Biology Reference
In-Depth Information
3
Microbial Degradation of Seafood
Françoise Leroi*
and
Jean-Jacques Joffraud
INTRODUCTION
The fl esh of living fi sh is sterile. However, the skin, mucus, gills and the
gastro-intestinal tract contain signifi cant microfl ora. The composition of
the bacterial community is determined to a large extent by the bacteria in
the aqueous medium surrounding the fi sh when it is still in its larval stage
(Hansen and Olafsen, 1999) and thus it varies according to a large number
of hydrological parameters. The bacterial contents commonly observed
vary from 10
2
to 10
5
bacteria/cm² in the skin, 10
3
to 10
7
bacteria/cm² in the
gills and 10
3
to 10
5
bacteria/g in faeces (Abgrall, 1988). At the time of fi sh
death, there is fi rst a loss of freshness due to autolytic enzyme activity. Then
microorganisms present in the fi sh can contaminate the fl esh by moving
through the muscle fi bres or by spreading during the processing stages
(gutting, head cutting, fi lleting, etc.) and their activity leads to spoilage,
characterised by off-odours, taste and degradation of texture.
This chapter is devoted to the bacterial degradation of the fl esh of fi sh
and shrimp, the most consumed shellfi sh in the world. Molluscs are not
dealt with here because the process of bacterial degradation does not
usually begin before consumption and molluscs are most frequently eaten
alive or immediately after being cooked.
THE MICROFLORA OF LIVING FISH AND SHELLFISH
It is generally agreed that the fl ora of fi sh found in temperate waters consist
of Gram-negative psychrotolerant bacteria, whose growth is possible
at 0°C but optimal around 25°C. Among these, the majority belongs to
the subclass
of proteobacteria:
Pseudomonas
,
Shewanella
,
Acinetobacter
,
Ifremer, Laboratoire Science et Technologie de la Biomasse Marine, BP 21105, 44311, Nantes, France
*Corresponding author: Tel.: +33 2 40 37 41 72; Fax: 33 2 40 37 40 71; E-mail:
fl eroi@ifremer.fr
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