Preliminary evaluation of Graciano pomace extract as a potential alternative to SO2: Impact on enological parameters and phenolic and volatile composition of Tempranillo wines.

Sulphur dioxide (SO2) is widely used in winemaking due to its antioxidant and antimicrobial properties; however, growing concerns regarding its sensory and health effects have driven the search for natural alternatives. In this study, a phenolic-rich extract obtained from Graciano grape pomace was evaluated as a partial or total substitute for SO2. Six assays, carried out in triplicate, were considered: a control (SO2); Graciano pomace extract (GPE); and four mixtures of these two additives: M1 (1/2 SO2 + 1/2 GPE); M2 (1/3 SO2 + 2/3 GPE); M3 (1/4 SO2 + 3/4 GPE); and M4 (1/5 SO2 + 4/5 GPE). The wines were analysed for their enological parameters, volatile profile (GC-MS) and phenolic composition (HPLC-DAD). Regarding wine general parameters, malic acid degradation followed a similar trend among control and GPE wines. However, in all the wines with addition of SO2 and GPE, malic acid degradation was the highest, results consistent with the development of spontaneous malolactic activity. Concerning antioxidant protection, GPE wines showed lower values for colour parameters, such as a* coordinate, total polyphenol index, and total phenols than the control wines. Moreover, GPE wines exhibited a phenolic and volatile profile similar to that of the control, except for lower levels of octanoic acid and total stilbenes. In contrast, the combined use of both additives resulted in changes in the phenolic and volatile composition of the wines. Consequently, this preliminary study suggests that Graciano pomace extract could be a promising potential tool to replace SO2 in winemaking, while enabling the valorisation of winery by-products.