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

When grapes are exposed to wildfire smoke, several smoke-related aroma compounds can be transferred to the berries and become glycosylated. Although the compounds do not contribute to grape aroma in the glycosylated form, the free volatile phenols can be released throughout winemaking and wine aging to produce undesirable "smoke tainted" wines. Measurement of the intact glycosides provides insight on the potential flavor of a wine and provides information on the effect of winemaking practices on 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 developed here was applied to monitor changes associated with smoke exposure in 31 volatile-phenol glycosides during winemaking. The most hydrolytic time period during the winemaking process was the first half of fermentation with Saccharomyces yeast (EC-1118), after which 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 measurement of the glycosides. The information can be used to improve knowledge of the changes in smoke-taint glycosides and release of phenolic compounds that affect sensory properties of smoke-affected grapes and wines.