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 Al and Fe chelates in pH 6-7 were evaluated by spectrophotometry (380-700nm) and colorimetry (CIE-Lab) during dark, ambient storage (48h). Increased substitution generally increased λ 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 λ 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).