Biology Reference
In-Depth Information
In smoked salmon, the major species are
Carnobacterium maltaromaticum
and
Lactobacillus curvatus
or
sakei
. Other species such as
Carnobacterium
divergens
,
Lactobacillus farciminis, Lb. alimentarius, Lb. plantarum,
Lb. homohiochii
,
Lb.
delbrueckii, Lb. casei, Lb. coryneformys
,
Leuconostoc
mesenteroides,
Enterococcus faecalis
and
Weisella kandleri
are more rarely
isolated (Leroi et al., 1998; Truelstrup Hansen et al., 1998; Jorgensen et
al., 2000b; Gonzales-Fandos et al., 2004; Rachman et al., 2004). Despite
this predominance, quite often the number of enterobacteria, strains of
Ph.
phosphoreum
and
Br. thermosphacta
are also fairly high (Truelstrup
Hansen et al., 1998; Jorgensen et al., 2000a; Jorgensen et al., 2000b; Rachman
et al., 2004). In contrast, yeasts are rarely present, except sometimes when
the product contains a high concentration of salt or phenol (Leroi and
Joffraud, 2000). Nevertheless, they do not reach high enough population
levels to contribute to spoilage. To illustrate the complexity of the fl ora of
smoked salmon, Gonzales-Fandos et al. (2004) have shown that out of 96
isolates coming from 30 batches of smoked salmon in Spain and preserved
for 3 wk at 2°C, 49% were LAB, 20% enterobacteria, 16% micrococci
(mostly coagulase-negative staphylococci), 5%
Br. thermosphacta
, 5%
Gram-negative
(Moraxella, Acinetobacter
and
Pseudomonas)
, 2.5% mobile
Aeromonadaceae and 2.5%
Bacillus.
Recently, temporal temperature or denaturating gradient gel
electrophoresis (TTGE, DGGE) molecular methods have been applied to
smoked salmon. In some cases, these techniques have given similar results
to the culture method (predominance of
Lactobacilli
,
Ph.
phosphoreum
and
Ph.
iliopiscarium
at the end of preservation) (Olofsson et al., 2007). In contrast,
Cambon-Bonavita et al. (2001) found clones corresponding to Gram-negative
bacteria
(Vibrio
,
Photobacterium
,
Enterobacteriaceae
,
Alteromonas)
and assumed
that this technique is biased because it does not allow a good amplifi cation
of the DNA of Gram-positive bacteria. Nevertheless, in both studies, clones
no doubt corresponding to new species of
Photobacterium
and
Vibrio
were
identifi ed by the culture-independent technique, underlining how these
tools can complement classic culture methods.
The role of LAB in the sensory deterioration of smoked salmon is still
not very clear. Several authors have shown that there is no correlation
between the total lactic fl ora and sensory spoilage. Paludan.Müller et al.
(1998), however, were able to prolong the shelf life of smoked salmon
by inhibiting LAB with nisine, suggesting a possible spoilage effect by
this bacterial group. By inoculating cubes of smoked salmon sterilised
by ionisation, Stohr et al. (2001) clearly demonstrated that certain species
of LAB spoilt a lot (i.e.,
Lb. sakei)
while others had no effect at all (i.e.,
Lb. alimentarius)
. However, the potential for spoilage seems to vary
according to the strain tested.
Lb. sakei
generally produces sulphurous and
acidic odours (Truelstrup Hansen et al., 1995; Nilsson et al., 1999; Stohr
