Oxidative evolution of (+)-catechin in model white wine solutions containing sulfur dioxide, ascorbic acid or gallotannins

The effects of some antioxidant (sulfur dioxide, ascorbic acid (aa) and gallotannins) and their mixtures, on the oxidative evolution of model wines containing (+)-catechin, has have been compared by monitoring O2 consumption, browning development and (+)-catechin decay. The contextual generation of xanthylium pigments has been further evaluated with the aim of deepening our understanding of the kinetics and the mechanisms underlying the oxidative spoilage of flavanols in wine-like conditions. Novel data on the efficacy of gallotannins in controlling the (+)-catechin oxidative decay in model wine solutions are furnished, together with its comparison with the ones offered by SO2 and ascorbic acid. Ascorbic acid was found to promptly reduce the amount of dissolved oxygen in samples, while the presence of SO2 or tannins resulted in a significantly lower consumption. Under our experimental conditions and at least for 30 days, browning rate was best controlled by sulfite and ascorbic acid (even if to a different extent) while gallotannins failed in such a task. However, a longer storage (120 days) under oxidative conditions revealed a large augmentation of browning rate in samples with aa and/or SO2, added which became yellower than untreated samples. The amounts of (+)-catechin declined the fastest in all the solutions with aa added. Chemical reactions underlying the obtained results, have been discussed.