Copigmentation and anti-copigmentation in grape extracts studied by spectrophotometry and post-column-reaction HPLC

Copigmentation is a very important contributor to colour in young red wines. Further understanding of the copigmentation effect has been elucidated by investigating the contribution of various fractions of grapes - skin, pulp, and seed - in varieties Shiraz, Sangiovese and Pinot Noir. A series of spectrophotometric and HPLC experiments elucidated the effect of this interaction in grape extracts simulating wine conditions. A post-column reaction method was developed to permit the evaluation of the reactivity of each grape anthocyanin with different reagents: pure compounds (quercetin and caffeic acid) and extracts of grape sections (seed, Semillon skin, Semillon pulp). Certain extracts produced a decrease in colour, suggesting that competing equilibria are important in the copigmentation effect and that an "anti- copigmentation" effect is possible. Flavonols appear to be the best copigmentation cofactors, and the concentration of quercetin 3-O-glucoside was found to correlate with the strength of copigmentation. Flavonols appear capable of displacing cofactors derived from seed extracts.