Armando Alcazar Magana, Michael Qian,* Ruiwen Yang, and Yanping L. Qian
*Oregon State University, 100 Wiegand Hall, Corvallis OR 97331, Corvallis, OR 97331 (michael.qian@oregonstate.edu)

The United States wine industry is facing smoke-exposure issues due to the increasing incidence of wildfires. Exacerbated by climate change, wildfires have increased in both number and size in recent years, intensifying smoke exposure issues in wine. Smoke taint is an off-aroma described as smoky, dirty, burnt, medicinal, and ashy character in the wine. The off-aroma is caused by grape or grapevine exposed to bushfire smoke before harvest. During a wildfire, smoke constituents like volatile phenols can permeate the grape cuticle and bind to sugar molecules, creating volatile phenol glycosides. These glycosides can be hydrolyzed during winemaking, releasing the aglycone volatile moieties such as guaiacol or cresols into the wine. Gas chromatography-mass spectrometry (GC-MS) is frequently used to study volatile phenols in smoke-exposed wine after hydrolyzing the glycosides. Although GC-MS offers a powerful tool to analyze volatile phenols, it lacks the capability to determine the chemical nature of intact phenolic glycosides or other smoke precursor compounds. We employed a state-of-the-art untargeted metabolomics approach using high-performance liquid chromatography combined with high-resolution accurate mass LC-MS/MS and the latest generation of bioinformatics tools to discriminate smoke-related com- pounds present in wines from 2020 wildfire-exposed and control wines (N = 14 for control wines; N = 26 for smoke-tainted wine). Using this technique, we detected hundreds of molecular features (containing structural and elemental composition) only present in smoke-exposed wine and dozens of volatile phenol glycosides. Univariate data analysis was used to establish differences or similarities between control and smoke-exposed wines. By understanding the chemical nature of phenolic glycosides and other smoke-related compounds, different strategies can be explored to reduce smoke compounds’ negative impact on wine quality.

Funding Support: Oregon Wine Board, American Vineyard Foundation (grant #2020- 2312)