Biology Reference
In-Depth Information
ready-to-eat shrimps represent the largest shrimp consumption in France.
They may or may not be peeled, are often packed under a CO
2
-enriched
protective atmosphere, and can also pass through brine containing salt
and different organic acids (citric, ascorbic, benzoic, etc.). Thanks to the
increasing consumption, the shrimp market has been steadily expanding
over the last 10 yr.
In the recent literature, knowledge of this product's microbiology
has focused on the Nordic shrimp
(Pandalus borealis)
. The fl ora of fresh
shrimps is greatly reduced during the cooking stage of processing
(70-80°C throughout) and the spoilage fl ora is seemingly the result of a
recontamination by Gram-positive bacteria before or during packaging. The
microorganisms are then selected according to the different characteristics
of the product and the storage conditions. More specifi cally, the shelf life
and development of the microfl ora depend on the initial contamination,
the characteristics of the product (i.e., brined or not) and the storage
conditions (modifi ed atmosphere, temperature). The combined effect of
these different parameters could create a barrier effect against microbial
development.
Brined Shrimps
From and Huss (1990) carried out one of the fi rst studies on brined Nordic
shrimps. The spoilage microfl ora was dominated at 5°C by yeasts and
LAB
(Streptococcus
sp.,
Lactobacillus
sp.). Another study by Einarsson and
Lauzon (1995) on brined Nordic shrimps demonstrated the importance
of benzoate and sorbate in preventing the development of fl ora at 4.5°C.
When the fl ora is fully developed, it is dominated by coryneform bacteria
and
Moraxella
sp.
Dalgaard and Jorgensen (2000) studied Nordic and tropical shrimps
(
Penaeus
sp.) that had been brined, drained, packed in a modifi ed
atmosphere and stored at different temperatures between 0 and 25°C. They
showed that the effect of temperature on shelf life was even greater than
with other seafood products. For example, batches at 8°C had a shelf life
15 to 33 times longer than those stored at 25°C. Certain variations in the
composition of the product, no matter how small, could have a large effect
on this shelf life. Thus, shelf life at 5°C was over 3 mon for tropical shrimps
containing 2.3% salt in an aqueous solution and over 6 mon for Nordic
shrimps with 3.3% salt. The initial pH of these products was between 5.7
and 5.9. TVBN levels were relatively low when the products were spoilt
(20 mg/100g at 15 and 25°C and 10 mg/100g at the end of the shelf life
for tropical shrimps stored at lower temperatures). Most of the spoilage
fl ora could not be identifi ed, but LAB made up an important part of the
total microfl ora, whatever was the storage temperature. Amongst these
bacteria, several strains isolated from products stored at 15 and 25°C had
