Comparison of Clostridium perfringens spore germination and outgrowth in cooked uncured products
during cooling for different meat species is presented. Cooked, uncured product was inoculated with
C. perfringens spores and vacuum packaged. For the isothermal experiments, all samples were incubated
in a water bath stabilized at selected temperatures between 10 and 51 C and sampled periodically. For
dynamic experiments, the samples were cooled from 54.4 to 27 C and subsequently from 27 to 4 C for
different time periods, designated as x and y hours, respectively. The growth models used were based on
a model developed by Baranyi and Roberts (1994. A dynamic approach to predicting bacterial growth in
food. Int. J. Food Micro. 23, 277e294), which incorporates a constant, referred to as the physiological
state constant, q0. The value of this constant captures the cells’ history before the cooling begins. To
estimate specific growth rates, data from isothermal experiments were used, from which a secondary
model was developed, based on a form of Ratkowsky’s 4-parameter equation. The estimated growth
kinetics associated with pork and chicken were similar, but growth appeared to be slightly greater in
beef; for beef, the maximum specific growth rates estimated from the Ratkowsky curve was about
2.7 log10 cfu/h, while for the other two species, chicken and pork, the estimate was about 2.2 log10 cfu/h.
Physiological state constants were estimated by minimizing the mean square error of predictions of the
log10 of the relative increase versus the corresponding observed quantities for the dynamic experiments:
for beef the estimate was 0.007, while those for pork and chicken the estimates were about 0.014 and
0.011, respectively. For a hypothetical 1.5 h cooling from 54 C to 27 and 5 h to 4 C, corresponding to
USDA-FSIS cooling compliance guidelines, the predicted growth (log10 of the relative increase) for each
species was: 1.29 for beef; 1.07 for chicken and 0.95 log10 for pork. However, it was noticed that for pork
in particular, the model using the derived q0 had a tendency to over-predict relative growth when the
observed amount of relative growth was small, and under-predict the relative growth when the observed
amount of relative growth was large. To provide more fail-safe estimate, rather than using the derived
value of q0, a value of 0.04 is recommended for pork.
Comparison of Clostridium perfringens spore germination and outgrowth in cooked uncured productsduring cooling for different meat species is presented. Cooked, uncured product was inoculated withC. perfringens spores and vacuum packaged. For the isothermal experiments, all samples were incubatedin a water bath stabilized at selected temperatures between 10 and 51 C and sampled periodically. Fordynamic experiments, the samples were cooled from 54.4 to 27 C and subsequently from 27 to 4 C fordifferent time periods, designated as x and y hours, respectively. The growth models used were based ona model developed by Baranyi and Roberts (1994. A dynamic approach to predicting bacterial growth infood. Int. J. Food Micro. 23, 277e294), which incorporates a constant, referred to as the physiologicalstate constant, q0. The value of this constant captures the cells’ history before the cooling begins. Toestimate specific growth rates, data from isothermal experiments were used, from which a secondarymodel was developed, based on a form of Ratkowsky’s 4-parameter equation. The estimated growthkinetics associated with pork and chicken were similar, but growth appeared to be slightly greater inbeef; for beef, the maximum specific growth rates estimated from the Ratkowsky curve was about2.7 log10 cfu/h, while for the other two species, chicken and pork, the estimate was about 2.2 log10 cfu/h.Physiological state constants were estimated by minimizing the mean square error of predictions of thelog10 of the relative increase versus the corresponding observed quantities for the dynamic experiments:for beef the estimate was 0.007, while those for pork and chicken the estimates were about 0.014 and0.011, respectively. For a hypothetical 1.5 h cooling from 54 C to 27 and 5 h to 4 C, corresponding toUSDA-FSIS cooling compliance guidelines, the predicted growth (log10 of the relative increase) for eachspecies was: 1.29 for beef; 1.07 for chicken and 0.95 log10 for pork. However, it was noticed that for porkin particular, the model using the derived q0 had a tendency to over-predict relative growth when theobserved amount of relative growth was small, and under-predict the relative growth when the observedamount of relative growth was large. To provide more fail-safe estimate, rather than using the derivedvalue of q0, a value of 0.04 is recommended for pork.
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Comparison of Clostridium perfringens spore germination and outgrowth in cooked uncured products
during cooling for different meat species is presented. Cooked, uncured product was inoculated with
C. perfringens spores and vacuum packaged. For the isothermal experiments, all samples were incubated
in a water bath stabilized at selected temperatures between 10 and 51 C and sampled periodically. For
dynamic experiments, the samples were cooled from 54.4 to 27 C and subsequently from 27 to 4 C for
different time periods, designated as x and y hours, respectively. The growth models used were based on
a model developed by Baranyi and Roberts (1994. A dynamic approach to predicting bacterial growth in
food. Int. J. Food Micro. 23, 277e294), which incorporates a constant, referred to as the physiological
state constant, q0. The value of this constant captures the cells’ history before the cooling begins. To
estimate specific growth rates, data from isothermal experiments were used, from which a secondary
model was developed, based on a form of Ratkowsky’s 4-parameter equation. The estimated growth
kinetics associated with pork and chicken were similar, but growth appeared to be slightly greater in
beef; for beef, the maximum specific growth rates estimated from the Ratkowsky curve was about
2.7 log10 cfu/h, while for the other two species, chicken and pork, the estimate was about 2.2 log10 cfu/h.
Physiological state constants were estimated by minimizing the mean square error of predictions of the
log10 of the relative increase versus the corresponding observed quantities for the dynamic experiments:
for beef the estimate was 0.007, while those for pork and chicken the estimates were about 0.014 and
0.011, respectively. For a hypothetical 1.5 h cooling from 54 C to 27 and 5 h to 4 C, corresponding to
USDA-FSIS cooling compliance guidelines, the predicted growth (log10 of the relative increase) for each
species was: 1.29 for beef; 1.07 for chicken and 0.95 log10 for pork. However, it was noticed that for pork
in particular, the model using the derived q0 had a tendency to over-predict relative growth when the
observed amount of relative growth was small, and under-predict the relative growth when the observed
amount of relative growth was large. To provide more fail-safe estimate, rather than using the derived
value of q0, a value of 0.04 is recommended for pork.
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