Spectral and colorimetric characteristics of metal chelates of acylated cyanidin derivatives.

Colorants derived from nature are increasingly popular due to consumer demand. Anthocyanins are a class of naturally occurring pigments that produce red-purple-blue hues in nature, especially when interacting with metal ions and co-pigments. The role of various acylations of cyanidin (Cy) derivatives on color expression and stability of Al3+ and Fe3+ chelates in pH 6-7 were evaluated by spectrophotometry (380-700nm) and colorimetry (CIE-L∗a∗b∗) during dark, ambient storage (48h). Increased substitution generally increased λmax of Cy chelates: malonic acid monoacylation<triglycosylated Cy<Cy monoacylated with hydroxycinnamic acids<diacylated Cy. Patterns were similar regarding bathochromic shifts. Acyl moieties of diacylated Cy with smaller substitution patterns resulted in greater λmax, and no pattern emerged for monoacylated cyanidin. Pigment stability was improved with increasing proportions of metal ions and acylation. Stability followed that diacylated cyanidin (p-coumaric-sinapic>ferulic-sinapic>sinapic-sinapic)>monoacylated (malonic≈sinapic>ferulic>p-coumaric).