Aim: Wine is a very complex medium and is often evaluated according to its main components like alcohol, sugar, tannins, and acid levels. Proteins are rarely considered in this evaluation because their concentrations are only a few mg/L of wine. However, in an enological context, proteins appear to be more and more important, in particular for the stability of wines with protein haze problems. The study of proteins is less obvious in red wines than in white wines because the proteins are strongly tied to tannins, which makes their extraction and analysis even more difficult.
Methods and results: This article describes a technique for the separation of proteins from tannins thanks to a methanol/chloroform emulsion in an acid solution. The protein extract, obtained after 4 hours, was later analyzed by SDS-Page and the protein profile of the wine established. Experiments showed that the protein profiles remained the same during the different stages of the winemaking process, whereas the overall amount of proteins decreased. Characteristic protein profiles of different grape varieties were established, and it was also possible to visualize the presence of exogenous proteins from fining agents like albumin and casein.
Conclusion: This procedure allowed the extraction of proteins from 8 red wine samples within 4 hours. It also made it possible to analyze the extracted proteins by SDS-Page without tannin interference within 2 hours.
Significance and impact of the study: This method shows in a very promising manner how proteins might be extracted from red wines after being separated from their tannins. The extracted proteins are then available for analysis using even more advanced techniques such as ESI-QTof or ELISA.
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