Thermal Inactivation of Salmonella senftenberg and Listeria innocua in
Ground Chicken Breast Patties Processed in an Air Convection Oven
R. Y. Murphy,*,1 E. R. Johnson,* B. P. Marks,* M. G. Johnson,† and J. A. Marcy‡
*Department of Biological and Agricultural Engineering and †Department of Food Science, and
‡Department of Poultry Science, University of Arkansas, Fayetteville, Arkansas 72701
patties were processed to a final center temperature of
70 to 80 C, 1 to 4 log10 (cfu/g) of S. senftenberg and 3 to
5 log10(cfu/g) of L. innocua were detected in the cooked
patties. A significant difference in the thermal inactivation
of S. senftenberg and L. innocua was obtained between the
chicken patties cooked in an air convection oven and
the patties cooked in a water bath. More surviving S.
senftenberg and L. innocua were found in the patties cooked
in an air convection oven than in the patties cooked in a
water bath.
ABSTRACT Ground chicken breast patties were thermally processed in a lab-scale air convection oven at air
temperatures of 163, 177, 190, 204, or 218 C to final patty
center temperatures of 50, 55, 60, 65, 70, 75, or 80 C. The
cooking time increased with increasing product temperature and decreased with increasing oven air temperature.
Prior to thermal processing, ∼7 log10(cfu/g) of Salmonella
senftenberg and Listeria innocua were inoculated into the
chicken patties. Survival of S. senftenberg and L. innocua
decreased with increasing patty temperature. After the
(Key words: poultry, Salmonella seftenberg, Listeria innocua, convection cooking)
2001 Poultry Science 80:515–521
medium and condition used and is difficult to apply in
commercial operations in which real products are processed under completely different sets of conditions such
as convection cooking.
In their studies, Simpson and Gilmour (1997) found that
the pressure tolerance of L. monocytogeneses was greatly
affected by the suspended medium. Similarly, Casadei et
al. (1998) also found that the heat resistance of L. monocytogenes in dairy products was affected by the growth medium. Therefore, the results derived from the studies in
liquid media are not adequate to determine the thermal
inactivation of pathogen in real food products under convection cooking (Murphy et al., 1999).
Poultry and poultry products could be one of the
sources of Salmonella infection in humans (Tietjen and
Fung, 1995; Peplow et al., 1999). Several studies have
established the D-values for Salmonella in liquid broth
(Goodfellow and Brown, 1978). Considerable research
had been done on the survival of Salmonella in various
cooked meat systems (Bayne et al., 1965; Wilkinson et al.,
1965; Bryan et al., 1968; Brown and Twedt, 1972; Goodfellow and Brown, 1978). Although the reported incidents of
listeriosis has decreased in recent years, L. monocytogenes
continues to be an extremely important foodborne pathogen, primarily due to the severe symptoms and high number fatalities from the disease (Simpson and Gilmour,
INTRODUCTION
Development of thermal processing methods to increase processing efficiency includes the goals of reducing
energy and labor costs, increasing volume, and improving
yield. However, any methods that achieve these goals
must be evaluated in terms of maintaining or improving
the bacterial safety of final products. Inadequate cooking
of meat product has been one of the major causes of
foodborne disease outbreak associated with pathogens
(Wang et al., 1996). Processing methods could directly
affect the bacterial safety of the finished meat. Therefore,
care must be taken to ensure that any process schedule
is capable of eliminating pathogens such as Salmonella
and Listeria monocytogeneses to guarantee the safety of
such processed food.
The heat resistance of pathogens can be affected by
many intrinsic and environmental parameters (Fernandez
and Peck, 1997; Murphy et al., 1999). One important factor
is the nature of the suspending medium (Simpson and
Gilmour, 1997; Murphy et al., 1999). Several previous
studies on the effects of temperature, pH, water activity,
and nitrite on pathogens were conducted in laboratory
medium (Whiting and Buchanan, 1994; Oscar, 1999). The
information from such studies is limited to the specific
Received for publication May 19, 2000.
Accepted for publication November 20, 2000.
1
To whom correspondence should be addressed: rymurph@comp.
uark.edu.
Abbreviation Key: FDA = Food and Drug Administration; TSB =
tryptic soy broth.
515
516
MURPHY ET AL.
1997). However, no complete information was found on
Salmonella and Listeria survival in convection-cooked
chicken products. Reports on thermal inactivation of Salmonella and Listeria in processed meat product by convection cooking are very limited in the literature. At the
time of present research, no studies were available in the
published literature on evaluating the potential for such
treatment to inactivate pathogens in internally and uniformly inoculated ground chicken patties.
The objective of this study was to evaluate the thermal
inactivation of Salmonella and Listeria in ground chicken
breast patties during convection cooking. Based on a previous study on thermal inactivation of Salmonella in
chicken meat, Salmonella senftenberg was the most heat
resistant among six Salmonella serotypes including S. senftenberg, S. typhimurium, S. heidelberg, S. mission, S. montevideo, and S. california (Murphy et al., 1999). Therefore, S.
senftenberg was used in this study.
Whereas it would be advantageous to monitor L. monocytogenes under actual process conditions, it is generally
undesirable to risk working with this pathogen in food
processing laboratories. Often, biological indicators are
used in challenge studies, because they are nonpathogenic and are typically more resistant than the pathogen,
providing the processor with a margin of safety (Fairchild
and Foegeding, 1993). Therefore, L. innocua M1 was used
in this study as an indicator organism for L. monocytogenes
(Fairchild and Foegeding, 1993).
This study was conducted in a laboratory convection
oven under five different air temperatures of 163 C (325
F), 177 C (350 F), 190 C (375 F), 204 C (400 F), and 218 C
(425 F) to an end-point product temperature of 50, 55, 60,
65, 70, 75, or 80 C. The survival of S. senftenberg and L.
innocua upon thermal processing was evaluated.
MATERIAL AND METHODS
Chicken Meat
Chicken breast meat was ground through a 3-mm diameter extruder.2 The proximate analysis was conducted
based on AOAC (1990) methods. The total water content
was ∼71% (wt/wt, wet basis), using an oven drying
method at 110 C for 24 h. The total protein content was
∼96% (wt/wt, dry basis), using the Kjeldahl method.3 The
total lipids content was ∼0.2% (wt/wt, dry basis), using
the Soxhlet4 method. The total ash content was ∼2.1% (wt/
wt, dry basis), using a gravimetric method and heating the
sample at 550 C in a muffle furnace5 for 24 h.
2
Tyson Foods, Inc., Springdale, AR 72764.
Labconco Unit, Labconco Corp., Kansas City, MO 63132.
4
Soxtec HT system, Fisher Scientific, Itasca, IL 60143.
5
Thermolyne Furnatrol 133, Fisher Scientific, Itasca, IL 60143.
6
American Type Culture Collection, Rockville, MD 20852.
7
P. M. Foegeding, Department of Food Science, North Carolina State
University, Raleigh, NC 27695.
8
DIFCO, Becton Dickinson and Co., Sparks, MD 21152.
9
Model 8287, 1450 W, Montgomery Ward Co., Inc., Chicago, IL.
3
Prior to the thermal treatments, the meat samples were
screened, per Food and Drug Administration (FDA)
methods (Andrews et al., 1995; Hitchins, 1995), for the
presence of naturally occurring Salmonella and Listeria and
were found free of both.
Bacterial Strains
Salmonella senftenberg (ATCC 43845)6 was purchased
from American Type Culture Collection. A nalidixic acidresistant culture of S. senftenberg was prepared by growing the organisms in basal medium (tryptic soy broth,
TSB) and adding increasing amounts of nalidixic acid.
Cells grown on 10 ppm of nalidixic acid media were
transferred sequentially to 20 ppm, then 40, 80, 100, and
finally 200 ppm of nalidixic acid media. One large colony
was streaked onto the agar containing 200 ppm of nalidixic acid and streaked again onto a new plate after incubation. The growth from this plate was used as the starting stock culture.
Listeria innocua M1 was obtained from P. M. Foegeding.7
The Listeria culture was resistant to 50 ppm of rifampicin
and 250 ppm of streptomycin. The lyophilized culture
was revived in TSB8 at 37 C for 24 h before use.
Culture Preparation
According to Heddleson et al. (1991), the maximum
heat resistance of bacteria occurred at 24 h in the stationary phase. Therefore, for each trial, a 24-h culture was
prepared individually at 37 C in TSB for Listeria and TSB
plus 200 ppm nalidixic acid for the Salmonella. The counts
for the Salmonella and Listeria in those 24-h cultures were
∼109 cfu/ml.
Preparation of Inoculated Chicken Patties
A known weight of refrigerated ground chicken meat
was transferred to a sterile mixer bowl and inoculated
dropwise with equal volumes of Salmonella and Listeria
to obtain ∼107cfu/g. Inoculated meat was mixed for 4
min to ensure even distribution of the organism. Then, the
inoculated ground chicken meat was weighed aseptically
into 30-g portions. A sterile former was used to form
patties of 50 mm diameter × 13 mm thick. The formed
patties were refrigerated (4 C) immediately after the inoculation until use for the cooking trial (∼2 h). Two of the
inoculated ground chicken patties served as controls.
Thermal Processing of the Inoculated
Chicken Patties
A convection oven9 with a cavity dimension of 375 mm
width × 254 mm height × 384 mm depth was used to
cook the inoculated chicken patties. An inoculated patty
was placed on a metal rack with diagonal-shaped openings of 42 mm length × 22 mm width. The meat on the
rack was placed in the center of the oven. The inoculated
patties were individually processed under various treat-
SALMONELLA AND LISTERIA IN COOKED CHICKEN
ment conditions at different combinations of air temperatures 163 C (325 F), 177 C (350 F), 190 C (375 F), 204 C
(400 F), and 218 C (425 F) and product temperatures 50.0,
55.0, 60.0, 65.0, 70.0, 75.0, and 80.0 (±0.5) C. Four type E
thermocouples were placed at the patty center (parallel
to the patty diameter), on the top and bottom surfaces,
and in the air to monitor the temperature via a data
acquisition system. After thermal treatment, the samples
were immediately removed from the oven, placed in a
sterile Stomacher bag, broken into smaller segments by
hand while still in the bag, and immersed in an ice-water
bath. The cooling process was <10 s.
Microbial Enumeration
Enumerations of Salmonella and Listeria were based on
FDA procedures (Andrews et al., 1995; Hitchins, 1995)
with the following modifications. The processed patty (30
g) was combined with 270 mL of sterile peptone solution
(0.1%) in a Stomacher bag and blended in the bag for 2
min. In each case, the strained fluid was serially diluted,
and 0.1 mL (for >10 cfu/g) or 1 mL (for <10 cfu/g) was
spread-plated over two or three plates, in duplicate, for
each dilution. A total of three to five serial dilutions were
plated for each treatment. Salmonella was plated on TSBN agar, containing 200 ppm of nalidixic acid,10 sodium
salt. Listeria was plated on TSB-YE-R-S agar, containing
0.6% yeast extract, 50 ppm of rifampicin,10 and 250 ppm
of streptomycin.10
The plates were incubated at 37 C for 24 to 72 h for
Salmonella and for 48 to 144 h for Listeria, and the colonies
were then counted. The plates were returned to the incubator each day and recounted until viable counts did not
increase. For the heated chicken meat samples, a minimum 144-h incubation was conducted to allow a completely recovery of heat-injured Listeria cells.
Thermal Inactivation Kinetics
Although the sample temperature does not vary with
the time, the thermal inactivation rate of Salmonella and
Listeria can be expressed as a first-order kinetic equation
(Toledo, 1991).
dN/dt = −kN
[1]
where N is the number of viable organisms at a given
time, t is time in min, and k is a reaction rate constant in
min−1, at t = 0, N = N0, which is the original number
at inoculation.
The reaction rate constant, k, is a function of temperature and the type of microorganism. The effect of temperature on the reaction rate constant, k, might be expressed
by an Arrhenius-type equation (Toledo, 1991).
10
Sigma, St. Louis, MO 63178.
CR23X Micrologger, Campbell Scientific, Inc., Logan, UT.
11
k = a e−E/RT
517
[2]
where a is an empirical constant (Arrhenius constant), R
is the gas constant in kilojoules per mole kelvin, T is
absolute temperature of sample in kelvin, and E is the
activation energy in kilojoules per gram mole. Substituting Equation [2] into Equation [1] and integrating from
t = 0 to t:
Ln (N0/N) = a ∫ e−E/RT dt
[3]
In this study, the sample temperature changed with
heating time during convection cooking. Therefore, in
Equation [3], parameter T was a function of heating time.
Empirical equations were be developed to establish the
relationship between the survivors of Salmonella and Listeria, the center temperature of patty, and the heating time
during convection cooking. A second-order polynomial
equation was used to describe the changes of patty center
temperature with heating time.
T = α t2 + β t + σ
[4]
where T is the patty center temperature in C; t is the
heating time in minutes; and α, β, and σ are the coefficient
of the quadratic term, the coefficient of the linear term,
and the constant, respectively.
A first-order regression was used to fit the changes of
Salmonella or Listeria survivors with heating time for the
ground chicken breast patties during convection cooking.
Log10(N) = δ t + η
[5]
where N is the survivors of Salmonella or Listeria in colonyforming units per gram, t is heating time in minutes, δ is
the slope of the linear regression, and η is the intercept
of the linear regression.
Calculation of Cumulative Lethality
The temperature-time history was recorded by the data
acquisition unit.11 The effective process lethality, F0 =
∫ 10(T−To)/z dt, was calculated based on the Simpson’s rule
(Toledo, 1991). T(t) was the transient temperature during
a process. The reference temperature To was 71.1 C. The
z values of 5.4 C (Veeramuthu et al., 1998) and 5.1 C
(Moody et al., 1998) were used in the integration of F0
for S. senftenberg and L. innocua, respectively.
Data Analysis
At each combination of cooking conditions, 4 to 6 patties were individually processed. For each treatment, the
means and standard errors of these patties were calculated. Significant differences were evaluated using a t-test.
518
MURPHY ET AL.
cooking time increased with increasing final center temperature of the patty. This result is reasonable because
more time was required to cook the patties to a higher
center temperature than to a lower center temperature.
At the same final center temperature, the cooking time
decreased with increasing air temperature, which indicated that at a higher air temperature, less time was
needed to cook the patties to the same final center temperature. A second-order polynomial equation, T = b t2 + c
t + d, was used to correlate the patty temperature T (C)
with cooking time t (min). A correlation coefficient (R2)
of 0.97 to 0.99 was obtained at an oven air temperature
of 163 to 218 C (Table 1).
Survival of Salmonella and Listeria
FIGURE 1. Temperature and time history of chicken patties cooked
at an air temperature of 163 C to a final patty center temperature of 55 C.
RESULTS AND DISCUSSION
Thermal History and Cooking Time
Figure 1 shows examples of thermal profiles used to
process patties in the air convection oven. In Figure 1,
patties were heated from 4 C to a final center temperature
of 55 C at an oven air temperature of 163 C. Depending
on the oven air temperature during thermal processing,
the surface temperature of the patty could be 4 to 13 C
higher than the temperature at the center of the patty.
Figure 2 shows the relationship of patty center temperature with cooking at an oven air temperature of 163 to
218 C. For each data point, an average of five replicates
was used. The maximum standard error for the data in
Figure 2 was 11.6%. At the same air temperature, the
For years, the color, or degree of doneness, of meat
product has been directly related to the maximum internal temperature attained in the product. Destruction of
microorganisms, including Salmonella and Listeria, by heat
is time and temperature dependent. This study has evaluated the effect of convection cooking on the survival of
Salmonella and Listeria in ground chicken patties. The survival of Salmonella and Listeria decreased with increasing
final patty center temperatures (Figures 3 and 4). The
maximum standard errors of enumeration were 27.3 and
18.8%, respectively, for Salmonella and Listeria. There were
no significant differences (at α = 0.05) on the survivors
of Salmonella and Listeria between oven air temperatures
of 163 C and 218 C.
In this study, Salmonella and Listeria were detected in
the patties cooked to a center temperature of 80 C. Four
to one log10(cfu/g) of Salmonella were detected in the
patties after the patties reached to a final center temperature of 70 to 80 C. Five to three log10(cfu/g) of Listeria
were detected in the patties after the patties reached a
final center temperature of 70 to 80 C.
The results from this study were different from that of
Murphy et al. (1999) who found a 7 log10(cfu/g) reduction
for Salmonella and Listeria when chicken breast meat was
cooked to 70 C in a water bath. For the cooking in a
water bath, the cooking medium is saturated with water.
However, in this study, because steam was not introduced, the relative humidity in the air convection oven
was calculated to be 6 to 10%.
Comparing Air Convection
Cooking with Water Bath Cooking
FIGURE 2. Relationship between final center temperature of chicken
patties and total heating time for the patties processed under oven air
temperatures of 163 to 218 C.
No published information was found on the thermal
inactivation of Salmonella and Listeria in ground chicken
patties cooked in an air convection oven. Therefore, for
S. senftenberg, the results in this study were compared
with the study by Veeramuthu et al. (1998) for ground
turkey thigh meat cooked in a water bath and that by
Murphy et al. (1999) for ground chicken breast meat
cooked in a water bath. The activation energy (E) and
Arrhenius constant (a) were 380.81 kJ/mol and 5.641 ×
1058 min−1, respectively, for S. senftenberg (Veeramuthu et
519
SALMONELLA AND LISTERIA IN COOKED CHICKEN
TABLE 1. Regression parameters of the second-order polynomial equations for patty center temperature
vs. heating time for ground chicken patties cooked in an air convection oven
at different oven air temperatures1
Air temperature (C)
Quadratic term
Linear term
Constant
R2
163
177
190
204
218
−0.0338
−0.0576
−0.0587
−0.1379
−0.1979
2.8644
3.7417
4.3725
6.8606
8.4009
23.9930
20.9070
15.4470
−0.0990
−5.2466
0.9697
0.9767
0.9800
0.9930
0.9974
1
The coefficients for the quadratic term, linear term, and the constant are the α, β, and σ in the equation of
T = α t2 + β t + σ, in which T is patty center temperature in C, and t is heating time in minutes.
al., 1998). From the study by Murphy et al. (1999), the
activation energy (E) and Arrhenius constant (a) for Salmonella were 329.63 kJ/mol and 2.177 × 1051 min−1, respectively. For L. innocua, the comparison was made between
this study and Murphy et al. (1999) for ground chicken
breast meat cooked in a water bath. The activation energy,
E, of 342.49 kJ/mol, and Arrhenius constant, a, of 1.557
× 1053 min−1, were obtained for L. innocua (Murphy et
al., 1999).
Because a relatively small sample size was used in the
studies by Veeramuthu et al. (1998, 2 g) and by Murphy et
al. (1999, 8.5 g), the temperature throughout the samples
cooked in a water bath could be considered uniform.
However, in the present study, a temperature gradient
existed between the surface and center of a patty (30 g)
during convection cooking. For the purpose of comparison, the lowest temperature (at patty center) was used.
Figures 3 and 4 show the experimental values of Salmonella and Listeria survivors after convection cooking at
oven air temperatures of 163 to 218 C and the values from
water bath cooking obtained by Veeramuthu et al. (1998)
and Murphy et al. (1999).
At a final center temperature of patties lower than 65
C, Salmonella survival was not substantially different between this study and that found in the literature. The
FIGURE 3. Comparison of Salmonella senftenberg survival in chicken
patties cooked in an air convection oven with the literature values
obtained from Veeramuthu et al. (1998) and Murphy et al. (1999) for
meat cooked in a water bath.
Salmonella survival in this study was especially close to
the data from Murphy et al. (1999), apparently because
the same raw material (chicken breast meat) was used in
both studies. The Salmonella survival in turkey thigh meat
(Veeramuthu et al., 1998) was higher than that in this
study.
When a final center temperature of the patty was
greater than 65 C, higher survival of Salmonella and Listeria
was obtained in this study than that in the literature.
Using the kinetic parameters from water bath cooking
would overpredict the thermal lethality of Salmonella by
1.5 to 4 log and the thermal lethality of Listeria by 3 to 5
log for the ground chicken breast patties cooked at an
oven air temperatures 163 to 218 C. Because of the existing
temperature gradients throughout a patty, the average
temperature of a cooked patty was higher than the center temperature. Therefore, if an average patty temperature was used, a greater deviation would be obtained
between this study and those conducted in a water bath.
Substantial difference in the survival of Salmonella and
Listeria in cooked chicken patties between air convection
cooking and water bath cooking was likely due to the
humidity of the environment during cooking. Other published articles have demonstrated that dry heat roasting
of beef had a lower effect than moist heat in killing Salmonella (Blankenship, 1978; Goodfellow and Brown, 1978).
FIGURE 4. Comparison of Listeria innocua survival in chicken patties
cooked in an air convection oven with the literature values obtained
from Murphy et al. (1999) for chicken meat cooked in a water bath.
520
MURPHY ET AL.
TABLE 2. Linear regression parameters of the empirical equations for Salmonella and Listeria
in chicken patties cooked at different oven air temperatures
Culture
Air temperature (C)
Slope
Intercept
R2
Salmonella
163
177
190
204
218
163
177
190
204
218
−0.2130
−0.2636
−0.4374
−0.4971
−0.5847
−0.1192
−0.1783
−0.2758
−0.3815
−0.4346
9.162
9.3508
10.895
11.308
11.412
8.4592
8.9094
9.7888
10.780
10.564
0.877
0.903
0.947
0.956
0.929
0.868
0.981
0.931
0.906
0.912
Listeria
1
The linear regression equation is expressed as Log10(N) = δ t + η, in which δ is slope, η is intercept, the
Log10(N) is the logarithmic surviving Salmonella or Listeria in Log10(cfu/g), and t is heating time in minutes.
Blankenship (1978) demonstrated that Salmonella survived on beef roast after the internal temperature reached
64.2 C in a gas fired oven without humidity control. Goodfellow and Brown (1978) showed that cooking beef in a
dry oven below 121 C permitted Salmonella survival on
beef. However, when steam was injected into a 79.4 C
oven for 30 min, Salmonella was eliminated after the beef
was cooked to an internal temperature of 54.4 C (Goodfellow and Brown, 1978).
Empirical Equations for Salmonella
or Listeria Survivors vs. Heating Time
During convection cooking, the patty temperature varied with cooking time. The survivors of Salmonella and
Listeria depended on the final temperature of the patties.
Therefore, the survival of Salmonella and Listeria was also
a function of cooking time. Linear regression was used
to fit survivor numbers of Salmonella and Listeria, Log10(cfu/g), vs. cooking time in minutes. A correlation coefficient, R2 of 0.87 to 0.98 was obtained (Table 2). At oven
air temperatures of 163 to 218 C, increasing the oven air
temperature from 163 to 218 C, caused the slope of the
regression to decrease 1.7-fold for Salmonella and 2.6-fold
for Listeria (Table 2). This result indicated that the thermal
inactivation of Salmonella and Listeria increased with increasing oven air temperature.
In the past, thermal processing regulations required
that uncured poultry products reach a minimum internal
temperature of 71.1 C. In this study, cumulative process
lethality, F0, at a reference temperature of 71.1 C was
integrated from the temperature-time histories of the processed patties. The z values of 5.4 C (Veeramuthu et al.,
1998) and 5.1 C (Moody et al., 1998) were used for S.
senftenberg and L. innocua, respectively. Table 3 shows
that after the internal temperature of the patty reaches
65 C, the F0 values (at a reference temperature of 71.1 C)
are greater than 2 s. Based on the definition of F0, the
obtained temperature-time histories in Table 3 should
be sufficient to reach 7-D lethality. However, surviving
Salmonella and Listeria were detected in all of the trials
used for the calculations in the Table 3.
The USDA-Food Safety Inspection Service has published a final rule by converting the regulations governing
the processing of poultry products into performance standards. The new rule allows the use of any processing
schedule that meets a lethality performance standard of
a 7-D reduction for Salmonella. However, care should be
TABLE 3. Cumulative lethality (F0) calculated at a reference temperature of 71.1 C
for Salmonella senftenberg and Listeria innocua
Oven air
temperature (C)
Patty center
temperature (C)
F0 for S. senftenberg
(min)
163
65
70
75
65
70
75
65
70
75
65
70
75
65
70
75
0.1208
1.1850
9.8905
0.0744
1.3998
7.4594
0.0782
0.8152
7.8657
0.0732
0.5918
6.6521
0.0541
0.5706
4.6420
177
191
204
218
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
0.0208
0.0922
2.7183
0.0107
0.6946
1.3295
0.0080
0.1557
1.5531
0.0067
0.0913
1.8699
0.0063
0.0165
0.5102
F0 for L. innocua
(min)
0.09916
1.0981
10.4511
0.0611
1.2925
7.8620
0.0642
0.7593
8.2602
0.0606
0.5502
7.0183
0.0448
0.5336
4.9142
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
0.01719
0.0829
2.9233
0.0088
0.6493
1.3800
0.0067
0.1456
1.6031
0.0058
0.1052
1.9712
0.0053
0.0159
0.5506
1
The z values of 5.4 C (Veeramuthu et al., 1998) and 5.1 C (Moody et al., 1998) were used in the calculation
of F0 for Salmonella senftenberg and Listeria innocua, respectively.
SALMONELLA AND LISTERIA IN COOKED CHICKEN
taken in applying the results from one thermal treatment
condition to another.
ACKNOWLEDGMENTS
This research was partially supported by the US Poultry
and Egg Association research grant. The chicken meat
was graciously provided by Tyson Foods, Inc., Springdale, AR.
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