Biomedical Engineering Reference
In-Depth Information
cells were detected in any of the cheese samples inoculated with bacteriocin producers.
The authors concluded that the application of reduced pressures combined with
bacteriocin-producing enterococci can improve cheese safety while decreasing the
deleterious effects on cheese quality caused by HHP at higher pressures.
During the manufacture of smear-ripened cheeses, smear operations increase the
risk for surface contamination and cross-contamination with
L. monocytogenes
. In
the process of Taleggio smear cheese making, inoculated
E. faecium
7C5 was
reported to produce bacteriocin (Giraffa et al.
1995a
) and to inhibit the growth of
L. monocytogenes
Ohio on the cheese surface (Giraffa and Carminati
1997
). When
E. faecium
WHE 81, a multi-bacteriocin producer isolated from Munster cheese,
was inoculated on the cheese surface during smearing operation, further inoculation
of the cheeses with a low level inoculum of
L. monocytogenes
(50 CFU/g) resulted
in suppression of the listeria or its complete growth inhibition compared with the
controls inoculated with a bac
−
strain (Izquierdo et al.
2009
). The inoculated entero-
cocci had no detrimental effects on the on pH, fungal fl ora or pigmented bacteria in
the cheese rind during ripening.
Thermophilic streptococci are important as dairy starters used in large scale in
the production of yogurt and certain cheese varieties. The bacteriocin-producer
strain
Streptococcus salivarius
subsp.
thermophilus
B was tested as a thermophilic
starter in yogurt to control
L. monocytogenes
and
S. aureus.
The counts of
Listeria
were reduced below detectable levels, but the staphylococci survived in the pro-
duced yogurt. Use of the bac + starter was reported to extend the product shelf-life
by 5 days (Benkerroum et al.
2002
).
Pediococci are not well adapted to dairy substrates, due to their lack or very slow
lactose fermentation activity (Papagianni and Anastasiadou
2009
). However, some
strains such as
Pediococcus acidilactici
NRRL-B-18925 are particularly effective in
producing bacteriocin in milk based media. Since pediocin PA-1/AcH is not inhibi-
tory to bacterial species employed as yogurt starters (Gonzalez and Kunka
1987
)
there is a great interest for application of producer strains in developing more natu-
rally preserved yogurts and to avoid proliferation of cross-contaminating pathogens
during yogurt processing. Vedamuthu Ebenezer (
1995
) patented a method for pro-
ducing a yogurt product which contains bacteriocin active against undesirable
microbiota. The yogurt product can be dried for use in various foods. Pediocin pro-
duction in milk has been reported in coculture with yogurt starter cultures, at the
expense of the excess sugar released from lactose hydrolysis by the starters (Somkuti
and Steinberg
2010
). While no bacteriocin production was detected when
P. acidi-
lactici
was inoculated into milk as a monoculture, when grown in combination with
the yogurt starter cultures
Streptococcus thermophilus
and
Lactobacillus delbrueckii
ssp.
bulgaricus
, pediocin concentration reached 3,200-6,400 units/ml after 8 h of
incubation.
The development of pediocin-producing genetically-engineered
L. lactis
strains
can be another approach to solve the problems associated with the use of pediococci
in dairy substrates. Pediocin-producing lactococci have shown signifi cant potential
for inhibition of foodborne pathogens in cheeses. Examples are recombinant
L. lactis
MM217 as a pediocin-producing starter culture in Cheddar cheese (Buyong et al.
