2.2.3. Odour (orthonasal) and aroma (retronasal) detection thresholds
method
Odour detection and recognition threshold values (orthonasal)
and the aroma detection threshold (retronasal) for guaiacol in orange
juice were evaluated using the forced-choice ascending concentration
method described by ISO (ISO, 2002). Thus, the Best
Estimate Threshold (BET) for each panellist as well as the group
BET for the whole panel was determined. The BET for each panellist
was calculated as the geometric mean from the highest concentration
that was not recognised as differing from the others and the
lowest concentration that was identified as differing from the
other samples in the test. The panel BET detection values for guaiacol
odour and aroma in orange juice were calculated as the arithmetic
mean of the BET of the 3 replicates for each panellist and for
each individual assessor replication.
Series of five three-alternative forced choice (3-AFC) tests were
presented to the panellists at one time. In each triangle test the
assessor is presented with three samples, one of which is the orange
juice spiked with the guaiacol and the other two being control samples
(with no guaiacol). The assessor is instructed to indicate the
differing sample for each discriminating test although they could
not perceive the difference. Samples within each set were presented
to assessors in random order and panelists were instructed
to smell from left to right. All evaluations were tested in triplicate.
The value for the detection threshold was defined as the level at
which the differing sample is selected correctly by the panel without
being able to describe the medicinal odour or aroma of the guaiacol.
The recognition threshold was defined as the level at which
the differing sample is selected correctly by the panel and they
could correctly describe the medicine odour or aroma of guaiacol.
2.3. Gas chromatography–mass spectrometry
Headspace Solid-Phase Micro Extraction, SPME, gas chromatography–
mass spectrometry (GC–MS) was used to isolate, concentrate
and quantify guaiacol in orange juice using the standard
addition method (Ouyang & Pawliszyn, 2008). Orange juice samples
were fortified with guaiacol from 0.5 to 100 lg/l.
Sampling was accomplished by adding a 10 ml aliquot of the
juice to a 40 ml glass vial fitted with a Teflon lined cap. The vial
headspace was purged with nitrogen before sealing with the cap.
The sample was equilibrated for 10 min in a 40 C water bath. A
SPME fibre (50/30 lm DVD/Carboxen/PDMS on a 2 cm StableFlex
fibre, Supelco Bellefonte, PA) was manually inserted into the vial
and exposed for 30 min, following the headspace sampling
technique developed in a previous orange juice guaiacol study
(Gocmen et al., 2005). To increase the diffusion of volatile
compounds from orange juice into the headspace, the juice was
stirred using a 4 mm magnetic stirring bar. The exposed SPME
was transferred to the GC injector and desorbed for 5 min at
240 C. All analyses were done in triplicate.
Analyses were performed using a Perkin/Elmer Clarus 500
quadrupole mass spectrometer equipped with Turbo Mass soft-