Effect of chlorogenic acid on spectral properties and stability of acylated and non-acylated cyanidin-3-O-glycosides.

Spectral characteristics and heat stability (90°C, 5h) of six isolated, structurally related cyanidin-3-O-glycosides from black carrot were investigated in aqueous solutions (pH 3.6 and 4.6) supplemented with chlorogenic acid (molar anthocyanin:co-pigment ratios 1:62.5-1:250). Chlorogenic acid supplementation generally increased absorbance of non-acylated anthocyanins by up to 97.9 and 122.9% at pH 3.6 and 4.6, respectively, being mainly attributed to the formation of intermolecular anthocyanin:co-pigment complexes. The effect significantly decreased when the chain length of the 3-O-linked non-acylated anthocyanins was increased from mono- to di- to triglycosyl moieties, possibly due to steric interferences of bound sugars and co-pigments. Intermolecular co-pigmentation was investigated for the first time for feruloylated and sinapoylated cyanidin-3-O-triglycosides. They exhibited weaker effects (10.8-16.0%) at pH 4.6, and no spectral response was observed at pH 3.6. Chlorogenic acid addition evoked weak enhancement of thermal pigment stability at pH 3.6, while it was highly detrimental for all anthocyanins at pH 4.6.