Biology Reference
In-Depth Information
shrimps in brine composed of benzoic, citric and ascorbic acid were host
to
En. faecalis
-like,
Leuconostoc pseudomesenteroides
, coagulase-negative
Staphylococcus
and yeasts, whereas manually-processed shrimps also had
Ps. fl uorescens
,
En. malodoratus
,
Cb. maltaromaticum
and
Lb. sakei.
Adding
diacetate to the brine inhibited the growth of
Ps. fl uorescens,
coagulase-
negative
Staphylococcus
sp. and
Enterococcus
sp. When the brine contained
acetic, citric and lactic acid, the microfl ora was composed exclusively of
yeasts and LAB, such as
Lb. sakei,
which were responsible for unpleasant
sour and buttery odours. When the yeasts dominated the fl ora, 10
6
CFU/g
was enough to spoil the product.
Whatever the composition of the brine at the start of the process, the
spoilage microfl ora of brined, drained and MAP shrimps was dominated
by
Lb. sakei
. Spoilage of the industrial product led to sour fl avours and a
release of gas in the packaging, probably produced by
Lb. sakei
.
The spoilage of some brined shrimp samples with a reduced microfl ora
was due to oxidation rather than the microbial activity.
The microbial ecosystem of commercial, cooked, peeled, brined and
drained tropical shrimps (
Penaeus vannamei
) stored at 5°C and 15°C has
been studied using a polyphasic approach combining culture-dependent
and culture-independent methods including PCR-TTGE (Jaffrès et al.,
2009). When samples were spoilt, bacterial strains were isolated and
identifi ed by phenotypic and molecular tests. LAB constituted the major
group with principally
Carnobacterium
(
Cb. divergens, Cb. maltaromaticum
and
Cb. jeotgali
),
Enterococcus
(
En. faecalis and En. faecium
) and
Vagococcus
including the novel species
Vagococcus penaei
(Jaffrès et al., 2010). The other
groups corresponded to
Brochothrix thermosphancta
and
Enterobacteriaceae
(Serratia liquefaciens).
From PCR-TTGE profi les some of DNA fragments
were assigned to those of standard strains
(
Br. thermosphacta, Se. liquefaciens,
En. faecalis, Cb. maltaromaticum
and
Cb. divergens
) and additional informations
were provided by fragment cloning (
Psychrobacter
sp. and
Citrobacter
sp.).
Shrimps without Brine
Cooked, peeled, frozen or unfrozen Nordic shrimps without brine and
packed in a modifi ed atmosphere (50% CO
2
) had an initial pH of 7.7, a
salt content of 1.9% in aqueous solution and a TVBN of 10mg/100mg
(Mejlholm et al., 2005). If the product was frozen for 4 mon preceding
refrigerated storage then the initial concentration of microorganisms
was reduced, but the rate of growth, the maximum level of fl ora and the
shelf life remained the same. The latter was 26 d at 2°C, 16 d at 5°C and
10 d at 8°C. A low production of TVBN, lower than 20mg/100g, and no
production of TMA, organic acids or biogenic amines were observed.
From 116 isolates, Mejlholm et al. (2005) identifi ed 60%
Cb. maltaromaticum
,
