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

- Without added acids, cyanidin 3,5 triglycosylated showed blue hues in pH 7-8.
- Unbound hydroxycinnamic acids had little effect on color of cyanidin or chelates.
- Hydroxycinnamic acids acylation had clear impact on color of cyanidin or chelates.
- Metal chelation impacted cyanidin color more strongly than molecular interactions.
- Acylation and metal chelation resulted in widest expression of blue hues.

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 × [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, λmax and absorbance was greatest for cyanidin with diacylation > monoacylation > increasing [acids]. Hydroxycinnamic acids added to cyanidin solutions weakly impacted color characteristics (ΔE < 5); while acylation (covalent acid attachment) resulted in ΔE 5-15. Triglycosylated cyanidin expressed blue color (pH 7-8), suggesting glycosylation pattern also plays a role. Al3+ chelation increased absorbance 2-42× and λmax ≳ 40 nm (pH 5-6) compared to added hydroxycinnamic acids. Metal chelation and aromatic diacylation resulted in the most blue hues.