Yan Wen, Cristina Medina Plaza, Andrew Waterhouse, and Anita Oberholster*
*UC Davis, One Shields Avenue, Davis, CA 95616 (aoberholster@ucdavis.edu)

The increased frequency of wildfires on the West Coast of the United States are seen as a significant risk for the grape and wine industry. High levels of smoke-related compounds can accumulate in winegrapes, which can result in smoke-impacted wines. Among hundreds of volatile compounds reported in wildfire smoke, volatile phenols and their corresponding precursors are widely considered the main markers of smoke taint. However, understanding of the absorption mechanism of smoke-taint markers onto grapes is limited, making it challenging to propose strategies to mitigate or prevent smoke impact. Another challenge is measuring smoke-taint markers in the air generated by wildfires, and how that relates to the amount absorbed by grapes. In this study, different strategies were applied to trace absorption of volatile phenols (VFs) from air into grapes. A well-sealed system containing known concentrations of vaporized VFs was designed to investigate their absorption efficiency onto grape clusters. Experimental factors were optimized to reach sufficient sensitivity and reproducibility, including the headspace sampling conditions, equilibrium of VFs in the vapor phase, and adsorption time. After VFs exposure (absorption), grape berries were extracted to determine the concentrations of all selected markers using a proposed LLE-GC-MS method. The glucoside precursors of VFs were analyzed using a well-developed SPE-UHPLC-QTOF-MS method. Isotopic standards were used as indicators during the whole process. The results show the transfer potential of smoke- taint markers from air to grapes and their glycosylation, expanding our knowledge of the formation of smoke-taint flavor. This controlled system is a first step toward understanding the absorption process that will lead to developing preventative strategies during wildfire events. In the next steps, different grape barrier sprays will be evaluated in this contained atmospheric system. Those applications that prove successful will be included in a larger field study.

Funding Support: American Vineyard Foundation