Composition and molar mass distribution of different must and wine colloids

Abstract

A major problem for winemakers is the formation of proteinaceous haze after bottling. Although the exact mechanisms remain unclear, this haze is formed by unfolding and agglomeration of grape proteins, being additionally influenced by numerous further factors. For instance, increased levels of polyphenols and sulfate ions, high pH and ionic strength, and increased storage temperatures have been discussed to promote haze formation. In contrast, organic acids and polysaccharides appear to inhibit protein agglomeration (Albuquerque et al. 2021). To avoid haze formation, winemakers use bentonite to reduce protein levels in the wine before bottling. However, the bentonite treatment imposes negative side effects such as losses in wine quantity and quality, as well as costs of bentonite waste disposal (van Sluyter et al. 2015). To better understand haze formation and to find alternative procedures for protein removal e.g. by enzymatic treatments, detailed insights into the composition of the wine colloids might be helpful.
Prior to characterization, colloids were isolated from five different musts (four varieties from five vineyards, three with pectinase treatment) and their corresponding wines by ultrafiltration (10 kDa cut-off) and freeze-drying. Protein and carbohydrate composition were determined after hydrolysis by ion chromatography and high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD), respectively. Molar mass distribution of colloids was determined by size exclusion chromatography with multi angle light scattering in combination with an UV and RI detector (SEC-UV-MALS-RI).
Colloids were found to contain a wide range of 8.9 to 67.1 g protein and 28.1 to 78.0 g carbohydrates per 100 g dry matter. Thus, protein concentrations in must and wine were been between 0.06 and 0.40 g/L and carbohydrate concentrations between 0.17 and 0.65 g/L. While there were just minor differences in the amino acid composition between the musts and wines, the carbohydrate composition was different in the samples. For instance, arabinose and galactose were the main sugars found in all hydrolyzed must colloids, while galacturonic acid was present in higher amounts in those not treated with pectinase. After fermentation, mannose was found to be the main sugar in hydrolyzed wine colloids. SEC-UV-MALS-RI showed that the colloids contained three main fractions. Two carbohydrate-rich fractions with average molar masses from 931 to 22,617 kDa and from 80 to 495 kDa as well as a proteinaceous fraction with an average molar mass between 16 to 44 kDa.
Our results indicate that colloid concentration and composition in wine is heavily influenced by variety, vineyard and oenological practices. The isolated colloids and the analytical methods will in the future be used to screen for enzyme preparations suitable to degrade proteins in must and wine to avoid haze formation.

References

Albuquerque, Wendell; Seidel, Leif; Zorn, Holger; Will, Frank; Gand, Martin (2021): Haze Formation and the Challenges for Peptidases in Wine Protein Fining. In: Journal of Agricultural and Food Chemistry 69, S. 14402–14414.
van Sluyter, Steven C.; McRae, Jacqui M.; Falconer, Robert J.; Smith, Paul A.; Bacic, Antony; Waters, Elizabeth J.; Marangon, Matteo (2015): Wine Protein Haze: Mechanisms of Formation and Advances in Prevention. In: Journal of Agricultural and Food Chemistry 63 (16), S. 4020–4030.