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28/09/2010 Safe heating and cooling in catering 2 DTU Food, Technical University of Denmark
Goals of the models
- Establishment of safe heating
- Documentation of safe heating and cooling
cooling in the catering supply chain Tina Beck Hansen Bjarke Bak - - PowerPoint PPT Presentation
cooling in the catering supply chain Tina Beck Hansen Bjarke Bak - - PowerPoint PPT Presentation
Conceptual models for safe heating and cooling in the catering supply chain Tina Beck Hansen Bjarke Bak Christensen from National Food Institute, DTU, Denmark Heidi Friis Hansen Birgitte Sterup Hansen Anette Kamuk Gitte Gross from Viffos,
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28/09/2010 Safe heating and cooling in catering 3 DTU Food, Technical University of Denmark
Model assumptions
Log-linear inactivation kinetics: D- and z-values Pasteurization value:
Time to obtain a lethal effect of a heat treatment at a given temperature and z-value. Lethal effect of heat treatment: T = Temperature in the food Tref = Reference temperature z = z-value t = heat treatment time
t PV
end start z Tref T z Tref
) / ) ((
10
Equivalent treatments:
PVTnew
z = 10((Tref – Tnew)/z) PVTref z
Tnew = New temperature Tref = Reference temperature z = z-value
Log-reductions:
Log reduction = PVT
z / DT
T = Temperature PVT
z = lethal effect at temp. T
DT = D-value at temperature T
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28/09/2010 Safe heating and cooling in catering 4 DTU Food, Technical University of Denmark
Cool down for later use Keep chilled for longer time use
Safe heating and cooling – performance criteria
- Prevalence
- Numbers
- Heat tolerance
- Growth potential
- Severity
- Susceptibility
- L. monocytogenes – 4D
Source: Hansen & Knøchel 2001, IJFM 63, pp. 135
- Cl. botulinum (psychrotrophic) – 6D
Source: Peck 1997, Trends FST 8, pp. 186
- Cl. perfringens – 1 log10 increase
Source: Andersen et al. 2004, JFP 67, pp. 83
Heat gently for immediate use
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28/09/2010 Safe heating and cooling in catering 5 DTU Food, Technical University of Denmark
Heat tolerance – influence of product type
Listeria monocytogenes
- 2.0
- 1.5
- 1.0
- 0.5
0.0 0.5 1.0 1.5 2.0 50 55 60 65 70 75 Heating temperature (°C) Log D-value
Salmon Cod Milk Beef Lineær Source: Doyle et al. 2001, JFP 64, pp. 410
z = 6.5oC z = 7.0oC z = 5.5oC z = 6.0oC
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28/09/2010 Safe heating and cooling in catering 6 DTU Food, Technical University of Denmark
Heat tolerance – influence of salt content
5 10 15 0.5 3 6 9 20 % salt i vandfasen 4D
Source: Jørgensen et al. 1995, JAB 79, pp.274
Heat tolerance – 4D (min) % salt in the water phase
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28/09/2010 Safe heating and cooling in catering 7 DTU Food, Technical University of Denmark
Heat tolerance – influence of heat injury
Heat treatment Degree of heat injury Days until growth at 3°C Days until growth at 10°C pH 5.6 pH 6.2 pH 5.6 pH 6.2 Start population Injured 0%
- Not-injured
100% >30 <10 <10 <10 1D – 2D Injured 95-99% >30 >30 10-20 <10 Not-injured 1-5% >30 >30 10-20 10-20 3D – 4D Injured >99.9% >30 >30 >30 >30 Not-injured <0.1% >30 >30 >30 >30
Source: Hansen & Knøchel 2001, IJFM 63, pp. 135
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28/09/2010 Safe heating and cooling in catering 8 DTU Food, Technical University of Denmark
Safe heating – process criteria
Questions to answer ANSWER
Product type? (fish, meat, vegetables, other) FISH Is the product intended for consumption immediately after heating? (YES, NO) YES Is the product intended for keeping at one of the following conditions
- 3oC?
- 5oC for max. 10 days?
- 5-10oC for max. 5 days?
(YES, NO) Not relevant in this example Does the product contain >3% salt-in-water? (YES, NO) NO Wanted end-temperature in the product? ( 60oC) 65oC
A safe heating process should have a PV corresponding to
4.8 min at 65oC
in the coldest spot
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28/09/2010 Safe heating and cooling in catering 9 DTU Food, Technical University of Denmark
- 5
5 10 15 20 25 30 35 40 45 50 55 60 65 10 20 30 40 50 60 70 Heating time, min at 80°C Temperature in coldest spot (°C)
Filet of cod in oven
Documentation – the coldest spot
PV65(fish) = 5.3 min PV65(fish) = 3.1 min
- Unequal product size
(Hansen et al. 1995, IJFST 30, pp. 365)
- Start-temperature
(Knøchel et al. 1997, ZLUF 205, pp. 370)
- Location in oven
(Hansen 1996, PhD Afh., p. 47)
- HTST vs. LTLT
(Hansen 1996, PhD Afh., p. 47)
Factors affecting PV
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28/09/2010 Safe heating and cooling in catering 10 DTU Food, Technical University of Denmark
Safe cooling – process criteria BACKGROUND
- That temperature profiles during cooling
follow exponentially decreasing relationships when the cooling conditions are constant
Source: Blankenship et al. 1988, AEM 54, pp. 1104
- That Clostridium perfringens should not reach
a hazardous level
Source: Andersen et al. 2004, JFP 67, pp. 83
A safe cooling process should pass the interval from
50 to 15°C in max. 3 h
in the hottest spot
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Simulation of cooling
10 20 30 40 50 60 70 80 90 100 1 2 3 4 5 6 Cooling in water (hours) Product temperature (°C) Start-temperature 87oC Cooling time 5.5 timer End-temperature 2oC
Rice pudding
1 h 48 min
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Conclusions
- The present work served as an example of
using the risk management concept, performance criterion, for the definition of safe heating and cooling in the catering industry
- It was demonstrated how these performance