Characterization of grape marcs from native and foreign white varieties grown in northwestern Spain by their polyphenolic composition and antioxidant activity

Northwestern Spain wine production is mainly focused on high-quality white wines, generating substantial quantities of grape marc as a by-product that can be exploited as a source of bioactive polyphenols. An optimized PLE method was applied to the extraction of polyphenols from marc of white grape varieties. The study of the polyphenolic composition of the extracts in addition to the determination of their antioxidant capacity was used to characterize the marcs obtained from autochthonous white grape varieties (Albariño, Caiño blanco, Godello, Loureiro, Torrontes, and Treixadura) cultivated in five protected areas of production (Denomination of Origin, DO). Also, the marcs obtained in the winemaking of non-native varieties grown experimentally in the region (Chardonnay, Gewürztraminer, Pinot blanc, Pinot gris, Riesling, and Sauvignon blanc) were included in the characterization study and compared with the native ones. Three vintage years (2010–2012) were considered to account for climate variability. Significant differences in the phenolic composition and the antioxidant capacity of grape marcs obtained from the white varieties were found, which could be helpful for a selective exploitation of winemaking by-products.