Profiling Aroma Volatiles and their Glycosidic Precursors in Grapes and Wines
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 grapes and wines. We also developed a method for monitoring the ‘aroma potential’ of grapes and wines without the need for initial isolation of the glycoside precursor fraction. However, this method still depended on indirect measurement of the glycosides and acid or enzymatic hydrolysis is needed to release the volatile aglycone which can result in artifact formation. We subsequently validated a novel method using UHPLC-qTOF MS/MS for direct analysis of intact aroma glycosides in grapes with minimal artifactual changes in composition. Using this method, we tentatively identified 27 monoterpene glycosides including two monoterpene trisaccharide glycosides, tentatively identified for the first time in any plant; the method was used to monitor monoterpene glycosides during fermentation of red and white grapes. The method was also expanded to measure 31 volatile-phenol glycosides in grapes exposed to wildfires and to measure 102 glycosidically bound precursors of monoterpenoids, norisoprenoids, volatile phenols, aliphatic alcohols, and sesquiterpenoids in grapes.