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 Protein, polysaccharide, and tannin levels varied significantly across the wines [1, 2]. Electrophoretic analysis demonstrated that all proteins in the wines exist as high molecular weight aggregates, likely including tannins. Moreover, the wines could be categorized into two groups based on the mobility of the protein aggregates which seemed related to the quantity of protein-reactive tannins [1]. Asymmetrical Flow-Field Flow Fractionation (AF4) with online multidetection was used to isolate and characterize 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 [3]. A correlation analysis of red wines' compositional data and their colloidal content and structures, as determined by MALS detection, showed that polymeric pigments associated with proteins should be important for red wine colour [2, 4]. Overall, the findings allowed for the proposal of an updated model for colloidal aggregation in red wines, suggesting that this process occurs through the assembly of protein-tannin sub-aggregates and their interaction with polysaccharides. The compactness of these colloidal particles has been linked to the wine protein content, with colloids containing a high protein level being less compact. These findings highlight the central role of proteins in determining red wine colloidal structure and their significance for red wine colour. This work 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.