3.2. Gas chromatography–mass spectrometry results
Headspace solid phase micro extraction, SPME, is a solvent-free
sample preparation technique which combines both extraction and
concentration of headspace volatiles in a single step (Zhang &
Pawliszyn, 1993). In the present study, the sample was equilibrated
at 40 C for 10 min and the fibre exposed 30 min as these
conditions had been shown in an earlier study (Gocmen et al.,
2005) to produce an optimum balance between exposure time
and amounts of off-flavour volatiles captured.
3.2.1. MS spectral identification of guaiacol in orange juice
Fig. 1 shows the mass library spectrum of guaiacol versus the
spectrum from the peak thought to be guaiacol from an orange
juice which possessed a medicinal off flavour (LRI 1899). It can
be seen that the three major mass fragments for guaiacol occur
at m/z 124 (M+), m/z 109 (the base ion, which corresponds to the
loss of a methyl group) and m/z 81. All major mass fragments from
standard guaiacol were also seen in the fragmentation pattern
from the corresponding off flavoured orange juice peaks. Thus, by
having two independent means of identification and as the retention
time and mass spectrum matched that of standard guaiacol,
the peak from the orange juice sample can be identified as guaiacol
with a high degree of confidence (Molyneux & Schieberle, 2007).
3.2. Gas chromatography–mass spectrometry resultsHeadspace solid phase micro extraction, SPME, is a solvent-freesample preparation technique which combines both extraction andconcentration of headspace volatiles in a single step (Zhang &Pawliszyn, 1993). In the present study, the sample was equilibratedat 40 C for 10 min and the fibre exposed 30 min as theseconditions had been shown in an earlier study (Gocmen et al.,2005) to produce an optimum balance between exposure timeand amounts of off-flavour volatiles captured.3.2.1. MS spectral identification of guaiacol in orange juiceFig. 1 shows the mass library spectrum of guaiacol versus thespectrum from the peak thought to be guaiacol from an orangejuice which possessed a medicinal off flavour (LRI 1899). It canbe seen that the three major mass fragments for guaiacol occurat m/z 124 (M+), m/z 109 (the base ion, which corresponds to theloss of a methyl group) and m/z 81. All major mass fragments fromstandard guaiacol were also seen in the fragmentation patternfrom the corresponding off flavoured orange juice peaks. Thus, byhaving two independent means of identification and as the retentiontime and mass spectrum matched that of standard guaiacol,the peak from the orange juice sample can be identified as guaiacolwith a high degree of confidence (Molyneux & Schieberle, 2007).
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