Carotenoid

Carotenoids (also: carotenoids ) refers to a broad class of natural dyes, which cause a yellow to reddish color. Carotenoids are among the terpenes. In the meantime, 800 different carotenoids have been identified.

They occur mainly in the chromoplasts and plastids of plants, in bacteria, but also in the skin, in shell ( snail shells and mussel shells) and tanks of animals and in the springs and in the yolk of birds. The animal in question take their food on dye-containing plant material. Only bacteria, plants and fungi are able to synthesize this pigment de novo.

Some carotenoids are approved as food additives in the EU. These carry the E-numbers E 160a- E 160 and E 161 to E g 161 h

Structure

Most of the Carotenoids consist of unsaturated hydrocarbon chains and their oxidation products. Carotenoids are formally constructed from eight isoprene units. They are divided into

• Carotenes, which are built up only from carbon and hydrogen, and
• Xanthophylls, oxygenated derivatives of carotenes.

The absorption spectrum of the carotenoids is 400 to 500 nanometers in wavelength.

Physiology in humans

The best known and most abundant carotenoid is β -carotene (carrots ), which is also known as provitamin A. About 50 carotenoids have this effect, that is, are implemented in the human body into retinol. This effect is suppressed with the help of so-called retinol, with about 6 mg of β -carotene and 12 mg mixed carotenoids correspond to a Retinoaläquivalent. The carotenoids great value for health is also awarded otherwise. In the human body 6 carotenoids play an important role: β -carotene, α -carotene, lycopene, β -cryptoxanthin, lutein and zeaxanthin. Most of them have the function of antioxidants. Thus they are intended to prevent many diseases such as cancer, arteriosclerosis, rheumatism, Alzheimer's and Parkinson's, cataracts or skin aging.

Of all Nahrungscarotinoiden lycopene ( in tomatoes ) the greatest antioxidant potential, and is considered the most effective protection against the very reactive singlet oxygen. Lycopene inhibits the growth of tumor cells more effective than α - or β -carotene.

The anticarcinogenic effect of carotenoids obtained theoretically from their capacity to be able to establish a good communication between the cells. In particular, β -carotene, cryptoxanthin and canthaxanthin, stimulate the exchange between the cells by causing the synthesis of connexin. This compound has been instrumental in the formation of gap junctions, the number of which is decreased in cancer cells. However, carotenoids are to be used only in the prevention, as they show in the actual treatment of cancer or in the prevention of relapses no effect. Especially when already suffering from cancer patients is warranted with high-dose preparations caution.

In liver, eyes, skin and adipose tissue specific carotenoids are present in much higher concentration than in other body tissues. In the retina of the eye, in the so-called yellow spot ( macula ), the carotenoids lutein and zeaxanthin are found in larger quantities. These carotenoids act here probably as a natural protective mechanisms, because the retina is particularly vulnerable to the attack of free radicals with their particularly oxidation-sensitive polyunsaturated fatty acids.

As for the other phytochemicals applies to carotenoids that they should not be included in the form of isolated, highly concentrated preparations, but a natural combination with other food ingredients. Taking high doses of preparations even potentially dangerous. Although a veritable intoxication with carotenoids is not possible, β -carotene supplements can but may increase the risk of cancer.

Color of skin, scales and feathers

Besides melanins play in birds and carotenoids in the emergence of the colors involved. They are included in the diet, leading to red, orange and yellow hues. Birds, in which carotenoids are involved in the pathogenesis of the colors, for example, the Yellow Wagtail ( Motacilla flava), the willow warbler (Phylloscopus trochilus ), the blue tit ( Cyanistes caeruleus), the great tit (Parus major) and the oriole ( Oriolus oriolus ). In contrast, the robin red breast (Erithacus rubecula) is caused by pheomelanin. If the food contains too little carotenes, the corresponding spring areas after the next moult are white. Mutations that lead to disorders of Carotinoidanreicherung in the spring, are rare.

Fish, amphibians and reptiles

In fish, amphibians and reptiles the color of skin and scales arises from the fact that light interacts with three different types of chromatophores (pigment cells, dye -forming cells), the melanophores, xanthophores and iridophores. The xanthophores contain, in addition pteridines and flavins also from the food taken carotenes. These three types of dyes are responsible for yellowish or red colors.

Function in photosynthesis

The primary function of carotenoids in photosynthesis in plants is to protect chlorophyll molecules from destruction by photo-oxidation. They function as photoprotective agents which protect the plant cell by quenching nonphotochemisches against reactive oxygen species. They also enhance the absorption spectrum of photosynthetic organisms in the blue- green spectral region and partly also on the energy transfer within the antenna complexes and photosystems involved. There they work as light harvesting pigments in the light harvesting complex that absorb photons and transfer the energy to the photosynthetic reaction center. They are therefore referred to, together with the phycobilins as accessory pigments in 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 a year.

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

Industrial importance and synthesis

Of the approximately 700 known natural carotenoids some possess greater technical importance and are synthesized on an industrial scale: β -carotene, astaxanthin, canthaxanthin, 8' -apo- β - carotenate, 8' -apo- β - carotinaldehyd, citranaxanthin, lycopene and zeaxanthin. The industrial production of nature-identical carotenoids was first developed in the Hoffmann -La Roche AG and BASF SE. The processes are complex and involve as universi elle join methods:

• Wittig reaction
• Sulfonverknüpfung by Julia
• Enol ether condensation
• Saucy Marbet rearrangements.

Since frequently (E, Z)- isomers arise often photochemical isomerization (transformation) involves the most undesired (Z )-form in the desired (E) - form.

Biotechnological production

It is possible to introduce genes for the biosynthesis of carotenoids in fungi, bacteria and plants, or to increase the content rate-limiting enzymes in order to increase the carotenoid production. The yeast Phaffia rhodozyma can be genetically modified to produce more astaxanthin and Different type of carotenoids. It is also possible to significantly increase the zeaxanthin accumulation in potato tubers. Especially for developing countries, the transgenic rice was developed with the nickname golden rice to counteract the vitamin A deficiency.

Use as dye

Carotenoids are often added as a feed additive to affect, for example, color of the meat on farmed salmon, which would turn gray when fed with fishmeal chunks in captivity without additives. These take the dye usually on by eating small crustaceans. These provide not astaxanthin itself, but eat small algae.

For the same reason, flamingos at the zoo diet is supplemented with carotenoids, as they can not absorb carotene-containing crabs and seaweed there and would otherwise lose their plumage coloration. Similarly, the color of the yolk by feed additives for chickens can be affected because the animals eat hardly any grass or maize, which contains natural carotenoids. Foods that are dyed directly with carotenoids, for example, margarine and fruit juices.