70 Chapter 3
ation was found. It is believed that a single
dose of 4.87 log 10 cfu could have been suf-
fi cient to cause illness among this particu-
larly susceptible group.
Olsen et al. (1988) and Holliday et al.
(2003) reported that L. monocytogenes can
grow between 7 and 14 days at 4 ° C, 13 ° C,
and 21 ° C in butter containing 1.2% salt.
Subsequent reduction in numbers of L. mono-
cytogenes is generally slower at refrigeration
temperatures (Holliday et al., 2003 ) com-
pared to elevated temperatures. Surveys of
butter samples in the United States and Italy
found no L. monocytogenes in samples tested
(Kozak et al., 1996 ; Massa et al., 1990 ).
Salmonella can grow in butter at 25 ° C and is
not eliminated by refrigeration or freezing
(Sims et al., 1970 ). The same authors reported
that NaCl content (1% to 4%) as usually
employed in the butter industry was not
appreciably bactericidal to S. typhimurium
var. copenhagen. Holliday et al. (2003) found
that salmonellae grew in sweet cream salted
butter at 21 ° C after inoculation and tempera-
ture abuse at 37 ° C. Escherichia coli 0157 : H7
has been shown to survive in butter and
butter production facilities (Abbar and
Mohamed, 1987 ) and growth was observed
in whipped salted butter (Holliday et al.,
2003 ). These authors reported a number of
factors infl uencing the growth, survival, and
inactivation of bacterial pathogens on butter,
yellow fat spreads, and margarine, including
fat content, pH, the presence of salt, and the
presence of other preservatives.Butter Spoilage
Commercially produced butter is less prone
to microbial spoilage than perhaps home-
made products. Microbial spoilage is caused
predominantly by psychrotrophic bacteria
because butter is normally stored under
refrigeration conditions. Like cream, Gram -
negative rods, including pseudomonads, may
contaminate the product post pasteurization
and can cause rancidity due to hydrolysisspoilage issues within the fi nal product, pro-
vided plant operation has not been defi cient.
Cream used for the traditional batch or con-
tinuous butter - making processes is generally
heated to 74 ° C to 80 ° C for 15 seconds and
cooled to 5 ° C to 8 o C, whereas cream for
ripened butters is usually pasteurized at a
higher temperature (90 ° C to 95 ° C for 15
seconds) or fl ash treated at greater than
100 ° C before cooling to ripening tempera-
tures (20 ° C to 27 ° C). The heat treatments
applied should be suffi cient to remove veg-
etative pathogens, lactobacilli, and other
microbial contaminants with thermoduric
microorganisms removed with the higher
temperatures applied to the cream for ripen-
ing. Furthermore, many butters are salted
(3% to 13%), which also helps with
preservation.
Butter Safety
Butter is generally regarded as a low - risk
product with regard to food poisoning,
although its use as an ingredient could present
growth conditions for pathogens (if present)
to proliferate and cause a health risk. The
increased use of large containers of butter
and other yellow fat spreads in restaurants,
kitchens, and homes, where containers are
frequently removed from refrigerated condi-
tions (temperature abuse), also leads to the
possibility of cross contamination.
Robinson (2002) noted that one cluster of
listeriosis in the United States was attributed
to butter contaminated by L. monocytogenes ,
and there have been a number of recalls of
butter contaminated with this organism. An
outbreak of listeriosis in Finland in 1998
and 1999 was attributed to butter contami-
nated with L. monocytogenes serotype 3a
(Lyytikainen et al., 2000 ). All 23 cases (6
deaths) were in a tertiary care hospital that
had been supplied with the butter in 7 - g pack-
ages. The outbreak strain was isolated from
the butter - producing equipment and the dairy
environment, although no error in plant oper-