Biomedical Engineering Reference
In-Depth Information
30 days of storage (25 °C) of the treated milk samples (Alpas and Bozoglu
2000
). In
another study, the combination of nisin and lysozyme with HHP improved inactiva-
tion of pressure-resistant
E. coli
in skim milk, although the effi cacy of the combined
treatment decreased as the fat content of milk increased (García-Graells et al.
1999
).
Lacticin 3147 is another lactococcal bacteriocin with a high potential for appli-
cation in the preservation of dairy foods (Ross et al.
1999
; O'Sullivan et al.
2002b
).
The effects of lacticin 3147 preparations on the inactivation of
L. monocytogenes
in
reconstituted demineralized whey poder and
S. aureus
in reconstituted skimmed
milk. Lacticin addition at 10,000 AU ml achieved a 0.7 log reduction in viability for
both bacteria after 30 min incubation, while 20,000 AU achieved a 2.1 log reduction
of the listeria population (Morgan et al.
2000
). Microbial inactivation increased
greatly when lacticin preparations were tested in combination with HHP treatments.
The combination of 250 MPa and lacticin 3147 resulted in more than 6 logs of kill
for both bacteria. It was also shown that the antibacterial activity in concentrated
preparations of this lacticin against
L. monocytogenes
and
S. aureus
could be
enhanced in combination with HHP treatment (150-275 MPa), thereby reducing the
amounts of bacteriocin required (Morgan et al.
2000
).
Only a few enterocins have been investigated in milks. For example, enterocin
CCM 4231 was able to inhibit
L. monocytogenes
and
S. aureus
in milk (Lauková
et al.
1999
). Enterocin AS-48 (50
g/ml) added to skim cow milk partially reduced
the population of inoculated
S. aureus
during the fi rst 10 h of incubation at 28 °C,
but did not avoid overgrowth at 24 h (Muñoz et al.
2007
). However, a lower bacte-
riocin dose (20
ʼ
g/ml) in combination with a mild heat treatment (65 °C, 5 min) was
highly effective in reducing the population of staphylococci in the milk below
detectable levels within the fi rst 8 h of incubation and also to avoid overgrowth of
staphylococci at 24 h.
Enterococcus faecalis
INIA 4 produces enterocin 4, which is
identical to enterocin AS-48. In bacteriocin fi ltrates prepared by cultivation of this
strain on skimmed ewe's milk, the levels of inoculated
L. monocytogenes
Ohio and
Scott A strains were reduced by 3.23 and 2.13 log CFU/ml respectively, after 24 h
incubation at 30 °C. Reductions obtained under similar conditions for a collec-
tion of
L. monocytogenes
strains isolated from dairy environments were in the
range of 0.52-3.48 log cycles (Rodríguez et al.
1997
). Enterocin AS-48 can now be
produced as a dry powder based on a whey permeate that is essentially free of dairy
allergens. Addition of this bacteriocin preparation to skim milk, rapidly inactivated
the inoculated
L. monocytogenes
cells and progressively reduced the counts of
S. aureus
(Ananou et al.
2010
).
Microbial inactivation in skim milk improved when bacteriocins were tested in
combination with PEF. The combinations of enterocin AS-48 with or without nisin
and PEF treatment increased the inactivation of
S. aureus
(Sobrino et al.
2009
). A
maximum of 4.5 logs reduction was achieved for AS-48 (28 AU/ml) and PEF
(35 kV/cm). This reduction factor increased up to 6 logs when 28 AU/ml of AS-48
and 20 IU/ml of nisin were added to the milk before PEF treatment. The combined
treatment extended the shelf life of milk by at least 1 week compared to a conven-
tional pasteurisation treatment.
ʼ
