Metabolic Profiling of Grape and Wine Aromas

The complex aroma of wine is derived from many sources, with grape-derived components being responsible for the varietal character. The ability to monitor grape aroma compounds would allow for better understanding of how vineyard practices and winemaking processes influence the final volatile composition of the wine. Previously we developed a procedure using GC-MS combined with solid-phase microextraction (SPME) for profiling the free volatile compounds in Cabernet Sauvignon grapes. During the current funding year we have modified this procedure in order to determine the volatile glycoside content of grapes using acid and enzyme hydrolysis conditions. The results indicate acid hydrolysis at low pH and high temperature can release from 50-80%of the total aglycone present in the sample. However, extensive degradation of many free volatile aglycones also occurs, with the effect being dependent on the compound studied and the hydrolysis conditions. This makes it difficult to use acid hydrolysis conditions to predict the ?potential? volatile composition of the grapes. This information is needed to understand the effects of viticultural practices on grape aroma composition and to be able to evaluate the effects of winemaking processes on changes in grape composition throughout the winemaking process. Further study is needed in order to minimize artifactual changes occurring from acid hydrolysis of volatile glycosides in grapes while maximizing their hydrolysis prior to analysis. As recently noted by Hayasaka et al. (2010), availability of rapid, sensitive profiling methods is important in assessing the nonvolatile fraction of grapes for a wide variety of industry applications.