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Physical and chemical properties of simple phenolic compounds. I

Phenols are compounds whose molecules contain an aromatic (benzene) ring associated with one or more -OH groups. A high content of phenols is characteristic of plant cells.

In the animal body, benzene rings are not synthesized, but can only be transformed, so they must constantly be supplied to the body with food. At the same time, many phenolic compounds in animal tissues perform important functions (ubiquinone, adrenaline, thyroxine, serotonin, etc.).

Today, several thousand different phenolic compounds have already been found in plants. They are classified according to the structure of the carbon skeleton:

1. C 6-phenols

2. C 6 -C 1 -phenolic acids

3. C 6 -C 3 -hydroxycinnamic acids and coumarins

4. C 6 -C 3 -C 6 -flavonoids

5. Oligomeric phenolic compounds.

6. Polymer phenolic compounds.

C 6 -Phenols. Compounds whose benzene ring is connected to several hydroxyl groups are called polyphenols.

Free phenols are found rarely and in small quantities in plants. Thus, phenol was found in pine needles and cones, in blackcurrant essential oil, pyrocatechin - in onion scales, in bergenia leaves, hydroquinone - in pear bark and leaves, in bergenia leaves. More often there are derivatives of phenols, where they are associated with any carbon chain or cycle. For example, urushiol and tetrahydrocannabinol.

Urushiol is a toxic substance found in sumac leaves. Tetrahydrocannabinol is the hallucinogenic component of cannabis.

When phenols are oxidized, quinones (benzoquinones) are formed. Quinones are not found in a free state in plants, but their derivatives are common. For example, derivatives of benzoquinones are electron carriers in the ETC of photosynthesis and respiration - plastoquinone and ubiquinone. Benzoquinone derivatives also include the pungent substance of primrose - primin and the red pigment of the fly agaric - muscaruphine.

C 6 -C 1 -phenolic acids. Phenolic acids are common in plants. More often they are in tissues in a bound state and are released during excretion and hydrolysis.

Salicylic acid is released as an allelopathic agent into the environment. At the same time, its regulatory effect on a number of physiological and biochemical processes in the plant (ethylene formation, nitrate reduction, etc.) has now been discovered.

Protocatechuic acid is found in onion scales.

Vanilla and gallic acids are found in wood. The latter is part of some tannins and can form dimers - digallic acid, in the molecule of which two gallic acid residues are connected by an ester bond.

Derivatives of phenolic acids - aldehydes and alcohols - have been found in plants. For example, salicylic alcohol is present in willow bark. But vanillin is especially famous - vanilla aldehyde. It has a very pleasant smell and is found in the form of a glycoside - glucovanillin - in the fruits and branches of the vanilla tree. The glycoside and vanillin itself are widely used in the confectionery, soap and perfume industries.

Phenolic acids can be linked by ester bonds with sugars, most often with glucose. Glycogallin has been isolated from a number of plants (rhubarb, eucalyptus), in which the carboxyl group of gallic acid is linked to the glycosidic hydroxyl of glucose.

C 6 -C 3 -hydroxycinnamic acids and coumarins. Hydroxycinnamic acids are widely distributed in plants. Usually they are in a bound state, and in a free state, except for coffee, they are rarely found.

It has been shown that cis-isomers of hydroxycinnamic acids are activators of plant growth processes, while trans-isomers do not have such properties.

In plants, hydroxycinnamic alcohols are found - derivatives of the corresponding acids: coumaric - coumaric alcohol, ferulic - co-niferyl alcohol, sinapic - synapic alcohol. Alcohols usually do not accumulate, but are apparently used to form lignin, of which they are monomers.

Hydroxycinnamic acids can form esters with organic acids of the aliphatic series. Thus, caffeic acid forms esters with malic and tartaric acids. The first ester is called phaseolinic acid. It is present in bean leaves. The second is chicoric acid. It is found in chicory leaves.

Esters of hydroxycinnamic acids and sugars, most often glucose, are common in plants. Thus, in the flowers of petunia and snapdragon, esters of caffeic, coumaric, and ferulic acids were found, and in cereals in general, the majority of hydroxycinnamic acids are represented by esters. At the same time, hydroxycinnamic acids are part of polysaccharides and proteins. For example, ferulic acid is found in the xylans of wheat flour and in the polysaccharides of pineapples.

Coumarins are lactones that are formed by ring closure between the hydroxyl and carboxyl groups in the hydroxycinnamic acid molecule.

Coumarin is a colorless crystalline substance with a pleasant smell of freshly cut hay. Coumarin is not found in free form in plants. It is usually found in the form of glycosides (melilot flowers and leaves). In herbaceous plants, the cell sap contains a glycoside containing ortho-coumaric acid. During haymaking, plant tissues are damaged and membrane permeability is impaired. Glycosides from cell sap come into contact with cytoplasmic enzymes. Sugars are split off from glycosides, and coumaric acid, after trans-cis isomerization, is closed into a lactone-coumarin. At the same time, the withering grass takes on the smell of hay.

Hydroxylated coumarins are often found in plants as glycosides. For example, esculetin from the pericarp of horse chestnut and scopoletin from the roots of Japanese scopolia. Both of these coumarins have P-vitamin activity and are used in medicine as capillary-strengthening agents.

Dicoumarin was found in white sweet clover, which prevents blood clotting. This and other dicoumarins are used as drugs to prevent blood clots.

C 6 -C 3 -C 6 -flavonoids. This is one of the most diverse and widespread groups of phenolic compounds. At the root of the structure of flavonoid molecules is the flavan structure, which consists of two benzene rings and one heterocyclic (pyran).

Flavonoids are divided into several groups.

1. Catechins.

2. Anthocyanins.

3. Chalcones.

Catechins- the most reduced flavonoids. Οʜᴎ do not form glycosides. Catechin was first isolated from the wood of Acacia catechu, hence its name. Catechins are found in more than 200 plant species. Among the catechins, the most famous are catechin and gallocatechin.

They can form esters with gallic acid - catechin gallates and gallocatechin gallates. Catechins are found in many fruits (apples, pears, quinces, cherries, plums, apricots, strawberries, blackberries, currants, lingonberries, grapes), in cocoa beans, coffee beans, in the bark and wood of many trees (willow, oak, pine , fir, cedar, cypress, acacia, eucalyptus). There are especially many catechins in the leaves and young shoots of tea (up to 30%). Oxidative transformations of catechins play an important role in tea production and winemaking. The oxidation products, which are mainly catechin dimers, have a pleasant, slightly astringent taste and a golden-brown color. This determines the color and taste of the final product. At the same time, catechins have high P-vitamin activity, strengthen capillaries and normalize the permeability of vascular walls. The catechin dimers in tea have the same activity. Catechins as monomers are part of condensed tannins.

Anthocyanins- the most important plant pigments. They color flower petals, fruits, and sometimes leaves in blue, indigo, pink, red, and violet colors with various shades and transitions. All anthocyanins are glycosides. Their aglycones are anthocyanidins. Anthocyanins are water soluble and are found in cell sap.

Today, more than 20 anthocyanidins are known, but 4 are the most widely distributed: pelargonidin, cyanidin, delphinidin and malvidin (methylated derivative of delphinidin).

Anthocyanins contain glucose, galactose, rhamnose, xylose, and less frequently arabinose as monosaccharides, and most often rutinose, sophorose, and sambubiose are found as disaccharides. Sometimes anthocyanins contain trisaccharides, usually branched. For example, anthocyanin was found in currants and raspberries, in which a branched trisaccharide is associated with cyanidin.

The color of anthocyanins depends on a number of factors:

1. concentration of anthocyanins in cell sap;

2. pH of cell sap;

3. complexation of anthocyanins with cations;

4. copigmentation - a mixture of anthocyanins and the presence of other phenolic substances in the cell sap;

5. combinations with the coloring of plastid pigments.

Let's take a closer look at these factors.

1. The concentration of anthocyanins in cell sap can vary over a wide range - from 0.01 to 15%. For example, regular blue cornflower contains 0.05% cyanin anthocyanin, and dark purple cornflower contains 13-14%.

2. Due to the fact that anthocyanin molecules have free valency, the color can change based on the pH value. Typically, in an acidic environment, anthocyanins have a red color of varying intensity and shades, and in an alkaline environment they are blue. Such changes in anthocyanin color can be observed by adding an acid or alkali to the colored juice of currants, cherries, beets or red cabbage. In nature, sharp changes in the pH of cell sap do not occur, and this factor does not play a major role in the color of anthocyanins. One can only notice that some pink and red flowers turn blue when they wither. This indicates a change in pH in dying cells.

3. The ability of anthocyanins to chelate with metal ions is of great importance in the color of flowers and fruits. This is clearly seen in the example of cornflower and rose. Their petals contain the same anthocyanin - cyanin. In the petals of blue cornflower, cyanine forms a complex with Fe ions (4 cyanine molecules are bound to one Fe atom). Red rose petals contain free cyanine. Another example.
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If an ordinary hydrangea with pink flowers is grown on a mineral medium containing aluminum and molybdenum, the flowers acquire a blue color.

4. Usually, the cell sap of many flowers and fruits contains not one, but several pigments. In this case, coloring depends on their mixture, and it is called copigmentation. Thus, the color of blueberry fruits is due to the copigmentation of delphinin and malvin. There are 10 different anthocyanins found in purple potato flowers.

The color pattern of the petals of many flowers is determined either by a local increase in the concentration of one pigment (digitalis), or by the superposition of an additional pigment on the main one (in the center of poppy flowers, a high concentration of cyanine is superimposed on the general background of pelargonin).

The color is also affected by the copigmentation of anthocyanins with other substances, for example, tannins. Thus, purple and dark red roses contain the same cyanin, but in dark red roses it is copigmented with a large amount of tannin.

5. The combination of blue anthocyanins in cell sap and yellow-orange carotenoids in chromoplasts results in the brown color of the petals of some flowers.

Table Some plant anthocyanins

Anthocyanin	Aglycone	Sugar	Plants
Pelargonin	Pelargonidin	2 glucose	Pelargonium, asters
Cyanine	Cyanidin	2 glucose	Roses, cornflowers
Keratsyanin	Cyanidin	Glucose, rhamnose	Cherries
Prunicianin	Cyanidin	Rhamnose, glucose	Plums
Idain	Cyanidin	Galactose	Cowberry
Chrysanthemum	Cyanidin	Glucose	Asters, blueberries, elderberries
Malvin	Malvidin	2 glucose	Mallow
Enin	Malvidin	Glucose	Grape
Dolphinium	Delphinidin	Rhamnose, glucose	Spur
Viglanin	Delphinidin	Glucose, rhamnose	Coltsfoot

Halcones, or anthochlors, are flavonoids with an open heterocycle. They give the flower petals a yellow color. Their distribution is limited to nine families. They are found in the form of glycosides. Chalcones, for example, are isosalipurposide from yellow clove flowers and phloridzin from apple bark and leaves. Phloridzin is an apple growth inhibitor. When ingested by a person, it causes a one-time intense release of glucose into the blood - “phloridzin diabetes”.

Oligomeric phenolic compounds. This includes lichen acids. Οʜᴎ are formed in lichens from two or more orsellinic acid residues. Lecanoric and evernic acids are composed of two orsellinic acid residues. Evernic acid is the main component of the evernia acid complex (oak moss), which is used in perfumery as an aromatic substance and at the same time as a fixative in the manufacture of the best types of perfumes.

Among lichen acids there are colored ones. They give lichens a variety of colors - yellow, orange, red, purple. Usnea lichen contains usnic acid, which is an effective bactericidal agent.

Dimers of hydroxycinnamic alcohols are found in the bark, wood, fruits and leaves of many plants. They form oligomers and flavonoids, especially catechins. Catechin dimers are found in apples, chestnuts, hawthorn, cocoa beans, and eucalyptus wood.

Polymeric phenolic compounds. Polymeric phenolic compounds include tannins, or tannins, lignins and melanins.

Tannins, or tannins. They got their name from their ability to tan animal skins, turning them into leather. Tanning is based on the interaction of tannins with the skin protein - collagen. In this case, numerous hydrogen bonds are formed between the protein and tannin.

Natural tannins are a complex mixture of compounds with similar compositions with a molecular weight of 500-5000.

A lot of tannins are contained in the bark and wood of oak, eucalyptus, chestnut wood, in the rhizome of sorrel, rhubarb, and sumac leaves. There are many of them in the bark and wood of legumes, myrtles, and roses. The galls that form on the leaves when they are damaged by the gallworm (up to 50-70%) are distinguished by a particularly high content of tannins.

Tannins (usually food tannins) are also called lower molecular substances that have a pleasant astringent taste, but are not capable of true tanning. Οʜᴎ are present in many fruits (quinces, apples, persimmons, grapes), and in tea leaves.

Tannins are widely used not only in the leather industry. They are used in the production of plastics, binders in the production of plywood and sawdust boards, and as a mordant for dyeing. Οʜᴎ are used in installations for boiling water as colloid stabilizers, to regulate the viscosity of solutions when drilling wells.

The use of tannins in winemaking is associated with their inhibitory effect on enzymes and microorganisms, which prevents clouding of wines and improves their quality. Tea tannin is used to stabilize betacyanin, a red food coloring obtained from beets.

In medicine, tannins are used as astringents, bactericidal, anti-radiation and antitumor agents.

Lignin is part of the cell membranes of wood tissues. It is deposited between cellulose microfibrils, which gives cell membranes hardness and strength. At the same time, the connection between cells is disrupted, which leads to the death of living contents; therefore, lignification is the final stage of cell ontogenesis.

Lignin is an amorphous substance, insoluble in water, organic solvents and even concentrated acid.

Lignin has another important property: it is resistant to microorganisms. Only a few microorganisms, and then very slowly, decompose it.

Lignin is a three-dimensional polymer whose monomers are hydroxycinnamic alcohols. Thus, in conifers, co-niferyl alcohol predominates in lignin, in cereals - coumaric alcohol, in many deciduous trees - synapic alcohol.

Large amounts of lignin accumulate as waste in the pulp and paper industry and hydrolysis plants. It is used to produce activated carbon, plastics, and synthetic resins.

Melanins- polymers of phenolic nature, which are a product of tyrosine oxidation. Their structure has not yet been fully elucidated.

Melanins are black or brown-black in color. Their formation explains the rapid darkening of the surface of a cut apple, potato tuber, and some mushrooms. Melanins are also present in animal organisms, causing the color of wool and hair. At the same time, plant and animal melanins differ in the composition of monomers. When hydrolyzed, plant melanins form pyrocatechol, and animal melanins form dihydroxyindole. In other words, plant melanins, unlike animals, are nitrogen-free substances.

Functions of phenolic compounds in plants. 1. Phenols participate in redox processes: phenols are converted into quinones and vice versa with the participation of the enzyme polyphenol oxidase. At the same time, various compounds (amino acids, organic acids, phenols, cytochromes, etc.) can be oxidized in a non-enzymatic way.

2. Some phenolic compounds are carriers of electrons and protons in the ETC of photosynthesis and respiration (plastoquinone, ubiquinone).

3. A number of phenols have an effect on plant growth processes, sometimes activating, more often inhibiting. This effect is mediated by the effect on phytohormones. Thus, it is known that some phenolic compounds are necessary during the synthesis of auxin, others - during its breakdown. The presence of coumaric acid ester is extremely important for the formation of ethylene. It has been established that under stress, plants accumulate a large amount of phenols, which leads to inhibition of growth processes and an increase in their resistance to unfavorable conditions.

4. Phenols perform a protective function in plants: Phenolic compounds give plants resistance to diseases. For example, resistance to a number of diseases on onions with colored skins is associated with the presence of protocatechuic acid in it. When plant tissues are mechanically damaged, phenols accumulate in the cells and, condensing, form a protective layer. Some plants, in response to damage by pathogenic fungi, form protective substances - phytoalexins, many of which are phenolic in nature.

5. Many phenols are antioxidants and protect membrane lipids from oxidative destruction. Some of them are used in the food industry to protect fats from rancidity (gallic acid esters, flavonoids, etc.).

6. The role of phenolic compounds in the process of plant reproduction is very important. This is not only due to the color of flowers and fruits, but also to the direct participation of phenols in fertilization. Thus, flavonoids take part in the process of fertilization of the Chlamydomonas algae and the higher forsythia plant.

7. Phenols can act as allelopathic substances in some plants. For example, such a substance in oak should be salicylic acid.

8. Some phenols act as activators or inhibitors on certain processes and enzymes (cell division, protein synthesis, oxidative phosphorylation, etc.).

Phenolic compounds - concept and types. Classification and features of the category "Phenolic compounds" 2017, 2018.

Phenolic compounds are one of the most common and numerous classes of secondary compounds with various biological activities. These include substances of aromatic nature that contain one or more hydroxyl groups bonded to the carbon atoms of the aromatic nucleus. These compounds are very heterogeneous in chemical structure; they are found in plants in the form of monomers, dimers, oligomers and polymers.

The classification of natural phenols is based on the biogenetic principle. Modern ideas about biosynthesis make it possible to divide phenolic compounds into several main groups, arranging them in order of complexity of the molecular structure. The simplest are compounds with one benzene ring - simple phenols, benzoic acids, phenolic alcohols, phenylacetic acids and their derivatives. Based on the number of OH groups, simple phenols are distinguished into monoatomic (phenol), diatomic (pyrocatechol, resorcinol, hydroquinone) and triatomic (pyrogallol, phloroglucinol, etc.). Most often they are found in bound form in the form of glycosides or esters or are structural elements of more complex compounds, including polymeric ones (tannins). More diverse phenols are derivatives of the phenylpropane series (phenylpropanoids), containing one or more C6-C3 fragments in their structure. Simple phenylpropanoids include hydroxycinnamic alcohols and acids, their esters and glycosylated forms, as well as phenylpropanes and cinnamoylamides. Compounds biogenetically related to phenylpropanoids include coumarins, flavonoids, chromones, dimeric compounds - lignans and polymeric compounds - lignins. A few groups of phenylpropanoid compounds make up original complexes that combine derivatives of flavonoids, coumarins, xanthones and alkaloids with lignans (flavolignans, coumarinolignans, xantholignans and alkaloidolignans). A unique group of biologically active substances are the flavolignans of Silybum marianum (L.) Gaertn. (siliban, silydianin, silicristin), which exhibit hepatoprotective properties.

Most phenolic compounds originate from a common precursor, shikimic acid. The shikimate pathway for the biosynthesis of phenolic compounds begins with the metabolic products of sugars formed as a result of photosynthesis and passes through several stages to the stage of a specific precursor of shikimic acid. Further, aromatic amino acids are formed from it: L-phenylalanine, L-tyrosine, L-tryptophan. Flavonoids and catechins are formed from L-phenylalanine through the intermediate stage of hydroxycinnamic acids (phenylpropanoids). In the most numerous and widespread group of phenolic compounds in plants, flavonoids, the molecule contains two aromatic rings, one of which is formed along the shikimate pathway, and the second from three molecules of activated acetate.

Main biological activity

Food plants contain compounds of the phenolic group with one or two aromatic rings, which have pronounced biological activity:

Adaptogenic and stimulating to the central nervous system - salidroside (Rhodiola rosea, or golden root);

P-vitamin - rutin (Japanese Sophora, catechins (tea), vitamin P (fruits of mountain ash and cinnamon rose hips, black currant berries and chokeberry).

Antihypertensive - flavones (scutellaria baicalensis), lignans (Eucommia vysolifolia) are used for hypertension and functional disorders of the nervous system, for cardiovascular diseases;

Antispasmodic - furocoumarins, chromines (parsnips, Siberian pustules, ammi dentalum) are used for coronary insufficiency and neuroses;

Stimulating - lignans (Thai lemongrass) are used as a general strengthening and tonic;

Sedative - flavonols (motherwort cordial) are used for cardiovascular neuroses, hypertension, insomnia;

Diuretic - kaempferol, isoflavonoids (birch buds, field steelhead root) are used as a diuretic;

Choleretic - flavonols (tansy, sandy immortelle, peppermint, artichoke, rose hips) are used for acute and chronic diseases of the liver, gall bladder, bile ducts;

Hemostatic - flavonols, quercetin (knotweed, knotweed, pepper knotweed) are used for uterine bleeding;

Antimicrobial - hydroquinone, arbutin (bearberry, lingonberry) are used for diseases of the kidneys and urinary tract as a diuretic and disinfectant;

Antihemorrhagic - lignans (jute).

Phenolic compounds with one aromatic ring

Phenolic alcohols. Phenolic alcohols and their glycosides are contained in Rhodiola rosea and increase the body's performance and resistance to adverse effects.

Hydroxycinnamic acids. Hydroxycinnamic acids (p-coumaric, caffeic, ferulic and sinapic acids) in various combinations, in free form or as part of glycosides and esters, are found in many higher plants. The most common in nature are caffeic acid and its derivatives (chlorogenic acid and its isomers), which have anti-inflammatory and choleretic effects. Chlorogenic acid is present in large quantities in coffee beans, blueberry leaves, mountain arnica, chamomile, etc. The sum of caffeic, chlorogenic, ferulic, coumaric and other caffeoylquinic acids has a hypoazotemic effect, enhances kidney function, and stimulates the antitoxic function of the liver. Hydroxycinnamic acids are also found in echinacea, burdock roots, hawthorn, and rhubarb.

Benzoic and salicylic acids of chamomile flowers, meadowsweet, willow bark, black and red currant have antiseptic properties. Malic, tartaric, citric, and hydroxycarboxylic acids take part in alkalizing the body. The main component of Garcinia Cambogia - hydroxycitric acid - suppresses appetite, slows down the conversion of excess carbohydrates into fats, increases the body's energy potential, helps reduce cholesterol levels in the blood, and reduces fatty liver. Tartronic acid, contained in large quantities in cabbage, inhibits the conversion of carbohydrates into fats, thereby preventing obesity and atherosclerosis.

Coumarins, oxycoumarins. Coumarins have versatile biological activity. They are characterized by photosensitizing (fruits of psoralea, ammi major, fig tree leaves), antispasmodic (fruits of parsnip, roots of Siberian spleen and mountain gorychnik), P-vitamin (chestnut seeds) activity. In their pure form, they exhibit anticoagulant (dicumarol), antimicrobial (umbelliferon), estrogenic (clover coumestrols), and antitumor (osthol) effects.

Oxycoumarins are of some importance in the prevention of heart attacks and strokes due to the ability of these substances to reduce blood clotting.

Chromones. Chromones have antispasmodic, coronary dilation, antibacterial, biostimulating, antiallergenic, and antibacterial effects. Kellin, which is used for urinary tract spasms, bronchospasms and chronic angina, is considered to be the standard for the antispasmodic activity of chromones.

Xanthones. Xanthones have a wide range of biological activity: they are stimulants of the central nervous system, exhibit cardiotonic, antitumor, diuretic activity, antibacterial, antiviral, antifungal and antituberculosis effects.

Mangiferin. Stimulates the central nervous system, and in large doses has cardiotonic, diuretic, antibacterial and anti-inflammatory effects.

Quinones, ubiquinones. Quinones from senna, rhubarb, and buckthorn (anthraquinones) can enhance the peristalsis of the large intestines, which causes their laxative effect. Some anthraquinones, chrysophanolic acid and other oxyanthraquinones, as well as aminoalloxyl derivatives, have antitumor activity and are immunosuppressants.

Ubiquinones (coenzyme Q) are a universal component of not only plant, but also animal and human tissues. They are part of other cellular organelles - mitochondria - and are indispensable and constant participants in the process of cellular respiration.

Lignans. Lignans have stimulating and adaptogenic (schizandrin and syringoresinol derivatives), antitumor (podophyllotoxin), antihemorrhagic (sesamin), antimicrobial (arctiin), hepatoprotective (silibin) effects.

Phenolic compounds with two aromatic rings

Flavonoids. Flavonoids are called "natural biological response modifiers" due to their ability to alter the body's response to allergens, viruses and carcinogens. This is evidenced by their anti-inflammatory, anti-allergic, antiviral and anti-carcinogenic properties. In addition, flavonoids act as strong antioxidants, providing protection against oxidation and free radical damage.

In 1936, the Hungarian biochemist Albert Szent-Györgyi (1893‑1986, Nobel Prize laureate 1937 in medicine and physiology, since 1947 worked in the USA) isolated a substance from lemon peel, the pharmacological use of which reduced fragility and permeability of blood capillaries. It was called vitamin P. Other names: rutin, thioctic acid, vitamin N. This discovery laid the basis for subsequent research into a large group of substances that are significant for the human body, called flavonoids. These studies began in the 60s of the 20th century. Particular attention was paid to the study of the importance of flavonoids for the human body at the end of the 20th and beginning of the 21st centuries.

Currently, about 4000 flavonoids have been identified. They are polyphenolic compounds whose structure is based on a diphenylpropane carbon skeleton. Most of the flavonoids are found in cells in the form of compounds with sugars (glycosides) and organic acids. Examples of flavonoids that are important for humans are rutin and quercecin. Those flavonoids that are bound to one or more sugar molecules are called flavonoid glycosides. Flavonoids that are not bound to a sugar molecule are called aglycones. With the exception of flavones, flavonoids are found in most plant foods in the form of glycosides. Most flavonoid glycosides that enter the digestive tract are not digested and reach the small intestine unchanged. Flavonoids aglycones and flavonoid glucosides are absorbed in the small intestine, where they are rapidly metabolized (methylated, glucuronidated or sulfated). Colon bacteria play an important role in the metabolism and absorption of flavonoids. Flavonoids and their metabolites that are not absorbed in the small intestine are metabolized by bacterial enzymes in the cavity of the colon and can be absorbed. In general, the proportion of flavonoids absorbed and delivered through the systemic circulation to target tissues is relatively small and is limited by both their rapid and intensive metabolism and rapid excretion from the body. The activity of flavonoid metabolites is not always similar to the activity of the parent flavonoids. Laboratory studies (in vitro) show that flavonoids are effective free radical scavengers. Thus, under artificial conditions, flavonoids are active antioxidants.

Although most research on flavonoids relates to their antioxidant function, there is compelling evidence that flavonoids modulate the mechanisms of matter and information transfer within and between cells and are thus involved in many cellular functions. In particular, flavonoids perform the following actions:

1) Stimulate the activity of enzymes that catalyze reactions that promote the removal of potentially toxic or carcinogenic substances from the body.

2) They protect the regulation of the normal cell cycle from disturbances. Each cell, from one division to the next, goes through a sequence of developmental stages (cell cycle). If DNA is damaged, the cell cycle is blocked. If the degree of damage is small and DNA repair is possible, the damage is a signal for DNA repair. Uncompensated consequences of damaging effects are a signal for cell death (apoptosis). Dysregulation of the normal cell cycle can lead to the reproduction of mutations and the development of malignant neoplasms.

3) They inhibit proliferation and trigger apoptosis. Unlike normal cells, cancer cells rapidly proliferate and lose the ability to respond to death signals that induce the cell to undergo apoptosis.

4) They inhibit the initial invasion of the tumor and angiogenesis in neoplasms. Cancer cells invade normal tissue through enzymes called matrix metalloproteinases. A malignant neoplasm that has invaded normal tissue grows rapidly, provided it receives sufficient nutrition from the newly developing blood vessels in it (angiogenesis).

5) Inhibit the development of inflammation. Inflammation is accompanied by the secretion and elimination of inflammatory enzymes. They cause a local increase in the production of free radicals. Similarly, the release of inflammatory mediators promotes cell proliferation, angiogenesis and inhibits apoptosis.

6) Prevent diseases of the cardiovascular system. Currently, atherosclerosis is classified as an inflammatory disease. Atherosclerosis and some other types of inflammation are associated with an increased risk of myocardial infarction.

7) Reduce the ability of blood vessel cells to adhere to leukocytes. In the early stages of the development of atherosclerosis, as an inflammatory disease, leukocytes involved in the implementation of inflammation are mobilized from the blood stream to the artery wall. This phenomenon depends on the removal by endothelial cells lining the inner surface of the artery of molecules of a substance that promotes the adhesion of leukocytes to the inner surface of the artery.

8) Reduce the activity of endothelial nitric oxide synthase. Nitric oxide synthase is an enzyme that catalyzes the production of nitric oxide by endothelial cells. Nitric oxide is a vasodilator (vasodilator), a means of controlling the tone of the arteries and their lumen. Disturbance in the formation of nitric oxide is considered one of the reasons for the increased risk of cardiovascular diseases.

9) Reduce the ability of blood platelets to aggregate. Aggregation of blood platelets is the first step in the formation of a blood clot, which can clog the coronary artery that supplies the myocardium or arteries of the brain. This may result in myocardial infarction or stroke. Inhibition of platelet aggregation is considered an important measure for the prevention of diseases of the cardiovascular system.

10) It is believed that the anti-inflammatory effect of flavonoids, their antioxidant effect and the ability to bind metals play an important role in the etiology and pathogenesis of a number of neurodegenerative diseases, in particular Parkinson's disease and Alzheimer's disease. Therefore, scientists are working to create special diets to prevent neurodegenerative diseases.

The antioxidant properties of flavonoids have a wider spectrum than those of antioxidants such as vitamins C and E, selenium, and zinc. Flavonoids also have choleretic, antiulcer, antiviral, diuretic, antispasmodic, antihemorrhoidal and other effects. Different flavonoids have different effects.

Isoflavones. Isoflavones have an estrogenic effect. Soy isoflavones (daizin, daidzein, glycitein, genistrin, genistein) act selectively, exhibiting both estrogenic and antistrogenic activity depending on the amount of estrogens contained in the blood. Soy isoflavones are used as a means of lowering blood pressure and strengthening the cardiovascular and nervous systems. Having a natural origin, without side effects, unlike hormonal contraceptives, soy isoflavone well compensates for the lack of estrogen in a woman’s body. The main isoflavones in soybeans are genistein and daidzein.

The following health benefits are attributed to isoflavones:

1) Reduces symptoms of menopause. The beneficial qualities of soy not only prevent cancer in the long term, today's developments have shown that soy isoflavones reduce various signs of menopausal syndrome, such as shortness of breath, fatigue, night sweats, mood swings and strengthens the bone tissue of women. By the way, many health problems during and after menopause can result from a lack of isoflavones in a typical oriental diet.

2) Prevents the risk of heart disease. Soy isoflavones also appear to reduce the risk of cardiovascular disease through various mechanisms. They inhibit the deposition of atherosclerotic plaques in the vessels that clog the artery. Blood clots form in these arteries, leading to a heart attack. Isoflavones have been proven to be the active components of soy that are responsible for controlling blood cholesterol levels.

3) Protects against prostate problems. By consuming foods rich in isoflavones, you can prevent prostate enlargement in men. Research shows that isoflavones prevent the growth of prostate cancer cells and remove them from the prostate gland. Isoflavones act in the same way against cancer cells as many conventional drugs prescribed to treat this disease.

4) Isoflavones help strengthen bone tissue. Isoflavones help strengthen bone tissue and help prevent osteoporosis. Osteoporosis is extremely rare in Chinese and Japanese populations, despite their low dairy consumption, while the opposite is true in Europe and North America. Unlike estrogen, which helps prevent bone destruction, isoflavones also help form new bone tissue.

5) Prevents benign and malignant neoplasms. Isoflavone competitively binds in tissues to estrogen receptors produced by the body or introduced into the body, thus preventing the reaction of estrogen receptors, reducing the possibility of hormone-related cancer cell development. Isoflavones also help prevent the proliferation of blood vessels inside the tumor, thus leaving the tumor without a source of nutrition.

Flavone derivatives. Flavones have bactericidal, antispasmodic, and hypotensive effects. They dissolve well in many organic solvents, but poorly in water. In concentrated H 2 SO 4 dissolve with violet fluorescence, forming an unstable benzo-pyrylium salt. When heated with alcoholates, flavone forms α-hydroxyacetophenone and benzoic acid (the reaction is used to determine the structure of flavonoid derivatives). Over 500 flavone derivatives have been isolated in nature. The flavone itself is found in the form of a coating on the leaves and flowers of some types of primroses.

Flavonols, depending on their structure, have a diverse effect on the body: - kaempferol, morin, myricetin have a diuretic effect; - gossypetin, morin, quercetagetin, quercetin, etc. - antioxidant; - ramnetin, morin - bactericidal; - myricetin, quercetagetin, isorhamnetin stimulate the activity of the heart; - robinin, lespedin, biorobin, diorobin, hyperoside have hypoazotemic properties; - gossypol - anti-carcinogenic. Among flavonones, the most common are the flavone glycoside hesperidin, the main flavonoid in orange juice, and the flavonone glycoside naringin, the main flavonoid in grapefruit juice, which has a positive effect on blood composition. Hesperidin belongs to a complex of bioflavonoid compounds that can reduce the permeability and fragility of capillary blood vessels. It is widely used for hypo- and avitaminosis P and the treatment of many diseases of the blood vessels (for example, “purpuric disease” - thrombopenic purpura, hemorrhagic diathesis, retinal hemorrhages, radiation sickness), as well as for hypertension, measles, scarlet fever, typhus and etc. In addition, it has been established that quercetin and hisperidin have a pronounced antiallergic effect and have a beneficial effect on the walls of blood vessels.

Eugenol, which is part of the essential oils of bay and clove trees, is a strong antiseptic; thymol, contained in thyme, has the same effect. Phloroglucinol derivatives found in ferns have an antihelminthic effect, and apiol from parsley fruits exhibits antispasmodic properties. Arbutin is found in lingonberries and bearberry; has diuretic properties and prevents a number of kidney diseases. Hydroquinone, formed as a result of the hydrolysis of arbutin, exhibits bactericidal properties and inhibits fat oxidation. Vaccinin is a glycoside specific to lingonberries and cranberries, it is a compound of glucose with benzoic acid and has a bactericidal effect. Vaccimirtillin - a bitter glycoside of blueberries and blueberries, contained in them in an amount of 1.2 - 1.8 mg per 100g, prevents diabetes. Flavonoids from Rhodiola rosea (“golden root”) have adaptogenic and immunostimulating properties.

Proanthocyanidins. This is one of the most healing groups of flavonoids. They maintain the collagen structure and prevent its destruction by promoting the binding of collagen fibers, thereby strengthening the connective tissue matrix. Complexes of biologically active substances of grape pomace extract effectively neutralize free radicals, suppress the synthesis of lipid peroxides, inhibit enzymes involved in the formation of reactive oxygen species (for example, xanthine oxidase), prevent the breakdown of collagen by enzymes secreted by leukocytes during inflammation and microorganisms during tissue infection, the synthesis of histamine, serine proteases, leukotrienes. The anti-inflammatory effect of proanthocyanidins is associated with this mechanism. Their antioxidant effect is 50 times higher than that of vitamin E, and 20 times higher than that of vitamin C.

Extracts from grape seeds are more preferable, since due to the content of gallic esters of proanthocyanidins they have increased activity. These substances are the most active of all currently known antioxidants. These properties are associated with an important area of their use for the prevention of cardiovascular diseases, including myocardial infarction, damage to the vascular endothelium, and lowering blood cholesterol levels. Grape pomace extract helps improve microcirculation and is effective in the treatment of angiopathy, retinopathy, as well as inflammatory processes due to inhibition of the biosynthesis of anti-inflammatory leukotrienes.

Polymeric phenolic compounds (polyphenols)

Tannins. They are used as astringents, anti-inflammatory and bactericidal agents (cinquefoil erect, knotweed, burnet, rhizomes of bergenia, sulfur alder “cones”, etc.) for acute and chronic diarrhea, enterocolitis (blueberry, bird cherry fruits), as well as for stomatitis, gingivitis and other inflammatory processes in the oral cavity, larynx, pharynx, etc.

Tanids. Tannides are used for poisoning with alkaloids and heavy metals. Their astringent, anti-inflammatory and hemostatic effect is due to the fact that they coagulate proteins and form a protective film.

Catechins. Catechins are organic substances from the group of flavonoids. They are polyphenolic compounds and are strong antioxidants. Characteristic representatives of the family are the stereoisomers catechin and epicatechin.

The most catechins are found in white tea, slightly less in green tea. They are found in large quantities in many fruits and berries (apples, quinces, apricots, peaches, plums, cherries, strawberries, currants, raspberries, etc.). Catechins are also found in dark chocolate and apples. Tannin is the general name for isomers of one of the catechins, which is present in white, yellow and green tea in higher concentrations than in black. Due to oxidation processes during tea fermentation, the content of catechins in black tea is reduced. Catechins are polyphenols, good antioxidants.

The antioxidant properties of many plant products are largely due to the content of catechins. The beneficial protective properties of catechins can be illustrated using tea as an example. Tea contains four main catechin components: EC, ECg, EGC and EGCg. Each of these compounds can be called catechin. Epigallocatechin (EGC) is the most powerful antioxidant of the four main tea catechins, 25-100 times stronger than vitamins C and E. One cup of green tea per day provides 10-40 milligrams of polyphenols. The antioxidant effect is also inherent in catechins from broccoli, spinach, carrots, and strawberries. Being a strong antioxidant, green tea reduces the amount of free radicals in the human body, to a certain extent preventing the occurrence of cancer.

Catechins are rarely used in their pure form. However, redox transformations of catechins play an important role in the technology of many food industries, such as tea fermentation, winemaking, and cocoa production.

In addition, tea catechins have antimicrobial properties and are used in the treatment of dysentery. Catechins are also believed to be useful for strengthening the immune system and treating tumors. Catechins are classified as substances with P-vitamin activity. Medicines and dietary supplements containing catechins and other bioflavonoids are widely used in the treatment of diseases associated with impaired capillary function, edema of vascular origin, etc.

Epicatechin gallate is considered the most active among polyphenols. These compounds have pronounced antioxidant properties, the ability to increase the functional activity of detoxification systems of foreign compounds and, due to these properties, significantly reduce the risk of developing tumors of the mammary glands, prostate, lungs, intestines, etc.

Prevalence in nature

Flavonoids are widely distributed in the plant world. Particularly rich in flavonoids are higher plants belonging to the families Rosaceae (various types of hawthorns, chokeberry), legumes (Japanese sophora, field steelhead, licorice), buckwheat (various types of mountaineers - pepper, kidney, avian: buckwheat), asteraceae (sandy immortelle, marshweed, tansy), Lamiaceae (motherwort), etc.

Flavonoids are more often found in tropical and alpine plants. Also found in lower plants: green algae (duckweed), spore-bearing algae (mosses, ferns), horsetails (horsetail), as well as in some insects (marbled white butterfly).

Flavonoids are found in various organs, but more often in above-ground organs: flowers, leaves, fruits; There are significantly fewer of them in stems and underground organs (licorice, Baikal skullcap, field steelhead). Young flowers and unripe fruits are richest in them. Localized in cell sap in dissolved form.

Flavonoids accumulate in many medicinal plants: licorice roots (Glycyrrhiza glabra L.), motherwort herb (Leonurus cordiaca L.), immortelle flowers (Helichryzum arenarium L.) - and are characterized by a wide range of pharmacological effects. They have choleretic, bactericidal, antispasmodic, and cardiotonic effects. In medicine, the property of many flavonoids, for example rutin, which accumulates in many plants (P-vitamin effect), to reduce the permeability and fragility of capillaries, is widely used. Flavonoids have also been shown to have anti-cancer and anti-radiation effects; they bind and remove radionuclides from the body. The absence of toxic properties and selectivity of action on the human body increases the value of flavonoid compounds and opens up a great future for the creation of new drugs based on them.

The chemical classification of natural phenolic compounds is based on the biogenetic principle. In accordance with modern ideas about biosynthesis, phenols can be divided into several main groups, arranging them in order of complexity of the molecular structure:

1. C 6 - compounds with one benzene ring.

The simplest representative of phenolic compounds is phenol itself, which was found in pine needles and cones, as well as in the essential oil of black currant leaves and some other plants.

Among the simple monomeric phenols there are di- and triatomic phenols:

These compounds are rarely found in free form in plants; they are more often found in the form of esters, glycosides, or are a structural unit of more complex compounds, including polymers.

2. C 6 -C 1 - compounds. These include benzoic acids and their corresponding alcohols and aldehydes.

Hydroxybenzoic acids in plants are in a bound form and are released after hydrolysis. An example is glucogallin, found in rhubarb roots and eucalyptus leaves.

A dimer of gallic acid, m-digallic acid, is found in many plants, which is a monomer of hydrolyzable tannins.

An ester bond formed by the phenolic hydroxyl of one hydroxybenzoic acid molecule and the carboxyl group of another is called a depside bond, and compounds containing such bonds are called depsides.

The group of C 6 -C 1 compounds includes lichen acids - specific phenolic compounds of lichens. The starting component in the formation of these acids is orselic (6-methylresocylic) acid.

3. C 6 -C 3 compounds (phenylpropane compounds). These include hydroxycinnamic acids, alcohols, aldehydes and coumarins.

Hydroxycinnamic acids are found in almost all plants, where they occur in the form of cis- and trans-isomers, differing in physiological activity. When irradiated with UV light, the transforms transform into cis forms, which stimulate plant growth.

In plants they are present in free form or in the form of glycosides and depsids with quinic or shikimic acids.

Hydroxycinnamic alcohols in their free form do not accumulate, but are used as starting monomers in the biosynthesis of lignins.

This group includes coumarin - a lactone of the cis-form of coumaric acid

Coumarin itself is not a phenolic compound, but plants contain its hydroxy derivatives.

5. C 6 -C 1 -C 6 - compounds

These include benzophenone derivatives and xanthones.

6. C 6 -C 2 -C 6 compounds

This group includes stilbenes, which are monomers of hydrolyzable tannins.

These compounds in the form of aglycones and glycosides are found in pine wood, eucalyptus, rhubarb roots, and in some types of legumes.

7. C 6 -C 3 -C 6 compounds, diphenylpropane derivatives

This is the most extensive group of phenolic compounds, which is ubiquitous in plants. They consist of two benzene rings connected by a three-carbon moiety, i.e. six-membered oxygen-containing heterocycle, formed by intramolecular condensation of most C 6 -C 3 -C 6 compounds, is a derivative of pyran or g-pyrone

8. C 6 -C 3 -C 3 -C 6 dimer compounds consisting of two phenylpropane units. Lignans belong to this group.
9. Compounds consisting of two or three fused rings and containing hydroxyl and quinoid groups - naphthoquinones and anthraquinones.
10. Polymer compounds - tannins, lignans, etc.;
11. Compounds of a different structure - limitedly distributed chromones, or representing mixed phenols - flavolignans.

Phenolic compounds are substances containing aromatic rings with a hydroxyl group, as well as their functional derivatives. Phenolic compounds that have more than one hydroxyl group on their aromatic ring are called polyphenols.

Classification of phenolic compounds

The classification of phenolic compounds is based on the main carbon skeleton - the number of aromatic rings and carbon atoms in the side chain. Based on these characteristics, phenolic compounds are divided into groups: simple phenols; phenolic acids; phenolic alcohols, phenylacetic acids, acetophenols; hydroxycinnamic acids, coumarins, chromones; lignans; flavonoids; tannins.

Properties

Phenolic compounds are colored or colorless substances with a characteristic odor, solid, crystalline or amorphous, less often liquid. As a rule, they are highly soluble in ethyl alcohol, diethyl ether, chloroform, and less often in water. They have acidic properties and form phenolates with alkalis.

The most important property of phenolic compounds is the ability to oxidize to form forms such as quinones. Polyphenols are especially easily oxidized by atmospheric oxygen in an alkaline environment. Complexes of phenols with heavy metal ions are brightly colored. This property of phenol is widely used to determine their qualitative content in solutions.

The biological role of phenols in plants is diverse. Redox reactions in the process of respiration and photosynthesis occur with the obligatory participation of phenolic compounds, which are components of the respiratory chain.

Many phenolic compounds are activators and inhibitors of plant growth and development. The antioxidant activity of many phenols used in the food industry as antioxidants is known.

Polyphenolic compounds significantly affect the quality and nutritional value of fruits, berries, and vegetables. The change in polyphenols in plant raw materials under the influence of technological influence during canning is one of the main reasons for the change or even loss of color, aroma, and taste in fruits and vegetables characteristic of the original fresh raw materials.

Violation of the integrity of tissue cells of fruits and vegetables and the resulting darkening and development of oxidative processes when heating canned raw materials is largely the result of measuring the chemical structure of polyphenolic compounds.

Alkaloids

Alkaloids- these are complex nitrogen-containing organic compounds of a basic nature that have a strong physiological effect on the body. Their chemical structure is very diverse and complex. Alkaloids are found in the form of salts with organic acids - oxalic, malic, citric - in a dissolved state in cell sap. They accumulate in all parts of plants, but more often they predominate in only one organ, for example, in tea leaves, in the herb of celandine, in the fruits of Datura, in the rhizome of scopolia, and in the bark of the cinchona tree. Most plants contain not one, but several alkaloids. Thus, over 30 different alkaloids were found in ergot, and about 50 in Rauwolfia serpentine. Most often, one or 2-3 alkaloids predominate quantitatively in one plant, while others are contained in smaller quantities.

Alkaloids- these are natural nitrogen-containing organic compounds of a basic nature, having a complex composition and having a strong specific effect. Most of them refer to compounds with a heterocyclic nitrogen atom in the ring, less often nitrogen is in the side chain. They are synthesized mainly by plants.

In translation, the term "alkaloid" (from Arabic "alkali" - alkali and Greek "eidos" - similar) means alkaline-like. Like alkalis, alkaloids form salts with acids.

Spreading.

In the plant world they are distributed unevenly. There are few of them in lower plants. They are found in the club moss family (moss moss). They are rare in cereals and sedge plants. The richest in alkaloids are plants of the poppy, nightshade, lily, madder, celery, amaryllis, legume, and buttercup families. In plants, alkaloids are found in cell sap in dissolved form. The content ranges from thousandths of a percent to several percent, and in cinchona bark from 15 to 20%.

Phenols are compounds whose molecules contain an aromatic (benzene) ring associated with one or more -OH groups. A high content of phenols is characteristic of plant cells.

In the animal body, benzene rings are not synthesized, but can only be transformed, so they must constantly be supplied to the body with food. However, many phenolic compounds in animal tissues perform important functions (ubiquinone, adrenaline, thyroxine, serotonin, etc.).

Currently, several thousand different phenolic compounds have already been found in plants. They are classified according to the structure of the carbon skeleton:

1. C 6-phenols

2. C 6 -C 1 -phenolic acids

3. C 6 -C 3 -hydroxycinnamic acids and coumarins

4. C 6 -C 3 -C 6 -flavonoids

5. Oligomeric phenolic compounds.

6. Polymeric phenolic compounds.

C 6 -Phenols. Compounds whose benzene ring is connected to several hydroxyl groups are called polyphenols.

Urushiol is a toxic substance found in sumac leaves. Tetrahydrocannabinol is the hallucinogenic component of cannabis.

C 6 -C 1 -phenolic acids. Phenolic acids are common in plants. More often they are in tissues in a bound state and are released during excretion and hydrolysis.

Salicylic acid is released as an allelopathic agent into the environment. In addition, its regulatory effect on a number of physiological and biochemical processes in the plant (ethylene formation, nitrate reduction, etc.) has now been discovered.

Protocatechuic acid is found in onion scales.

Vanilla and gallic acids are found in wood. The latter is part of some tannins and can form dimers - digallic acid, in the molecule of which two gallic acid residues are connected by an ester bond.

Phenolic acids can be linked by ester bonds with sugars, most often with glucose. Glycogallin, in which the carboxyl group of gallic acid is linked to the glycosidic hydroxyl of glucose, has been isolated from a number of plants (rhubarb, eucalyptus).

It has been shown that cis-isomers of hydroxycinnamic acids are activators of plant growth processes, while trans-isomers do not have such properties.

Esters of hydroxycinnamic acids and sugars, most often glucose, are common in plants. Thus, in the flowers of petunia and snapdragon, esters of caffeic, coumaric, and ferulic acids were found, and in cereals in general, the majority of hydroxycinnamic acids are represented by esters. In addition, hydroxycinnamic acids are part of polysaccharides and proteins. For example, ferulic acid is found in xylans in wheat flour and in pineapple polysaccharides.

Coumarins are lactones that are formed by ring closure between the hydroxyl and carboxyl groups in the hydroxycinnamic acid molecule.

Dicoumarin was found in white sweet clover, which prevents blood clotting. This and other dicoumarins are used as drugs to prevent blood clots.

C 6 -C 3 -C 6 -flavonoids. It is one of the most diverse and widespread groups of phenolic compounds. The structure of flavonoid molecules is based on the structure of flavan, which consists of two benzene rings and one heterocyclic (pyran).

Flavonoids are divided into several groups.

1. Catechins.

2. Anthocyanins.

3. Chalcones.

Catechins- the most reduced flavonoids. They do not form glycosides. Catechin was first isolated from the wood of Acacia catechu, hence its name. Catechins are found in more than 200 plant species. Among the catechins, the most famous are catechin and gallocatechin.

They can form esters with gallic acid - catechin gallates and gallocatechin gallates. Catechins are found in many fruits (apples, pears, quinces, cherries, plums, apricots, strawberries, blackberries, currants, lingonberries, grapes), in cocoa beans, coffee beans, in the bark and wood of many trees (willow, oak, pine, fir , cedar, cypress, acacia, eucalyptus). There are especially many catechins in the leaves and young shoots of tea (up to 30%). Oxidative transformations of catechins play an important role in tea production and winemaking. The oxidation products, which are mainly catechin dimers, have a pleasant, slightly astringent taste and a golden-brown color. This determines the color and taste of the final product. At the same time, catechins have high P-vitamin activity, strengthen capillaries and normalize the permeability of vascular walls. The catechin dimers in tea have the same activity. Catechins as monomers are part of condensed tannins.

Anthocyanins- the most important plant pigments. They color flower petals, fruits, and sometimes leaves in blue, blue, pink, red, purple colors with various shades and transitions. All anthocyanins are glycosides. Their aglycones are anthocyanidins. Anthocyanins are water soluble and are found in cell sap.

Currently, more than 20 anthocyanidins are known, but the most widely distributed are 4: pelargonidin, cyanidin, delphinidin and malvidin (methylated derivative of delphinidin).

Anthocyanins contain glucose, galactose, rhamnose, xylose, and less commonly arabinose as monosaccharides, and most often rutinose, sophorose, and sambubiose are found as disaccharides. Sometimes anthocyanins contain trisaccharides, usually branched. For example, anthocyanin is found in currant and raspberry berries, in which a branched trisaccharide is associated with cyanidin.

The color of anthocyanins depends on a number of factors:

1. concentration of anthocyanins in cell sap;

2. pH of cell sap;

3. complexation of anthocyanins with cations;

4. copigmentation - a mixture of anthocyanins and the presence of other phenolic substances in the cell sap;

5. combinations with the coloring of plastid pigments.

Let's take a closer look at these factors.

1. The concentration of anthocyanins in cell sap can vary over a wide range - from 0.01 to 15%. For example, regular blue cornflower contains 0.05% cyanin anthocyanin, while dark purple cornflower contains 13-14%.

2. Due to the fact that anthocyanin molecules have free valency, the color may change depending on the pH value. Typically, in an acidic environment, anthocyanins have a red color of varying intensity and shades, and in an alkaline environment they are blue. Such changes in anthocyanin color can be observed by adding an acid or alkali to the colored juice of currants, cherries, beets or red cabbage. In nature, sharp changes in the pH of cell sap do not occur, and this factor does not play a major role in the color of anthocyanins. One can only notice that some pink and red flowers turn blue when they wither. This indicates a change in pH in dying cells.

3. The ability of anthocyanins to chelate with metal ions is of great importance in the color of flowers and fruits. This is clearly seen in the example of cornflower and rose. Their petals contain the same anthocyanin - cyanin. In blue cornflower petals, cyanine forms a complex with Fe ions (4 cyanine molecules are bound to one Fe atom). Red rose petals contain free cyanine. Another example. If an ordinary hydrangea with pink flowers is grown on a mineral medium containing aluminum and molybdenum, the flowers acquire a blue color.

Copigmentation of anthocyanins with other substances, such as tannins, also affects color. Thus, purple and dark red roses contain the same cyanin, but in dark red roses it is copigmented with a large amount of tannin.

5. The combination of blue anthocyanins in cell sap and yellow-orange carotenoids in chromoplasts results in the brown color of the petals of some flowers.

Table Some plant anthocyanins

Halcones, or anthochlors, are flavonoids with an open heterocycle. They give the flower petals a yellow color. Their distribution is limited to nine families. They are found in the form of glycosides. Chalcones, for example, are isosalipurposide from yellow clove flowers and phloridzin from apple bark and leaves. Phloridzin is an apple growth inhibitor. When taken orally by a person, it causes a one-time intense release of glucose into the blood - “phloridzin diabetes”.

Oligomeric phenolic compounds. This includes lichen acids. They are formed in lichens from two or more orsellinic acid residues. Lecanoric and evernic acids are composed of two orsellinic acid residues. Evernic acid is the main component of the Evernia acid complex (“oak moss”), which is used in perfumery as an aromatic substance and at the same time as a fixative in the manufacture of the best types of perfumes.

Among lichen acids there are colored ones. They give lichens a variety of colors - yellow, orange, red, purple. Usnea lichen contains usnic acid, which is an effective bactericidal agent.

Polymeric phenolic compounds. Polymeric phenolic compounds include tannins, or tannins, lignins and melanins.

Natural tannins are a complex mixture of compounds with similar compositions with a molecular weight of 500-5000.

Many tannins are found in the bark and wood of oak, eucalyptus, chestnut wood, in the rhizome of sorrel, rhubarb, and sumac leaves. There are many of them in the bark and wood of legumes, myrtaceae, and roses. The galls that form on the leaves when they are damaged by the gallworm (up to 50-70%) are distinguished by a particularly high content of tannins.

Tannins (usually food tannins) are also called lower molecular substances that have a pleasant astringent taste, but are not capable of true tanning. They are present in many fruits (quinces, apples, persimmons, grapes), and in tea leaves.

Tannins are widely used not only in the leather industry. They are used in the production of plastics, binders in the production of plywood and sawdust boards, and as a mordant for dyeing. They are used in installations for boiling water as colloid stabilizers, to regulate the viscosity of solutions when drilling wells.

In medicine, tannins are used as astringents, bactericidal, anti-radiation and antitumor agents.

Lignin is part of the cell membranes of wood tissues. It is deposited between cellulose microfibrils, which gives cell membranes hardness and strength. However, in this case, the connection between cells is disrupted, which leads to the death of living contents, therefore lignification is the final stage of cell ontogenesis.

Lignin is an amorphous substance, insoluble in water, organic solvents and even concentrated acid.

Lignin has another important property: it is resistant to microorganisms. Only a few microorganisms, and then very slowly, decompose it.

Lignin is a three-dimensional polymer whose monomers are hydroxycinnamic alcohols. Thus, in conifers lignin is dominated by coniferyl alcohol, in cereals - coumaric alcohol, in many deciduous trees - synapic alcohol.

Large amounts of lignin accumulate as waste in the pulp and paper industry and hydrolysis plants. It is used to produce activated carbon, plastics, and synthetic resins.

Melanins- polymers of phenolic nature, which are a product of tyrosine oxidation. Their structure has not yet been fully elucidated.

Melanins are black or brown-black in color. Their formation explains the rapid darkening of the surface of a cut apple, potato tuber, and some mushrooms. Melanins are also present in animal organisms, causing the color of wool and hair. However, plant and animal melanins differ in the composition of monomers. When hydrolyzed, plant melanins form pyrocatechol, and animal melanins form dihydroxyindole. In other words, plant melanins, unlike animals, are nitrogen-free substances.

2. Some phenolic compounds are carriers of electrons and protons in the ETC of photosynthesis and respiration (plastoquinone, ubiquinone).

3. A number of phenols have an effect on plant growth processes, sometimes activating, more often inhibiting. This effect is mediated by the effect on phytohormones. Thus, it is known that some phenolic compounds are necessary during the synthesis of auxin, others during its breakdown. For the formation of ethylene, the presence of coumaric acid ester is necessary. It has been established that under stress, plants accumulate a large amount of phenols, which leads to inhibition of growth processes and an increase in their resistance to unfavorable conditions.

7. Phenols can act as allelopathic substances in some plants. For example, such a substance in oak may be salicylic acid.

8. Some phenols act as activators or inhibitors on certain processes and enzymes (cell division, protein synthesis, oxidative phosphorylation, etc.).

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