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 pomace as potential sources 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; 4) High Performance Thin Layer Chromatography for separation of phenolic substances and assessment of their antioxidant activity. The results showed significant differences among varieties; however, grape pomace, particularly when containing seeds, are generally a good source of polyphenols with a noticeable antioxidant activity supporting its use in formulating healthy products.