Andrew Waterhouse,* Lingjun Ma, Christoph Bueschl, and Rainer Schuhmacher
*University of California, Department of Viticulture and Enology, Davis, CA 95616 (alwaterhouse@ucdavis.edu)

Quinones are key reactive intermediates formed during wine oxidation that have a key impact on wine characters, degrading color, and flavor. They can readily react with nucleophiles like SO2 and glutathione. Some nucleophiles have been reported to react with quinones in model wines, but some of the corresponding products have not been confirmed in real wines and questions remain regarding which products do, in fact arise in wine. Here, a stable M+6 isotope labelling approach was used with liquid chromatography coupled to time-of-flight mass spectrometry. By finding products with the unique isotopic ratio (M+6), it is possible to demonstrate which substances in the wine were produced by reacting with the quinone. A list of predicted products based on known wine nucleophiles was prepared and compared to the data extracted that was filtered based on the M+6 isotopic pattern using a program called MetExtract.  This yielded a list of 17 compounds.  Reactions were shown to occur with glutathione, methanethiol, bisulfite, and numerous flavonoids, particularly anthocyanins, and with complex products with multiple new bonds. This labeling technique can reveal real products in a very complex system, and demonstrates a means to further probe the complex oxidation reactions in wine.

Funding Support: American Vineyard Foundation