Appraising California Zinfandel Exposure to Wildfire Smoke Using Natural Product Phenolic Diglycoside Biomarkers.

Zinfandel grapes are ubiquitous in California and its wine quality could be negatively impacted from wildfire smoke. Thus, the occurrence of fires prior to grape harvest presents a persistent problem to both viticulture and enology processes. This is the first broad study on Zinfandel to investigate wine quality defects produced by natural wildfires. The project, guided by UHPLC separations and MS2 multiple reaction monitoring, involved measuring natural product phenolic diglycosides (PDs) bioaccumulated in grapes, and expands outcomes published in 2022 by our team (called the Santa Cruz Campaign, SCC). The plan was implemented by exploiting a panel of six marker PDs 1-6 and their deuterated analogues. Examined in the study were 24 different Zinfandel wines obtained from 2016 to 2021 vintages of nine different American Viticulture Areas (AVAs) that were also within five of the eight California Zinfandel viticulture zones. The goal was to extend understanding on PD variations using patterns that possibly change as a function of appellation and fire intensity. Preliminary data was obtained to examine the relative amounts of PDs localized in berry skin versus pulp. The baseline of <15 ppb was proposed by surveying 18 distinct unsmoked Zinfandel wines. It was proposed to estimate the smoke impact on other Zinfandel wines by using seven PD ppb concentrations categories. A pilot study was also launched to assess conclusions by comparing ppb-based ratings versus sensory evaluation quality estimates. General findings presented herein should provide an important foundation to build understanding of using PD patterns to forecast possible Zinfandel wine wildfire damage.

Natural Product Phenolic Diglycosides Created from Wildfires, Defining Their Impact on California and Oregon Grapes and Wines.

Forest fires produce malodorous phenols, bioaccumulated in grapes as odorless phenol glycosides (mono- to tri-), and produce unpleasant smoke tainted wines when these complexes are transformed by glycosidases in saliva. Metabolomic analyses were used to further understand smoke taint by quantitating marker phenolic diglycosides via UHPLC separations and MS/MS multiple reaction monitoring. A collection of grapes and wines provided data to forecast wine quality of grapes subjected to wildfire smoke infestations; the analytics used a panel of reference compounds (1-6). Overall, eight different Vitis vinifera varietals were examined from 2017-2021 vintages involving >218 distinct samples (wines and/or grapes) from 21 different American Viticulture Areas. Results acquired allowed correlation of phenolic diglycoside levels as a function of grape cultivar, varietal clones, and intensity of wildfire smoke. Baseline data were tabulated for nonsmoked samples (especially, Cabernet Sauvignon having a sum 1-6 of <6 µg/L) and then compared to those exposed to six other levels of smoke. Outcomes established that (1) analyzing paired samples (bottled wines versus smoke-exposed grapes) can provide diagnostic metabolomic data, (2) phenolic diglycosides are stable in wines aged for >2.5 years, and (3) major gaps exist in our current understanding of this pool of metabolites.