series or parallel will combine to achieve
desired levels of safety. Therefore, with
respect to L. monocytogenes, we can think
of a number of hurdles to address this
pathogen. We know that we adequately
kill any Listeria organism that may exist
on our raw material with cooking
processes. We have decreased the likelihood of recontamination after cooking
by at least a factor of 50 in the last 10
years through sanitary equipment
design, better cleaning and sanitizing
procedures and “seek and destroy” environmental monitoring programs. These
hurdles keep the organism out of the finished product. Many companies go beyond this step to add additional hurdles
to either treat the product in the package
to inactivate any pathogens that made it
past the original hurdles or to add ingredients that will inhibit their growth.
Post-package approaches have a long
history of use in food processing. Canning was invented in 1810 by Nicolas
Appert to prevent spoilage (and toxic
botulinal growth) in foods used by
Napoleon’s army. The more mild thermal treatment of pasteurization was developed in the late 1800s and is effective
against vegetative microbes like
Salmonella, Listeria and lactic acid spoilage bacteria. Some consider these principles as
enabling the development of large-scale
food processing that has evolved over
the past 200 years. Modern refinements
have used computing power and
time/temperature lethality relationships
described in the Ball equation to verify
that thermal processes deliver safe RTE
foods for consumers. The last few
decades have also seen application of
ultra high-pressure treatment or exposure
of packaged products to ionizing radiation from gamma- or beta-ray sources to
achieve the same effects.
Two other approaches have been historically used to maintain safety of food
during distribution and storage. Drying
to reduce moisture content to a point
where bacteria cannot grow was once a
primary approach, but today, with the
advent of refrigeration and anaerobic
packaging, it is much less common. Salting or the introduction of ingredients or
additives that prevent or retard bacterial
growth also have a long history of use.
Sodium nitrite as a curing agent in meat
processing plays an important role in
botulinal and other pathogen protec-
tion. Salt and nitrite as two basic ingredi-
ents were considered sufficient for food
safety until 25–30 years ago when we
began to recognize that L. monocytogenes
infections had, among other causes, a
amounts are required. However, in com-
bination with sodium diacetate, realistic
levels can be used and a balance
achieved between growth inhibition and
product quality. Sodium diacetate is an
interesting ingredient. Chemically, it can
be considered a half-neutralized acetic
acid (often derived from vinegar) or a
“We know that we adequately kill any Listeria
organism that may exist on our raw material with
cooking processes.”
processed meat and poultry transmission
vector. Thus, in the late 1990s and early
2000s, a search was on at universities and
industry research and development
groups for other ingredients that could
be of use. The first wide-scale approach
involved addition of sodium or potassium lactate in combination with
sodium diacetate to cured RTE products.
Sodium and potassium lactate salts
were originally introduced to the meat
and poultry industry in the 1980s when
processed turkey products became much
more popular. This coincided with the
development of cook-in-the-bag packaging and processing advances for large-sized products used in foodservice. Since
poultry products were traditionally uncured (i.e., made without nitrite) and
had much lower salt levels than their red
meat counterparts, many in the industry
had a concern around the risk of botulinal growth under temperature abuse.
The lactate salts provided an additional
protective barrier or hurdle especially for
uncured, cook-in-the-bag products. They
had lesser use in sliced or repackaged uncured products because the contaminating bacteria introduced by such handling
were felt to provide a similar food safety
measure by spoiling the product before
pathogens could grow. The concept of
using bacterial spoilage of a product as a
food safety measure is no longer considered a reliable approach.
Lactate salts by themselves will in-
hibit the growth of Listeria in processed
meats; however, unreasonably large
complex of a molecule of acetic acid and
a molecule of sodium acetate. The
beauty of both lactate and diacetate is
that they are metabolites in human en-
ergy metabolism, so chemical safety con-
cerns about them as ingredients are
minimal. Meat also has a background
level of lactate between 0.5 and 1%, aris-
ing from the postmortem metabolism of
glycogen stores in muscle.
Effects on Foodborne Illness
It is noteworthy to look at the effects
of inhibiting growth on the likelihood of
illness. FDA and USDA released an
exhaustive risk analysis for foodborne listeriosis in 2003. In that report, the quantitative exposure to L. monocytogenes
versus the probability of illness and mortality was estimated for three groups of
humans: unborn children; normal; and
elderly, using the best available data at
the time. We still need more data to im-
