Oxygen exposure during red wine fermentation modifies tannin reactivity with poly-l-proline

Area of Science:

• Enology
• Food Chemistry
• Wine Science

Background:

• Tannins are key phenolic compounds in red wine, influencing color, astringency, and aging.
• The interaction between wine tannins and proteins like poly-l-proline affects mouthfeel and stability.
• Gas exposure during fermentation can significantly impact wine composition and sensory properties.

Purpose of the Study:

• To investigate the impact of nitrogen versus oxygen exposure during red wine fermentation on tannin structure.
• To analyze the reactivity of these modified tannins with poly-l-proline.
• To understand how these changes influence wine astringency.

Main Methods:

• Red wines were fermented with either nitrogen or oxygen exposure.
• Tannins were purified post-fermentation and after three years of storage.
• Tannin structure (galloylation, pigmentation) and self-aggregation (nanoparticle tracking analysis) were assessed.
• Tannin-poly-l-proline interactions were studied using isothermal titration calorimetry.

Main Results:

• Nitrogen-treated wine tannins showed lower galloylation and pigmentation compared to oxygen-exposed tannins.
• Oxygen exposure led to larger tannin particle size due to increased self-aggregation.
• Interactions between oxidized tannins and poly-l-proline were more hydrophobic and entropy-driven, involving altered solvation.
• Nitrogen-treated tannins exhibited more hydrogen bonding in their interaction with poly-l-proline.

Conclusions:

• Oxygen exposure during fermentation significantly alters red wine tannin structure, pigmentation, and aggregation.
• These structural changes modify tannin reactivity with proteins, impacting their hydrophobic and hydrogen bonding interactions.
• The observed changes in tannin properties due to oxygen exposure may have direct implications for wine astringency and sensory perception.