Location: Plant Gene Expression Center
Project Number: 2030-12210-003-011-A
Project Type: Cooperative Agreement
Start Date: Sep 1, 2025
End Date: Aug 31, 2026
Objective:
In conjunction with ongoing smoke exposure trials being conducted by the Washington State University (WSU) lab, this Cooperative Agreement will focus on the following objectives:
1. Continuation of a project focusing on the role that commercial yeast strains may play in the hydrolysis of glycosides of smoke related volatile phenols during model wine and red wine fermentations.
2. Evaluation of the role that commercial yeast strains may play in the production/modification of thiophenols in model wine and red wine fermentations
3. Evaluation of the use of Gordonia spp as a protective measure when applied to field-planted grapevines (or to the fruiting zone only) prior to smoke exposure.
4. Investigation into the mechanism of guaiacol degradation by Gordonia species.
Approach:
The Washington State University (WSU) lab has done some preliminary work on Objectives 1 during the 2024 growing season. Using a selection of commercial wine yeast strains, bucket scale fermentations of fruit exposed to smoke from ongoing field trials. No differences in the concentration of several smoke related volatile phenols nor volatile glycosides measured by acid hydrolysis. This study did not attempt to analyze concentrations of individual glycosides before and after fermentation, nor were volatiles entrained in the CO2 released during fermentation measured. Results from a separate study in the Collins lab suggest that the efficiency of enzymatic hydrolysis of glycosides of phenols varies widely by specific glycoside.
As several glycosides of smoke related phenols are now commercially available, this study will initially evaluate the ability of a smaller selection of commercial yeast strains to hydrolyze several specific smoke related glycosides during model juice fermentations spiked with these glycosides. Once a suitable assay for yeast hydrolysis ability has been developed, additional strains will be tested using model juice fermentations. If yeast strains with sufficient hydrolysis activity can be identified, additional testing will be down in red wine fermentations, first spiked with specific glycosides, then using fruit from smoke exposure trials.
Successful trials with yeast strains that have sufficient hydrolytic activity would be subjected to RNA transcriptomic, proteomic and metabolomic evaluation to elucidate the basis for their hydrolytic activity. If the enzyme(s) involved can be purified, further work could be done to immobilize the enzyme(s) on inert supports for used in an immobilized enzyme bed for the hydrolysis of smoke related glycosides.
Similarly, the WSU lab has done some preliminary work with commercial yeast strains selected for the production of volatile thiols during fermentation. Following the model outlined for Objective 1, a small number of thiol-enhancing strains will be tested in model juice fermentations spiked with volatile phenols, smoke related thiophenols and with or without glutathione and cysteine additions. The redox state of these fermentations will be monitored initially, and the redox state will be managed for some fermentations to evaluate the role that redox may play in the formation/degradation of thiophenols during fermentation.
Again, once suitable conditions for thiophenol production/degradation are established, an assay will be developed to test additional strains, and evaluation of yeast performance will be further tested in red wine fermentations, as outlined in Objective 1.
Objective 3 will evaluate whether inoculation of grape clusters with Gordonia spp would have the potential to establish presence of an organism with the ability to degrade guaiacol. Initial work would focus on the ability to establish a population of Gordonia spp on clusters. If an enduring population can be established, then inoculated clusters and control clusters can be exposed to smoke to evaluate whether the population can provide a beneficial impact on guaiacol levels in smoke exposed fruit.