Post-Fermentative Addition of Grape Seed Protein Hydrolysates and Their Impact on Wine Colour-Related Polyphenols

This study evaluates the effect of protein hydrolysates, obtained from grape seed meal (industrial waste), as colour stabilisers in red wines from warm climates. Protein hydrolysates were added to the wine after fermentation and maceration. Assays were performed using different types and doses of protein hydrolysates. Two grapevine-growing seasons were monitored over 8 months. Attention was focused on different families of polyphenolic compounds, copigmentation, and polymerisation, and colour changes were assessed by differential tristimulus colourimetry. Regardless of doses and typology, wines with protein hydrolysates suffered a decrease in the amount of phenolics and an increase in % polymerisation. Only wines treated with 3 g/L of hydrolysates showed lower colour intensity and greater clarity and hue after 8 months, while treatment with 0.5 g/L produced brownish wines. The addition of hydrolysates from a low hydrolysis time did not affect the copigmentation balances or produced negative visually perceptible colour differences over time. These results indicate that the post-fermentation addition of protein hydrolysates does not seem to significantly improve the stabilisation of the wine colour, in contrast to the addition at other stages. This information is of great interest to wineries to consider the application of this novel technique at the optimal time.