Characterization of phenolics, in vitro reducing capacity and anti-glycation activity of red grape skins recovered from winemaking by-products

Red grape skins recovered from ten winemaking processes were analyzed for total phenolic content(Folin Ciocalteu assay), proanthocyanidins (n-butanol/HCl assay), individual phenolics (UPLC-DAD-MS), in vitro ferric ion reducing capacity and anti-glycation activity by bovine serum albumin/fructose and bovine serum albumin/methylglyoxal model systems. The aim was to assess if these by-products have potential as dietary anti-glycation agents, to prevent the glyco-oxidative stress associated with type-2 diabetes. Variability was observed in total phenolics (12.1–53.6 g gallic acid Eq/kg), proanthocyanidins (7.2–51.1 g/kg), anthocyanins (2.5–13.8 g malvidin 3-O glucoside Eq/kg), flavonols (0.3–2.6 g quercetin 3-O glucoside Eq/kg) and reducing capacity (103–511 mmol Fe(II) Eq/kg). For all samples, the anti-glycation effectiveness was higher than that of commercial nutraceutical preparations. Hence, in spite of differences in cultivar, location of the vineyard and winemaking procedures, these by-products could be used as a source of cost-effective anti-glycation agent either as a food ingredient or as a nutraceutical preparation.