A study on the relationship between the volatile composition of Moscato and Prosecco Grappa and enzymatic activities involved in its production

The enzymatic transformations during storage of pomaces greatly affect the composition of Italian Grappa. This study examines the impact of pectin methylesterase (PME), β- glucosidase (βG) and esterases (ESTs) on the composition of Moscato and Prosecco Grappa. Grape pomaces were fermented for differing periods of time. After protein extraction, the enzymatic activities were detected by spectrophotometric and electrophoretic methods. To determine by gas chromatography the evolution of methanol, terpenes, ethyl acetate and lactate in pomaces and Grappa samples, distillations by Cazenave equipment and a traditional copper alambic were performed. Sensorial evaluation was carried out. There is a close relationship between the PME activity of grape pomaces, the degree of pectin methylation, and the concentration of methanol before distillation. The results obtained suggest that inhibition of grape pomaces PME may be adopted to control methanol concentration. The glycosidases of grape and/or yeast seem to have a limited effect on the release of volatile compounds from glycosides located in grape skins. As regards the contribution of grape and microorganism esterase, several hypotheses are discussed.