What are carotenoids, why are they needed and where can they be found? Carotenoids are plant pigments that give red, orange and yellow colors to fruits and vegetables. Sources of carotenoids

CAROTENOIDS, natural organic pigments from yellow to red-violet, produced by bacteria, fungi, plants. Widely distributed in nature: about 600 different carotenoids are found in the cells and tissues of all representatives of wildlife in a free state or in the form of glycosides, fatty acid esters, carotene-protein complexes. Carotenoids determine the color of some flowers, fruits, roots, and autumn foliage of plants; carotenoids, obtained by animals with food, stain the integument of many species of fish, birds, insects, and crustaceans. Carotenoids are found in the greatest amount in carrot roots, parsley leaves, onions, spinach, fruits of apricots, tomatoes, pumpkins, sea buckthorn.

Carotenoids have an isoprenoid structure; in carotenoid molecules, four isoprene fragments are linked into a polyene chain - formula I (R and R' are mainly cyclohexene or aliphatic isoprene fragments or oxygen-containing derivatives of cyclohexene).

Carotenoids are divided into tetraterpene hydrocarbons (carotenes) of the general formula C 40 H 56 , oxygen-containing derivatives of tetraterpene hydrocarbons (xanthophylls) and carotenoids containing more or less than 40 carbon atoms in molecules. In higher plants, carotenoid hydrocarbons are most widely represented, mainly β-carotene (R = R' = II; makes up 20-30% of natural carotenoids), lycopene (R = R' = III), γ-carotene (R = II, R ' = III). Carotenoid hydrocarbons are soluble in ethers, chloroform, benzene, fats and oils, insoluble in water. Easily oxidized O 2 air, unstable in the light and when heated in the presence of acids and alkalis. β-Carotene is isolated by extraction from carrots, alfalfa, buckwheat, palm oil and other vegetable raw materials; in industry, they are obtained by microbiological or chemical synthesis (dark ruby ​​crystals, t pl 182-184 ° C). Lycopene is isolated from tomatoes or synthesized (red-violet crystals, mp 174°C).

Among the oxygen-containing carotenoids, the most common are carotenoids whose molecules contain hydroxyl groups, for example, lutein (R = IV, R' = V; yellow crystals, mp 193°C), cryptoxanthin (R = IV, R' = I; yellow crystals , mp 174 ° C. There are carotenoids containing carbonyl groups, for example, canthaxanthin (R = R' = VI), epoxy groups, for example, violaxanthin (R = R' = VII), carboxyl groups, for example, bixin (R = COOH, R' = COOSH 3), etc.

Carotenoids are involved in photosynthesis (as auxiliary light-absorbing pigments), oxygen transport through cell membranes, and protection of chlorophyll from photooxidation. Carotenoids containing the fragment R = II in the molecule are precursors of vitamin A (in the animal body, as a result of enzymatic cleavage, they are converted into vitamin A). In animals, carotenoids stimulate the activity of the sex glands, in humans they increase the immune status, protect against photodermatosis, play an important role in the processes of light perception by the retina; are natural antioxidants. Carotenoids are used as food dyes, components of animal feed, in medical practice - for the treatment of skin integuments.

For research on carotenoids, two Nobel Prizes were awarded: P. Carrer in 1937 and R. Kuhn in 1938.

Lit.: Britton G. Biochemistry of natural pigments. M., 1986; Karnaukhov VN Biological functions of carotenoids. M., 1988; Kudritskaya S. E. Carotenoids of fruits and berries. K., 1990.

To the group of carotenoids include substances that are colored yellow or orange. The most famous representatives of carotenoids are carotenes - pigments that give a specific color to the roots of carrots, as well as lutein - a yellow pigment contained along with carotenes in the green parts of plants. The color of yellow corn seeds depends on the carotenes and carotenoids they contain, called zeaxanthin and cryptoxanthin. The color of tomato fruits is due to the carotenoid lycopene. Carotenoids play an important role in the metabolism of plants, participating in the process of photosynthesis.

The group of carotenoids includes about 65-70 natural pigments. Carotenoids are found in most plants (with the exception of some fungi). Probably in all animal organisms, but their concentration is almost always very low. The content of carotenoids in green leaves is approximately 0.07-0.2% based on the dry weight of the leaves. In some exceptional cases, however, a very high concentration of carotenoids is observed. For example, the anthers of many lily species contain very high amounts of lutein and a carotenoid called antheraxanthin. One of the characteristic features of carotenoids is the presence in them of a significant number of conjugated double bonds that form their chromophore groups, on which color depends. All natural carotenoids can be considered as derivatives lycopene- a carotenoid found in the fruits of tomatoes, as well as in some berries and fruits. Empirical formula lycopene C40H56.

By forming a ring at one or both ends of the lycopene molecule, its isomers are formed: alpha-, beta- or gamma-carotenes. Comparing the formulas, it can be seen that alpha-carotene differs from the beta-isomer by the position of the double bond in one of the cycles located at the ends of the molecule. Unlike alpha and beta isomers, gamma-carotene has only one cycle.

Plants rich in carotenoids

The green parts of plants and the carrot root are richest in carotenes.

Natural carotenoids - derivatives of carotene and lycopene

Carotenes are the substances from which vitamin A is formed. Since lycopene and carotenes contain 40 carbon atoms, they can be considered as being formed by eight isoprene residues. Without exception, all other natural carotenoids are derivatives of the four above hydrocarbons: lycopene and carotenes. They are formed from these hydrocarbons by introducing: hydroxyl, carbonyl or methoxy groups, or by partial hydrogenation or oxidation. As a result of the introduction of two hydroxy groups into the beta-carotene molecule, a carotenoid is formed, which is contained in corn grain and is called zeaxanthin. С40Н56О2. The introduction of two hydroxy groups into the alpha-carotene molecule leads to the formation of lutein C40H56O2 (3,3-dioxy-alpha-carotene), an isomer of zeaxanthin, which is found along with carotenes in the green parts of plants. As a result of the addition of one oxygen atom to the beta-carotene molecule with the formation of a furanoid structure, the carotenoid citroxanthin C40H56O is obtained, which is contained in the peel of citrus fruits. The oxidation products of carotenoids containing 40 carbon atoms in a molecule are C20H2404 crocetin, C25H30O4 bixin, and C30H40O2 beta-citraurine. Crocetin is a coloring matter contained in the stigmas of crocus in combination with two molecules of disaccharide gentiobiose in the form of crocin glycoside. Bixin is a red pigment found in the fruits of the tropical plant Bixa orellana; used for tinting butter, margarine and other food products. Brown algae contain the carotenoid fucoxanthin C40H60O6, which takes part in the process of photosynthesis as a so-called auxiliary pigment.

The role of carotenoids in the human body

In the body of animals and humans, carotenoids play an important role as starting substances from which vitamins of group A are formed, as well as "visual purple" involved in the visual act. Carotenoids play an important role in the process of photosynthesis in plants. Based on the chemical structure of carotenoids containing a significant amount of double bonds, it can be assumed that they are carriers of active oxygen in the plant and take part in redox processes. This is indicated by the wide distribution in plants of oxygen derivatives of carotenoids - epoxides, which give up their oxygen extremely easily. Carotenoids easily form peroxides, in which an oxygen molecule is added at the double bond site and can then easily oxidize various substances.

Carotenoids - fat-soluble pigments of yellow, orange, red color - present in the chloroplasts of all plants. They are also part of the chromoplasts in non-green parts of plants, for example, in carrot roots, from the Latin name of which (Daucus carota L.) they got their name. In green leaves, carotenoids are usually invisible due to the presence of chlorophyll, but in autumn, when chlorophyll is destroyed, it is the carotenoids that give the leaves their characteristic yellow and orange color. Carotenoids are also synthesized by bacteria and fungi, but not by animals. Currently, about 400 pigments belonging to this group are known.

Structure and properties. The elemental composition of carotenoids was established by Wilstetter. From 1920 to 1930, the structure of the main pigments of this group was determined. Artificial synthesis of a number of carotenoids was first carried out in 1950 in the laboratory of P. Carrera. Carotenoids include three groups of compounds: 1) orange or red pigments carotenes(C 40 H 56); 2) yellow xanthophylls(C 4 oH 56 O 2 and C 40 H 51 O 4); 3) carotenoid acids - products of oxidation of carotenoids with a shortened chain and carboxyl groups (for example, C 20 H 24 O 2 - crocetin having two carboxyl groups).

Carotenes and xanthophylls are readily soluble in chloroform, benzene, carbon disulfide, and acetone. Carotenes are readily soluble in petroleum and diethyl ethers, but almost insoluble in methanol and ethanol. Xanthophylls are highly soluble in alcohols and much worse in petroleum ether.

All carotenoids are polyene compounds. The carotenoids of the first two groups consist of eight isoprene residues that form a chain of conjugated double bonds. Carotenoids can be acyclic (aliphatic), mono- and bicyclic. The cycles at the ends of carotenoid molecules are derivatives of ionone (Fig. 1).

Fig.1. Structural formulas of carotenoids and the sequence of their transformations

An example of an acyclic carotenoid is lycopene(C 40 H 56) - the main carotene of some fruits (in particular, tomatoes) and purple bacteria.

Carotene(Fig. 1) has two β-ionone rings (double bond between C 5 and C 6). Upon hydrolysis of β-carotene at the central double bond, two molecules of vitamin A (retinol) are formed. α-Carotene differs from β-carotene in that it has one ring β-ionone, and the second - J-ionone (double bond between C 4 and C 5).

Xanthophyll lutein- derivative of a-carotene, and zeaxanthin- β-carotene. These xanthophylls have one hydroxyl group in each ionic ring. Additional inclusion in the zeaxanthin molecule of two oxygen atoms on double bonds C 5 -C 6 (epoxy groups) leads to the formation violaxanthin. Name

"violaxanthin" is associated with the release of this compound from the petals of yellow pansies (Viola tricolor). Zeaxanthin was first obtained from corn kernels (Zea mays). Lutein (from lat. luteus- yellow) is found, in particular, in the yolk of chicken eggs. The most oxidized isomers of lutein are fucoxanthin(C 40 H 60 O 6) - the main xanthophyll of brown algae.

The main carotenoids of plastids of higher plants and algae are β-carotene, lutein, violaxanthin and neoxanthin. The synthesis of carotenoids starts from acetyl-CoA through mevalonic acid, geranylgeranyl pyrophosphate to lycopene, which is the precursor of all other carotenoids. Synthesis of carotenoids occurs in the dark, but is sharply accelerated by the action of light. The absorption spectra of carotenoids are characterized by two bands in the violet-blue and blue regions from 400 to 500 nm (see Fig. 4.3). The number and position of absorption maxima depend on the solvent. This absorption spectrum is determined by the system of conjugated double bonds. With an increase in the number of such bonds, the absorption maxima shift to the long wavelength region of the spectrum. Carotenoids, like chlorophylls, are non-covalently bound to proteins and lipids of photosynthetic membranes.

The role of carotenoids in photosynthesis

Carotenoids are essential components of the pigment systems of all photosynthetic organisms. They perform a number of functions, the main of which are: 1) participation in the absorption of light as additional pigments, 2) protection of chlorophyll molecules from irreversible photooxidation. It is possible that carotenoids take part in oxygen exchange during photosynthesis.

The importance of carotenoids as additional pigments that absorb light in the blue-violet and blue parts of the spectrum becomes apparent when considering the distribution of energy in the spectrum of total solar radiation on the Earth's surface. As follows from Figure 2, the maximum of this radiation falls on the blue-blue and green parts of the spectrum (480 - 530 nm). Under natural conditions, the total radiation reaching the Earth's surface is composed of a direct solar radiation flux to a horizontal surface and scattered sky radiation.

Fig. 2. Distribution of energy in the spectrum of total and scattered radiation in a cloudless sky

Scattering of light in the atmosphere occurs due to aerosol particles (water drops, dust particles, etc.) and fluctuations in air density (molecular scattering). The spectral composition of the total radiation in the region of 350 - 800 nm with a cloudless sky during the day almost does not change. This is explained by the fact that an increase in the proportion of red rays in direct solar radiation at a low standing of the Sun is accompanied by an increase in the proportion of scattered light, in which there are many blue-violet rays. The Earth's atmosphere scatters the rays of the short-wavelength part of the spectrum to a much greater extent (the scattering intensity is inversely proportional to the wavelength to the fourth power), so the sky looks blue. In the absence of direct sunlight (cloudy weather), the proportion of blue-violet rays increases. These data indicate the importance of the short-wavelength part of the spectrum when terrestrial plants use scattered light and the possibility of carotenoids participating in photosynthesis as additional pigments. Model experiments show high efficiency of light energy transfer from carotenoids to chlorophyll A, moreover, molecules of carotenes, but not xanthophylls, have this ability.

The second function of carotenoids is protective. For the first time, data that carotenoids can protect chlorophyll molecules from destruction were obtained by D. I. Ivanovsky. In his experiments, test tubes containing the same volume of chlorophyll solution and different concentrations of carotenoids were exposed to direct sunlight for 3 hours. It turned out that the more carotenoids were in the test tube, the less chlorophyll was destroyed. Subsequently, these data received numerous confirmations. Thus, carotenoid-free chlamydomonas mutants die in the light in an oxygen atmosphere, while in the dark, with a heterotrophic mode of nutrition, they develop and multiply normally. In the maize mutant, which lacked the synthesis of carotenoids, the chlorophyll formed under aerobic conditions under strong illumination was rapidly destroyed. In the absence of oxygen, chlorophyll was not destroyed.

How do carotenoids prevent the destruction of chlorophyll? It has now been shown that carotenoids are able to react with chlorophyll in the triplet state, preventing its irreversible oxidation. In this case, the energy of the triplet excited state of chlorophyll is converted into heat.

Fig.3. Reaction of carotenoids with chlorophyll

In addition, carotenoids, interacting with excited (singlet) oxygen, which nonspecifically oxidizes many organic substances, can transfer it to the ground state.

Fig.4. Reaction of carotenoids with excited oxygen

The role of carotenoids in oxygen exchange during photosynthesis is less clear. In higher plants, mosses, green and brown algae, light-dependent reversible deepoxidation of xanthophylls occurs. An example of such a transformation is violaxanthin cycle.

Fig.5. Violaxanthin cycle

The significance of the violaxanthin cycle remains unclear. Perhaps it serves to eliminate excess oxygen. Carotenoids in plants perform other functions not related to photosynthesis. In the light-sensitive "eyes" of unicellular flagellates and in the tops of the shoots of higher plants, carotenoids, by contrasting the light, help determine its direction. This is necessary for phototaxis in flagella and phototropism in higher plants.

Carotenoids determine the color of the petals and fruits of some plants Carotenoid derivatives - vitamin A, xanthoxin, acting like ABA, and other biologically active compounds. The chromoprotein rhodopsin, found in some halophilic bacteria, absorbs light and functions as an H + -pump. The chromophore group of bacteriorhodopsin is retinal, the aldehyde form of vitamin A. Bacteriorhodopsin is similar to the rhodopsin of the visual analyzers of animals.

In a review article by V. G. Ladygin and G. N. Shirshikova, modern ideas about the functions of carotenoids - yellow, red and orange pigments - in plants are presented. Carotenoids play a very important role in the operation of the molecular machinery of photosynthesis. They perform three main functions: photoprotective (protecting chlorophyll and other vulnerable components of photosystems from light "overexcitation"), light harvesting (which allows plants to use the energy of light in the blue region of the spectrum - a task that chlorophyll cannot cope without the help of carotenoids) and structural ( serve as necessary structural elements, "bricks" of photosystems).

Carotenoids are a widespread class of pigments found in bacteria, unicellular eukaryotes, fungi, plants, and animals. Unlike a number of other pigments, such as heme (coloring the blood and muscles of mammals red) or chlorophyll (responsible for the green color of plants), carotenoid molecules do not contain metals. They consist only of carbon, hydrogen and oxygen, and their ability to "work" with light quanta is determined by a system of conjugated double bonds between carbon atoms arranged in a chain. Double bonds are called conjugated, separated by one single bond.

Carotenoids absorb light with a wavelength of 280–550 nm (these are the green, blue, violet, and ultraviolet regions of the spectrum). The more conjugated double bonds in a molecule, the longer the wavelength of absorbed light. Accordingly, the color of the pigment also changes. Carotenoids with 3–5 conjugated double bonds are colorless and absorb light in the ultraviolet region. Seven-linked zeta-carotene is yellow, nine-linked neurosporin is orange, and 11-linked lycopene is orange-red.

The functions of carotenoids in wildlife are not limited to working with light, sometimes they play an important role in metabolism (remember, for example, vitamin A is a derivative of beta-carotene). And yet their main functions (whether in the organs of vision of animals or in chloroplasts - the organelles of plant photosynthesis) are inextricably linked with light. The article by Ladygin and Shirshikova discusses the role of carotenoids in chloroplasts, plant cell organelles that originate from symbiotic cyanobacteria. The main function of chloroplasts is photosynthesis, that is, the production of organic matter from carbon dioxide due to the energy of sunlight. Chloroplast membranes contain protein-pigment complexes - photosystems I and II, which include a variety of proteins, as well as pigments - chlorophylls and carotenoids.

Chlorophyll, the main photosynthetic pigment, is itself capable of absorbing and using light only in the red region of the spectrum (650–710 nm). Carotenoids absorb blue-green light and transfer its energy to chlorophylls. This function of carotenoids is light-harvesting- is especially important for algae, since blue-green light penetrates much deeper into the water column than red.

The second function of carotenoids in chloroplasts is light-protective. They protect photosystems from light "overloads" that can lead to overexcitation and malfunction of photosystems. Carotenoids serve as a kind of "emergency valve" that allows you to dump excess energy, convert it into heat. Carotenoids do this in a number of different ways: simply by "filtering" the incoming light, by taking on excess light energy, or by de-energizing overexcited chlorophyll. Carotenoids can also “extinguish” reactive oxygen species, that is, they serve as antioxidants.

One of the ways that carotenoids "dump" excess energy in excess light is through cyclic chemical reactions, during which one carotenoid is converted into another. The most common of these reactions is called the violaxanthin cycle. In strong light, the carotenoid violaxanthin is converted to zeaxanthin, and oxygen is released. When light is reduced, zeaxanthin is converted back to violaxanthin, while oxygen is consumed. Both reactions - both direct and reverse - are catalyzed by enzymes whose genes are located in the chromosome of the chloroplast, and not in the central (nuclear) genome of the plant cell.

The third function of carotenoids is structural. Carotenoids are essential structural components of the photosynthetic membranes of chloroplasts. It has been experimentally shown that photosystems become unstable without carotenoids. Carotenoid molecules occupy strictly defined positions in photosystems, and without them, the whole structure simply falls apart.

The authors note that in recent years a lot of new things have become known about carotenoids, but a number of details remain to be clarified. In particular, the evolutionary origin of carotenoids, as well as biochemical and photochemical reactions with their participation, is not yet fully understood. It is not clear to what extent carotenoids can be used in phylogenetics, that is, to reconstruct the evolutionary development of organisms. In many old works, sets of carotenoids characteristic of one or another group of organisms were used as an important taxonomic feature. It is not entirely clear how reliable such signs are, especially considering that the same carotenoids can be found, for example, in plant chloroplasts and in the eyes of mammals.

Hello friends!

I noticed such an interesting thing.

Sometimes you write a post and you understand that an ordinary person who does not delve deeply into various medical or biochemical terms does not quite understand what this can mean☺

Therefore, I decided to write a small series of posts and explain in simpler terms some of the concepts that I use very often in my articles.

All of them are powerful antioxidants that protect our body from free radicals. The red color of the oil is due to the presence in its composition of a large number of carotenoids, and their content in the oil is 15 times higher than in carrots!!!

And yes, remember, this is not about that surrogate palm oil, which everyone is afraid of ☺ But about real red palm oil!!!

I buy this, add it to food and just put it on the skin like a mask!!!

• Carrot
• Rowan
• orange pepper
• Corn
• Citrus
• Pumpkin
• Rose hip
• Sea ​​buckthorn

Also, carotenoids are present in flower petals (especially marigolds), algae, pollen. There are many of them in egg yolk and some types of fish, as well as spruce needles.

How are carotenoids absorbed in the body?

The assimilation of carotenoids and their conversion into vitamin A occurs in our body in the small intestine under the influence of certain enzymes.

But, studies have found that carotenoids are far from being fully absorbed by the body.

This process is best from finely ground and pre-processed foods in which cell membranes have been destroyed.

In addition, an important factor for the absorption of carotenoids by the body is the presence of a fatty environment. Back in 1941, it was found that the amount of carotene absorbed by the body from raw carrots on a fat-free diet does not exceed 1%. Under the same conditions, 19% of carotene is absorbed from boiled carrots. After adding oil, the absorption of carotene increases up to 25%.

Therefore, a salad with chopped carrots and butter will be healthier than just a raw carrot salad.

Daily rate

The recommended daily allowance for beta-carotene for adults is 2 to 6 mg. For example, 100.0 carrots contain about 8 mg. (I think you have not forgotten that not all 8 mg will be absorbed by our body)

IMPORTANT!!!

Large doses of cartonoids and vitamin A are dangerous for long-term smokers, as they can cause lung cancer. Also, an excess of vitamin A is dangerous during pregnancy.

It is also worth considering the factor that, unfortunately, the amount of carotenoids gradually decreases in products during storage. They are quickly destroyed in the light and with free access to atmospheric oxygen.

Therefore, the carrots that are sold to the supermarket, clean and washed in bags, are practically devoid of these important components.

In order for carrots to retain all their useful properties to the maximum, they must be stored in a dark, cool place and not peeled from the ground.

Is a carotenoid deficiency possible in modern humans?

Unfortunately yes.

According to the Research Institute of Nutrition of the Russian Academy of Medical Sciences, in Russia, a chronic deficiency of carotenoids in the diet is observed in 40-60% of the population. So be sure to include foods rich in carotenoids in your diet.

If you feel that your nutrition is inadequate, buy vitamins or quality dietary supplements isolated from natural organic vegetables or fruits.

I did not describe in this post in detail all the scientific details, the chemical composition, the bioavailability of carotenoids.

All the same, I have a blog, not Wikipedia ☺. I think that I was able to convey the general concept of carotenoids and why we need them. I hope so ☺

I will be very glad if this information is useful to you and you share it with your friends on social networks. I look forward to your feedback and comments.

I would be very grateful for the helpful tips ☺

Alena Yasneva was with you, bye everyone!