Proteins in white wines: Thermo-sensitivity and differential adsorbtion by bentonite

Protein fractions in a Chardonnay wine (invertases, glucanases, chitinases and thaumatin-like proteins) were identified using 2D-electrophoresis and mass spectrometry. The sensitivity of these fractions to heat-induced denaturation and precipitation following heat-treatments at different temperatures was studied and compared to their affinity for bentonite, a clay used to adsorb proteins and stabilise wines with regards to protein hazes. The different proteins exhibited different sensitivity with regards to heat-induced precipitation, glucanases being the most sensitive and invertases the least. Thaumatines and chitinases were characterised by a wide range of behaviours attributed to structural micro-heterogeneities. Protein depletion upon the addition of increasing bentonite doses was also dependent on the considered fraction. A good correlation was shown between protein affinity for bentonite and their sensitivity to heat precipitation. Results were discussed considering the current winemaking practices used to assess white wine stability and define bentonite doses needed to achieve their stabilisation.