Anthocyanins are a very large group of red-blue plant pigments. Anthocyanins occur in all higher plants, mostly in flowers and fruits but also in leaves, stems, and roots. In these parts they are found predominantly in outer cell layers. The amounts are relatively large: one kilogram of blackberry for example contains approximately 1.15 gram, and red and black legumes can contain 20 mg per gram.

The colour of anthocyanins depends on the structure, but also on the acidity of the fruit. Many antocyanins are red at acidic conditions and turn blue at less acid conditions.

Chemically anthocyanins are subdivided into the sugar-free anthocyanidine aglycons and the anthocyanin glycosides. They are used as food additive with E number E163.

Over 500 different anthocyanins have been isolated from plants. They are all based on a single basic core structure, the flavyllium ion.

The flavylium ion, the basic structure of anthocyanins. 

Interested in knowing more about anthocyanidins?  See this page from Wageningen University, The Netherlands :