8E Identification of Impact Odorants of Wines 407
them making use of the formation of derivatives with pentafluorobenzyl
hydroxylamine (Cullere et al. 2004a; Mateo-Vivaracho et al. 2006) or with
3-methylbenzothiazolidin-2-onehidrazone (Ledauphin et al. 2006a).Volatile sulfur compounds. Volatile sulfur compound are best determined in the
headspaces using a sulfur selective detector. Different alternatives, based on
direct headspace of headspace-SPME, have been developed (Rauhut et al. 1998;
Mestres et al. 2000; L ́opez et al. 2007).Polyfunctional mercaptans. Polyfunctional mercaptans are some of the most
powerful odorants in nature, and they must be quantified at extremely low levels.
The methods developed for their determination make use either of a selective
separation usingp-hydroxy-mercurybenzoate (Tominaga et al. 1998; Tominaga
and Dubourdieu 2006; Ferreira et al. 2007), of covalent chromatography (Schnei-
der et al. 2003) or of the derivatization with pentaflurobenzyl bromide (Mateo-
Vivaracho et al. 2006, 2007). A recent report using non-selective headspace
isolation with SPME has also been published, but the limits of quantification
are more than one order of magnitude above the odor thresholds (Fedrizzi et al.
2007).Polar trace compounds, such as sotolon and furaneol, are often directly deter-
mined by GC-MS of a polar extract obtained directly from wine (Cutzach
et al. 1998; Camara et al. 2004; Moreno et al. 2005). However, this strategy only
works when the compounds reach relativelyhigh concentrations. For a deter-
mination at lower concentrations, a selective SPE isolation procedure has been
proposed (Ferreira V et al. 2003a)Methoxypyrazines are compounds with very low detection thresholds which
must be determined at very low levels. For these compounds, different selec-
tive isolation methods have been proposed (Allen et al. 1994; Sala et al. 2002).
Some authors use a simple extraction (Kotseridis et al. 1999; Falcao et al. 2007)
or an optimized headspace SPME procedure (Chapman et al. 2004; Prouteau
et al. 2004) using in most cases isotopically-labelled internal standards to com-
pensate for matrix effects. In spite of the claims of the authors, all these methods
present some difficulties to accuratelydetermine the compounds at the lowest
levels at which they can be found. A recent report has presented an advanced
method combining the preconcentration ability of headspace SPME with the
selectivity of comprehensive GC (Ryan et al. 2005).8E.5 Assessment of the Sensory Role Played by the Different
Odorants
At this point in the chapter it is convenient to introduce a discussion about the role
that the different wine odorants can play in the aroma of wine. This discussion is
based on the experience gained in the last few years, which have shown that there
are different and clearly identifiable roles in the way in which aroma compounds
contribute to the formation of the different aroma nuances of wine.