Gillean MILLER1, Lisa PILKINGTON1, Bruno FEDRIZZI1, David BARKER1, Rebecca DEED1,2
1 School of Chemical Sciences, University of Auckland, New Zeland
2 School of Biological Sciences, University of Auckland, New Zeland
Email contact: gmil851[@]aucklanduni.ac.nz
γ-Nonalactone has been identified as a significant contributor to the aroma profile of a range of wines and is associated with stonefruit and coconut descriptors.1 The exact route of γ-nonalactone biosynthesis in wine has not been fully elucidated; however, precursors including linoleic acid, 13-hydroxyoctadeca-9,11-dienoic acid (13-HODE) and 9-hydroxyoctadeca-10,12-dienoic acid (9-HODE) have been identified in incubation experiments.2 Wines produced from grapes infected with “noble rot” caused by Botrytis cinerea fungus generally show higher concentrations of γ-nonalactone compared to non-botrytized white wines, but the relative contribution of potential formation pathways has not been elucidated.3
To assess the effect of linoleic acid on the production of γ-nonalactone in wine, fermentations with and without added linoleic acid were carried out in synthetic grape must (SGM) at 28 °C using commercial Saccharomyces cerevisiae EC1118. Prior to γ-nonalactone quantitation in the finished wines and in a subset of six Australian and New Zealand commercial wines, several routes for the synthesis of a deuterated analogue of γ-nonalactone were attempted, before the deuterated d6-analogue of γ-nonalactone from its non-deuterated analogue was produced successfully. Subsequently, attempts were made to utilise the d6-γ-nonalactone analogue as an internal standard for the measurement of γ-nonalactone using gas chromatography-mass spectrometry. However, the synthetic d6-γ-nonalactone analogue proved to be an inappropriate internal standard for this purpose, due to back-exchange of deuterium atoms in wine. 2-Octanol was instead utilised as a surrogate internal standard for the measurement of γ-nonalactone.
γ-Nonalactone was successfully identified (above the limit of detection, 4.12 μg L-1) in two commercial New Zealand botrytized wine samples, and one fermentation sample to which linoleic acid (132 mgL-1) had been added. This suggests a possible link between the effect of Botrytis cinerea and/or linoleic acid, and increased levels of γ-nonalactone in wine. Further research is needed in this area to determine the mechanism of γ-nonalactone biosynthesis and to more accurately quantify γ-nonalactone in wine, using a more effective internal standard.
(1) Cooke, R. C.; van Leeuwen, K. A.; Capone, D. L.; Gawel, R.; Elsey, G. M.; Sefton, M. A. Odor Detection Thresholds and Enantiomeric Distributions of Several 4-Alkyl Substituted γ-Lactones in Australian Red Wine. J. Agric. Food Chem. 2009, 57 (6), 2462–2467.
(2) Garbe, L.-A.; Lange, H.; Tressl, R. Biosynthesis of γ-Nonalactone in Yeast. In Aroma Active Compounds in Foods; Takeoka, G. R., Güntert, M., Engel, K.-H., Eds.; ACS Symposium Series; American Chemical Society: Washington, DC, 2001; Vol. 794, pp 176–182.
(3) Cooke, R. C.; Capone, D. L.; van Leeuwen, K. A.; Elsey, G. M.; Sefton, M. A. Quantification of Several 4-Alkyl Substituted γ-Lactones in Australian Wines. J. Agric. Food Chem. 2009, 57 (2), 348–352.