Food Protection with High Temperatures
429
was found by Stumbo et al.
55 to have a D r value of 2.47 in cream-style corn, whereas flat-sour (FS)
spore strain 617 was found to have a D r of 0.84 in whole milk.
The approximate heat resistance of spores of thermophilic and mesophilic spoilage organisms may
be compared by use of D r values.
Geobacillus stearothermophilus:
4.0–5.0
Thermoanaerobacterium thermosaccharolyticum:
3.0–4.0
Clostridium nigrificans:
2.0–3.0
C. botulinum (types A and B):
0.10–0.2
C. sporogenes (including PA 3679):
0.10–1.5
B. coagulans:
0.01–0.07
The effect of pH and suspending menstrum on D values of C. botulinum spores is presented in Table
17–9. As noted above, microorganisms are more resistant at and around neutrality and show different
degrees of heat resistance in different foods.
In order to determine the z value, D values are plotted on the log scale, and degrees Fahrenheit are
plotted along the linear axis. From the data presented in Figure 17–3, the z value is 17.5. Values of z
for C. botulinum range from 14.7 to 16.3, whereas for PA 3679, the range 6.6–20.5 has been reported.
Some spores have been reported to have z values as high as 22. Peroxidase has been reported to have
a z value of 47; and 50 has been reported for riboflavin, and 56 for thiamine.
12-D Concept
The 12-D concept refers to the process lethality requirement long in effect in the canning industry
and implies that the minimum heat process should reduce the probability of survival of the most
resistant C. botulinum spores to 10
−12 . Because C. botulinum spores do not germinate and produce
toxin below pH 4.6, this concept is observed only for foods above this pH value. An example from
Stumbo
54 illustrates this concept from the standpoint of canning technology. If it is assumed that each
container of food contains only one spore of C. botulinum, F 0 may be calculated by use of the general
survivor curve equation with the other assumptions noted above in mind:
F 0 = D r (log a − log b),
F 0 = 0.21(log 1 − log 10
−12 ),
F 0 = 0.21 × 12 = 2.52
Processing for 2.52 minutes at 250
◦ F, then, should reduce the C. botulinum spores to one spore in 1
of 1 billion (10
12 ) containers. When it is considered that some flat-sour spores have D r values of about
4.0 and some canned foods receive F 0 treatments of 6.0–8.0, the potential number of C. botulinum
spores is reduced to nondetectable levels.
SOME CHARACTERISTICS OF THERMOPHILES
On the basis of growth temperatures, thermophiles may be characterized as organisms with a
minimum of around 45
◦ C, an optimum between 50
◦ C and 60
◦ C, and a maximum of 70
◦ C or above.
By this definition, thermophilic species/strains are found among the cyanobacteria, archaebacteria,
actinomycetes,
58 the anaerobic photosynthetic bacteria, thiobacilli, algae, fungi, bacilli, clostridia,
429
was found by Stumbo et al.
55 to have a D r value of 2.47 in cream-style corn, whereas flat-sour (FS)
spore strain 617 was found to have a D r of 0.84 in whole milk.
The approximate heat resistance of spores of thermophilic and mesophilic spoilage organisms may
be compared by use of D r values.
Geobacillus stearothermophilus:
4.0–5.0
Thermoanaerobacterium thermosaccharolyticum:
3.0–4.0
Clostridium nigrificans:
2.0–3.0
C. botulinum (types A and B):
0.10–0.2
C. sporogenes (including PA 3679):
0.10–1.5
B. coagulans:
0.01–0.07
The effect of pH and suspending menstrum on D values of C. botulinum spores is presented in Table
17–9. As noted above, microorganisms are more resistant at and around neutrality and show different
degrees of heat resistance in different foods.
In order to determine the z value, D values are plotted on the log scale, and degrees Fahrenheit are
plotted along the linear axis. From the data presented in Figure 17–3, the z value is 17.5. Values of z
for C. botulinum range from 14.7 to 16.3, whereas for PA 3679, the range 6.6–20.5 has been reported.
Some spores have been reported to have z values as high as 22. Peroxidase has been reported to have
a z value of 47; and 50 has been reported for riboflavin, and 56 for thiamine.
12-D Concept
The 12-D concept refers to the process lethality requirement long in effect in the canning industry
and implies that the minimum heat process should reduce the probability of survival of the most
resistant C. botulinum spores to 10
−12 . Because C. botulinum spores do not germinate and produce
toxin below pH 4.6, this concept is observed only for foods above this pH value. An example from
Stumbo
54 illustrates this concept from the standpoint of canning technology. If it is assumed that each
container of food contains only one spore of C. botulinum, F 0 may be calculated by use of the general
survivor curve equation with the other assumptions noted above in mind:
F 0 = D r (log a − log b),
F 0 = 0.21(log 1 − log 10
−12 ),
F 0 = 0.21 × 12 = 2.52
Processing for 2.52 minutes at 250
◦ F, then, should reduce the C. botulinum spores to one spore in 1
of 1 billion (10
12 ) containers. When it is considered that some flat-sour spores have D r values of about
4.0 and some canned foods receive F 0 treatments of 6.0–8.0, the potential number of C. botulinum
spores is reduced to nondetectable levels.
SOME CHARACTERISTICS OF THERMOPHILES
On the basis of growth temperatures, thermophiles may be characterized as organisms with a
minimum of around 45
◦ C, an optimum between 50
◦ C and 60
◦ C, and a maximum of 70
◦ C or above.
By this definition, thermophilic species/strains are found among the cyanobacteria, archaebacteria,
actinomycetes,
58 the anaerobic photosynthetic bacteria, thiobacilli, algae, fungi, bacilli, clostridia,