typical greenish-brown outer layer of the lobster shell is the carotenoid, astaxanthin (Figure A), an oxygenated derivative of p-carotene, also known as the molecule that imparts the orange color to carrots. 

Annatto is a colored pigment that is extracted from the Central and South American plant Bixa orellana. The color comes from the resinous outer covering of the seeds of the plant, which is composed of the carotenoid pigments bixin and norbixin and their esters. The central portion of those molecules is the same as that of the molecule beta-carotene, and the yellow-orange color of annatto comes from the same physical chemistry origins as the orange color of beta-carotene. 

The extinction coefficients of carotenoids have been listed completely bnt solvent effects can shift the absorption patterns. If a colorant molecnle is transferred into a more polar environment, then the absorption will be snbjected to a bathochro-mic (red) shift. If the colorant molecnle is transferred into a more apolar enviromnent, the absorption will be subjected to a hypsochromic (blue) shift. If a carotenoid molecule is transferred from a hexane or ethanol solution into a chloroform solution, the bathochromic shift will be 10 to 20 nm. 

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. ... 

The photoprotective role of carotenoids is demonstrated in plant mutants that cannot synthesize essential leaf carotenoids. These mutants are lethal in nature since without carotenoids, chlorophylls degrade, their leaves are white in color, and photosynthesis cannot occur. Generally, the carotenoids are effective for visible light but have no effects in ultraviolet, gamma, or x-radiation. The reactions are listed as follows ... 

De Ritter, A.E., Carotenoid analytical methods, in Carotenoids as Colorants and Vitamin A Precursors, Bauemfeind, J.C., Ed., Academic Press, New York, 1981, 815. Krinsky, N.I., The biological properties of carotenoids. Pure Appl. Chem., 66, 1003,1994. 

In the Unites States, the daily intake of 3-carotene is around 2 mg/day Several epidemiological studies have reported that consumption of carotenoid-rich foods is associated with reduced risks of certain chronic diseases such as cancers, cardiovascular disease, and age-related macular degeneration. These preventive effects of carotenoids may be related to their major function as vitamin A precursors and/or their actions as antioxidants, modulators of the immune response, and inducers of gap-junction communications. Not all carotenoids exert similar protective effects against specific diseases. By reason of the potential use of carotenoids as natural food colorants and/or for their health-promoting effects, research has focused on better understanding how they are absorbed by and metabolized in the human body. 

As for anthocyanins, betalains are found in vacuoles and cytosols of plant cells. From the various natural sources of betalains, beetroot (Beta vulgaris) and prickly pear cactus (Opuntia ficus indica) are the only edible sources of these compounds. In the food industry, betalains are less commonly used as natural colorants from plant sources than anthocyanins and carotenoids, probably related to their more restricted distribution in nature. To date, red beetroot is the only betalain source exploited for use as a natural food coloring agent. The major betalain in red beetroot is betanin (or betanidin 5-0-P-glucoside). Prickly pear fruits contain mainly (purple-red) betanin and (yellow-orange) indicaxanthin and the color of these fruits is directly related to the betanin-to-indicaxanthin ratio (99 to 1, 1 to 8, and 2 to 1, respectively in white, yellow, and red fruits)." ... 

Mercadante, A.Z., Composition of carotenoids from annatto, in Chemistry and Physiology of Selected Food Colorants, Ames, J.M. and Hofmann, T.E., Eds., ACS Symposium Series 775, Washington, 2001, chap. 6. 

Natural pigment production for food coloration includes the entire spectrum of biotechnologies. For example, biological production of carotenoid pigments has medical implications because carotenoids are nutritive (pro-vitamin A), antioxidant, and photoprotective. Carotenoids are produced alternately in agricultural systems (plants), industrial bioreactors (bacterial and fungi), and marine systems (cyanobacteria and algae). 

The aroma and red color of the spice saffron are partly due to the style-specific accumulation of carotenoid cleavage products produced by both enzymatic and thermal degradation. M. Giaccio reviewed the renewed interest in saffron as a colorant, spice, and nutraceutical. " Crocetin is a C20 apocarotenoid derived from zeaxanthin (Figure 5.3.4B). ... 

The availability of precursor IPP may ultimately be most influential over accumulation of carotenoid metabolites. While over-expression of DXS and DXR in color complementation systems leads to hyperaccumulation of carotenoids (discussed in Section 5.3.3.3), over-expression of plant Dxs genes has not always been effective. Over-expression of DXS resulted in increased carotenoid accumulation in transgenic tomato and Arabidopsis, but over-expression of daffodil DXS in rice endosperm did not increase pigment accumulation. ... 

Genomic and molecular tools have made great impacts on plant biotechnology and offer potential for manipulation of carotenoids as natural colorants and also for applications in human and animal health. While microbial and other non-plant systems have been successfully used, plant modification eliminates need for expensive bioreactors and offers economically feasible opportunities for less developed nations for production of nutraceuticals and other chemical products. 

Armstrong, G.A., Eubacteria show their true colors genetics of carotenoid pigment biosynthesis from microbes to plants, J. Bacterial. 176, 4795, 1994. 

Other applications — P-carotene is used in various pet foods as both a colorant and a precursor to vitamin A. It can be applied to an array of animal foods designed for dogs, cats, fish, and birds. The antioxidant and precursory vitamin A properties increase the appeal and application of P-carotene in pet foods. Additionally, P-carotene is an important carotenoid that may assist in improving the color of birds, fish, and crustaceans. Dunaliella salina can serve as a source of algal feed for fish and crustaceans. The microalgae provide carotenoids that are essential for flesh coloring, particularly of salmon and crustaceans. 

Breithanpt, D.E., Simultaneons HPLC determination of carotenoids nsed as food coloring additives applicability of accelerated solvent extraction. Food Chem., 86, 449, 2004. 

Melendez-Martlnez, A.J. et al.. Color and carotenoid profile of Spanish Valencia late nltrafrozen orange juices. Food Res. Int., 38, 931, 2005. 

Lee, H.S. and Castle, W.S., Seasonal changes of carotenoid pigments and color in Hamlin, Earlygold, and Budd blood orange juices, J. Agric. Food Chem., 49, 877, 2001. 

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