The Chemical Evolution and Preservation of Color in Red Wine Aging

During the last year we have been working on the production of labeled malvidin 3-glucoside. Using unlabeled material, we have been able to optimize the conditions of enzymatic synthesis as well as the purification of malvidin-3-glucoside from starting material and side-products so that the reaction will yield adequate material to continue the project. Labeled malvidin-3-glucoside is not commercially available and there is no published method to produce it, which made the synthesis particularly difficult. An alternative procedure based on chemical labeling, which was tried first, did not work due to the ionization of anthocyanins, but it has produced other anthocyanins not described in the literature, and so these products may be interesting to analyze at some point later on. We have also advanced the understanding of red colored polymeric structures and the analytical procedures to measure them. We have found a poor agreement between two analytical procedures, the traditional method of SO2 bleaching and the newly developed Normal Phase – HPLC methodology. It is necessary to resolve the causes of these differences and also to compare them with the Adams’ assay (based on tannin precipitation). This wine study will unequivocally show the origin of the pigmented polymers and clarify the best method to measure them.