Weibull Model for Inactivation of Geobacillus stearothermophilus Spores in Superheated Steam

1. Weibull Model for Inactivation of Geobacillus stearothermophilus Spores in Superheated Steam Dagmara Head and Stefan Cenkowski Department of Biosystems Engineering, University of Manitoba, Winnipeg, MB CSBE-SCGAB 2009 Annual Conference, Rodd’s Brudenell River Resort,Prince Edward Island, 12 – 15 July 2009

2. Superheated steam (SS) SS – water vapour heated to temperature above boiling point at given pressure SS processing: • rapid transfer of heat • air-free environment • energy savings – condensate reuse Introduction Objectives Conclusions Results Materials & Methods

3. Hi, I’m G. stearothermophilus spore, and I’m TOUGH!!! Geobacillus stearothermophilus • Gram positive, thermophilic bacterium • Forms highly heat-resistant spores Introduction Objectives Conclusions Results Materials & Methods

4. Presumed to follow the first order kinetics model: Where: No - initial number of microorganisms (cfu/g), N - number of microorganisms at time t (cfu/g), t - treatment time (min), k – a rate constant (1/min) Non-linearity of survivor curves (shoulders, tails, upward or downward concavity) Thermal inactivation of microorganisms Introduction Objectives Conclusions Results Materials & Methods

5. Survivor curves for G. stearothermophilus spores exposed to SS Introduction Objectives Conclusions Results Materials & Methods

6. The Weibull model • Fit of the model Introduction Objectives Conclusions Results Materials & Methods

7. The Weibull model Where: No - initial number of microorganisms (cfu/g), N - number of microorganisms at time t (cfu/g), t - treatment time (min), α- scale parameter (min), β - shape parameter (non-dimensional) Introduction Objectives Conclusions Results Materials & Methods

8. 6.3 cm Superheated Steam Processing System Introduction Objectives Conclusions Materials & Methods Results

9. Processing conditions • SS at 0.35 m/s and 130-175oC (15oC increments) • Geobacillus stearothermophilus ATCC 10149 + sand: @ low inoculum: 3 log cfu/g @ high inoculum: 6 log cfu/g Introduction Objectives Conclusions Materials & Methods Results

10. α and βparameters of the Weibull model Introduction Objectives Conclusions Materials & Methods Results

11. The shape and scale parameters as functions of SS temperature Where:a1, a2, b1, b2are coefficients, Tis SS temperature (oC) The expanded Weibull model Introduction Objectives Conclusions Materials & Methods Results

12. Validation of the Weibull model – low inoculum R2 0.82-0.97; slope 0.78-1.09 Introduction Objectives Conclusions Materials & Methods Results

13. Validation of the Weibull model – high inoculum R2 0.7-1; slope 0.82-1.28 but for 130oC R2 0.17; slope 0.15 Introduction Objectives Conclusions Materials & Methods Results

14. The Weibull model  to predict survival of Geobacillus stearothermophilus spores exposed to SS at 145-175oC • Survival predicted based on SS temperature and treatment time Materials & Methods Introduction Objectives Results Conclusions

15. Hi again, Do you have questions?