Microbiological Aspects of Dairy Ingredients 79strains of salmonella have been shown to
grow slightly during cheddar cheese manu-
facture. In addition to the increase due to
entrapment during curd formation, salmo-
nella could be detected in cheddar cheeses
produced from cheese milk artifi cially con-
taminated with 10^5 cfu/ml salmonella after 9
months of ripening at pH 4.5, 10 ° C. Naturally
contaminated cheese recovered from a previ-
ous outbreak and ripened at 5 ° C contained
viable salmonella up to 240 days (D ’ Aoust
et al., 1985 ).
Leuschner and Boughtfl ower (2002) have
demonstrated the survival of three S. enterica
serovars — typhimurium , enteritidis, and
dublin — during the manufacturing stage of a
soft cheese which included a cooking step at
45 ° C for 4 hours. Low inocula (1 to 10 cfu/
ml) were used in the study and the strains
could be detected in the fi nal product at con-
centrations between 1 and 50 cfu/g after a
four - week storage period.
The manufacture of mozzarella and
cottage cheese, both of which have high
cooking temperatures, appears to eliminate
salmonella. Eckner et al., (1990) reported the
complete inactivation of salmonella during
the molding and stretching of mozzarella
cheese curd. McDonough et al. (1967)
reported similar inactivation of salmonella
during cottage cheese curd cooking at 52 ° C
for 20 minutes. However, caution must
persist with such products and ingredients
open to post pasteurization whereby contami-
nating organisms may survive even though
conditions do not favor growth.
Escherichia coli. Enterotoxigenic E. coli
(ETEC), enteroinvasive E. coli (EIEC), and
verotoxigenic E. coli (VTEC) have all been
linked to cheese - related outbreaks and spo-
radic cases (Table 3.3 ). While strains of the
VTEC group have emerged as the predomi-
nant public health concern, strains of EIEC
and ETEC have been linked to major cheese -
related outbreaks in the United States and
Europe (MacDonald et al., 1985 ; Marier
et al., 1973 ). In the large US multi - state andcattle, and farm environments (Marth, 1969 ;
Ryser, 2001 ). Other strains not typically
associated with dairy products and global
regions have also been isolated from out-
breaks, for example, S. stanley from Swiss
soft cheese (Pasture et al., 2008 ).
Raw milk used for cheese making can be
a source of salmonella. Isolation rates include
4.7% (US, McManus and Lanier, 1987 ),
8.9% (US, Steele et al., 1997 ), 0.1% (Ireland,
Rea et al., 1992 ), 2.9% (France, Desmasures
et al., 1997 ), 0% (Belgium, De Reu et al.,
2004 ), 0% (Switzerland, Stephan and
Buehler, 2002 ), and 0% (US; D ’ Amico and
Donnelly, 2008 ). Despite the number of
cheese - related salmonellosis outbreaks, sal-
monella are rarely recovered from commer-
cially produced cheeses.
Many studies have failed to isolate salmo-
nella from freshly prepared and aged cheddar
(Brodsky, 1984a, 1984b ), goat cheese (Mor -
Mur et al., 1992 ), raw milk and fresh cheeses
(De Reu et al., 2004 ; Coveney et al., 1994 ),
and raw and pasteurized ripened and semi -
hard cheeses (Little et al., 2008 ). In follow -
up investigations to some of the reported
salmonellosis outbreaks, the occurrences
within the cheese have been sporadic and
levels of salmonella were invariably below
10 organisms/100 g, which may suggest a
low oral infective dose. In addition, in many
of the outbreaks, the source of contamination
in the raw milk has been traced to a single or
small number of cows within a herd shedding
the organisms in their milk. Therefore, co -
mingling of milk and the dilution factor may
be considerable.
All salmonella are readily inactivated
by standard vat and HTST pasteurization.
Inadequate pasteurization or post pasteuriza-
tion contamination of milk can present an
issue for the cheese maker prior to cheese
making. Salmonella can grow, albeit slowly,
at 10 ° C to 20 ° C in fl uid milk.
The persistence of salmonella during the
manufacture and ripening of a number of
cheeses has been investigated. Different