Profiling Volatile Phenols in Grapes as a Tool to Track the Impact of Wildfire Smoke during Berry Development
Juliano Toniato,* Yan Wen, Larry A. Lerno,
Ignacio A. Perez, Anita Oberholster, and Susan E. Ebeler
*University of California – Davis, 801 J Street, #11, Davis, CA,
95616 (jtoniato@ucdavis.edu)
Recent wildfires have significantly impacted the winegrape growing regions on the West Coast. Research has shown that wildfires release large quantities of phenols to the air that can absorb into grapes, impacting grape and wine quality. However, as the wildfire-released phenols also occur naturally at different levels in different grape varieties, it is essential to determine ‘baseline’ levels to determine elevated levels due to wildfire smoke exposure. Current known smoke marker compounds are guaiacol, 4-methylguiacol, o-, m-, and p-cresol, 4-methylsyringol, syringol, and their glycosylated precursors. The glycosides are naturally present in grapes and can also form enzymatically in grapes during smoke exposure as part of the plant defense mechanism. Currently, there is no baseline data available to the industry to facilitate interpretation of grape smoke marker compound levels. The current project seeks to develop robust baseline data for the seven main varieties (Cabernet Sauvignon, Merlot, Pinot noir, Zinfandel, Syrah, Chardonnay, and Sauvignon blanc) in several AVAs over multiple seasons. Total, free, and bound volatile phenols are determined using liquid/liquid extraction with GC-MS/MS and UPLC-QTOF-MS methods. Air quality data during the growing seasons were obtained from governmental sources and used to ascertain whether the volatile phenol profile was affected by ambient smoke. Initial results for Cabernet Sauvignon and Chardonnay in several California wine regions show good agreement with the literature, with syringol being the most-abundant volatile phenol. Data also indicate similar volatile concentrations for grape samples from close-proximity locations. This project is the first step in creating a robust database for the normal range of volatile phenols in different grape varieties. Because annual variations in growing conditions and climate can impact the natural levels of volatile phenols in grapes, data from several seasons will be needed.
Funding Support: American Vineyard Foundation
