Investigation on the heat stability and the pH-driven changes in the protein profile of an Italian white wine

In the recent years, there is a great interest concerning the relation between wine pH and the formation of turbidity in unfined white wines. Actually, a haze in bottled wine can reduce or invalidate its commercial value, and winemakers typically perform fining treatments to avoid wine turbidity. In the present study, the protein profile of the Erbaluce wine, one typical Italian white wine, was analyzed in relation to the haze-forming tendency and pH variation. A pH range from 3.00–3.60 was obtained experimentally and the corresponding heat stability was analyzed. The results indicated increased heat stability at lower pH, which was indicated by a lack of haze formation even above 70°C. The increase in pH was accompanied by a progressive shift in the haze formation from 50–60°C to 70–80°C. The proteins extracted from the wine samples at different pHs were separated by SDS-PAGE and identified by mass spectrometry analyses. Proteins derived from both yeast and grape tissues were present in the wine extracts. The statistical analysis of band intensities revealed that the solubility of certain yeast and grape proteins was modified by the pH shift. Interestingly, most of the proteins were glycosylated inducing the hypothesis that the sugar chain may have an influence on the differential solubility of wine proteins in response to pH. This finding could encourage researchers to consider wine to be a more complex model fluid with respect to those currently taken into account in wine heat stability studies.