Read this article to learn about Anthocyanins. After reading this article you will learn about: 1. Functions of Anthocyanins 2. Occurrence of Anthocyanins 3. Uses.
Functions of Anthocyanins:
i. In flowers, bright reds and purples due to anthocyanin pigments help attract pollinators. In fruits, the colorful skins also attract the attention of animals, which may eat the fruits and disperse the seeds.
ii. In photosynthetic tissues (such as leaves and sometimes stems), anthocyanin have been shown to act as a “sunscreen“, protecting cells from high-light damage by absorbing blue- green light, thereby protecting the tissues from photo-inhibition, or high-light stress. This has been shown to occur in red juvenile leaves, autumn leaves, and broad-leaved evergreen leaves that turn red during the winter.
iii. It has also been proposed that red coloration of leaves may camouflage leaves from herbivores blind to red wavelengths, or signal un- palatability, since anthocyanin synthesis often coincides with synthesis of unpalatable phenolic compounds.
iv. In addition to their role as light-attenuators, anthocyanins also act as powerful antioxidants.
Anthocyanidins:
Flavylium cation derivatives
Occurrence of Anthocyanins:
i. Anatomically, anthocyanins are found in the cell vacuole, mostly in flowers and fruits stems, and roots. In these parts they are found predominantly in outer cell layers such as the epidermis and peripheral mesophyll cells.
ii. Other plants rich in anthocyanins are black- current, chokeberry, cherry, eggplant, blue grape, Vaccinium and red cabbage and also the Usambara-violet.
iii. Anthocyanins are less abundant in banana, asparagus, pea, fennel, pear and potato.
iv. Most frequent in nature are the glycosides of cyanidin, delphinidin, malvidin, pelargonidin, peonidin and petunidin.
v. Roughly 2% of all hydrocarbons fixated in photosynthesis are converted into flavonoids and their derivatives such as the anthocyanins. This is not less than 109 tons per year.
The pigment components of anthocyanidins, the sugar-free anthocyanins, can be identified based on the structure of a large group of polymethine dye, the benzopyrylium (chromenylium) ion. In particular anthocyanidins are salt derivatives of the 2-phenylchromenylium cation also known as flavylium cation.
As shown in the figure below, the phenyl group at the 2-position, can carry different substituents. The counterion of the flavylium cation is mostly chloride. With this positive charge the anthocyanins differ from other flavonoids.
Anthocyanins: Glucosides of Anthethocyanidins:
The anthocyanins, and anthocyanidins with sugar group, are mostly 3-glucosides of the anthocyanidins. The anthocyanins are subdivided into the sugar-free anthocyanidin aglycones and the anthocyanin glycosides. As of 2006 more than 550 anthocyanins had been reported.
The difference in chemical structure that occurs in response to changes in pH is the reason why anthocyanins are often used as pH indicator, as they change from red in acids to blue in bases.
More than five enzymes are thus required to synthesize these pigments, each working in concert. Any even minor disruption in any of the mechanism of these enzymes by either genetic or environmental factors would halt anthocyanin production.
Uses of Anthocyanins:
i. Food additives
ii. Powerful antioxidants
iii. Scientists provided laboratory evidence for potential health effects against
(a) Cancer
(b) Aging and neurological diseases
(c) Inflammation
(d) Diabetes
(e) Bacterial infections