Changes in Smoke-Taint Volatile-Phenol Glycosides in Wildfire Smoke-Exposed Cabernet Sauvignon Grapes throughout Winemaking

When grapes are exposed to wildfire smoke, several of the smoke-related aroma compounds can be transferred into the berries and become glycosylated. In the glycosylated form, the compounds do not contribute to grape aroma, but the free volatile phenols can be released throughout winemaking and wine ageing to produce undesirable “smoke tainted” wines. Measurement of the intact glycosides gives insights to the potential flavor of a wine and provides information on how winemaking practices impact release of volatile aroma compounds from glycosidic precursors. Smoke taint associated volatile-phenol glycosides in Vitis vinifera cv. Cabernet Sauvignon grape berries were tentatively identified and semi-quantitated using a comprehensive database coupled with ultra-high performance liquid chromatography and accurate-mass time-of-flight tandem mass spectrometry. Eight trisaccharide volatile-phenol glycosides were tentatively identified for the first time in grapes. The method was applied to monitor changes during winemaking of 31 volatile-phenol glycosides associated with smoke exposure. The first half of fermentation with Saccharomyces yeast (EC-1118) was the most hydrolytic time period during the winemaking process. After that time, there was little effect on the phenolic glycosidic profile of fermenting wines. This is the first report to monitor changes of these 31 phenolic glycosides during winemaking using direct measurements of the glycosides. The information can be used to better understand changes in smoke-taint glycosides and release of phenolic compounds that impact sensory properties of smoke-affected grapes and wines.