Using A Model System to Trace Glycosidically-Bound Smoke Taint Markers from Grape to Wine
Yan Wen, Anita Oberholster,* and Ignacio
Arias-Pérez
*University of California Davis, One Shields Avenue, Davis, CA,
95616 (aoberholster@ucdavis.edu)
The increasing frequency of wildfires on the West Coast of the United States is a significant risk for the grape and wine industry. During wildfires, large quantities of volatile phenols (VPs) are released into the air due to thermal degradation of lignin. Besides the detectable free forms of these VPs, grapes can store a large portion of VPs as various nonvolatile glycosides, then release them during fermentation and wine aging. It is difficult to predict the smoke taint potential of a particular wine by simply measuring free VPs or their corresponding acid-labile forms, because the VP glycosylation mechanism is not clear, including the various glycosides formed from a particular volatile phenol compound. In this study, clusters of Cabernet Sauvignon grapes were exposed to isotopic VPs in a contained atmospheric system. After exposure, the glycosylation of absorbed isotopic VPs in grapes was traced and identified by UHPLC-qTOF-MS. In addition, both the free and acid-labile forms of isotopic VPs in the exposed grape were analyzed by gas chromatography-mass spectrometry (GC-MS). Exposed grapes were microfermented and the isotopic VPs’ levels of juice/must were monitored every two days until fermentation was complete. Finally, the obtained wines were analyzed by GC-MS for free and acid-labile VPs, while the related glycosides were determined by UHPLC-qTOF-MS. Grape enzyme activity showed variable ability to form mono-, di-, and trisaccharide VPs when exposed to VPs in this in vitro study. By tracing the formation of isotopic VP-glycosides and the hydrolyzed levels of related isotopic VPs during microfermentations, this study expands the knowledge of the correlation between different forms of VPs and their related glycosides.
Funding Support: USDA-ARS
