The role of protein-phenolic interactions in the formation of red wine colloidal particles

Colloids play a crucial role in red wine quality and stability, yet their composition and formation mechanisms remain poorly understood. Recent studies from the D-Wines (Diversity of the Italian Wines) project aimed to elucidate the structure, composition, and formation mechanisms of red wine colloids by analysing monovarietal wines from 10 Italian red grape varieties. Colloid-forming molecules, specifically proteins, polysaccharides, and tannins, were examined in over 100 wines, showing a wide diversity across the samples. Electrophoretic analysis demonstrated that all proteins in the wines exist as high molecular weight aggregates, likely including tannins. Moreover, the wines could be categorised into two groups based on the electrophoretic mobility of the protein aggregates, which appeared to be related to the quantity of protein-reactive tannins in each variety. Asymmetrical Flow-Field Flow Fractionation (AF4) with online multidetection was used to isolate and characterise red wine colloids in their native state, revealing diverse colloidal populations across wines. This diversity was attributed to the varying proportions of proteins, polysaccharides, and phenolics present in the colloidal particles. These latter were coloured, indicating the presence of red pigments in the colloids. A correlation analysis of the compositional data of the wines and their colloidal particles indicated that the association of proteins with polymeric pigments should be important for red wine colour. Overall, the findings led to the proposal of an updated model for colloidal particles in red wines, suggesting that the process for their formation occurs through the assembly of protein-tannin sub-aggregates, followed by their interaction with polysaccharides. The compactness of these colloidal particles has been linked to the wine’s protein content, with colloidal particles containing higher protein levels being less compact. These findings suggest that proteins likely play a role in determining the structure and properties of red wine colloidal particles. Moreover, this study provides an updated framework for understanding how compositional differences among grape varieties, particularly the content of protein-reactive tannins, shape colloidal structures, ultimately impacting key wine quality parameters such as colloidal stability and colour