Biomedical Engineering Reference
In-Depth Information
lactococci. Food-grade lactococcal starters which produce the lantibiotics lacticin
3147 and lacticin 481 have also been reported (O'Sullivan et al.
2003
). Lacticin
production by lacticin 3147 modifi ed starters successfully inhibited
L. monocyto-
genes
in Cottage cheese, in semi-hard raw-milk cheeses and on the surface of a
mould-ripened cheese and smear-ripened cheese (O'Sullivan et al.
2006
). In Cottage
cheese inoculated with a
L.lactis
transconjugant strain, the bacteriocin concentra-
tion in the curd reached 2,560 AU/ml, and bacteriocin activity could be detected
throughout the 1 week storage period. In cottage cheese samples held at 4 °C, there
was at least a 99.9 % reduction in the numbers of
L. monocytogenes
Scott A in the
bacteriocin-containing cheese within 5 days, whereas in the control cheeses, num-
bers remained essentially unchanged. At higher storage temperatures, the kill rate
was more rapid (McAuliffe et al.
1999
). In a smear-ripened cheese, applications of
a live lacticin 3147-producing culture on a cheese surface containing
Listeria,
the
viable cell concentrations of the pathogen were found to be up to 100-fold lower
than in the cheese treated with a bac-
L. lactis
strain as control. The lactococci have
also been tested for heterologous production of other bacteriocins such as enterocin
A. The resulting starter derivative successfully controlled the levels of
L. monocyto-
genes
during Cottage cheese fermentation (Liu et al.
2008
).
Enterococci are well adapted to grow in milk, and can produce suffi cient bac-
teriocin amounts in milk substrates as to inhibit pathogenic bacteria such as
L.monocytogenes
and others. For example,
E. faecalis
EJ97 produced enterocin
EJ97 during cocultivation in half-skimmed milk, although its capacity to control
L. monocytogenes
was limited to listerial populations of low densities (
10
3
CFU/
ml; García et al.
2004
).
Enterococcus faecium
strain F58, isolated from Moroccan
jben goat's cheese, was also able to produce bacteriocin in milk and to achieve a
partial inhibition of
L. monocytogenes
during cocultivation in goat milk (Achemchem
et al.
2006
). In addition, pre-cultivation of strain F58 in milk for 12 h before inocula-
tion of the listeria (at 3 log CFU/ml) produced enough bacteriocin to completely inacti-
vated the inoculated listeria during further incubation. The enterocin AS-48 producer
strain
E. faecalis
A-48-32 was able to produce enough bacteriocin in nonfat cow
milk to reduce the population of co-inoculated
B. cereus
below detectable levels
after 72 h of cocultivation at 30 °C (Muñoz et al.
2004
). In cocultures done with
skim milk, this strain was also able to control
S. aureus
(Muñoz et al.
2007
).
Enterococci are very often found as part of the adventitious microbiota in
fermented foods, including many traditional cheeses, and exhibit many biochemical
properties of technological interest in dairy fermentations such as production of
organic acids and acidifi cation, proteolytic and peptidolytic activities, lipolytic and
esterase activities, and citrate and pyruvate metabolism, together with their capacity
to produce bacteriocins (Giraffa
2003
). Bacteriocin-producing enterococci have
been investigated as adjunct cultures for cheese making because of their robustness,
natural presence in cheeses, and production of several bacteriocins with strong anti-
listerial activity (Giraffa
1995
; Foulquié Moreno et al.
2003
; Franz et al.
2007
;
Gálvez et al.
2008
). Inoculation of Jben goats' milk cheese with bacteriocinogenic
strain
E. faecium
F58 as an adjunct culture, caused a sharp decrease in the concen-
tration of viable
L. monocytogenes
, which were undetectable after 1 week of cheese
≤
