Dephenolisation and bleaching of defatted grape seed meal peptide hydrolysates: impact on chemical composition and antioxidant capacity

Defatted grape seed meal (DGSM) can be hydrolysed to produce antioxidant soluble peptide hydrolysates to be used as colour stabiliser in red wines. This study focuses on the bleaching of hydrolysates to minimise the influence of its colour when added to wine. DGSM was dephenolised using 75% methanol (MeOH), 1% potassium metabisulphite (PMB) or sequential 75% MeOH+1% PMB. The most dephenolised sample was selected for further bleaching trials, using different agents and concentrations: polyvinylpolypyrrolidone (30 and 150 g/hL PVPP), activated charcoal (1 and 5 g/L AC), resin (25% and 50% v/v R), and a sequential treatment with 5 g/L AC followed by 50% R (AC + R). Dephenolisation process did not significantly (p < 0.05) affect the nitrogen content peptide. The highest dephenolisation and the lowest colour intensity was achieved with the sequential treatment. After bleaching, resin treatments resulted in the lowest content in nitrogen peptide (≈12–21% peptide loss) and amino acids, while R50 and AC + R produced the highest lightness and the lowest chroma. PVPP and low dose AC did not significantly reduce antioxidant activity. Overall, bleaching with AC5, R50, and AC + R produced promising bleached soluble peptide hydrolysates, with notable antioxidant capacity, producing viable candidates for further colour stabilisation in red wine.