Antioxidant properties of traditional balsamic vinegar and boiled must model systems

Traditional balsamic vinegar (TBV) is a natural product prepared with cooked and concentrated locally grown grape must. It has been demonstrated that TBV contains phenols and shows antioxidant activity. In this study we investigated the antioxidant properties of TBV in relation to its content in phenolic compounds, polymeric tannins and Maillard reaction products (MRPs). Results show that TBV has a high antioxidant activity measured with both FRAP and ABTS assay that is higher or equal to those obtained in some red wine. About 45% of the antioxidant activity of TBV is due to the total polyphenolic fraction. Among polyphenols, tannins contribute to about 50% of the antioxidant activity of the total polyphenolic fraction. The residual antioxidant activity of TBV is due to the melanoidins (about 45%) synthesized during the boiling of the must and the ageing of TBV and to other compounds such as low molecular weight MRPs. When we investigated the effect of heating on the browning and on the formation of antioxidant MRPs in must model systems we observed a major formation of antioxidant MRPs for the model system containing both amino acids and sugars with respect to the model system containing only sugars. We also tested the effect of some representative phenolic compounds present in must. Only polyphenols were stable in the model solution, however, in our experimental conditions they did not influence the browning and the formation of MRPs. Indipendently of their bioavailability, dietary antioxidants play an important role in protecting the gastrointestinal tract itself from oxidative damage and could protect against a built up of peroxides and their assimilitation in the digestive tract.