Biomedical Engineering Reference
In-Depth Information
On smoked salmon slices inoculated with
L. monocytogenes
and surface-treated
with nisin (400 or 1,250 IU/g) or ALTA™ 2341 (1 %), both antimicrobials reduced the
growth of listeria to some extent (Szabo and Cahill
1999
). When the treated smoked
salmon was packaged in 100 % CO
2
, counts of
L. monocytogenes
were reduced below
detectable levels (2 logs) in both cases during 21 days of storage at 4 °C. Addition of
these bacteriocins also showed a potential preservation and safety advantage if prod-
uct was exposed to short-term temperature abuse (Szabo and Cahill
1999
).
Chemical preservatives potassium sorbate, sodium lactate and sodium diacetate
have strong inhibitory effects on growth of
L. monocytogenes
in CSS. For smoked
salmon fi llets, the most effective treatment was 2.4 % sodium lactate/0.125 %
sodium diatetate, which was able to inhibit the growth of
L. monocytogenes
in
smoked salmon fi llets for 4 weeks of storage at 4 °C. Nisin showed greatest inhibi-
tory effects in combination with potassium sorbate (0.00125 % nisin/0.15 % potas-
sium sorbate), being able to inhibit the growth of
L. monocytogenes
to levels below
4 log CFU/g for 3 weeks (Neetoo et al.
2008b
). Addition of nisin or sodium lactate
also inhibited the growth of
L. monocytogenes
in cold-smoked rainbow trout, but
the combination of the two compounds was more effective (Nykanen et al.
2000
).
Nisin, sodium lactate or their combination were injected into rainbow trout at an
industrial scale before the smoking process, or injected into the fi nished smoked
product. Best results were obtained when the combination of nisin and sodium lac-
tate (120-180 IU nisin/g+18 g lactate/ kg) were injected into the smoked fi sh,
decreasing the count of
L. monocytogenes
from 3.26 to 1.8 log CFU /g over 16 days
of storage at 8 °C. In the fi sh injected before smoking, the combination of 3.6 %
sodium lactate and 240-360 IU/g nisin or 1.8 % sodium lactate and 120-180 IU/g
nisin inhibited growth of
L. monocytogenes
(to almost constant levels of 4.7-4.9 log
CFU/g) for 29 days at 3 °C in the vacuum-packed cold smoked samples (Nykanen
et al.
2000
). In both cases (before or after smoking), application of the combined
antimicrobial treatments did also reduce mesophilic aerobic counts in the cold-
smoked product. The treatments did not affect the sensory characteristics.
The effi cacy of bacteriocins in seafoods can improve with immobilisation in
packaging materials. Packaging CSS in plastic fi lm coated with bacteriocin from
Lactobacillus curvatus
CWBI-B28 caused
L. monocytogenes
inactivation late dur-
ing refrigeration storage (Ghalfi et al.
2006
). However, best results (complete inacti-
vation of
L. monocytogenes
during storage for 22 days) were reported for CSS
treated with bacteriocin adsorbed to its heat-inactivated producer cells. In CSS vac-
uum-packed inside nisin-coated plastic fi lms, nisin (2,000 IU/cm
2
) inhibited the pro-
liferation of a cocktail of
L. monocytogenes
strains (Neetoo et al.
2008a
). Viable
counts were 3.9 log CFU/cm
2
lower compared with controls for samples inoculated
with 5 × 10
2
CFU/cm
2
of
L. monocytogenes
after 56 days of storage at 4 °C or 49 days
at 10 °C. In addition, nisin inhibited the proliferation of background microbiota (aer-
obic, anaerobic, and LAB counts) on smoked salmon at both storage temperatures
although the bacteriostatic effect was much more pronounced at 4 °C (Neetoo et al.
2008a
). Chitosan dosed with 500 IU/cm
2
nisin slowed down growth of
L. monocyto-
genes
on CSS for 10 days at room temperature by approximately 1 log unit (Ye et al.
2008
). Chitosan-coated plastic fi lms dosed with sodium lactate (2.3 mg/cm
2
) in com-
