Smoke taint has become a significant concern for the wine industry, partly due to climate change. Smoke taint is an off-aroma describing the wine with smoky, medicinal, and ashy characters. This unpleasant taint is caused by grapes or grapevine exposed to bushfire smoke before grape harvest. Guaiacol, 4-methylguaiacol, o-, m-,p-cresols, and other volatile phenols have been found to be related to smoke taints. When the grapes and the grapevines were exposed to wildfire smoke, they will absorb these volatile phenols and convert them to the corresponding glycosides or other bound forms. These glycosides and the bound form precursors do not exhibit aroma themselves, but can be converted back to the odorants during the winemaking and wine aging process. Grape maturity, grape varieties, and bottle aging can all influence smoke taint intensity in wines. Thus, it is crucial to analyze these volatile phenols in grapes and wine reliably. In this study, solid-phase microextraction-GC-MS (SPME-GC-MS) and stir bar sorptive extraction-GC-MS (SBSE-GC-MS) methods were compared and verified for volatile phenol analysis. For SPME-GC-MS analysis, stable isotope standards need to be employed, guaiacol, 4-methylquaiacol, 4-ethylguaiacol, and o-cresol m-cresol, p-cresol, 4-ethylphenol can be analyzed in 30 min in wine. For SBSE-GC-MS analysis, an ethylene glycol-polydimethylsiloxane (EG-PDMS) copolymer was used for volatile phenol extraction. The wine pH was adjusted to 7 to minimize the extraction of fermentation fatty acids from the wine.  Both methods can quantitate volatile phenols down to 0.1 ug/L in wine, with good repeatability and linear response. The methods can also be used to analyze total volatile phenols after acid hydrolysis.

Comparison of stir-bar sorptive extraction-GC-MS and solid-phase micro-extraction -GC-MS for volatile phenol analysis in wine to assess the smoke impact

ACS Spring Meeting 2021

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