Accumulation of volatile phenol glycoconjugates in grapes following grapevine exposure to smoke and potential mitigation of smoke taint by foliar application of kaolin
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The accumulation of volatile phenol glycoconjugates in smoke-exposed grapes was monitored following grapevine exposure to smoke, with different glycoconjugate profiles observed for fruit sampled 1 and 7 days after smoke exposure, and at maturity. Foliar application of kaolin reduced the concentration of volatile phenol glycoconjugates in smoke-exposed fruit, but efficacy depended on the rate of application and extent of coverage.
Smoke taint can be found in wines made from grapes exposed to smoke from bushfires or prescribed burns. It is characterized by objectionable smoky and ashy aromas and flavors, which have been attributed to the presence of smoke-derived volatile phenols, in free and glycoconjugate forms. This study investigated: (1) the accumulation of volatile phenol glycoconjugates in grapes following the application of smoke to Sauvignon Blanc, Chardonnay and Merlot grapevines at approximately 10 days post-veraison; and (2) the potential mitigation of smoke taint as a consequence of foliar applications of kaolin (a clay-based protective film) prior to grapevine smoke exposure. Varietal differences were observed in the glycoconjugate profiles of smoke-exposed grapes; the highest glycoconjugate levels were found in Merlot grapes, being pentose-glucosides of guaiacol, cresols, and phenol, and gentiobiosides of guaiacol and syringol. Changes in volatile phenol glycoconjugate profiles were also observed with time, i.e., between fruit sampled 1 day after smoke exposure and at maturity. The application of kaolin did not significantly affect the glycoconjugate profiles of Sauvignon Blanc and Chardonnay grapes, but significantly lower volatile phenol glycoconjugate levels were observed in Merlot fruit that was treated with kaolin prior to smoke exposure. The potential for control and smoke-exposed grapes to be differentiated by measurement of spectral reflectance was also demonstrated.
KeywordsCultivars Glycosylation Guaiacol Reflectance spectroscopy Syringol Wine
This research was conducted by the Australian Research Council Training Centre for Innovative Wine Production (www.adelaide.edu.au/tc-iwp/), which is funded as a part of the ARC’s Industrial Transformation Research Program (Project No IC130100005) with support from Wine Australia and industry partners. L.vdH. was the recipient of a Wine Australia supplementary scholarship (GWR Ph1403); J.C. was supported by Australian grapegrowers and winemakers through their investment body, Wine Australia, with matching funds from the Australian Government. The authors gratefully acknowledge the AWRI’s Commercial Services Laboratory for chemical analysis of fruit and Jeffrey Borgas, Radomir Ristic, Louise Bartle and Morgan LeCoq for technical assistance with field work.
Compliance with ethical standards
Conflict of interest
The authors declare no conflicts of interest.
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