Anthocyanins

Anthocyanins are glycosides containing, as aglycone-anthocyanidin, hydroxy- and methoxy-substituted salts of flavilia (2-phenylchromenilium), in some anthocyanins, hydroxyls are acetylated. The carbohydrate part is associated with the aglycone usually in position 3, in some anthocyanins in positions 3 and 5, with the monosaccharides ( glucose , rhamnose , galactose ) and di- and trisaccharides acting as the carbohydrate residue.

Being pyrylium salts, anthocyanins are easily soluble in water and polar solvents, slightly soluble in alcohol and insoluble in non-polar solvents.

The structure of anthocyanins was established in 1913 by the German biochemist R. Willstatter , the first chemical synthesis of anthocyanins was carried out in 1928 by the English chemist R. Robinson.

Anthocyanins and anthocyanidins usually distinguished from acid extracts of plant tissues at moderately low values of pH, in this case the aglycon of anthocyanin part anthocyanin or the anthocyanin exist in the form flavilievoy salt in which electron heterocyclic oxygen atom is involved in the heteroaromatic system benzpirilievogo (hromenilievogo) cycle which is the chromophore responsible for the color of these compounds - in the group of flavonoids, they are the most deeply colored compounds with the highest shear m maximum absorption in the longwave region.

The number and nature of substituents affects the color of anthocyanidins: hydroxyl groups carrying free electron pairs cause a bathochromic shift with an increase in their number. For example, pelargonidine , cyanidin, and delphinidin , bearing one, two, and three hydroxyl groups in the 2-phenyl ring, respectively, are colored orange, red, and purple. Glycosylation, methylation, or acylation of the hydroxyl groups of anthocyanidins leads to a decrease or disappearance of the bathochromic effect.

Due to the high electrophilicity of the chromenyl cycle, the structure and, accordingly, the color of anthocyanins and anthocyanidins is determined by their sensitivity to pH: in an acidic environment (pH <3), anthocyanins (and anthocyanidins) exist in the form of pyrylium salts, with increasing pH to ~ 4—5 hydroxide ion to give a colorless psevdoosnovaniya, with a further increase up to ~ pH 6-7, water is split off to form quinoid form , which in turn, at pH ~ 7-8 cleaves to form a proton phenolate , and finally at pH you e quinoid 8 phenolate form is hydrolyzed with a gap chromene cycle and form the corresponding chalcone :

The formation of complexes with metal cations also affects the color, the monovalent cation K ⁺ gives purple complexes, divalent Mg ²⁺ and Ca ²⁺ - blue, and adsorption on polysaccharides can also affect the color.

Anthocyanins are hydrolyzed to anthocyanidins in 10% hydrochloric acid, anthocyanidins themselves are stable at low pH values ​​and decompose at high ones.

These compounds are synthesized in the cytoplasm and deposited in the cell vacuoles using a glutathione pump. Anthocyanins are found in special vesicles - anthocyanoplasts, chloroplasts, as well as in crystalline form in the plasma of some types of onions and in the cell sap of orange fruit.

The well-known fact of the activation of the biosynthesis of anthocyanins in plants under stress conditions has not yet received a deep physiological and biochemical study. It is possible that anthocyanins do not carry any functional load, but are synthesized as the final product of the saturated flavonoid pathway, which received a vacuolar branch with the aim of final deposition of phenolic compounds unnecessary to the plant.

On the other hand, anthocyanin induction caused by certain environmental factors, as well as the predictability of anthocyanin production from year to year during periods of specific leaf development stages, their vivid manifestation in particular ecological niches, may contribute to the adaptation of plant organisms to certain stressful conditions.

Anthocyanins very often determine the color of the petals of flowers, fruits and autumn leaves. They usually give a purple, blue, pink, brown, red color. This color depends on the pH of the cellular content.

The solution of anthocyanins in an acidic environment is red in color, in neutral - blue-violet, and in alkaline - yellow-green. ^[one]

The color, caused by anthocyanins, can change during the ripening of fruits, the flowering of flowers - processes, accompanied by a change in the pH of the cellular content. For example, the buds of a soft honey crayfish have a pink tint, and the flowers have a blue-violet color.

Many anthocyanins are quite soluble, for example, when extracting grape juice from the rind of the fruit, they turn into red wines (see color burgundy ).

The most common anthocyanin is cyanidin .

Many popular books do not accurately indicate that the color of autumn leaves (including red) is simply the result of the destruction of green chlorophyll , which masked the already existing yellow, orange and red pigments ( xanthophyll , carotenoid and anthocyanin, respectively). And if this is true for carotenoids and xanthophylls, then anthocyanins are not present in the leaves until the level of chlorophylls in the leaves begins to decrease. It is then that the plants begin to synthesize anthocyanins, probably for photoprotection in the process of moving nitrogen.

Anthocyanins are considered as secondary metabolites . They are permitted as food additives ( E163 ) .

Anthocyanin-rich plants such as Sicilian orange (red orange), blueberries , cranberries , raspberries , blackberries , black currants , cherries , eggplants , black rice , Concorde grapes and nutmeg grapes, red cabbage , and some peppers, like stingy so and so on. sweet In medicine, blueberry anthocyanins are widely used (as part of blueberry extract ).

In the hot peppers, several species have also been observed, in which anthocyanin is present not only in the fruits, but also in the leaves. Moreover, in this case, the anthocyanin is synthesized the more, the brighter the sunlight falling on the plant. These peppers include Black Pearl, Pimenta da Neyde and others. But in the Black Pearl, the ripe fruit completely loses anthocyanin, and the berry fruit turns red, while in Pimenta da Neyde, the fruit-pod in the sun always remains dark.

Anthocyanins help reduce inflammatory reactions and oxidative stress in the intestines, while consuming excess amounts of fats and carbohydrates and improve the intestinal barrier functions. ^[2]

• Chub V. Why anthocyanins are needed // Floriculture. - 2008. - № 6 . - pp . 22-25 .

• Spectrophotometric determination (discussion of methods)

• Flavonoids