Influence of Acetaldehyde, pH, and Temperature on Transformation of Procyanidins in Model Wine Solutions

Abstract

Various natural procyanidins were extracted from grape seeds (itis vinifera L.) and fractionated by gel chromatography. Selected flavanols were isolated, purified, and identified, and their degradation kinetics in different conditions were studied in model wine solutions. Acetaldehyde, pH, and temperatures were tested independently. Degradation of the studied procyanidins in the presence of acetaldehyde followed apparent first-order kinetics, and the rate constants increased and the half-life times decreased with acetaldehyde content. Disappearance of the procyanidins with pH was also found to be a first-order apparent reaction. Degradative constant rates were higher and half-life times were lower at the lowest pH value (2.0) for all procyanidins studied, which seemed to be more stable at pH 3.2 than at higher or lower pH values. Procyanidin transformations were faster with increasing temperatures, presenting first-order constant rates depending on temperatures. Half-life times of all compounds increased with decreasing temperature. Comparing the different flavanols studied, trimer C1 and T2 reacted intensively in the presence of acetaldehyde, were more easily transformed at lower pH values, and presented higher degradative constant rates with temperature. When compared to the others, dimeric procyanidins B1, B2, and B3 were the most stable compounds at the different acetaldehyde, pH, and temperature conditions assayed. For the same degree of polymerization, the presence of (+)-catechin in the oligomer seemed to increase their stability, when compared to the same molecule without (+)-catechin. However, the strength of the interflavan bond within oligomeric structures seemed to be related to the length of the molecule rather than to the nature of the constitutive units.