Biology Reference
In-Depth Information
likely that this microorganism, or others resistant to CO
2
, is responsible for
the spoilage of packed seafood products (Van Spreekens, 1974; Dalgaard
et al., 1993). Indeed, Emborg et al. (2002) have shown that
Ph. phosphoreum
is the specifi c spoilage bacteria of MAP salmon. Hovda et al. (2007)
have shown that Atlantic halibut
(Hippoglossus hippoglossus)
packed in
a CO
2
/O
2
(50/50) enriched atmosphere has a microfl ora dominated by
Ph. phosphoreum
and, due to the presence of oxygen,
Pseudomonas
sp. as
well as
Brochothrix thermosphancta
on samples at the end of their shelf life.
Ph. phosphoreum
has also been found on pollock (Rudi et al., 2004) and
tuna from the Indian Ocean
(Thunnus albacares)
(Emborg et al., 2005).
Ph. phosphoreum
constitutes a heterogenic group whose taxonomy
has evolved over the last few years. Some strains isolated from seafood
products have characteristics that are not homogenous, notably in
luminous and non-luminous strains. For this reason, some of the strains
isolated from cod fi llets in a modifi ed atmosphere have been reclassifi ed
as
Ph. iliopiscarium
(Ast and Dunlap, 2005).
The effi ciency of MAP has also been demonstrated for warm-water
fi sh. Drosinos et al. (1997) and Drosinos and Nychas (1996) have identifi ed
Br. thermosphacta
as the dominant species on sea bream packed in a
CO
2
-enriched atmosphere (40%) at the end of their shelf life. This
microorganism could play a part in spoilage. Emborg et al. (2005) have
demonstrated that, for tropical tuna steaks, a CO
2
/O
2
(40/60) modifi ed
atmosphere is better than vacuum-packing for inhibiting the growth and
histamine production of the psychrotrophic,
Morganella
.
The combination of super-chilling and modifi ed atmosphere enabled
salmon fi llets to retain a high level of quality after 24 d of storage due to
the almost total inhibition of psychrotrophic bacterial growth (Sivertsvik
et al., 2003). The shelf life is 3 to 4 times longer than that of a refrigerated
product under air.
Shellfi sh
Amongst shellfi sh, Nordic and tropical shrimps are by far the most
consumed products worldwide and this section will be wholly devoted
to them.
Tropical shrimps (
Penaeus
sp.) are generally frozen shortly after catch
and sold frozen before being processed (usually cooked) on land. Nordic
shrimps
(Pandalus borealis)
are generally cooked after catch, sometimes
peeled, and then frozen.
The few studies concerning this product have shown that shrimps are
very sensitive to spoilage. This sensitivity is due to a relatively high pH
(> 7) and the fact that the intestinal tract containing enzymes and bacterial
fl ora is not removed immediately after catch. In addition, the muscle
contains large quantities of non-protein, water-soluble molecules such
