Biology Reference
In-Depth Information
The decarboxylation of amino acids leads to the formation of biogenic
amines, which are often linked to spoilage (Veciana-Nogues et al., 1997)
even though they have no particular odour in the product (Jorgensen et
al., 2000a). Tyrosine is a precursor of tyramine and cadaverine. Arginine
can be degraded into putrescine
via
the agmatine pathway in the presence
of arginine decarboxylase, as is the case with
Photobacterium
(Jorgensen
et al., 2000b)
.
Putrescine can also be produced by the decarboxylation of
ornithine, for example in the case of certain enterobacteria such as
Hafnia
alvei
and
Serratia liquefaciens
(Grimont and Grimont, 1992; Sakzaki and
Tamura, 1992). Histamine is a biogenic amine formed by the degradation of
histidine. It can provoke allergic-like reactions of varying intensity (redness
of the skin, swelling, headaches) and fi sh with high levels of histidine
are strictly regulated (Scombridae and Clupeidae, CE regulation NO.
2073/2005). In fi sh, the principal producers are mesophilic enterobacteria
such as
Morganella morganii, Hafnia alvei
and
Klebsiella pneumoniae
(Kim et
al., 2002; Kim et al., 2004), but recently psychrotolerant microorganisms
such as
Photobacterium phosphoreum
and
Morganella psychrotolerans
have
been clearly incriminated in cases of histamine poisoning (Kim et al., 2002;
Dalgaard et al., 2006).
SPOILAGE OF FRESH FISH AND SHELLFISH
Fish
Fish spoilage occurs at varying speeds depending on a large number of
parameters. Different fi sh species display a variety of surface characteristics
in terms of resistance of their skin texture and the composition of the mucus,
which may contain antibodies and bacteriolytic enzymes. Geographical
zone, in particular water temperature, also plays an important role as fi sh
from tropical waters keep much longer in ice than those from temperate
or cold waters. Rough handling of the fi sh can damage its integrity and
accelerate spoilage. The storage conditions (temperature and packaging)
also play a vital part in fi sh preservation.
When temperate-water sea fi sh (for example cod) are stored at chilled
temperatures, bacteria such as
Shewanella putrefaciens
are the specifi c
spoilage bacteria. Jorgensen et al. (1988) have shown that the number
of bacterial cells is inversely correlated to the remaining shelf life, and
consider that at approximately 10
8
CFU/g the sensory deterioration
of the product is no longer acceptable. The spoilage is characterised by
the production of TMA, H
2
S and other sulphurous compounds such as
methylsulphide and di-methylsulphide.
Sh. putrefaciens
consists of a
heterogeneous group whose taxonomy has greatly changed over the
last few years. Vogel et al. (2005) have shown that the large majority of
microorganisms that produce H
2
S isolated from Baltic Sea fi sh chilled
