Biology Reference
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et al., 2001), associated with the production of H
2
S, acetic acid, ethyl and
n-
propyl-acetate (Joffraud et al., 2001), but some strains of
Lb. sakei
do
not spoil the organoleptic qualities of this product (Weiss and Hammes,
2006). Similarly,
Lb. alimentarius,
which does not spoil smoked salmon, has
been identifi ed as the bacteria responsible for the sensory deterioration
of marinated herrings (Lyhs et al., 2001). The role of Carnobacteria is still
under study (Laursen et al., 2005; Leisner et al., 2007). Many studies have
shown that they are probably not responsible for spoilage in smoked
salmon. Inoculation by different strains of
Carnobacterium maltaromaticum
and
Cb.
divergens
results in no or few changes in organoleptic qualities
(Leroi et al., 1996; Paludan.Müller et al., 1998; Duffes, 1999; Nilsson
et al., 1999). When the Carnobacteria reach a suffi cient level, odours of
butter and plastic may be detected, associated with the production of 2,3-
butanedione (diacetyl) and 2,3-pentanedione (Joffraud et al., 2001; Stohr et
al., 2001), but these odours/fl avours do not lead the product to be rejected
by a specialist jury (Brillet et al., 2005).
Among the other bacteria frequently found in smoked salmon, Stohr
et al. (2001) showed that
Serratia liquefaciens
spoiled a lot, releasing
odours of amines, cheese, acid or rubber, associated with the molecules
TMA, dimethyldisulphur, 2,3-butanediol and 2-pentanol (Joffraud et
al., 2001). However,
Se. liquefaciens
was considered to spoil less than
Lb.
sakei
as the unpleasant odours were perceived much later (Joffraud et al.,
2006).
Brochothrix thermosphancta
also leads to the sensory rejection of the
product due to the odours of blue cheese and plastic, well correlated with
2-heptanone and 2-hexanone. Nevertheless, it is quite rare for these bacteria
to reach suffi ciently high levels in naturally contaminated products to be
the sole explanation for sensory rejection. Although strongly spoiling in
fresh fi sh packed in a modifi ed atmosphere,
Ph. phosphoreum
seems to
play a more moderate role in the deterioration of smoked salmon. Weak
odours of “acid”, “amine” and “feet” result in the product being judged
as moderately spoilt (Joffraud et al., 2006). Moreover, there is a great
variability according to the strain (Leroi et al., 1998; Stohr et al., 2001).
Jorgensen et al. (2000b) give much greater weight to the spoiling action
of this species. They have shown a good correlation between the sensory
quality of smoked salmon and the production of tyramine and histamine
(Jorgensen et al., 2000a), two potential chemical indicators
for spoilage.
Shewanella putrefaciens,
the most common spoilage bacteria in fresh fi sh,
and
Vibrio
sp. have never been implicated in the spoilage phenomena in
smoked salmon, even when inoculated at high concentrations.
Although the bacteria responsible for sensory deterioration are now
quite well identifi ed, spoilage remains a complex phenomenon because the
interactions between all these bacterial groups change their metabolism.
For example, when
Lb. sakei
was co-inoculated with
Se. liquefaciens
, spoilage
