posed to air (i.e., open packages) at
refrigeration.
Fermented and dried RTE meat products typically do not support the growth
of L. monocytogenes due to acidity, low
moisture and competition from the
starter culture. In fact, the pathogen decreases (dies off) on many of these products when held at room temperature or
under refrigeration. Behavior of L. monocytogenes and other foodborne bacterial
pathogens on both types of RTE meats
is reviewed below.
“When RTE meat products reach the packaging
environment in plants, they should be free of
harmful bacteria.”
Survival and Growth of
Foodborne Pathogens
Typical High-moisture, Non-fermented RTE
Meats
Researchers from Colorado State University simulated contamination of RTE
meats during slicing and handling at retail or at home.1 Uncured, cooked turkey
breast was vacuum-packaged and stored
at 4 °C ( 39. 2 °F) for 5, 15, 25 and
50 days before being opened, sliced and
inoculated with L. monocytogenes. Inoculated turkey breast was stored aerobically
in delicatessen bags at 7 °C ( 44. 6 °F) for
12 days. In this retail/home-contamina-tion simulation, mean growth rates
(log CFU/cm2/day) of the pathogen during aerobic storage ranged from 0.14 to
0.16 in product with lactate and diacetate, equating to about a 2-log increase
in L. monocytogenes on turkey breast
within about 14 days. In similar work
performed on cured ham with lactate
and diacetate, the growth rates ranged
from 0.18 to 0.25 log CFU/cm2/day, 2
equating to a 2-log increase on opened
packages of ham within about 10 days.
However, Pal and others from the
University of Minnesota3 did not see
growth of L. monocytogenes on cured,
sliced ham with lactate and diacetate
when stored in air at 8 °C ( 46. 4 °F). In
their work, growth rates of the pathogen
on uncured sliced turkey breast with lactate and diacetate were not markedly different at 8 °C ( 46. 4 °F) when stored in
vacuum-packages versus air. Times to
reach a 2-log increase were greater than
50 days.
Incidentally, the behavior of L. mono-
cytogenes in pork chops or ham does not
appear to be significantly different when
meat is vacuum-packaged versus modi-
fied atmosphere-packaged. 4 Packaging at-
mospheres comprised of 60% O2, 20%
CO2 and 20% N2 had only slight differ-
ences compared with 100% N2 on
growth of total viable bacteria and lactic
acid bacteria on cooked turkey breast
and pork sausage stored in film with an
OTR less than 35 cm2/m2.5
Fermented and Dried RTE Meats
Fermented and dried meats are not
favorable for the survival of vegetative
bacterial pathogens. E. coli O157:H7 declined slightly on fermented and dried
sausage during vacuum-packaged storage
for 8 weeks at 4 °C ( 39 °F). 10 A slight decline in E. coli O157:H7 was also observed on semidry cooked summer
sausage during vacuum-packaged storage
for 7 days at 4 °C ( 39 °F) and at 25 °C
( 77 °F). 11 Inoculated L. monocytogenes
declined on vacuum-packaged summer
sausage during storage over several weeks
at 4 °C ( 39 °F). 12
On a Norwegian-style fermented dry
sausage stored vacuum-packaged at 4 °C
( 39 °F) and 20 °C ( 68 °F), E. coli
O157:H7, L. monocytogenes and Salmo-
nella all declined by at least 1 log CFU,
and after 46 days, some of the pathogens
were undetectable. 13 These same three
foodborne pathogens were later shown
to decline on soudjouk-style fermented
semi-dry sausage stored vacuum-pack-
aged at refrigerated, ambient and abusive
temperatures.14 The rates of decline of
the pathogens increased with increasing
storage temperature. Others confirmed
that generic E. coli and L. monocytogenes,
as well as Yersinia enterocolitica, declined
when fermented sausage was stored in air
at 8 °C ( 46 °F) or 20 °C ( 68 °F). 15
