402 V. Ferreira and J. Cacho
lot of extra and in part, useless effort. In addition, wine extracts obtained following
the total extraction approach are extremely complex with many odors and the olfac-
tometric signals overlap, making very difficult the correct assignment of the identity
of the odorant (Cullere et al. 2004b; Escudero et al. 2004). In spite of all this, most
researchers keep on using these kinds of extracts for the GC-O screening of wine
aromas due to their simplicity and to the existence of some reasonable doubts about
the performance of headspace techniques.
The previous discussion leads to the conclusion that “a priori” headspace tech-
niques should be preferred although, as will be discussed, there are some questions
that as yet do not have a satisfactory answer. Here there are three different alter-
natives: static headspace sampling, dynamic headspace sampling and headspace
solid phase microextraction sampling. Static headspace sampling has been used only
rarely in the GC-O profiling of wines (Guth 1997a) and only as a complementary
technique of a total extraction strategy.Surely this is because a large volume of
headspace has to be injected to obtain clear olfactometric signals, and the presence
of ethanol and water creates serious problems in the chromatography if such a large
volume is injected. In addition, in classicalstatic headspace there is no extract, so
that, the GC-O experiment must be carried out on wine, which could cause problems
arising from the stability and homogeneity of the samples if the experiment is going
to take a long time.
The second possibility is the use of dynamic headspace sampling. This technique
fulfils a priori the requirements for the preparation of extracts for screening by
GC-O. However, the presence of ethanol in the headspaces decreases by factors
as high as two orders of magnitude the capacity of the sorbents most frequently
used for the trapping of volatiles, such as Tenax TA or Porapack Q resins, which
helps to explain why the technique is only seldom used out of our laboratory (Le
Fur et al. 2003). This limitation can be solved by increasing the size of the trap,
by reducing the volume of sample, by using thermal desorption or by using a
most efficient sorbent. The solution given by Le Fur et al. (2003) makes use of
an automated purge and trap unit. Aroma volatiles are purged by a gentle stream
of nitrogen on a small volume of wine and are further trapped in a cartridge filled
with 140 mg of Tenax TA. The volatiles are finally thermally desorbed directly
in the chromatographic column. In this strategy a new aliquot of wine is required
each experiment and the analysis of their results suggests that the technique fails
in transferring to the column some less-volatile but potentially important odorants,
since the last odor detected corresponds toβ-phenylethyl alcohol. Such limitation
could be due to the difficult transference of those compounds from the trap to the
column. The solution given in our laboratory makes use of a type of new generation
sorbents, initially devised for the extraction of polar pesticides from water. These
sorbents have demonstrated to have an amazing ability not only to extract aroma
compounds from wine (Ferreira et al. 2004) but also to trap compounds present in
effluents (Lopez et al. 2003a, 2007). In relation to Tenax TA, these sorbents can
be up to 200 times more efficient, which makes it possible to use a relatively small
amount of sorbent (400 mg) to collect efficiently all the volatiles purged out from
80 mL of wine heated at 37◦C (and diluted with synthetic saliva) by a large stream