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

Abstract

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.

Exploring Variation in Grape and Wine Volatile Phenol Glycoconjugates to Improve Evaluation of Smoke Taint Risk

“…Samples from 2015, 2018, and 2020 were research wines made from growing regions proximal to wildfires and thus, were classified as 'affected' by smoke exposure. This distinction was supported with historical wildfire data and an adapted classification scheme (Crews et al 2022). Additional details about the sources of wine can be found in Supplemental Table 2.…”

“…Additional glycoconjugates that met these criteria included cresol pentose glucoside and phenol glucoside. The potential for pentose glucosides to be included as additional markers of smoke taint has been supported by several other studies (Caffrey et al 2019, van der Hulst et al 2019, Szeto et al 2020, Crews et al 2022. In contrast, little evidence is available for the inclusion of phenol glucoside as an additional marker of smoke taint.…”

“…These glycoconjugates are a subset selected from over 20 VPGs that have been reported in the literature (Hayasaka et al 2013, Noestheden et al 2018b, Caffrey et al 2019, van der Hulst et al 2019. As yet, few studies have assessed whether this subset of glycoconjugates is relevant to grapevines exposed to wildfire smoke in regions outside of Australia (Crews et al 2022); thus, Cabernet Sauvignon wines made from grapes affected by different levels of smoke exposure in CA were examined.…”

“…Total glycoconjugate values correspond to the sum of the six glycoconjugates routinely measured by Affinity Labs in their smoke taint analysis. In a recent study, samples were classified into seven levels of smoke exposure based on quantitation of total glycoconjugates, comprising baseline (<6 µg/L), light (6 to 30 µg/L), modest (31 to 100 µg/L), significant (101 to 200 µg/L), elevated (201 to 300 µg/L), substantial (301 to 400 µg/L), and severe (>400 µg/L) (Crews et al 2022). Herein, wines were classified as 'minimally affected' and 'affected' based on the severity of relevant wildfire seasons and the latter classification scheme.…”

“…Cresol rutinoside, guaiacol rutinoside, and phenol rutinoside were typically the most abundant glycoconjugates, with mean values between 5 and 8 μg/L. The total glycoconjugate values suggest that wines from 2011 and 2012 were made from grapes with low-to-modest amounts of smoke exposure (i.e., based on the classification system proposed by Crews et al 2022); values for half of these samples (including all of the 2011 wines) fell within the sum of the 99 th percentile values reported for 32 Australian Cabernet Sauvignon wines made from non-smoke exposed grapes (Coulter et al 2022). Previous research found guaiacol glycoconjugates were stable during bottle aging (Ristic et al 2017).…”