Noah's nectar: the proteome content of a glass of red wine

Combinatorial peptide ligand libraries (CPLLs) have been adopted for harvesting and identifying traces of proteins present in red wines. Surprisingly, although it is stated that red wines are in general fined with egg albumin, for all Italian wines investigated (in the areas around Chiari and Verona as well as in the Chianti area) we find that the only fining agent used is bovine casein, just like in white wines. Although the typical levels of casein found range between 45 to 85μg/L, in one case as little as 3.8μg/L of casein could be detected, an extremely high level of sensitivity, close to our lower detection limit of 1μg/L reported for white wines. As a result of such treatments, very small amounts of residual proteins in red wines could be identified: essentially no residual grape proteins (except for thaumatin), but only traces of proteins from Saccharomyces cerevisiae and a few proteins from plant pathogens and fungi (e.g., Botryotinia fuckeliana, Sclerotinia sclerotiorum, Aspergillus aculeatus). Contrary to what has been found in white wines, the best capture efficiency with CPLLs has occurred at pH 7.2 and pH 9.3, with minimal capture at pH 3.3. The fact that such very low levels of fining agents can still be detected in treated red wines should be taken into consideration by winemakers in labelling their products and by EC rulers in issuing proper regulations.