**3. Chemistry**

Anthocyanins are naturally occurring pigments. They are phenolic compounds that are mostly hydroxy derivatives of flavylium salts or glycosides of methoxy derivatives. Anthocyanins vary in forms based on the attachment of acids and hydroxyl groups to the sugar moieties within their structure. The anthocyanins found in plants include: cyanidin, delphinidin, pelargonidin, malvidin, peonidin and petunidin. Of these, cyanidin 3-glucoside is the most widely found anthocyanin [51]. The anthocyanins have an ionic structure and thus their color in solution is pH dependent [52]. They possess colors in shades of blue as the solutions

*Anthocyanins: Natural Sources and Traditional Therapeutic Uses DOI: http://dx.doi.org/10.5772/intechopen.86888*

**Figure 3.**

*Biosynthesis of anthocyanins in plants.*

approach a neutral pH and a red color shade as the solutions are made acidic. Lower pH values provide higher stability to anthocyanins. The flavylium cations increases the solubility of colored pigments in water at low pH. With increase in protonation

caused due to increase in pH, the concentration and stability of pigments reduces. Polymerization reactions are also reported to increase their color stability. Purplecolored stable quinonoid anions are formed at neutral pH [53].

Plants synthesize anthocyanins and store them in vacuoles. The colors of anthocyanins in the vacuoles will vary depending on the existing pH conditions. A general flavonoid pathway is used by plants for their synthesis. 4-coumaroyl-CoA is formed from phenylalanine or tyrosine and further condensed with malonyl-CoA to produce naringenin chalcone. Chalcone isomerases convert naringenin chalcone to naringenin [54]. Naringenin then undergoes several hydroxylation steps to form anthocyanins. A schematic representation of the anthocyanin formation pathway is provided in **Figure 3**.
