**2. Brief overview of anthocyanin**

Anthocyanins are water soluble secondary metabolites that are present in the vacuoles of flowers, leaves, cereals, vegetables, and fruits [24–26]. These components belong to flavonoids and are a kind of phenolic compounds (polyphenolic). The molecular structure of anthocyanins contains three aromatic rings and multiple double bonds which gives nutraceutical properties as they can inhibit free radicals [27] acting as natural antioxidants. Anthocyanins possess protective and promoting effects on human health against neurodegenerative diseases, cancer, metabolic syndrome [12, 13].

Anthocyanins are dimers of an aglycone anthocyanidin and some sugar (xylose, galactose, arabinose, rutinose) or other compounds such as co-pigments, proteins, among others [28]. The anthocyanidin form is unstable and less soluble which is why the dimer form is the most common [29].

There are more than 700 anthocyanins and 23 anthocyanidins. The differences are in their chemical structure (number of hydroxyl or methoxyl groups, type, number, and position of sugar group bonded to anthocyanidin, and the presence of aliphatic or *Deep Eutectic Solvents: A Promising Technique to Anthocyanin Extraction for Food Coloring… DOI: http://dx.doi.org/10.5772/intechopen.105162*

aromatic acids bonded) [30, 31]. Most common anthocyanins are cyanidin (orangered), delphinidin (purple-blue), pelargonidin (orange tones), malvidin (purple), peonidin (purple) and petudine (dark red or purple) [15, 28]. The tone and intensity of color depend on the number of hydroxyl and methoxyl groups. Hydroxylation increases blueness and methylation induces redness. Also, copigmentation enhances the color by a hyperchromic effect [32]. A bathochromic effect is observed whit changes in pH of the solution or in the presence of copigments [15, 32].
