A comparison of new and traditional techniques for removing proteins responsible for haze in white wine

Abstract

Wine haze is a common quality problem for white wines where the proteins in wine denature over time or at high temperature and form a stable suspension reducing the clarity of the wine. Wine susceptibility to haze formation is assessed using the heat test, which involves heating the wine to 80 °C for two hours, followed by cooling for three hours and measuring the change in turbidity. Proteins responsible for wine haze can be removed using adsorbents such as bentonite, but results in wine losses of up to 10% and large volumes of lees from hydrated bentonite. amaea, a start up company, has developed three promising adsorbents, alginate bentonite hydrogel (ABH), and two polymer-based media named Protx and Phenx, for removing these proteins. Adsorption experiments were conducted on a typical unfinished, heat-unstable Sauvignon Blanc wine and compared to bentonite treated and heat-treated wine. The media and their performance were characterised through particle size analysis, surface area and pore size measurement, SEM structural and elemental analysis, ion exchange capacity tests, zeta potential, adsorption isotherms and kinetics, and small-scale batch heat stabilisation tests.

Protx had a mean diameter of 3.2 mm, and mean circularity of 0.55, and a surface area of 47 m2/g compared to PhenX which was 2.3 mm, 0.8, and 192 m2/g respectively. Protx had five times the cation exchange capacity and 10 times the anion exchange capacity of Phenx, had a zeta potential of -800 mV compared to -80 mV for Phenx and required 5 times the amount of HCl to reduce the zeta potential to zero. Protx had 30 times the affinity for wine proteins and had a 90 times greater rate of adsorption to the media surface compared to Phenx. ABH achieved the highest removal of wine proteins (85%), followed by Protx (74%), bentonite (64%), heat treatment (61%), and Phenx (55%), as measured by the Bradford method.

Wine samples before and after treatment were filtered, dialysed and freeze-dried to concentrate wine proteins for analysis. The alkaline Bradford assay, which was more sensitive to protein and less affected by phenolic compounds compared to the conventional Bradford method, was adopted for quantification. Protein analysis was conducted using SDS-PAGE electrophoresis using Any kDa stain-free gels, reverse phase high performance liquid chromatography, and gel filtration chromatography. Peak deconvolution of gel filtration spectra was performed using Origin 2024b. Positive correlations were found between total protein concentration with heat-induced turbidity. The 33 kDa and 21.6 kDa proteins contribute to haze formation; the 18.3 kDa proteins are possible TLPs isomers, with F2/4JRU being heat unstable and I/4L5H and/or H2/4MBT being able to refold after cooling; while the 49.2 and 61.2 kDa proteins may have minimal contribution to heat induced turbidity and partially precipitate during heating and cooling due to crossing linking with heat unstable proteins.