Effects of hydroxycinnamic acids on blue color expression of cyanidin derivatives and their metal chelates

Mechanisms to recreate many anthocyanin blue hues in nature are not fully understood, but interactions with metal ions and phenolic compounds are thought to play important roles. Bluing effects of hydroxycinnamic acids on cyanidin and chelates were investigated by addition of the acids to triglycosylated cyanidin (0-50 x [anthocyanin]) and by comparison to hydroxycinnamic acid monoacylated and diacylated Cy fractions by spectrophotometry (380-700 nm) and colorimetry in pH 5-8. With no metal ions, lambda(max) and absorbance was greatest for cyanidin with diacylation > monoacylation > increasing [acids]. Hydroxycinnamic acids added to cyanidin solutions weakly impacted color characteristics (Delta E < 5); while acylation (covalent acid attachment) resulted in Delta E 5-15. Triglycosylated cyanidin expressed blue color (pH 7-8), suggesting glycosylation pattern also plays a role. Al3+ chelation increased absorbance 2-42x and lambda(max) greater than or similar to 40 nm (pH 5-6) compared to added hydroxycinnamic acids. Metal chelation and aromatic diacylation resulted in the most blue hues. (C) 2017 Elsevier Ltd. All rights reserved.