copigment

A copigment is a molecule that forms non-covalent complexes with pigment molecules, most commonly anthocyanins, to modify their color properties in plants and foods. Copigmentation is especially relevant in flowers, fruits, and wine, where such interactions can intensify color and alter hue.

The color effects arise from non-covalent interactions such as π-π stacking, hydrophobic contacts, and hydrogen bonding between the pigment and the copigment. These interactions can stabilize the flavylium cation form of anthocyanins, reduce hydration, and shift the absorption spectrum. The result is a hyperchromic effect (increased color intensity) and often a bathochromic shift (toward longer wavelengths), which can move colors toward blue or purple tones under certain conditions. Copigmentation is influenced by pH, temperature, solvent composition, and ionic strength; higher temperatures or unfavorable conditions can weaken the complexes.

Copigmentation is observed in natural plant coloration and in winemaking, where anthocyanins interact with a range of phenolics to preserve red hues during aging. In flowers, copigments contribute to petal coloration and color variation among cultivars. Common copigments include hydroxycinnamic acids (such as p-coumaric and ferulic acids), flavonoids (like quercetin), tannins, and related phenolics.

Because copigmentation involves reversible non-covalent binding, it can respond to environmental changes and is a key factor in the visual appearance and stability of colored plant tissues and products.