Biomedical Engineering Reference
In-Depth Information
further cooking (such as cold-smoked seafood products) is a matter of concern, and
therefore extensive work has been carried out on application of bacteriocins in this
fi eld (O'Sullivan et al.
2002
; Chen and Hoover
2003
; Drider et al.
2006
; Calo-Mata
et al.
2008
; Galvez et al.
2008
). Several bacteriocins (such as nisin, psicocins, diver-
cin or sakacin P) have been tested, either by addition of bacteriocin preparations
(either by immersion, spraying, or mixing with food matrix) bacteriocin injection,
or immobilisation on plastic fi lms or coatings. In vacuum-packaged CSS stored at
10 °C for 3 weeks, purifi ed sakacin P added at 12 ng/g or 3.5
g/g partially or com-
pletely inhibited growth of
L. monocytogenes
(Aasen et al.
2003
). It was also
observed that bacteriocin titres in salmon tissue decreased during storage, which
was attributed to proteolytic degradation of the bacteriocin.
Duffes et al. (
1999a
) tested the effect of adding semipurifi ed divercin V41 from
Carnobacterium divergens
V41 (isolated from trout intestine) and piscicolins from
Carnobacterium piscicola
V1 on
L. monocytogenes
inoculated in CSS stored at 4 or
8 °C. Crude extracts of piscicocins were bactericidal at 4 °C and 8 °C, while divercin
V41 inhibited (4 °C) or delayed (8 °C) growth. In CSS stored at 10 °C, purifi ed diver-
gicin M35 (50
μ
g/g) as well as concentrated culture supernatants reduced viable
counts of
L. monocytogenes
by 1 log CFU/g at the beginning of storage and inhibited
or retarded growth for up o 21 days (Tahiri et al.
2009a
,
b
). Total lactic acid bacteria
counts were not affected by bacteriocin addition. Vaz-Velho et al. (
2005
) applied
a different strategy, based on immersion of salmon-trout fi llets for 30 s in diluted
C. divergens
V41 supernatant, before the cold-smoking process. Two trials were car-
ried out, one in summer, where temperature during the smoking process reached
33 °C, and one in winter with a lower temperature. In the fi rst trial, the bacteriocin
treatment achieved a maximum 3-log cycles reduction of
Listeria innocua
viable
counts at week 1 of storage, followed by regrowth of the bacterium. In the second
trial, a stronger listericidal effect was obtained. No cells of
L. innocua
were found
after smoking or at the end of the storage period (Vaz-Velho et al.
2005
). These
results underline the infl uence of food processing conditions on the effi cacy of bac-
teriocins, particularly those conditions affecting growth of the target bacterium.
In vacuum-packaged CSS, growth of
L. monocytogenes
could be prevented by a
combination of carbon dioxide, nisin, NaCl, and low temperature (Nilsson et al.
1997
). Preservation of vacuum packed CSS stored at 5 °C with nisin (500 or
1,000 IU/g) initially reduced the cell numbers of
L. monocytogenes
but did not fur-
ther prevent growth of survivors (Nilsson et al.
1997
), a behavior typically observed
when bacteriocins are used at sub-inhibitory concentrations. For that reason, nisin
was tested in combination with other antimicrobials, including modifi ed atmosphere
packaging, in order to improve control of this pathogen. In experiments carried out
in a culture broth, the antilisterial effect of nisin was improved in the presence of
100 % CO
2
and increasing NaCl concentrations (0.5-5.0 % w/v). In CSS packed
under MAP (70 %/30 % CO
2
/N
2
), addition of 500 and 1,000 IU nisin/g inhibited
growth of
L. monocytogenes
considerably, with lag phases of 8 and 20 days, respec-
tively, and the levels of
L. monocytogenes
remained below 10 CFU/g during 27 days
of storage at both concentrations of nisin (Nilsson et al.
1997
).
μ
