CAROTENOIDS: STRUCTURE, FUNCTIONS, CLASSIFICATION, FOOD - BIOLOGY - 2025

The carotenoids are chemical compounds that are present in a large amount of food ingested daily. This is a large group, encompassing several types of molecules.

Broadly speaking, carotenoids are divided into two groups: carotenes and xanthophylls. Inside each are a large number of compounds, such as beta-carotene and lutein. These compounds are of vital importance in the body, as they help improve certain functions such as eyesight.

Tomato is a source of carotenoids par excellence. Source: By Scott Bauer, USDA ARS, via Wikimedia Commons

The group of carotenoids is the object of study by many specialists who, with their research, have made really valuable contributions. However, these organic molecules continue to remain a little known group, but they have contributed greatly to the balance and maintenance of bodily functions.

It is important to take into account carotenoids when eating, since in addition to health benefits, they provide a delicious flavor and seasoning, unique in its kind.

Chemical structure

Carotenoids belong to the group of terpenoids, these being a series of compounds that come from mevalonic acid (derived from Acetyl CoA). Terpenes are derivatives of isoprene, a hydrocarbon consisting of five carbon atoms.

Specifically, carotenoids are tetraterpenes and are made up of forty carbon atoms. These atoms form conjugated chains that can end in carbon rings, substituted and unsaturated at each of their ends.

They have an isoprenoid structure, which means that they have a variable number of conjugated double bonds. This is important because it determines the wavelength of the light that the molecule will absorb. Depending on the type of light it absorbs, it will give a specific coloration to the vegetable or plant it is in.

Chemical structure of beta-carotene. Source: By KES47 (File: Beta-carotene.png), via Wikimedia Commons

Molecules that have few double bonds absorb light of a shorter wavelength. For example, there is a molecule that contains only three conjugated bonds, therefore it can only capture ultraviolet light, it is colorless.

There is another type of carotenoid that contains in its structure a total of eleven conjugated double bonds and absorbs even red.

Properties

Carotenoids are fat-soluble pigments, which means that they are highly soluble in oils and fats. Similarly, they are not synthetic, but are produced naturally by plants, some photosynthetic bacteria and algae. Likewise, they are soluble in organic solvents such as ketone, diethyl ether, methanol and chloroform, among many others.

When in contact with an acid, carotenoids are extremely unstable. This causes cyclization or isomerization reactions to occur.

Taking into account that they are hydrophobic, carotenoids are going to be found in environments related to lipids, such as the interior of cell membranes.

Due to the presence of double bonds in their chemical structure, these compounds are very sensitive to certain elements in the environment, such as: oxygens, peroxides, metals, acids, light and heat, among others.

Likewise, taking into account their chemical structure, many of the carotenoids that exist in nature are precursors of Vitamin A. For a carotenoid to be a precursor of vitamin A, two conditions must exist: the presence of ß- ionone and the ability within the animal's body to transform it into retinol.

Among the carotenoids that can function as precursors of vitamin A, we can mention: α-carotene, ß-zeacarotene and ß-cryptoxanthin, among many others (Approximately 50).

Classification

Carotenoids are classified according to the presence or absence of oxygen in their chain, into two large groups: Xanthophylls, which are those that have oxygen, and Carotenes, which are those that do not.

-Xanthophylls

Xanthophylls are chemical compounds belonging to the group of carotenoids that contain carbon, hydrogen and oxygen in their chemical structure. It is a particularly abundant pigment in many plants, being responsible for the yellow and orange coloration of some of them.

This pigment is not exclusive to plants and algae, as it is also present in some animal structures, such as the yolk of eggs and in the exoskeleton of some crustaceans.

Among the best known xanthophylls are:

Astaxanthin

It is a fat-soluble carotenoid. They can be found mainly in microscopic algae, yeasts and some animals such as crustaceans, trout and especially in the feathers of some birds.

The usefulness and importance of astaxanthin lies in its proven antioxidant, anticancer, antidiabetic and anti-inflammatory power. When astaxanthin is ingested regularly, certain benefits are obtained, such as: increased immune function, preservation of cardiovascular health and reduction of triglycerides in the blood, among others.

Likewise, astaxanthin has certain protective properties against the damaging actions of sunlight on the eyeball.

Lutein

It is a pigment that belongs to the group of carotenoids, specifically xanthophylls. This pigment provides vegetables in which there is an intense yellow color. It is a dihydroxy derivative of α-carotene.

Lutein is the most abundant xanthophyll. Among its beneficial properties for humans, it can be mentioned that it protects the eyes, as well as the skin.

Violaxanthin

It can be found in the rind of oranges and tangerines, as well as a large number of yellow flowers. It is obtained by oxidation of zeaxanthin.

-Carotenes

They are known by this name because they were isolated for the first time from the carrot (Daucuc carota). Carotenes are a family of chemical compounds that have the characteristic of presenting a coloration that is between red and yellow, passing through orange.

Chemically they are made up of a short hydrocarbon chain, which does not contain oxygen in its terminal rings.

Among the most studied carotenes we can mention:

Beta carotene

It is the most abundant carotenoid. It is a fundamental source of vitamin A for the body, since when it deserves it, beta-carotene is transformed into said vitamin.

All this occurs at the level of the intestinal mucosa. They have a large number of benefits for humans, among which one of the most important is that they are antioxidants.

Alpha carotene

It is generally found in the same foods, accompanying beta-carotene. This chemical compound is believed to protect the body from some types of cancer, such as cervical cancer.

Lycopene

It is found mainly in tomatoes, pin and peppers. Through various studies it has been determined that it reduces the chances of developing various types of cancers. Likewise, it is able to lower the cholesterol present in the blood.

Features

Carotenoids are chemical compounds that fulfill certain functions, among which we can mention:

• They are involved in the photosynthesis process. This is because they are pigments present in plants capable of absorbing light of various wavelengths.
• Carotenoids have a provitamin A function. This means that some carotenoids, such as carotenes, are precursor forms of retinol (Vitamin A). Once inside the body, through various biochemical mechanisms within cells, they are transformed into retinol, which has many benefits for humans. Especially at the level of the sense of sight.
• They are extremely beneficial for the human being, since they contribute to maintaining a good state of health, helping in the prevention of various pathologies such as cancer and eye diseases, among others.

Food sources of carotenoids

Carotenoids are important elements in the body, since they provide a wide variety of benefits in terms of optimizing and improving certain bodily functions. Despite this, the body does not have the mechanisms to synthesize them, so they are obtained through the daily diet.

Many people think that foods rich in carotenoids are necessarily red, orange or yellow. However, this is not the case, since there are even green vegetables in which there is a significant presence of these compounds.

Foods rich in carotenoids. Source: Pixabay

In this sense, carotenoids are present in a large number of foods, all vegetables, some of which are listed below:

• Carrot
• Cabbage
• Watercress
• Spinach
• Red pepper
• Tomato
• Lettuce
• Watermelon
• Papaya
• Apricot
• Orange
• Mango
• Guava
• Strawberry
• Plum
• Peppers
• Asparagus
• Parsley

These are just a few of the foods in which carotenoids can be found. It is vitally important to keep them in mind and include them in the daily diet.

Thanks to the enormous benefits they provide, they are, nowadays, an obligatory part of the daily intake and their benefits are widely recognized.

Benefits

Carotenoids represent a large number of benefits for humans. This is why they must be included in the daily diet in order to have availability of these compounds.

Various studies report that the benefits of these compounds are many, the best known being:

Antioxidant effect

This is one of the most famous effects of carotenoids, although how it occurs has not been properly understood.

In order to understand the antioxidant effect of carotenoids, it is important to take into account certain knowledge of the molecular biology of the organism. It has several mechanisms to purify the so-called free radicals, which cause significant damage to it.

In the body there are certain molecules that are highly harmful to it. These include: O ^-2, HO and NO (reactive oxygen and nitrogen species), as well as H ₂ O ₂ and HONO. Due to the tissue damage they cause, it is necessary for the body to get rid of them. And it does so through various processes.

One of these mechanisms uses certain chemical compounds that are capable of transforming or eliminating them. Among these compounds are: tocopherols, flavonoids and carotenoids, among others.

Some studies have suggested that carotenoids are an O2- suppressant, as well as an agent that helps prevent tissue damage from the so-called reactive oxygen and nitrogen species mentioned above.

It has been conclusively demonstrated that carotenoids are highly effective agents in the inactivation of O-2, largely avoiding the photoxidative damage of this molecule on tissues.

This damage would be given by the action of light, which acts on certain molecules, causing the formation of compounds that are potentially harmful to cells.

Cardiovascular system

It is a belief shared among the different experts in the area that the inclusion in the diet of foods rich in carotenoids contributes to a reduction in the risk of suffering diseases that compromise the cardiovascular system, such as hypertension and pathologies related to the coronary arteries.

The exact mechanism by which carotenoids contribute to the good health of the cardiovascular system is still a mystery. However, doctors agree that a balanced diet should include foods that contain carotenoids, whether they are carotenes or xanthophylls.

Anti-cancer effect

Some carotenoids, such as lycopene, reduce the incidence of some types of cancer, such as cancer of the prostate, lung and digestive tract.

In the same vein, carotenoids have compounds known as acetylenics, which are recognized because they help prevent the development of tumors.

However, this is a field in which much remains to be learned. The World Health Organization states that the claim that carotenoids protect against cancer is "possible, but insufficient", so we still have to wait for the results of many studies that are still in progress.

Despite this, everything seems to indicate that the results will be favorable and that carotenoids play an important role in the prevention of this terrible disease.

They are beneficial in eye health

Taking into account that some of the carotenoids are precursors of retinol (Vitamin A), they constitute an excellent source for the body to obtain the amount it requires.

Retinol is a chemical compound that acts at the level of the retina in order to optimize the functioning of eye receptors, and greatly improve visual acuity, especially with regard to night vision.

They strengthen the immune system

To date, there are several studies that have shown that carotenoids have, among their many benefits, strengthening the immune system. This is important, since this is the one in charge of dealing with any pathogen that can damage the body, such as bacteria and viruses, among others.

References

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