Biomedical Engineering Reference
In-Depth Information
While the single antimicrobial packaging treatment was able to inhibit growth of
L.
monocytogenes
during the fi rst 8 days of storage at 6 °C, and the single HHP pre-
treatment attained a ca. 3.4 logs reduction of viable counts for about the same period
followed by regrowth of the listeria in both cases, the combined treatment extended
the lag phase of listeria to 22 days, and the slight growth observed afterwards did not
exceed 1.8 log CFU/g by the end of storage (day 60). For samples stored at 1 °C, the
combined treatment of HHP and enterocin fi lm caused a faster decline of
L. mono-
cytogenes
counts compared to HHP alone, but no regrowth was observed in either
case for 60 days, suggesting that at the lower temperature of storage, antimicrobial
packaging did not give additional protection against
L. monocytogenes
to pressur-
ized samples. However, after a simulated cold-chain break event at day 60, there was
a dramatic increase in the
L. monocytogenes
population for single HHP treatments
(8.5 log CFU/g), indicating the capacity of pressure-injured
L. monocytogenes
cells
to recover under favourable conditions. By contrast, for the combined treatment of
HHP and enterocin fi lms, the temperature abuse resulted in a slight increase until 1.7
log CFU/g at 90 days. The authors concluded the combination of antimicrobial pack-
aging with HPP could be useful to control and reduce the numbers of
L. monocyto-
genes
and to overcome temperature abuse. In a similar study, Jofré et al. (
2008
)
tested the effectiveness of the application of interleavers (composed by polypropyl-
ene/polyamide layers) containing enterocins A and B, sakacin K, nisin A, potassium
lactate and nisin plus lactate alone or in combination with a 400 MPa HHP treatment
in sliced cooked ham spiked with
Salmonella
spp. It was concluded that nisin was
the only treatment that produced absence of
Salmonella
24 h after pressurisation and
the application of nisin through interleavers and combined with an HHP treatment
appears as the most effective treatment to achieve absence of
Salmonella
in 25 g
samples during refrigeration storage of the sliced ham (Jofré et al.
2008
).
4.1.3
Fermented Meats
Bacteriocin preparations can be added to meat batters for reduction of the initial
levels of bacteriocin-sensitive populations and inactivation of microbial pathogens
in fermented meat products. The lower pH attained in sausages compared to fresh
meats may increase the solubility of some bacteriocins like nisin, and probably their
antimicrobial activity as well. Microbial inactivation by bacteriocin addition may
also be an attractive hurdle for slightly fermented sausages, in which the higher pH
and water content may facilitate survival and proliferation of certain pathogenic
bacteria.
Several bacteriocins such as nisin, enterocins (CCM 4231, A, B and AS-48) or
leucocins improved the reduction of
L. monocytogenes
or
S. aureus
populations in
fermented meats (Rodríguez et al.
2002
; Chen and Hoover
2003
; Aymerich et al.
2008
; Galvez et al.
2008
). Addition of nisin alone was effective in preservation of
bologna-type sausages against LAB spoilage (Davies and Delves-Broughton
1999
)
and in the inhibition of
L. monocytogenes
in sucuk, a Turkish fermented sausage
