Initially, model curry sauces containing each of the six spices
(Table 1) were prepared and subjected to headspace analysis using
the MSNose. The model curry sauces containing the low levels of
spices (chili, black pepper and ginger; all at 0.7 g/100 g sauce)
showed no headspace ions that were different to the curry sauce
background. Curry sauces containing coriander, cumin and turmeric
(4 g/100 g), however, showed additional ions from the headspace
analysis. Since the MSNose technique is designed to monitor
known compounds, GC–MS of the headspace above the curry
sauces was performed to assign compounds to the ions observed
in the MSNose spectra. Linalool (MW = 154) has been reported as
a key volatile compound in coriander (Raghavan, 2006) and GC–
MS analysis of the headspace above curry sauce containing 4 g/
100 g coriander showed linalool was the most abundant peak
(Fig. 1a). MSNose analysis showed the major ion in the coriander
curry sauce occurred at m/z 137 and this was proposed as the protonated
dehydrated molecular ion (M+HH2O)+ ion after headspace
of a pure linalool standard in water also produced this ion
in the MSNose spectrum. Accordingly, the ion at m/z 137 was selected
as a marker ion for coriander.
For the cumin curry sauce samples, GC–MS analysis of the headspace
showed a major peak that was identified as cuminaldehyde
(Fig. 1b), in line with the composition reported previously
(Raghavan, 2006). In the MSNose spectrum, m/z 149 was the most
abundant ion and this was tentatively associated with the
protonated molecular ion of cuminaldehyde (MW = 148) after
headspace analysis of pure cuminaldehyde in water by MSNose
produced the same major ion. Hence, the ion at m/z 149 was used
as the marker ion for cumin.