Winemaking by-products as a sustainable source of antioxidant and functional compounds

In the last years, the international guidelines encourage the reduction of food waste or processing by-products to promote a circular economy approach. Winemaking represents one of the sectors with the highest by-products generation, with several potential negative impact on the environment. Winemaking by- products are mainly used to produce distillates or fertilizers, but the interest in grape pomaceas a potential source of phenolic compounds has considerably increased. The aim of this study was the application of in vitro methods for the characterization of the phenolic fraction of winemaking by-products from different red grape varieties, and, in parallel, the evaluation of their antioxidant activity. The methods were: 1) Folin-Cocalteau's assay for the quantification of total polyphenol content; 2) the vanillin assay for the assessment of total flavan- 3-ols (proanthocyanidins) content; 3) the pH differential method for the quantification of total anthocyanin content; 4) DPPH assay for the measurement of total antioxidant activity; 5) High Performance Thin Layer Chromatography for separation of phenolic substances and assessment of their antioxidant activity. Although a significant differences among varieties, grape pomace, particularly when containing seeds, are generally a good source of polyphenols with a significant antioxidant activity supporting itsuse in formulating healthy products.