Study and quantification of monomeric flavan-3-ol and dimeric procyanidin quinonic forms by HPLC/ESI-MS. Application to red wine oxidation

Monomeric flavan-3-ols and dimeric procyanidins of red wine were oxidised by two processes, chemical and enzymatic. Unstable quinonic forms were stabilised by sulphonation, and the resulting sulphones were quantified by coupled HPLC/ESI-MS. The effects of temperature and UV light on the oxidation of phenolic compounds were also investigated. The concentration of quinones increased with increasing temperature, but the kinetics of the reaction was independent of temperature. Likewise, more quinones were formed in the presence of UV light than in its absence, but UV light also did not affect the kinetics of the reaction. Thus temperature and UV light affect the quantity of quinones formed but not the rate at which they appear. Les composes phenoliques dans le vin proviennent des grains et des peaux de raisin et du bois s'ils sont vieillis en fut. Ils peuvent etre sous forme polymerisee, complexee ou oxydee. Cette etude demontre la presence de procyanidines oxydees dans le vin. Tout d'abord, les formes quinoniques des composes phenoliques sont etudiees. Les resultats montrent la presence de flavan-3-ols monomeriques et de procyanidines dimeriques. Ces composes sont oxydes dans le vin par 2 procedes: enzymatique et chimique. Les formes oxydees de ces composes sont identifiees et quantifiees apres sulfonation par HPLC/ESI-MS. Les effets de la temperature et de la lumiere UV sont aussi etudies et les resultats montrent qu'ils affectent la quantite de quinones formes.