Rate and equilibrium constants for the dehydration and deprotonation reactions of some monoacylated and glycosylated cyanidin derivatives.

The rate and equilibrium constants for the pH-dependent hydration of a series of monoacylated anthocyanins semi-biosynthesized using a wild carrot suspension culture have been measured. The features of the acyl groups that decrease the hydration and thus decrease the loss of color of these anthocyanins are the presence of the side-chain double bond of the cinnamic acids and the presence of electron-donating substituents at the para-position of the acyl group. Methoxyl groups in the meta-position of the acyl groups have a greater effect than can be explained by their effects on the electron density in the acyl group. The data also suggest that there may be additional features of the acyl groups which contribute to the color retention in anthocyanins.