1. Response Surface Models for Effects of Previous Sodium Chloride and Temperature on Growth Kinetics of Salmonella Typhimurium on Cooked Chicken Breast Thomas P. Oscar USDA, ARS Microbial Food Safety Research Unit Princess Anne, MD

2. Previous Growth Conditions b Broth Culture Previous pH (5.5 to 8.5)Previous pH (5.5 to 8.5) b Cooked Chicken Breast Burgers Previous temperature (16 to 34°C)Previous temperature (16 to 34°C)

3. Model Development b Full 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, 40 o C10, 12, 14, 16, 20, 24, 28, 34, 40 o C b 55 Growth Curves

4. Stage 1: Pre-incubation b Brain Heart Infusion Broth, pH 6.4 0.5 to 4.5% NaCl0.5 to 4.5% NaCl b Salmonella Typhimurium ATCC 14028 34 o C for 23 h34 o C for 23 h

5. Stage 2: Incubation b Cooked Chicken Breast Burgers 10 to 40 o C10 to 40 o C b Salmonella Typhimurium 100,000 CFU per burger100,000 CFU per burger

6. Growth Curve Fit

7. Data Set

8. Lag Time Model

9. Lag Time Data

10. Growth Rate Model

11. Growth Rate Data

12. Model Validation b Full 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 b 16 Growth Curves

13. Validation Terms b Relative Error Predicted - Observed/ObservedPredicted - Observed/Observed b Mean Absolute Relative Error (MARE) Prediction AccuracyPrediction Accuracy b Median Relative Error (MRE) Prediction BiasPrediction Bias

14. Validation Results

15. RE of Lag Time

16. RE of Growth Rate

17. In-House Comparison

18. Poultry Food Assess Risk Model (Poultry FARM)

21. Conclusions b The models provide reliable predictions within the matrix of factors modeled. b Previous NaCl (0.5 to 4.5%) is not a major factor affecting growth of S. typhimurium.