Contribution of each caffeoyl residue of the pigment molecule of gentiodelphin to blue color development

To clarify the function of each caffeoyl residue in the diacylated anthocyanin gentiodelphin, a pigment from the blue flower of Gentiana makinoi, two mono-deacyl derivatives were compared for both color development and stability. In neutral solution, 3,5-di-O-beta-D-glucopyranosyl-3'-O-(6-O-caffeoyl-beta-D- glucopyranosyl)delphinidin was both bluer and more stable than 3,3'-di-O-beta-D-glucopyranosyl-5-O-(6-O-caffeoyl-beta-D- glucopyranosyl)delphinidin. Conformational analysis of each derivative under acidic conditions revealed only the 3'-O-caffeoylglucopyranosyl derivative to demonstrate intramolecular stacking. Additionally, the acyl residue in the B-ring contributed more to blue color development than that in the A-ring.