Model solutions/ Summary Proposed role of co-pigmentation Tannin-anthocyanin (T-A)/tannin-tannin (T-T) crosslinking under oxidative condi Propsed mechanisms leading to T-A and T-T adducts under non-oxidative condition You are here Procyanidins, Prodelphinidins How oak and oxygen  enhance red wine characters
General anthocyanin structure
General anthocyanin structure The second major class of compounds found in red wines are anthocyanins. They have a positive charge on the molecule which enables it to absorb light and thus have color. An anthocyanin has a carbohydrate (sugar, usually glucose) esterified at the 3 position. An anthocyanidin, termed the aglycone, does not have a sugar at the 3 position. Naturally occurring pigments from grapes always have a sugar bonded at the 3 position, though other compounds such as hydroxycinnamates and acetate may be involved. The presence of this sugar helps the anthocyanin maintain solubility in water. If the sugar is hydrolyzed or lost, the solubility decreases and the molecule will be destabilized and lost.

Major anthocyanin forms occurring at wine pH

Major anthocyanins

All naturally occurring anthocyanins are in equilibrium between the color flavylium cation and the colorless hydrated form. The equilibrium is driven to the left as the pH of the wine is decreased and to the right as pH is increased. At pH's above 4.5 other destabilizing reactions begin, such as ring opening of the C ring.

Major anthocyanins

Why is the hydrated or colorless form of the anthocyanin important? Véronique Cheynier has proposed that the hydrated form is actually the reactive form of the anthocyanin. When water hydrates the anthocyanin, it adds 2 electrons to the molecule, which in turn increases the electro-negativity at the 6 and 8 positions on the A ring. Generally, it appears that the 8 position is the favored postion of reaction.