Analysis of French and American oak chips with different toasting degrees by headspace solid-phase microextraction-gas chromatography–mass spectrometry

This paper describes the optimisation of headspace solid-phase microextraction (HS-SPME) conditions for the analysis of volatile compounds in oak chips used to accelerate wine aging as an alternative to traditional aging in oak barrels. The direct extraction of ground wood samples and the extraction of sample aqueous slurries using a divinylbenzene-carboxen-polydimethylsiloxane (DVB-CAR-PDMS) fibre were studied and compared. Optimal conditions for direct extraction were 110 °C and 60 min, whereas for aqueous slurries they were obtained by adding 2 mL of a 7.1 mol L−1 sodium chloride solution, at 70 °C and for 60 min. The two optimised HS-SPME approaches were compared in terms of repeatability and extraction efficiency; water addition to the sample prior to HS-SPME was selected because it yielded better repeatability (6.6% versus 8.5% relative standard deviation) and efficiency (around 1.4–4.8 times higher analyte amount extracted for most of the compounds). Finally, the method was applied in the analysis of oak chip samples from American and French oak with different degrees of toasting. Principal component analysis (PCA) of the results showed that the first principal component was correlated with the toasting degree whereas the second, which was strongly influenced by whisky lactones and eugenol, allowed us to differentiate between American and French oak chips.