Wine Chemistry and Biochemistry

8E Identification of Impact Odorants of Wines 401

worse alternatives, but that, unfortunately, there is not a perfect single solution. It

must be taken into account that in the gas chromatograph all the volatiles injected

are vaporized and chromatographied (provided that they do not decompose, react

or interact irreversibly with the column) so that the extract should reflect as closely

as possible the composition of the vapors reaching the pituitary during the olfaction

process and not the composition in volatiles of the original sample.

This means that the classical approach in which the extract contains quantita-

tively all the volatiles present in the product is very far from the optimal solution. In

the past, great effort was devoted to preparing total extracts “representative” enough

of the original sample (Abbot et al. 1993; Moio et al. 1995; Priser et al. 1997;

Bernet et al. 1999), since researchers were concerned mainly with the possibility

of creating artifacts or loosing relevant aroma compounds during the preparation

of the extract. However, all these techniques produce extracts whose composition

is very far from those of the headspaces reaching the pituitary. The major problem

with these extracts is that they ideally contain 100% of all the aroma molecules of

wine and hence the GC-O experiment will detect 100% of all the aroma molecules

originally present in the sample. However, during the normal olfaction (both ortho

or retronasal) some aroma molecules are transported very efficiently from the liquid

wine in the glass or in our mouth to the pituitary (the most volatile and nonpolar),

while others are transported just in a negligible proportion (the least volatile and

most polar) because they are strongly retained by the wine hydroalcoholic matrix.

Consequently, the sensory importance of the least volatile and most polar com-

pounds will be strongly overemphasized in the GC-O experiments, as it is schemat-
ically shown in Fig. 8E.2. It may be argued that such bias will be corrected by the

quantitative determination and by the use of olfactory thresholds, but this involves a

Vapor phase reaching

the pituitary during

orthonasal olfaction

Vapor phase

during

retronasal

olfaction

Extract obtained

by “total”

extraction

Fig. 8E.2Schematic drawing showing the compositional differences between the extract obtained
by a total extraction technique and the vapor phases reaching the pituitary during ortho or retronasal
olfaction. The extract is enriched in polar volatiles that cannot reach the pituitary either by ortho
or retronasal pathways