Thesis Defence: Investigation of the Uptake of Volatile Phenols in Smoke Exposed Vitis Vinifera Vines

Ieva Zigg, supervised by Dr. Wesley Zandberg, will defend their thesis titled “Investigation of the Uptake of Volatile Phenols in Smoke Exposed Vitis Vinifera Vines” in partial fulfillment of the requirements for the degree of Master of Science in Chemistry.

An abstract for Ieva Zigg’s thesis is included below.

Defences are open to all members of the campus community as well as the general public. Registration is not required for in person defences.

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ABSTRACT

Significant losses are incurred by the wine industry when smoke from wildfires taints the grapes, causing the fermented wine to taste disagreeably burnt and ashy. These unpleasant aromas are thought to be triggered by the presence – as low as parts per billion in concentration – of volatile phenols (VPs), a class of compounds found in smoke. Current research is focused on developing ways to remove VPs from wine or blocking their entry into grapes, but due to their low concentrations and the complex grape matrix even detecting them is challenging and expensive. Further, VP uptake, transport, metabolism in the grapevine are poorly understood.

This thesis compared two published methods for determination of smoke volatiles in grapes. Improvements to the extraction procedure were then introduced by selectively targeting specific steps in the literature methods, combining the most efficient ones and optimizing the complex, time-consuming parts. The final, optimized method is the first (published) to date that quantitates VPs within the entire grape (vs. only juice), more accurately reflecting the red wine-making process. Improved accuracy of VP detection will result in risk reduction to winemakers.

The new VP procedure was used to test if smoke can enter the berries through smoke exposed leaves or through the roots irrigated with smoke-contaminated water. Watering with tainted water had no effect of the grapes or leaves, a positive finding indicating that irrigation with lake or rain water during wildfire season should not ruin the crops. Further, this thesis developed a smoke taint research model using greenhouse-grown, potted Shiraz grapevines and a kitchen food smoker for treatment application. Filling plastic bags tied around parts of the vine with smoke from burning local fuel sources allowed for a convenient, targeted investigation of VP uptake and transport. No volatile phenols were detected moving out of tainted grapes, but some evidence was found that they may be transported into the berries from smoke exposed leaves. Thus, in addition to providing the community a new, accurate VP method, this thesis adds to our knowledge of VP uptake and storage within smoke-exposed grapevines, providing a foundation on which to build protection efforts.