Pyranoanthocyanins are naturally derived pigments formed by the reaction of anthocyanins with cofactors like hydroxycinnamic acids, a process occurring as wine ages. Generally, pyranoanthocyanins have vivid colors and impressive heat and bleaching stability, giving them strong potential as food colorants. Their chemical structure is defined by the reactants and influences these characteristics, with hundreds of possible pyranoanthocyanins with unique properties. Our objective was to evaluate the influence of pyranoanthocyanin hydroxyl and methoxy substitutions on color, molar absorptivity, and stability.
Eight pyranoanthocyanins were synthesized by reacting anthocyanins with hydroxycinnamic acid cofactors as shown below. Compound identity was confirmed with uHPLC-PDA-ESI-MS/MS. Pigments were isolated with semi-preparatory HPLC, dried, weighed, and dissolved in pH 1 and pH 3 KCl buffers and acidified MeOH at 40 μM. Spectra (260–700 nm) was monitored and used to calculate color data and molar absorptivity coefficients.
Pyranoanthocyanins produced colors from yellow (10-phenyl-pyranocyanidin-3-glucoside) to red (10-syringyl-pyranomalvidin-3-glucoside) with an increasing number of substitutions producing a bathochromic shift in λ_vis-maxand a lower hue angle. A substitution's location (-B or -E ring) had minimal influence on color yet affected the solubility in buffers with cyanidin pyranoanthocyanins more prone to precipitate. Pyranoanthocyanins' molar absorptivity coefficients were 3.6 to 7.5 times greater at pH 3 than their anthocyanin precursors. Pyranoanthocyanins’ versatile and intense colors contribute to their promising future as colorants, with small changes in structure influencing the hue and stability.

Chemical structures of the anthocyanins and cofactors used to synthesize the eight hydroxycinnamic acid pyranoanthocyanins evaluated in this study.

Lu Xun

Appearances