Two-dimensional gas chromatographic profiling as a tool for a rapid screening of the changes in volatile composition occurring due to microoxygenation of red wines
Microoxygenation (MOX) is a widely applied technique to deliver continuously trace amounts of oxygen to red wine during vinification and ageing in order to improve color stability and sensory properties. Proven by sensory means, the added oxygen modifies not only tannin structure and color of the wines, but also their composition of volatiles. In this study different microoxygenation treatments prior and after malolactic fermentation were carried out for Pinot noir, Cabernet Sauvignon and Dornfelder wines of the 2007 vintage. Volatile components of subsequent wines were analyzed using headspace-solid phase microextraction coupled to comprehensive two-dimensional gas chromatography–quadrupole mass spectrometry (GC × GC–qMS). Quantitative data were retrieved from two-dimensional images obtained from GC × GC chromatograms of volatile compounds applying a software package, which is commonly used in the field of proteomics for two-dimensional electrophoresis gels. This approach revealed a discrimination of the applied treatments by multivariate statistics based on volatiles alone, such as the clear distinction among wines treated before or after malolactic fermentation in case of Cabernet Sauvignon and Dornfelder or the effect of different oxygen doses. Besides the differentiation of MOX treatments from the untreated control, specific varietal and technological effects could be distinguished. The image processing of the GC × GC data offered valuable tools which were able to identify those areas in the 2D images that were most responsible for discrimination among different MOX treatments. Based on the loadings of individual aroma compounds a set of markers for the MOX-induced modifications of volatiles could be suggested.