response surface models for effects of previous sodium chloride and temperature on growth kinetics...
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Response Surface Models for Effects of Response Surface Models for Effects of Previous Sodium Chloride and Previous Sodium Chloride and
Temperature on Growth Kinetics of Temperature on Growth Kinetics of Salmonella Salmonella Typhimurium on Cooked Typhimurium on Cooked
Chicken BreastChicken Breast
Thomas P. OscarThomas P. Oscar
USDA, ARSUSDA, ARS
Microbial Food Safety Research Microbial Food Safety Research UnitUnit
Princess Anne, MD Princess Anne, MD
Previous Growth Previous Growth ConditionsConditions
Broth CultureBroth Culture
• Previous pH (5.5 to 8.5)Previous pH (5.5 to 8.5)
Cooked Chicken Breast BurgersCooked Chicken Breast Burgers
• Previous temperature (16 to 34°C)Previous temperature (16 to 34°C)
Model DevelopmentModel Development
Full 3 x 9 FactorialFull 3 x 9 Factorial
• 0.5, 2.5, 4.5% NaCl0.5, 2.5, 4.5% NaCl
• 10, 12, 14, 16, 20, 24, 28, 34, 4010, 12, 14, 16, 20, 24, 28, 34, 40ooCC
55 Growth Curves55 Growth Curves
Stage 1: Pre-incubationStage 1: Pre-incubation
Brain Heart Infusion Broth, pH 6.4Brain Heart Infusion Broth, pH 6.4
• 0.5 to 4.5% NaCl0.5 to 4.5% NaCl
Salmonella Salmonella Typhimurium ATCC Typhimurium ATCC
1402814028
• 3434ooC for 23 hC for 23 h
Stage 2: IncubationStage 2: Incubation
Cooked Chicken Breast BurgersCooked Chicken Breast Burgers
• 10 to 4010 to 40ooCC
Salmonella Salmonella TyphimuriumTyphimurium
• 100,000 CFU per burger100,000 CFU per burger
Growth Curve FitGrowth Curve Fit
0 4 8 12 16 20 24
0
1
2
3
4
5
6
7
8
r2 = 0.981 = 3.7 0.7 h = 0.218 0.013 log10 CFU/h
Previous growth NaCl = 0.5%Incubation temperature = 20 C
B)
Time (h)
Salmonella
Typ
him
uri
um
(lo
g10
CF
U/m
l)
Data SetData Set
pNaCl Temp. ln LT ln SGR0.5 10 3.38 -3.770.5 12 2.96 -3.11: : : :
2.5 24 0.94 -1.092.5 28 0.44 -0.79: : : :
4.5 34 -0.13 -0.474.5 40 -0.38 -0.20
Lag Time ModelLag Time Model
Parameter Estimate F Value P Value
Intercept 5.9115
pN -0.2013 3.03 0.0882
T -0.2754 129.54 0.0001
pN*T -0.0013 0.31 0.5790
pN*pN 0.0333 2.92 0.0941
T*T 0.0033 51.36 0.0001
R2 0.952
Lag Time DataLag Time Data
8 12 16 20 24 28 32 36 40-1
0
1
2
3
4
5
2.5% 4.5%0.5%
pgNaClA)
1.5% 3.5%
Temperature (oC)
ln
(h
)
Growth Rate ModelGrowth Rate Model
Parameter Estimate F Value P Value
Intercept -6.2251
pN -0.0114 0.02 0.8820
T 0.3234 411.83 0.0001
pN*T 0.0020 1.58 0.2154
pN*pN -0.0085 0.44 0.5098
T*T -0.0045 213.84 0.0001
R2 0.978
Growth Rate DataGrowth Rate Data
8 12 16 20 24 28 32 36 40-5
-4
-3
-2
-1
0
2.5% 0.5%4.5%
B)
1.5% 3.5%
pgNaCl
Temperature (oC)
ln
(lo
g10
CF
U/h
)
Model ValidationModel Validation
Full 2 x 8 FactorialFull 2 x 8 Factorial
• 1.5, 3.5% NaCl1.5, 3.5% NaCl
• 11, 13, 15, 18, 22, 26, 31, 37°C11, 13, 15, 18, 22, 26, 31, 37°C
16 Growth Curves16 Growth Curves
Validation TermsValidation Terms
Relative ErrorRelative Error
• Predicted - Observed/ObservedPredicted - Observed/Observed
Mean Absolute Relative Error (MARE)Mean Absolute Relative Error (MARE)
• Prediction AccuracyPrediction Accuracy
Median Relative Error (MRE)Median Relative Error (MRE)
• Prediction BiasPrediction Bias
Validation ResultsValidation Results
Model Data Cases MARE MRELT Development 55 20.2 -1.0
Validation 16 26.6 0.9
GR Development 55 14.1 1.4
Validation 16 15.4 5.2
RE of Lag TimeRE of Lag Time
0 10 20 30 40-100
-75
-50
-25
0
25
50
75
100Development
Validation
A)
observed (h)
Rel
ativ
e E
rro
r (%
)
RE of Growth RateRE of Growth Rate
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9-100
-75
-50
-25
0
25
50
75
100
Validation
DevelopmentB)
observed (log10 CFU/h)
Rel
ativ
e E
rro
r (%
)
In-House ComparisonIn-House Comparison
Model MARE MREpN LT 26.6 0.9
GR 15.4 5.2pP LT 7.8 -1.8
GR 6.6 -2.8pT LT 13.4 -3.0
GR 11.3 6.8
Poultry Food Assess Risk Poultry Food Assess Risk ModelModel(Poultry FARM)(Poultry FARM)Food Parameter
Previous NaCl (0.5 to 4.5%) 0.5
Temperature (10 to 40C) 25
Time of Abuse, h 4
Risk Parameters
Salmonella (CFU/serving) 1
Infection Dose (CFU) 100
Poultry Food Assess Risk Poultry Food Assess Risk ModelModel(Poultry FARM)(Poultry FARM)Growth Characteristics
Lag Time, h 2.7
Growth Rate, log CFU/h 0.40
Log Increase 0.5
Salmonella per Serving 3.4
Poultry Food Assess Risk Poultry Food Assess Risk ModelModel(Poultry FARM)(Poultry FARM)Health Outcomes
Risk of Infection 3.4%
Sick No
Doctor No
Hospital No
Intensive Care No
Death No
ConclusionsConclusions
The models provide reliable predictions The models provide reliable predictions
within the matrix of factors modeled.within the matrix of factors modeled.
Previous NaCl (0.5 to 4.5%) is not a Previous NaCl (0.5 to 4.5%) is not a
major factor affecting growth of major factor affecting growth of S. S.
typhimuriumtyphimurium..