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Carotenoids cause a yellowish to reddish color not only in carrots . As fat-soluble pigments in near-surface parts of fruits, flowers, plumage or a chitin shell, they shape the appearance of various plants and animals. Egg yolks and foods such as cheese or margarine also owe their characteristic color to the presence of carotenoids - sometimes only after they have been added as food coloring .

As carotenoids , and carotenoids , a large class of naturally occurring fat-soluble will pigments ( lipochromes ) refers to which a chemical as a framework tetraterpene common.

Their system of conjugated double bonds absorbs light of short wavelengths and, depending on the number, position and side chain in the carotenoid, gives it a yellowish to reddish color . The more than 800 known carotenoids are divided into carotenes and oxygen-containing xanthophylls . Carotenoids belong to the group of isoprenoids .


Occurrence in food
Carotenoid ( E number ) Occurrence
Astaxanthin (E 161j) Prawn, lobster , salmon
β-carotene (E 160a) Carrot, spinach, apricot, einkorn
Canthaxanthin (E 161g) Shrimp, lobster , chanterelle
Capsanthin (E 160c) paprika
Capsorubin paprika
Cryptoxanthin orange
Lutein (E 161b) Kale, spinach, egg yolk
Luteoxanthin orange
Lycopene (E 160d) Tomato, watermelon
Zeaxanthin (E 161h) Corn

Carotenoids are initially found in salt-loving archaea ( halobacteria ), in bacteria , in the chromoplasts and plastids of plants and in some fungi . These organisms are able to synthesize tetraterpenes de novo . Furthermore, they occur in various animals that ingest plant material containing dyes with their food. Thus carotenoids found then in snail shells , shells or tanks as well as in feathers and egg yolks of birds or humans in the skin and retina . Apart from a few exceptions such as some species of aphids and spider mites , animal organisms do not have genes for carotenoid synthesis.

Some carotenoids are approved as food additives in the EU ; they have the E numbers E 160a to E 160g and E 161a to E 161h. Some are used to color products.


Lycopene , a carotene
β-carotene, a carotene

Typical carotenoids have the basic structure of tetraterpenes , compounds made up of eight isoprene units , and thus contain 40 carbon atoms. The unsaturated hydrocarbon chains can be cyclized at one end or both ( ionone rings ) or not, as in the case of lycopene with the empirical formula C 40 H 56 . Modifications also exist in dehydrogenation / hydrogenation and the various types of oxidation products . Carotenoids are divided into two main groups

The maxima of the absorption spectra of carotenoids are mostly at wavelengths around 400 to 500 nanometers.

Importance as provitamin A

Retinol - not a carotenoid, but a vitamin A.

Animals and humans are not capable of de novo synthesis of vitamin A and therefore have to meet their needs with food. While carnivores take up vitamin A mainly in the form of retinyl esters or retinol , herbivores use certain carotenoids as a precursor. About 50 carotenoids are known to have provitamin A activity; they can be converted to vitamin A in the biological body. Of these, β-carotene has the greatest activity.

Human physiology

Humans can use retinol and retinyl ester as well as provitamin A to meet their vitamin A needs. The activity of dietary carotenoids as provitamin A is expressed with the help of so-called retinol equivalents, with about 6 mg β-carotene and 12 mg mixed carotenoids corresponding to one retinol equivalent. The carotenoids are also considered to be of great health importance. Six carotenoids play an essential role in the human body: β-carotene, α-carotene, lycopene , β-cryptoxanthin , lutein and zeaxanthin . Most of them have the function of antioxidants . This is intended to prevent many diseases such as cancer, arteriosclerosis , rheumatism , Alzheimer's and Parkinson's , cataracts or skin aging.

Of all dietary carotenoids , lycopene (e.g. in tomatoes) has the greatest antioxidant potential and is considered to be the most effective protection against the particularly reactive singlet oxygen . Lycopene also inhibits tumor cell growth more effectively than α- or β-carotene.

The anti-carcinogenic effect of the carotenoids also arises theoretically from their property of being able to establish well-functioning communication between the cells. In particular, β-carotene, cryptoxanthin and canthaxanthin stimulate the exchange between the cells by causing the synthesis of connexin . This connection plays a key role in the formation of gap junctions , the number of which is reduced in cancer cells. However, carotenoids should only be used for prevention, as they have no effect in actual cancer therapy or in preventing relapses. Particularly in patients already suffering from cancer, caution should be exercised with high-dose preparations.

Certain carotenoids are found in significantly higher concentrations in the liver, eyes, skin and fatty tissue than in other body tissues. The carotenoids lutein and zeaxanthin occur in large quantities in the retina of the eye, in the so-called yellow spot (macula) . These carotenoids probably act as natural protective mechanisms, since the retina, with its polyunsaturated fatty acids, which are particularly sensitive to oxidation, is particularly susceptible to attack by free radicals.

As for other phytochemicals , carotenoids should not be taken in the form of isolated, highly concentrated preparations, but in a natural combination with other nutritional ingredients. The ingestion of high-dose preparations even harbors dangers. Proper poisoning with carotenoids is not possible, but β-carotene supplements can potentially increase the risk of cancer.

Carotenoids as coloring agents in nature

Male of the great tit ( Parus major )
Brown trout ( Salmo trutta f. Fario )
In unkenreflex their warning coloration presenting yellow-bellied toad ( Bombina variegata )


In addition to melanins , various carotenoids also play a role in the plumage color of birds. Ingested with food, metabolically modified and stored in the growing feathers , they can lead to yellowish to reddish hues. More striking examples of carotenoid-colored plumage among songbirds are the blue tit ( Cyanistes caeruleus ), the great tit ( Parus major ), the yellow wagtail ( Motacilla flava ), the golden oriole ( Oriolus oriolus ) or the great spotted woodpecker . The red breast of the robin ( Erithacus rubecula ), on the other hand, is caused by reddish-brown pheomelanin . In geese birds carotenoids are rare as a spring pigments and so far only in the (probably extinct) Pink-headed duck and Australian pink-eared duck detected spectroscopically. If the food contains too few or no carotenoids, the corresponding areas of the feathers will be white after the next moult . Mutations that lead to disorders of the carotenoid accumulation in the feather are rare, those with altered melanin storage are more common.

Fish, amphibians and reptiles

In fish, amphibians and reptiles, the color of the skin and scales is caused by light interacting with three different types of chromatophores (pigment cells, dye- producing cells), the melanophores, xanthophores and iridophores. In addition to pteridines and flavins, the xanthophores also contain carotenes taken from food. These three types of dyes are responsible for yellowish or red colors.

Dinoflagellates and Bacteria

Red tide - algal blooms off the coast of San Diego
Structural formula of peridinin
Structure of sarcinaxanthin

The dinoflagellates , unicellular algae that occur in fresh and salt water and phytoplankton are wearing peridinin in the pigmentation. This carotenoid - an apocarotenoid with the empirical formula C 39 H 50 O 7 - forms a light-harvesting complex together with chlorophyll a in a ratio of 4: 1 bound to a protein structure . The complex captures photons , transfers their energy to the central chlorophyll atom and makes them usable for photosynthesis . In nutrient-rich waters can have a toxic by proliferation of dinoflagellate algae bloom caused even Red Dawn (English red tide called) whose coloring is mainly on peridinin. Other photosynthetically important carotenoids are fucoxanthin (C 42 H 58 O 6 ) and other derivatives that act as accessory pigments .

In the cell membranes of bacteria, various carotenoids are glycosylated or non-glycosylated and protect them from photooxidative destruction by UV light or free radicals. In the marine bacterium Micrococcus luteus , for example, the yellowish carotenoid sarcinaxanthin is represented, a glycosylated cyclic C 50 xanthophyll (C 50 H 72 O 2 ). The very similar yellow carotenoid decaprenoxanthin (C 50 H 72 O 2 ) occurs next to sarcinaxanthin in corynebacteria (e.g. Corynebacterium glutamicum , C. callunae , C. marinum ). In Staphylococcus aureus , the yellow-orange color is caused by staphyloxanthin (C 51 H 78 O 8 ), which, in addition to stabilizing the membrane through its antioxidant effect, also contributes to the pathogenicity of this pathogen.

Function in photosynthesis

The primary task of the carotenoids in plant photosynthesis is to protect chlorophyll molecules from being destroyed by photooxidation . They act as photoprotective agents that protect the plant cell from reactive oxygen species through nonphotochemical quenching . In addition, they expand the absorption spectrum of photosynthetic organisms in the blue-green spectral range and are partly involved in the energy transfer within the antenna complexes and photosystems . There they work as light harvest pigments in the light harvesting complex , which absorb photons and pass the energy on to the photosynthetic reaction center. They are therefore referred to together with the phycobilins as the accessory pigments of photosynthesis. In the xanthophyll cycle , which takes place in the chloroplasts, excess light radiation is absorbed and converted into harmless heat.

Estimates of the annual carotenoid synthesis by plants amount to 100 million tons per year.

The allocation of the carotenoids to the secondary plant substances is therefore not entirely correct, since, contrary to the definition of the secondary plant metabolites, clear primary functions in photosynthesis can be assigned to them.

Technical importance and synthesis

Of the approx. 700 known natural carotenoids, some are of greater technical importance and are synthesized on an industrial scale: β-carotene , astaxanthin , canthaxanthin , 8'-apo-β-carotenic acid ethyl ester, 8'-apo-β-carotenaldehyde, citranaxanthin , lycopene and zeaxanthin . The technical production of the nature-identical carotenoids was first developed at Hoffmann-La Roche AG and at BASF SE . The procedures are complex and include as universal linking methods:

Since ( E , Z ) isomer mixtures frequently arise, a photochemical isomerization (conversion) of the mostly undesired ( Z ) form into the desired ( E ) form often follows .

Biotechnological manufacturing

It is possible to introduce genes for the biosynthesis of carotenoids into fungi, bacteria and plants or to increase the content of rate-limiting enzymes in order to increase carotenoid production. The yeast Phaffia rhodozyma can be genetically modified so that it produces more astaxanthin and alien carotenoids. It is also possible to significantly increase the accumulation of zeaxanthin in potato tubers. The transgenic rice variety with the nickname Golden Rice was developed especially for developing countries to counteract the vitamin A deficiency.

Use as a dye

Ready-to-cook salmon, cut as a steak

Carotenoids are often added as a feed additive in order, for example, to influence the color of the meat in farmed salmon , which would be gray if it were fed with chunks of fishmeal in captivity without the addition. Wild salmon normally ingest the dye from eating small crustaceans. They don't make it themselves either, but instead eat small algae that contain the xanthophyll astaxanthin .

Astaxanthin , a xanthophyll

For a similar reason, flamingos in the zoo are also fed carotenoids, because they cannot ingest carotenoid-containing crustaceans and algae and otherwise lose their plumage color. The color of the egg yolk can also be influenced by additives in the feed for chickens, especially if the animals hardly find any grass or maize that contain natural carotenoids. Foods that are colored directly with carotenoids are, for example, margarine and fruit juices .

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Web links

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