Anthocyanin

Anthocyanins (English anthocyanins, from Ancient Greek ἄνθος anthos " flower ", " flower ", and ancient Greek κυάνεος kyáneos "dark blue ", " black blue", " dark colored" ) are water-soluble plant pigments that are found in almost all higher plants and flowers and fruits an intense red give, violet or blue staining. Ludwig Clamor Marquart in 1835 gave the name Anthokyan the first time a chemical compound, the flowers gives a blue color. 1849 was of FS Morot this as " cyan" designated dye isolated in impure form. 1913 succeeded Richard Willstätter the identification of anthocyanin of the cornflower. Later this term was introduced to describe a whole group of compounds chemically similar to the original " Blue Flowers ". It also recognized quickly that the crystallization of the oxonium salts dye ( flavylium salts ) fell considerably lighter than the cases of the neutral ( quinoid ) dyes.

Anthocyanins belong to the flavone - like substances, flavonoids, and be counted among the phytochemicals.

The good water solubility they owe a glycosidically bound sugar moiety. Color is the only determining factor of the sugar - free fraction, the aglycone of the anthocyanin, which is therefore also called anthocyanidins. The most important and anthocyanins derived from cyanidin and delphinidin. In Anglo-Saxon exclusively the term " anthocyanin " is used instead of the term " anthocyanin ".

• 6.1 analysis
• 6.2 Physiology

Occurrence

Anthocyanins are chymochrome dyes that are only found in the cell sap of land plants but not in animals, microorganisms or aquatic plants. This is because for the biosynthesis of anthocyanins products are required, resulting in photosynthesis of the plants. In aquatic plants, however, sales of photosynthesis is due to the low light intensity under water is not sufficient for production. But not all land plants contain anthocyanins: in the clove -like, cactus and Mollugogewächsen take betalaines the task of anthocyanins.

Anthocyanins are found in almost all higher plants, mostly in the flowers and fruits, but also in the leaves and roots. In the respective parts of the plant are to be found mainly in the outer cell layers such as the epidermal cells. The amounts found there are relatively large: One kilogram of blackberries, for example, about 1.15 grams anthocyanins of red and black legumes, up to 20 grams per kilogram of bowl win. Rich in anthocyanins are, for example, the açaí berry, aronia, cherries, red grapes, blueberries and red cabbage as well as African violets. Less common are anthocyanins, for example, bananas, asparagus, peas, fennel, pears and potatoes. Most frequently come before the glycosides of pelargonidin, cyanidin, delphinidin and their methyl malvidin, peonidin and petunidin in nature. An estimated 2% of the total carbon, which is fixed by photosynthesis in plants that reacted to flavonoids and their derivatives, such as anthocyanins. These are not less than 1 × 109 tons per year.

In plants, anthocyanins are together with other natural dyes, such as the chemically closely related flavones, carotenoids, and betalains Anthoxanthinen. You are responsible, alongside those for the color of the leaves in autumn, when photosynthesis is set and the chlorophyll is not reformed.

Even at relatively young plants in which chlorophyll and wax production has not yet been used and which thus would otherwise be exposed in front of UV light, anthocyanins produced increased. Parts or even the whole plant by means of dyes which are designated as Jugendanthocyane inked and protected. When the chlorophyll production begins, the production of Anthocyanfarbstoffe is reduced. The pattern of anthocyanin in plants is specific to the plant, since it depends on the soil conditions, light, heat and plant species or variety. That plants have only one anthocyanin as a dye, is extremely rare but it happens nonetheless facing. The absence or particularly strong occurrence of a specific anthocyanin in a plant is due to genetic factors.

Cyanidin -3-O -glucoside ( elder )

Cyanidin -3-O - galactoside (Aronia )

Peonidin -3-O -glucoside (blackcurrant )

Delphinidin -3-O - rutinoside (blackcurrant )

Pelargonidin -3-O -glucoside (strawberry )

Task in plants

Vegetable skins are invariably darker than the plants inside. They are therefore capable of absorbing visible light and converting part of the radiation energy into heat energy. The anthocyanins in plants have more tasks: they are

• Absorb in the shell, the short-wave UV light from the sun and emit radiant energy as heat to the plant. Thus damage to the proteins in the cell and the DNA in the cell nuclei is prevented.
• Attract by their color insects and other animals and so assist in the propagation of the plants.
• Free radicals in the plant sap bind the result of oxidative stress.

The first two points explain why the anthocyanins are found in the outer layers of the plant parts: Only here they can do their job. If plants are now exposed to strong ultraviolet light or ionizing radiation stimulates the plant via chemical messengers to the Anthocyanproduktion.

Structure

Basic structure elucidation in the field of plant pigments were performed by Willstätter and 1915 awarded the Nobel Prize for Chemistry.

Anthocyanidins have always in position 2 to a p-hydroxyphenyl substituents (B- ring ), and in position 3 a hydroxy group. The counter-ion of Benzopyryliumsalzen often act in nature mostly carboxylates of various water-soluble acids in laboratory preparations chloride. The most important natural anthocyanidins are available in 5 - and 7- hydroxy- position of the A ring.

The glycosides of anthocyanidins, anthocyanins (English anthocyanosides, anthocyanins ), C -3 sugar molecules via an O - glycosidic bond are usually linked to the hydroxyl group on the carbon atom. These may be, for example, glucose, galactose, arabinose, rhamnose and xylose in different saccharide forms. Acylation with aromatic plant acids at these results in the diversity of anthocyanins. The Glykosidform confers increased water solubility to the molecules, which is important for the transport in the plant cells, and an increased stability.

Properties

Anthocyanins are light and temperature sensitive, at pH values ​​below 3, they are most stable in the form of flavylium salts. Anthocyanins react with tannins and precipitate from aqueous solutions. Oxidant discolor anthocyanins, particularly sensitive they are alkaline.

Anthocyanins absorb light in the visible range between 450 and 650 nm, the wavelength range is influenced not only on the molecular structure and the pH value of the environment and they therefore appear red, purple or blue. Light of these wavelengths is filtered out of the visible light and the reflected light component appears to us as a color. The color spectrum ranges from blue to red. In the acidic environment outweighs the red color in basic are a lot of blues and purples to find. Color changes are also taking place in some plants: the flowers of the lung herb ( Pulmonaria officinalis) are first pink, later colored purple because changes the pH in the course of life. The berry skin of blackberries turns during ripening of pink to deep blue, which süßsäuerlicher juice, however, is deep red.

" Cabbage " and " red cabbage " differ during the preparation only by a slight vinegar - additive when cooking.

PH-dependence of color

The color changes based on chemical reactions.

• At pH values ​​below 3 are colored red and are in the form of Flavyliumkationen ago.

• PH values ​​4-5 lead by hydroxylation to colorless carbinol pseudo- base ( " Leuco bases " Chromenol ), so that the anthocyanins can no longer perform their duties in the plant.

• At pH values ​​between 7 and 8 of this molecule is deprotonated to Flavenolatanion having a blue color. Here the Π - electrons are delocalized over the entire molecule longest possible distance and therefore excited with lowest light energy.

• PH values ​​from 8 lead in the absence of Glycosidgruppen in the 5-position also Flavenolat dianions, but competes in the alkaline hydrolytic opening of the pyran ring. The molecule is converted irreversibly to a yellow chalcone anion.

• Compared with the pKa values ​​of diphenols (pKa approximately 9.5 and 11.7 ) anthocyanidins are more than 1000 times more acidic. Flavylium salts in water are more than 10 times more acidic than formic acid (pKa 3.8 ).

Blue delphinidin aluminum complex

Blue delphinidin -iron complex

Blue hydrangeas

Metal complexes

Anthocyanins with adjacent hydroxyl groups in the B- ring form in the presence of aluminum or iron salts and metal complexes. The complexation of the metal ions results in the absorption maximum of the compounds to 14-23 nm to shorter wavelengths ( blue shift, hypsochromic shift ) is moved. This gives complexed anthocyanins blue to violet color. Hydrangeas make their blue coloration of delphinidin in the presence of aluminum or iron salts in the soil.

Biosynthesis

The formation of anthocyanins follows the biosynthesis of all flavonoids (see: biosynthesis ). A biological precursor to the oligomeric proanthocyanidins. As a key enzyme in the synthesis pathway of anthocyanin, the chalcone synthase (CHS) has been identified, whose expression is regulated at the mRNA level. Various external factors, environmental influences such as temperature, light and water availability, it have influence. But plant stress may play a role.

When seedlings about the synthesis of the so-called Jugendanthocyans in the cotyledons and in the hypocotyl by the red and blue light component is excited in the sunlight, by which function as photoreceptors molecules phytochrome ( red light) and crypto chrome (blue light) is registered. Full-grown plants mainly produce ultraviolet exposure, which means stress for the plant, Anthocyanins in leaves and the shoot. The anthocyanins are only likely to provide the stable end products of the synthesis, it is important for the protection of the plant, however, the UV absorbing precursors.

Even with the foliage in autumn anthocyanins are formed that make up the red color of autumn leaves. The Anthocyanide here are the final product of the Zimtsäureweges, which is triggered by the breakdown of phenylalanine. In plants that fix nitrogen through symbiosis with bacteria, you will not find this pathway. Therefore here is from an autumn color by anthocyanins.

Basically Anthocyanide in leaves are always formed only in the outermost layer of the epidermis. In the shoot organs Anthocyanide form in the underlying subepidermis and leaf organs especially near the leaf veins and the leaf edge. Is due to the existence of this local limitation of genetic transcription factors in these areas, which allow the synthesis of the Anthocyanide in response to certain factors only. One speaks in this context of a competence model.

Extraction and use

The extraction of anthocyanins by extraction with sulfithaltigem water or by chromatographic methods from the constituents of various plants. The largest yield is mostly in the fruit peel or flowers.

In the EU, anthocyanins as food additive under the collective number E 163 no maximum limit ( quantum satis ) generally approved for food. ( Glycosides of pelargonidin E 163a, E 163b cyanidin, peonidin E 163c, delphinidin E 163d, 163e petunidin E, malvidin E 163f ). They are added as a food additive for coloring, for example, fruit jellies, confectionery, showers, jam, jams, canned fruit, baking ingredients for pastry, cakes, and ice cream coatings. Usually they are added to acidic products, since they are stable only in the latter. One use would be in some foods anyway not allowed as an illusion there was a danger, such as in bread, various dairy products, pasta and honey.

The dyes in the art they are not used because of their lack of stability.

Analysis

Anthocyanins can be most easily by means of chromatographic methods such as HPLC, usually with coupled mass spectrometry ( LCMS ), identify and quantify. In the HPLC, a C18 reversed- phase offers (see HPLC). Smaller quantities can be determined with an electrochemical, photometric to a larger detector.

In the analysis, it is advantageous to lower the pH with acids such as formic acid to less than 3, since the anthocyanins are most stable under those conditions. Because plants have a specific anthocyanidin / glycoside distribution pattern is detected by HPLC analysis of the ingredients, for example, whether a wine comes from a specified region and what grape it is. For longer storage of wines increasingly, polymers of anthocyanins, so the age of a wine can be determined by measuring the so-called Monomerindex. Polymers of anthocyanins caused by oxidative ( free radical running ) couplings of the dominant in the neutral quinoid compounds.

Physiology

The anthocyanins from red grape juice and blackcurrant juice are added only to a small extent by the body and / or rapidly metabolized, such as from low anthocyanin concentrations both in blood plasma (pH 7.4), as was also concluded in the urine. The daily intake varies greatly from person to person, so that average values ​​have hardly any significance. The bioavailability of anthocyanins is receiving a normal diet is only about 1 percent.

Anthocyanins have antioxidant effect of vitamin C and vitamin E, at least in vitro, is many times can exceed. However, it is doubtful that the anthocyanins in vivo can develop this strong antioxidant effect, since bioavailability is poor. In the human body they bind free radicals and protect the DNA and lipids and carbohydrates from damage. The anthocyanins are still attributed to other effects: They should improve the visual processes, anti-inflammatory and vasoprotective.

Anthocyanins are toxic only to a very small extent. From plants absorbed anthocyanins are not dangerous