Anthocyanin
|
|
Anthocyanin (Etymology: greek. anthos = Flower, kyáneos = purple) is a water soluble pigment that reflects the red to blue range of the visible spectrum. It is often observed in the plant kingdom, where it serves to color anything from fruits to the autumn leaves. The pigment acts as a powerful antioxidant helping to protect the plant from UV damage. It can be used as a pH indicator because it changes from red in acids to blue in bases. Anthocyanins belong to a class of compounds called flavonoids. The anthocyanins themselves are subdivided into the sugar-free anthocyanidine aglycons and the anthocyanin glycosides. They are considered secondary metabolites and allowed as a food additive with E-number 163. Approximately 250 different anthocyanins are known.
| Contents |
Occurrence
| foodstuff | Anthocyanin in mg per 100 g foodstuff |
|---|---|
| Chokeberry | 200-1000 |
| Aubergine | 750 |
| orange | ~200 |
| Blackberry | ~115 |
| Vaccinium | 80-420 |
| Raspberry | 10-60 |
| Cherry | 350-400 |
| Redcurrant | 80-420 |
| Grape (red) | 30-750 |
| red wine | 24-35 |
Anthocyanines are pigments that only occur in the cytoplasm of land plants but not in animals, microorganisms or waterplants. The reason for this is that anthocyanine biosynthesis requires chemical starting materials derived from plant photosynthesis. In waterplants the light intensity under water is not sufficient for this production. Not all land plants contain anthocyanin and in the Caryophyllales, Cactus and the galium mollugo they are replaced by betacyanins.
Anthocyanines occur in all higher plants, mostly in flowers and fruits but also in leaves and roots. In these parts the they are found predominantly in outer cell layers such as the epidermis. The amounts are relatively large: one kilogram of blackberry for example contains approximately 1,15 gram, from red and black legumes it is possible to obtain between 20 mg per 1 gram. Rich in anthocyanines are for example chokeberry, cherry, aubergine, blue grape, Vaccinium and red cabbage and also the Usambara-violet. Anthocyanins are less abundant in banana, asparagus, pea, fennel, pear and potato. Most frequent in nature are the glycosides of cyanidine, delphinidine, malvidine, pelargonidine, peodine and petunidine. Roughly 2 percent of all hydrocarbons fixated in photosynthesis are converted into flavonoids and their derivatives such as the anthocyanines. This is no less than 109 tons per year.
In plants anthocyanins are present together with other natural pigments like the chemically closely related flavones, carotinoids, anthoxanthins and betacyanins. Together with these compounds They are also responsible for the colouring of the leaves in the autumn, when photosynthesis has stopped and chlorophyll has not formed again. Also with still relatively young plants, with which chlorophyll and wax production has not yet begun and which would be unprotected from UV light, anthocyanin production increases. Parts or even the whole plant are dyed and protected with the help of dyes which are called juvenile anthocyanins. As soon as chlorophyll production begins, the production of the anthocyanin dye is reduced. The build-up of anthocyanin in plants is specific to the plant type, since it depends on the soil conditions, light, warmth and plant type and/or sort . The fact that plants only have a anthocyanin as pigment is extremely rare, but occurs nevertheless. The absence or particularly strong prevalence for a certain anthocyanin in a plant is due to genetic circumstances.
Function in plants
Anthocyanins in plants have several tasks. They must protect plants against strong UV light of the sun by absorbing certain wavelengths. In this way DNA damage in the cell is prevented. Anthocyanins help to attract insects and animals by producing colors with specific light-absorbing characteristics. They can help plants with reproduction. Anthocyanins bind Free radicals which develop with plant stress. The first two points explain why the anthocyanin is in the outside layers of the plant: only here they can fulfill their purpose. If plants are exposed to strong UV light or ionizing radiation the plant speeds up anthocyanin production over that of chemical messenger molecules.
Structure
Benzopyryliumsalz.png
The pigment components of the anthocyanins, the sugar-free anthocyaninidines, can be identified based on the structure of a large group of polymethine dye. As derivatives of benzopyrylium salts their basic structure consists of the oxygen-containing Heterocycle pyran with a fused benzene ring. The pyran ring in anthocyanin is connected to a phenyl group at the 2-position, which can carry different substituents. The counterion for the cationic oxygen in the pyran ring is mostly chloride. With this positive charge the anthocyanins differ from other flavonoids.
Anthocyane.png
| Anthocyanidine | R1 | R2 | R3 | R4 | R5 | R6 | R7 |
| Aurantinidine | -H | -OH | -H | -OH | -OH | -OH | -OH |
| Cyanidine | -OH | -OH | -H | -OH | -OH | -H | -OH |
| Delphinidine | -OH | -OH | -OH | -OH | -OH | -H | -OH |
| Europinidine | -OCH3 | -OH | -OH | -OH | -OCH3 | -H | -OH |
| Luteolinidine | -OH | -OH | -H | -H | -OH | -H | -OH |
| Pelargonidine | -H | -OH | -H | -OH | -OH | -H | -OH |
| Malvidine | -OCH3 | -OH | -OCH3 | -OH | -OH | -H | -OH |
| Peonidine | -OCH3 | -OH | -H | -OH | -OH | -H | -OH |
| Petunidine | -OH | -OH | -OCH3 | -OH | -OH | -H | -OH |
| Rosinidine | -OCH3 | -OH | -H | -OH | -OH | -H | -OCH3 |
Properties
Biosynthesis
Recent research
In December 2004 a peer-reviewed study at Michigan State University published by the American Chemical Society noted that anthocyanin could boost insulin production by up to 50%. However the study leader noted that despite the initial excitement, more study would be needed.
External link
- red leaves - Catalyst ABC (http://www.abc.net.au/catalyst/stories/s1310369.htm)
- Chemicals Found in Cherries May Help Fight Diabetes (http://www.sciencedaily.com/releases/2004/12/041220122203.htm)
- , Biochemicals found in dark raspberries may help fight Diabetes and Cancer (http://www.realhomepage.de/members/Blaue_Himbeeren/index.htlm) (in German)