Until the end of 1997, plasmatic proteins and blood cells could be used to clarify wines. The aim of our work was to study the persistence of these animal proteins in a dry white wine during clarification. The effects of some clarification parameters were also estimated.
We used two protocols to discriminate between blood paste proteins and native proteins of unclarified wine (e.g. from grapes, yeasts, bacteria). The first protocol was a radiolabel of blood paste proteins with chloroglycouril and Na125I. The 125I-labelled animal proteins were revealed with autoradiography of sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and quantified with a gamma scintillator. The second protocol was purification with affinity chromatography. The antibodies of this affinity chromatography were specific of whole beef serum. After this purification, harvested proteins were loaded onto two-dimensional gel electrophoresis (2D). After migration, proteins were silver-stained.
With the radiolabel protocol, we show that the concentration of animal proteins found in dry white wine after clarification and filtration increased with the concentration of blood paste proteins used during clarification. This relation is almost linear. The duration of the blend blood paste / wine incubation step is also a significant parameter. After incubation for one minute, about 40 p. cent of animal proteins were found in clarified and filtered wine. After four days of incubation, a maximum of 88 p. cent blood paste proteins were found in both clarified and filtered wine. The use of bentonite decreased 4-to 6-fold the concentration of blood paste proteins. The filtration step also strongly decreased the concentration of these proteins : quantitation with a phosphoimager showed that wine clarified (with 250 μg of blood paste proteins in 4 heures of incubation time, without bentonite) and filtered retained 6 p. cent, i.e. 12 mg of blood paste proteins. The membrane porosity (0,2 or 0,45 μ) for the filtration had no effect.
Affinity chromatography and 2D procedures also showed that proteins of animal origin could subsist in wine after clarification, while others in the original composition of wine disappeared.
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