Potential of landrace winery by-products (<i>Vitis vinifera L.</i>) as a source of phenolic compounds with antioxidant properties

Aim: To evaluate the potential of the main winery by-products – pressed pomaces, fermented pomaces and stems –, derived from minor grape varieties (Escursac, Gorgollassa and Sabater as red varieties, Giró ros and Quigat as white varieties) native to the Balearic Islands (Spain), as raw material for the production of phenolic concentrates with antioxidant properties. Methods and results: Total phenolics, tannins and anthocyanins, as well as antioxidant capacity of winery by-products were spectrophotometrically evaluated and compared to those of Cabernet sauvignon and Chardonnay varieties. In general, stems presented higher average total phenolic (5.57 ± 1.25 g/100 g dm) and total tannin (10.26 ± 2.10 g/100 g dm) contents than the corresponding pomaces, with the landrace variety Escursac being that which exhibited the highest values (p < 0.05). For pomaces, those sampled after the fermentation process presented larger amounts of polyphenols than those collected just after the pressing process, and the fermented pomaces from the autochthonous varieties Escursac and Sabater were those with the highest potential. Conclusion: The present research demonstrated that landrace minor varieties denoted similar, or even higher, phenolic and antioxidant potential than the reference grape varieties. The characterization performed might be the basis for their integrated use and revalorization as promising sources of phenolic concentrates, despite not having still undergone the selection process that the traditional grape varieties have been subjected to as a result of decades of intensive production. Significance and impact of the study: To the best of our knowledge, this is the first time that the phenolic composition and antioxidant properties of winery by-products from grape varieties native to the Balearic Islands are examined. Due to the increasing use of these minor grape varieties in winemaking, the phenolic characterization of their by-products is of great interest for the wine sector, which could exploit these underutilized resources more efficiently and extensively so as to support sustainable agricultural production