1. Temperature
August 31, 2016

2. Typical temperature ranges
Microorganisms
Minimum °C
Optimum
Maximum
Obligate Psychrophiles
Facultative Psychrophiles
-5 to +5
12 to 15
25 to 30
15 to 20
30 to 35
Mesophiles
5 to 15
30 to 40
40 to 57
Thermophiles
40 to 45
55 to 75
60 to 80
According to Adams and Moss, Food Microbiology, 3rd Edn.
“typical growth rates”: Bacteria (optimal): 2.3 h-1(m) or 0.3 h (doubling time)
Bacteria (limited nutrients): 0.2 h-1, 3.46 h
Psychrotrophs (5 oC): h-1, 30 h
Molds (optimal): h-1, h

3. D Value (Decimal reduction time)
Time of heating at a particular temperature to cause a 1 log or 90% reduction in the number of microorganisms
D121°C = X min (or sec)

4. Calculating the D-value
Suppose t = 121 oC
D121oC = t2 – t1
log10a – log10b t1 t2

5. Organism Medium Temperature (oC) D-value (min)
Salmonella enterica
Milk
65.6
Salmonella Senftenberg
Various
65.5
Escherichia coli
57.2
Yersinia enterocolitica 60
Listeria monocytogenes
63.3
Staphylococcus aureus
0.9
Clostridium botulinum
Vegetables
110
Bacillus cereus 95
Geobacillus stearothermophilus
Unknown
100
100-1,600

6. z = Temperature2 – Temperature1
Z Value
Temperature required for a 1 log or 90% reduction in the D value Da Db
Temp1
Temp2
z = Temperature2 – Temperature1
Log Da – Log Db
Example: Z = 10 oC

7. Utility of Z-value Organism A: Organism B:
D121C = 0.01 minutes D100C = 5 minutes
Z Celsius = 7 degrees ZCelsius = 10 degrees
D114C = 0.1 minutes, D107C = 1 minute, D100C = 10 minutes

8. Organism Medium Temperature (oC) Z-value (oC)
Salmonella enterica
Milk
65.6
Salmonella Senftenberg
Various
65.5
Escherichia coli
57.2
5.3
Yersinia enterocolitica 60
4-5.8
Listeria monocytogenes
63.3
5.5
Staphylococcus aureus
9.5
Clostridium botulinum
Vegetables
110
Bacillus cereus 95
Geobacillus stearothermophilus
Unknown
100
11.7