response surface models for effects of previous sodium chloride and temperature on growth kinetics...

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..