Simultaneous determination of free and bonded forms of odor-active carbonyls in wine using a headspace solid phase microextraction strategy

• Simultaneous determination of free and bonded forms of sensory relevant carbonyls.
• Sulfur dioxide-carbonyl apparent equilibrium formation constants calculated.
• Some wine odor-active carbonyls can be more than 95% under bonded forms.
• Deep implications on wine aging potential.

This paper presents a new strategy for the direct evaluation of odor-active carbonyls in the wine headspace and for the simultaneous estimation of their amounts in odorless bonded forms. In the final developed strategy, 25 mL of wine are spiked with internal and surrogate standards and let to equilibrate for at least 12 h in an oxygen-free chamber. Ten milliliter of the sample are then transferred to a standard headspace vial. Carbonyls in the headspace are preconcentrated on a PDMS/DVD fiber keeping the sample unstirred at 45 °C for just 10 min and are further analyzed on a GC–MS equipped with a quadrupole in SIM mode. Normalized peak analyte areas interpolated in calibration plots built with synthetic wines give estimations of the concentrations of free forms, while the ratios of the areas of surrogates observed in wines to those observed in synthetic wine make it possible to get estimations of the proportion of each analyte present in bonded non-volatile form. The validity of this approach has been demonstrated both via standard recovery experiments and via the analysis of samples previously incubated with glyoxal in order to break aldehyde-bisulfite complexes. In general, method detection limits (below 1 μg L−1), precision (RSD (%) < 10%) and accuracy are satisfactory for 12 studied carbonyls. Results demonstrate that wine contain relevant amounts of aldehydes (more than 95% in some cases) in the form of reversible odorless complexes, supporting a previous observation about the potential implication of these complexes on the development of oxidized aroma.