Antioxidant activity of musts from Pedro Ximénez grapes subjected to off-vine drying process

Free radical-scavenging activity of Pedro Ximénez must obtained in different stages of the off-vine grape drying process have been evaluated by using 2,2′-azinobis(3-ethylbenzothiazolinesulfonic acid) radical cation (ABTS+radical dot). Significant increases in the total antioxidant activity (TAA) of must obtained during the drying process were obtained, highlighting TAA at 12 days (11.2 mM trolox). High correlation coefficients between TAA-sugar concentrations (r = 0.970), TAA-absorbance at 420 nm (r = 0.915) and TAA-absorbance at 520 nm (r = 0.932) were also obtained. Similar results were obtained with synthetic samples, subjected to heat treatment, containing an amino acid extract and increasing concentrations of sugars. Increases obtained in the absorbances and in the TAA, in the synthetic samples, can be explained by the formation of Maillard reaction products. Therefore, it is possible that the Maillard reaction contributes in a significant way to the formation of brown pigments, as well as to the increase in the TAA of the musts from sun-dried grapes. This could enhance the beneficial effects, for human health, of a moderate intake of sweet wines obtained from off-vine sun-dried grapes.