White Grape Cell Walls as Fining Agents in Red Wine: Mechanistic Insights from ATR-FTIR Spectroscopy

The fining of red wines is a crucial process for enhancing their sensory quality, involving the elimination of compounds that compromise stability or generate undesirable attributes. Against the backdrop of growing interest in sustainable and allergen-free alternatives, this study examines the potential of using cell wall material from white grape pomace (Zalema, Pedro Ximénez and Moscatel varieties) as fining agents in red wine. Cell wall samples were isolated and characterised using attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). PCA applied to the cell wall spectra revealed homogeneous matrices dominated by structural polysaccharides, including cellulose, hemicellulose, lignin, pectins and arabinogalactans. Following the fining treatments, significant differences were observed in the generated sediments compared to the control, primarily due to signals attributable to phenols, proteins, and carbohydrates. This demonstrates the active involvement of these compounds in the formation of precipitates. The results confirm that the composition of the cell wall favours interaction with phenols and proteins in wine, thereby contributing to their elimination. Overall, this work demonstrates the potential of cell wall material from white grape pomace as plant-based oenological fining agents, providing new insights into the molecular mechanisms of action.