Copigments

Gomez-Miguez, M. et al., Influence of different phenolic copigments on the color of malvidin 3-glucoside, J. Agric. Food Chem., 54, 5422, 2006. 

The magnitude of the copigmentation is influenced by pH value, pigment and copigment concentrations, chemical structure of anthocyanin, temperature, and ionic strength of the medium. As to the effect of the solvent, the important issue is the hydrogen-bonded molecular structure of the liquid water, not the polarity of the medium. ... 

Stabilization of crude and purified anthocyanin extracts from agai by the addition of tannic acid resulted in a 65% half-life increase of anthocyanins from the crude extract and 610% of the half-life of the purified one. Although tannic acid was considered an efficient copigment,in general all cinnamic acids give unpleasant odors and tastes to solutions. 

Dangles, O., Wigand, M.C., and Brouillard, R., Anthocyanin anti-copigment effect. Phytochemistry, 31, 3811, 1992. 

Wilska-Jeszka, J. and Korzuchowska, A., Anthocyanins and chlorogenic acid copig-mentantion — Influence on the colour of strawberry and chokeberry juices, Z. Leb-ensm. Unters Forsch., 203, 38, 1996. 

Oszmianski, J., Bakowska, A., and Piacente, S., Thermodynamic characteristics of copigmentation reaction of acylated anthocyanin isolated from blue flowers of Scutellaria baicalensis Georgi with copigments, J. Sci. Food Agric., 84, 1500, 2004. 

Griesbach, R.J., Flavonoid copigments and anthocyanin of Phalaenopsis schilleriana, Lindleyana, 5, 231, 1990. 

Studies on the antioxidant properties of anthocyanins on human low-density lipoprotein (LDL) and lecithin liposome systems in vitro showed that the inhibition of oxidation increased dose-dependently with antioxidant concentration. The oxidation was catalyzed by copper in the LDL system and the effects of the anthocyanins were explained by several antioxidant mechanisms including hydrogen donation, metal chelation and protein binding [33]. Anthocyanins also prevented the oxidation of ascorbic acid (vitamin C), through chelate formation with the metal ions, and finally by the formation of an ascorbic (copigment)-metal-anthocyanin complex [49]. 

It involves, on one hand an anthocyanin under its flavylium or quinonoidal base form, and on the other hand another planar hydrophobic structure that can be another anthocyanin unit (self-association), or another colorless species (copigment), covalently bound (intramolecular copigmentation) or not (intermolecular copigmentation) to the anthocyanin pigment. 

Copigmentation is driven by hydrophobic vertical stacking between the anthocyanin and the copigment to form tt-tt complexes from which water is excluded. The flavylium cation as well as the quinonoidal base are planar hydrophobic structures and can be involved in such complexes whereas the hemiketal form cannot. The association thus results in displacement of the anthocyanin hydration equilibrium from the colorless hemiketal to the red flavylium form that can be easily measured by spectrophotometry. 

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