Biology Reference
In-Depth Information
27%
Br. thermosphacta
and 13%
Psychrobacter
sp. When inoculated together,
Cb. maltaromaticum
and
Br. thermosphacta
produced the same unpleasant
odours as spoiled products that had been contaminated naturally. This
was not the case when the two products were inoculated separately. The
mechanisms of this interaction had not yet been explained. The presence
of
Br. thermosphacta
had already been observed in MAP fi sh. Furthermore,
this microorganism had already been described as producing odours of
butter, blue cheese or feet.
Cb. maltaromaticum
produced an unpleasant
chlorine odour whereas in previous studies this bacterium was described
as non-spoiling only producing a buttery odour.
Psychrobacter
sp. did not
seem to play a part in the spoilage of cooked shrimps.
The potential for spoilage by
Carnobacterium
on cooked, peeled, MAP
Nordic shrimps without brine varied depending on the species and the
strain (Laursen et al., 2005).
Cb. divergens
and some
Cb. maltaromaticum
produced unpleasant odours whereas another group of
Cb. maltaromaticum
was not spoilt. Spoilage bacteria produced ammonia, tyramine, different
alcohols, aldehydes and ketones. These authors had confi rmed that
Br.
thermosphacta
and
Cb. maltaromaticum
cultured together led to some
bad odours (wet dog) those were not produced when these species
were grown separately. However, this association did not produce new
metabolites and consequently the “wet dog” odour did not come from
a metabiotic phenomenon in which a bacterium produced a metabolite
from a substrate formed by another bacterium. On the other hand,
Cb. maltaromaticum
decreased the formation of diacetyl by
Br. thermosphacta
and the latter reduced the activity of
Cb. maltaromaticum
. The “wet dog”
smell might be due to the interaction between metabolites formed by
Cb. maltaromaticum
,
Cb. divergens
, and partly by
Cb. mobile,
and those formed
by
Br. thermosphacta
. The presence of oxygen increased the potential for
spoilage and the number of metabolites produced by
Br. thermosphacta
. In
fact,
Br. thermosphacta
can be aerobiotic or anaerobiotic depending on the
respective percentages of O
2
and CO
2
. To reduce the potential for spoilage
in shrimps, it is therefore recommended to use an atmosphere with less O
2
and more CO
2
.
In contrast to cooked, peeled, MAP shrimps without brine, in which the
specifi c spoilage bacteria was well defi ned (Mejlholm et al., 2005; Laursen
et al., 2006), the characteristics of the spoilage fl ora of brined or brined/
drained and MAP shrimps were not as clearly established. The composition
of this spoilage fl ora depended on a large number of parameters: the initial
contamination, the preservation parameters (organic acids and salt) and
the storage conditions (atmosphere, temperature).
