Characterization of esterase activity of the Bianchetta Trevigiana grape variety under reducing conditions

While extensive research has been carried out on the enzymes responsible for ester synthesis and hydrolysis by wine strains of Saccharomyces cerevisiae, grape esterase activity is not well documented. In this study, the autochthonous grape variety Bianchetta Trevigiana, widespread in the Prosecco wine production area of Treviso, Conegliano and Asolo (Italy), was characterized according to its esterase activity. Since grape skin is very rich in compounds which impart qualitative characteristics to wine, the study of esterase was carried out on this part of the fruit. During extraction, the presence of the reducing agent β-mercapthoethanol allowed a better protein yield but reduced esterase activity. Further addition of increasing doses of reducing agents to grape skin protein extract such as of K2S2O5 (used in winemaking) and DTT reduced or inhibited esterase activity. Even though the zymographic profiles of the extracts obtained with and without β-mercapthoethanol were qualitatively equal, the intensity of enzymatic bands, measured by densitometry, was different. The presence of reducing agents affected esterase activity of grape skin esterase, and since this enzyme is involved in hydrolysis and synthesis of esters which are important compounds responsible for wine flavour, the addition of reducing agents could affect the aromatic profile of wine.