Meat + Poultry - June 2007 - 81

state or if spores are present. Certain
microorganisms, such as Clostrium and
Bacillus species, form a spore, which is a
resting state for the organism. Mold may
also form spores, which are more resistant. Table 4 shows the heat resistance
of the major pathogens. There are two
key terms to be aware of when it comes
to understanding heat resistance. These
are the D and Z values. D-values are the
time in minutes required to reduce the
number of organisms by 90 percent at
a given temperature. The Z-value is the
number of degrees one must traverse to
achieve a 90 percent reduction in the
number of organisms.
Heat resistance or thermal death
time is a rather complex science. The
heat resistance data shown in Table 2
are maximum reported heat resistance
values in buffer or in product. The heat
resistance of a microorganism, whether
it is a Clostridial spore or a Salmonella
sp., varies with product pH, water activity and product formulation. As the pH
drops from neutral values, that is, pH
6.0 - 7.0 to more acidic levels, the heat
resistance drops considerably. It is much
easier to destroy pathogens in acidic
foods than in neutral products.
Water activity also affects heat resistance. As water activity drops, the heat
resistance increases. The amount of fat
in a food also affects heat resistance.
Higher levels of fat impart greater heat
resistance. If a processor is manufacturing a product with high fat or reduced water activity, it is a good idea
to validate the heat resistance of target
pathogens in that product. One cannot simply assume the heat resistance
of a pathogen in a neutral pH will be
the same as that in a low water activity product.

Pathogens of concern
There are a number of microorganisms that will cause foodborne illness.
Table 3 lists some of these organisms,
the food in which they may be found
and the type of illness that they cause.
Table 2 shows how these organisms
may be inhibited or controlled. Some
of the pathogens presenting the great-

est threat to meat and poultry and some
of their characteristics follow:
Salmonella - Salmonella is an insidious creature. As is evident in Table 1,
it is most commonly found in proteinaceous foods, but has also been found
in many products used as ingredients
in formulated meat products. Salmonella has caused problems with several
products that one would never normally
suspect. A 1995 outbreak was traced to
beef jerky produced in New Mexico in
a facility that has since closed. Investigators were unable to determine whether
the cause was inadequate processing or
post-process contamination. Salmonella
has also cropped up in very unexpected
places. There was even an outbreak that
was traced to potato chips, which are
fried at between 350oF - 380oF. The cause
of the outbreak was a seasoning blend
that was contaminated with Salmonella.
Most formulated meats use some kind
of seasoning blend, so, given the nature of this organism, it is advisable to
set a zero tolerance for Salmonella on
all ingredients. For potentially sensitive
ingredients, processors are advised to
ask vendors for a certificate of analysis.
To determine what a sensitive ingredient is, conduct a risk assessment on the
ingredient and how it will be used. Of
course, processors relying exclusively
on certificates of analysis are asking for
trouble. If COAs are the only tool for ensuring Salmonella-free ingredients, it is
absolutely essential that each ingredient
for which one relies on a COA be verified at least once and preferably several
times a year.
Staphylococcus aureus - Staphylococcus aureus is one organism for
which processors spend far too much
time testing and writing into specifications. There are several problems with
S. aureus, however. One is that when
it grows in foods it generally does not
adversely affect flavor or appearance.
The second is that it is not the organism that causes problems but a heat
stable enterotoxin that the pathogen
produces. This toxin will survive in
dry products, including ingredients. It
is also found on the hands and in the

nasal passages of many humans and
is associated with infections such as
boils. This is one of the reasons persons with open wounds or sinus conditions should not work around food
being prepared. S. aureus is most often associated with foods containing a
protein source. Many of the problems
associated with summer time illnesses
are the result of staphylococcal enterotoxin that forms in meat-based salads.
Mayonnaise gets a bad rap here. It is
the meats, fish or eggs that provide the
food source. One of the major advances
in the meat processing industry in the
20th century was the development of
microbial cultures for the production of
fermented sausage products. The cultures help ensure the lactic acid bacteria grow quickly, thereby making the
environment very hostile for S. aureus.
Take a look at the products being produced and ingredients before writing
S. aureus into a specification. It may
be best to test for the enterotoxin and
not the organism, itself.
E. coli O157:H7 - While data for
other pathogens such as Salmonella indicates thousands of the organisms need
to be ingested to cause illness, ingestion
of only a few E. coli O157:H7 can cause
illness. It can cause simple gastrointestinal distress or become much worse.
If the organism gets into the system of
susceptible individuals, it can severely
damage the kidneys and cause death.
This stage is called Hemolytic Uremic
Syndrome or HUS. E. coli O157:H7 has
also been associated with recent outbreaks in fresh-cut spinach from the
Salinas Valley and the Taco Bell problems on the East Coast.
Listeria monocytogenes - This
is one of the relatively "new" pathogens, despite the fact that it has been
recognized as being a food and animal pathogen since the 1920's. Listeria
has been found in a large variety of
processing operations and foods. The
organism is, as noted earlier, a common environmental contaminant, so
practices which might contaminate the
food or allow the organism to grow in
a facility must be discouraged. Proper

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