Weibull Model for Inactivation of Geobacillus stearothermophilus Spores in Superheated Steam
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Transcript of Weibull Model for Inactivation of Geobacillus stearothermophilus Spores in Superheated Steam
Weibull Model for Inactivation Weibull Model for Inactivation of of Geobacillus Geobacillus
stearothermophilus stearothermophilus Spores in Spores in Superheated SteamSuperheated Steam
Dagmara Head and Stefan CenkowskiDagmara Head and Stefan Cenkowski
Department of Biosystems Engineering, University of Department of Biosystems Engineering, University of Manitoba, Winnipeg, MBManitoba, Winnipeg, MB
CSBE-SCGAB 2009 Annual Conference, Rodd’s Brudenell River CSBE-SCGAB 2009 Annual Conference, Rodd’s Brudenell River ResortResort,, Prince Edward Island, Prince Edward Island, 12 – 15 July 200912 – 15 July 2009
Introduction Materials & MethodsObjectives Results Conclusions
Superheated steam (SS)Superheated steam (SS)
SS – water vapour heated to SS – water vapour heated to temperature above boiling point at temperature above boiling point at given pressuregiven pressure
SS processing:SS processing:►rapid transfer of heatrapid transfer of heat►air-free environmentair-free environment►energy savings – condensate reuseenergy savings – condensate reuse
Introduction Materials & MethodsObjectives Results Conclusions
Geobacillus stearothermophilusGeobacillus stearothermophilus
► Gram positive, thermophilic bacteriumGram positive, thermophilic bacterium
► Forms highly heat-resistant sporesForms highly heat-resistant spores
Hi, I’m G. stearothermophilus spore, and I’m TOUGH!!!
Introduction Materials & MethodsObjectives Results Conclusions
Thermal inactivation of Thermal inactivation of microorganismsmicroorganisms► Presumed to follow the first order kinetics model: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, Non-linearity of survivor curves (shoulders, tails, upward or downward concavity)tails, upward or downward concavity)
t)(oN
Nlog k
Introduction Materials & MethodsObjectives Results Conclusions
Survivor curves for Survivor curves for G. stearothermophilusG. stearothermophilus spores exposed to SSspores exposed to SS
-5
-4
-3
-2
-1
0
1
0 20 40 60 80 100 120
Treatment Time (min)
Sur
vivo
rs,
log
(N/N
o)
105°C 130°C 145°C 160°C 175°C
Introduction Materials & MethodsObjectives Results Conclusions
►The Weibull model The Weibull model
►Fit of the modelFit of the model
Introduction Materials & MethodsObjectives Results Conclusions
The Weibull modelThe 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)
β
α
t
2.303
1
N
Nlog )()(
o
Introduction Materials & MethodsObjectives Results Conclusions
Superheated Steam Processing Superheated Steam Processing SystemSystem
condensate steam out water
processing chamber
condenser
steam generator superheater
sup
erh
eat
ed
st
ea
m
sample tray
6.3 cm
Introduction Materials & MethodsObjectives Results Conclusions
► SS at 0.35 m/s and 130-175SS at 0.35 m/s and 130-175ooC (15C (15ooC C increments)increments)
► Geobacillus Geobacillus stearothermophilusstearothermophilus ATCC 10149 ATCC 10149 + sand: + sand:
@ low inoculum: 3 log cfu/g@ low inoculum: 3 log cfu/g
@ high inoculum: 6 log cfu/g@ high inoculum: 6 log cfu/g
Processing conditionsProcessing conditions
Introduction Materials & MethodsObjectives Results Conclusions
αα and and ββ parameters of the Weibull modelparameters of the Weibull model
Temperature of SS (C)
Inoculum Level (log cfu/g) α β
130
145
160
175
36
36
36
36
1.905.88
3.8213.25
1.591.56
0.0050.35
0.350.21
0.391.08
0.611.29
0.180.72
Where: a1, a2, b1, b2 are coefficients, T is SS temperature (oC)
The shape and scale parameters as functions The shape and scale parameters as functions of SS temperatureof SS temperature
Taaα 12 Tbbβ 12
T)1
b2
(b
Taa
t
2.303
1
N
Nlog )()(
12o
The expanded Weibull modelThe expanded Weibull model
Introduction Materials & MethodsObjectives Results Conclusions
Validation of the Weibull model – low Validation of the Weibull model – low inoculuminoculum
Introduction Materials & MethodsObjectives Results Conclusions
-2.5
-2
-1.5
-1
-0.5
0
0 10 20 30 40 50 60 70 80 90Processing Time (min)
Sur
vivo
rs,
log(
N/N
o)
predicted at 130°C predicted at 145°C predicted at 160°C predicted at 175°C
measured at 130°C measured at 145°C measured at 160°C measured at 175°C
Low Inoculum
R2 0.82-0.97; slope 0.78-1.09
Validation of the Weibull model – high Validation of the Weibull model – high inoculuminoculum
Introduction Materials & MethodsObjectives Results Conclusions
-5.5
-4.5
-3.5
-2.5
-1.5
-0.5
0.5
0 20 40 60 80 100 120Processing Time (min)
Sur
vivo
rs,
log(
N/N
o)
predicted at 130°C predicted at 145°C predicted at 160°C predicted at 175°C
measured at 130°C measured at 145°C measured at 160°C measured at 175°C
High Inoculum
R2 0.7-1; slope 0.82-1.28 but for 130oC R2 0.17; slope 0.15
Introduction Materials & MethodsObjectives Results Conclusions
►The Weibull model The Weibull model to predict survival to predict survival ofof
Geobacillus stearothermophilus Geobacillus stearothermophilus spores spores exposed to SS at 145-175exposed to SS at 145-175ooC C
►Survival predicted based on SS Survival predicted based on SS temperature and treatment timetemperature and treatment time
Hi again,Do you have questions?