Biology Reference
In-Depth Information
been identifi ed as
Enterococcus faecalis
. This microorganism was probably
responsible for spoilage at these temperatures, but did not appear to
develop much, if at all, at temperatures between 0 and 8°C. The authors
also observed the presence of
Lactobacillus
curvatus
on tropical shrimps
stored at 0°C (Einarsson and Lauzon, 1995)
.
In continuing their studies on the fl ora isolated from these products,
Dalgaard et al. (2003) observed an evolution of the microfl ora from bacilli
to cocci between 5 and 8°C for Nordic shrimps and between 8 and 15°C
for tropical shrimps. At 25°C, the fl ora was dominated by cocci. Most
of the strains isolated at different temperatures had been identifi ed as
Carnobacterium
(Cb. divergens)
and
Enterococcus
(En. faecalis)
.
En. faecalis
was present on products stored at 15°C and higher whereas
Cb. divergens
and
Lb. curvatus
were found on products stored at 8°C and lower. Three
of the isolated strains correspond to an unknown
Carnobacterium
species.
At high concentrations,
En. faecalis
and
En. durans
could represent a health
risk for consumers. In this study, tyramine might represent a chemical
indicator of spoilage, but at these levels it was low enough not to present
a risk. Likewise, at low storage temperatures, the authors recommend that
the product should contain at least 3% salt in an aqueous solution so as to
avoid spoilage problems and health risks.
Mejlholm et al. (2008) studied Nordic shrimps that have been
either brined or brined and drained and then packed in a modifi ed
atmosphere. They focused on the effect of hygiene (during industrial or
manual processing), the composition of brine and the storage conditions
(atmosphere and temperature) on the overall evolution of the microfl ora
and the shelf life. Different groups of organic acids were tested: benzoic,
citric and ascorbic or acetic, citric and lactic, including the effect of
diacetate. The pH of brined shrimps was between 5.6 and 5.8. The shelf
life depended on the nature of the organic acids, their concentration, the
temperature and also the initial contamination, which had a signifi cant
effect. In fact, industrial products were more contaminated than products
processed manually, which led to shorter shelf lives and a more diverse
spoilage fl ora. This was especially true for brined and drained MAP
shrimps, which had a shelf life of over 75 d at 7°C for manually processed
products, but only 28-35 d for industrial products. Similarly, shrimps in
brine composed of acetic, citric and lactic acid had shelf lives of 69-84 d
and 42-49 d for manual and industrial products, respectively, at the same
temperature. The modifi ed atmosphere prolonged the shelf life of shrimps
from 53-60 d for brined shrimps to over 75 d for the same shrimps that
have been drained and packed in a modifi ed atmosphere, although these
results were not confi rmed by subsequent tests.
Brine composition infl uenced the nature of the fl ora that would
develop on the products. At the time of spoilage, industrially-produced
