The majority of Listeria species liberated both VOCs. L. grayi and
L. seeligeri did not liberate VOCs in quantifiable amounts therefore
VOCs were designated as not detected. L. seeligeri and L. grayi may
require a longer incubation time for the liberation of sufficient
VOCs for quantification purposes, particularly since Listeria species
are known to be slow growing [5]. The VOC profiles of all VOC
generating Listeria species are displayed in Fig. 3, which
particularly illustrates the overlapping of the VOC profiles of
L. monocytogenes NCTC 10357 and L. innocua. Although differentiation
of L. monocytogenes from all of the other Listeria species was
not possible, the detection of other Listeria species can be an
advantage. In addition, the different clustering for the VOC profiles
for both Listeria monocytogenes species could be useful to
investigate differences in metabolism between members of the
same species. The presence of non-pathogenic Listeria species can
often be an indicator of inadequate standards of hygiene during
food production and therefore the non-pathogenic species are
often regarded as a marker for L. monocytogenes [