Condensed Tannin Reacts with SO₂ during Wine Aging, Yielding Flavan-3-ol Sulfonates

Area of Science:

• * Food Chemistry
• * Enology
• * Wine Chemistry

Background:

• * Flavan-3-ols are key phenolic compounds in wine, influencing taste and mouthfeel.
• * Sulfur dioxide (SO₂) is widely used in winemaking for preservation and antioxidant properties.
• * The chemical interactions between SO₂ and wine phenolics during aging are not fully understood.

Purpose of the Study:

• * To investigate the formation and levels of sulfonated flavanol products in wine.
• * To explore the relationship between SO₂ concentration and the modification of flavan-3-ols during wine aging.
• * To understand the impact of SO₂ on tannin composition and protein-binding properties.

Main Methods:

• * Analysis of monomeric and oligomeric flavanol sulfonation products in 10 different wines.
• * Quantification of sulfonated flavan-3-ols and native flavan-3-ol monomers.
• * Assessment of protein-binding tannin levels, tannin activity, and mean degree of polymerization (mDP) in relation to SO₂ levels.

Main Results:

• * Sulfonated flavan-3-ols (monomeric and oligomeric) were detected in all wines, with levels often exceeding native flavan-3-ols.
• * Increasing SO₂ levels correlated with higher concentrations of sulfonate-modified flavan-3-ols and native monomers.
• * Wines with high SO₂ exhibited lower protein-binding tannin levels, reduced tannin activity, and lower mDP; acidic SO₂ treatment abolished protein binding.

Conclusions:

• * Sulfur dioxide reacts with wine flavan-3-ols, likely via carbocation intermediates, forming sulfonated derivatives.
• * SO₂ significantly alters wine tannin composition and properties during aging.
• * The formation of sulfonate-modified flavan-3-ols may contribute to the decreased astringency observed in aged red wines.