372 Chapter 21
not more than 560 degrees × hours when the
highest fermentation temperature is between
32 ° – 40 ° C, or less than 500 degrees × hours
when the highest fermentation temperature is
higher than 40 ° C. In this calculation, degrees
above 15 ° C are taken into account.
In the case of fermented sausages manu-
factured with the addition of lactic starter
culture, it is generally accepted that the safety
of these products is ensured by the combina-
tion of low pH (below 5.3) and low a w (below
0.95). It has to be mentioned, though, that
this pH - value remains as such mainly with
short fermented sausages and increases with
longer dried products (when, because of an
a w of lower than 0.95, safety is still guaran-
teed even with a higher pH - value), but a
rapid pH drop below 5.3 during incubation
period must not be omitted.
As for enterohemorrhagic E. coli and
Listeria monocytogenes , lower pH and
lower temperature have no such dramatic
inhibitory effect as on staphylococci, salmo-
nellae and other pathogenic bacteria. In 1994,
an E. coli O157:H7(EHEC) outbreak was
linked to (presliced) dry fermented salami in
the United States (Centers for Disease
Control and Prevention 1995a ; Tilden et al.
1996 ), followed by an outbreak in Australia
caused by a semidry fermented sausage
(Centers for Disease Control and Prevention
1995b ); since then, the good safety record of
dry sausages has been questioned, and drastic
treatments were worked out and required in
the United States, mainly because of ham-
burger - borne EHEC infections, hemolytic
uremic syndromes, and the resulting death
toll (Incze 1998 ). This kind of reaction has
not been typical in Europe, partly because
EHEC - infection is not so frequent, partly
because no dry sausage was involved and it
has been proven that EHEC growth is not
supported at an a w typical for dry sausage. It
has also been found that if sausages are
stored at ambient temperature, E. coli die
off through metabolic exhaustion (Leistner
2000 ).Products Manufactured with Lactic
Starter Cultures
Safety of the products that are manufactured
with the help of lactic acid starter cultures
relies on two bases: formation of lactic acid
and eventually some other compounds with
inhibitory effect (bacteriocins, peroxides,
etc.) on the one side, and the gradually
decreasing a w - value on the other. This
twofold effect, together with the possible
outgrowth of undesired microorganisms
from lactic acid bacteria, contribute to the
safety of a product where no other bacterio-
static or bactericidal treatment, such as
heating, high hydrostatic pressure, or irradia-
tion, is applied. It is of vital importance that
metabolic activity of lactic starter cultures
(i.e., formation of lactic acid and pH - drop
during the initial phase of ripening [incuba-
tion]) should take place as rapidly as possible
so that pathogenic and spoilage microfl ora
have no or very slight chance for growth;
otherwise, at a relatively high temperature of
incubation, they could grow. Although
Listeria monocytogenes and enterohemor-
rhagic E. coli are relatively tolerant to lower
pH, salmonellae and Staphylococcus aureus
are not; consequently, pH has to be lowered
in order to inhibit their growth. Since
Staphylococcus aureus tolerate lower a w ,
temperature has to be kept low until pH is
lowered. According to the voluntary guide-
lines of the American Meat Institute, tenure
of incubation above 15 ° C is considered criti-
cal, because above this temperature, growth
of staphylococci occurs. On the other hand,
high temperatures evidently affect the growth
of Staphylococcus aureus ; the higher the
temperature, the shorter the time that can be
tolerated in order to inhibit growth of staphy-
lococci, but this helps to retard growth of
other undesired microorganisms as well.
The process is correctly controlled if the
time elapse is not more than 720 degrees ×
hours until pH drops to 5.3, when the highest
fermentation temperature is below 32 ° C, or