642 Modern Food Microbiology
differences in thermal D values between different meat products, and the D 60 ◦ C values (minutes) and
products are noted below:
2
0.45–0.47
Beef
0.37–0.55
Pork sausage
0.38–0.55
Chicken
0.55–0.58
Turkey
The D values increased with increasing fat content, and this is a well-established phenomenon (see
Chapter 17). These findings support a previous study where D and z values for high-fat and lean beef
were as follows:
51
30.5% fat
D = 0.45 minute
z = 8.37
◦ F
2.0% fat
D = 0.30 minute
z = 8.30
◦ F
In another study, an inoculum of ∼10
3 /g of strain O157:H7 in low-fat ground beef was destroyed
when cooked to internal temperatures of 66
◦ , 68
◦ , or 72
◦ C.
25
A recent study on the thermal properties of EC O157:H7 in apple juice revealed that a 4-D process
could be achieved by heating at 60
◦ C for ∼1.6 minutes.
78 This is based on D values at 52
◦ C obtained
from 20 separate trials that ranged from 9.5 to 30 minutes with a mean of 18 minutes and a z of
4.8
◦ C. Although EC O157:H7 cells became more heat sensitive in apple juice when l-malic acid was
increased from 0.2 to 0.8%, or when pH was reduced from 4.4 to 3.6, benzoic acid at 1,000 ppm was
the most effective additive in increasing heat sensitivity.
78
The fate of EC O157:H7 along with Listeria monocytogenes and Salmonella Typhimurium in beef
jerky was studied, and neither could be found in finished and dried products after 10 hours with inocula
of ∼10
7 /g or after storage for 8 weeks.
36
Regarding radiation resistance of EHEC strains, there is no apparent basis for them to differ greatly
from other enteric bacteria. Using chicken and an EC O157:H7 strain, the D value at 5
◦ C was 0.27
kGy, whereas at -5
◦ C, D was 0.42 kGy.
82 Employing a nonpathogenic strain of E. coli, Fielding et
al.
26 found radiation D to be ∼0.34 kGy in broth with a pH around 7.0, but the D was 0.24 kGy when
cells were grown at pH 4.0 prior to irradiation. See Chapter 15 for more on irradiation of foods. In
apple juice, nonacid adapted strains had a range of 0.12–0.21 kGy but when acid-adapted, the values
increased to 0.22–0.31 kGy.
7
In regard to survival in ovine and bovine manure, E. coli O157:H7 was found to survive in the
former for 100 days at 4
◦ or 10
◦ C, and survival was unaffected by the possession of stx genes.
45
Prevalence in Foods
Overall, the incidence and prevalence of EHEC strains in meat, milk, poultry, and seafood products
are highly variable. Considerably more positives are found when DNA probes are used to detect for
EHEC strains than when EC O157:H7 is tested alone. The first published study on the prevalence in
meats of EHEC strains was that of Doyle and Schoeni,
22 who tested for EC O157:H7 and found this
strain in 3.7% of 164 beef, 1.5% of 264 pork, 1.5% of 263 poultry, and 2.0% of 205 lamb samples.
In Thailand, EC O157:H7 was recovered from 9% of retail beef, 8–28% of slaughterhouse beef, and
11–84% of cattle fecal specimens.
79 Although EC O157:H7 could not be recovered from sausage in
the United Kingdom, a DNA probe gave positive results on 25% of 184 samples for other EHEC
strains.
77 None were found in 112 samples from 71 chickens.
77 In a study of foods in the Seattle area
following the 1993 outbreak, 17.3% of 294 foods were positive for colonies that contained Stx1 and/or
differences in thermal D values between different meat products, and the D 60 ◦ C values (minutes) and
products are noted below:
2
0.45–0.47
Beef
0.37–0.55
Pork sausage
0.38–0.55
Chicken
0.55–0.58
Turkey
The D values increased with increasing fat content, and this is a well-established phenomenon (see
Chapter 17). These findings support a previous study where D and z values for high-fat and lean beef
were as follows:
51
30.5% fat
D = 0.45 minute
z = 8.37
◦ F
2.0% fat
D = 0.30 minute
z = 8.30
◦ F
In another study, an inoculum of ∼10
3 /g of strain O157:H7 in low-fat ground beef was destroyed
when cooked to internal temperatures of 66
◦ , 68
◦ , or 72
◦ C.
25
A recent study on the thermal properties of EC O157:H7 in apple juice revealed that a 4-D process
could be achieved by heating at 60
◦ C for ∼1.6 minutes.
78 This is based on D values at 52
◦ C obtained
from 20 separate trials that ranged from 9.5 to 30 minutes with a mean of 18 minutes and a z of
4.8
◦ C. Although EC O157:H7 cells became more heat sensitive in apple juice when l-malic acid was
increased from 0.2 to 0.8%, or when pH was reduced from 4.4 to 3.6, benzoic acid at 1,000 ppm was
the most effective additive in increasing heat sensitivity.
78
The fate of EC O157:H7 along with Listeria monocytogenes and Salmonella Typhimurium in beef
jerky was studied, and neither could be found in finished and dried products after 10 hours with inocula
of ∼10
7 /g or after storage for 8 weeks.
36
Regarding radiation resistance of EHEC strains, there is no apparent basis for them to differ greatly
from other enteric bacteria. Using chicken and an EC O157:H7 strain, the D value at 5
◦ C was 0.27
kGy, whereas at -5
◦ C, D was 0.42 kGy.
82 Employing a nonpathogenic strain of E. coli, Fielding et
al.
26 found radiation D to be ∼0.34 kGy in broth with a pH around 7.0, but the D was 0.24 kGy when
cells were grown at pH 4.0 prior to irradiation. See Chapter 15 for more on irradiation of foods. In
apple juice, nonacid adapted strains had a range of 0.12–0.21 kGy but when acid-adapted, the values
increased to 0.22–0.31 kGy.
7
In regard to survival in ovine and bovine manure, E. coli O157:H7 was found to survive in the
former for 100 days at 4
◦ or 10
◦ C, and survival was unaffected by the possession of stx genes.
45
Prevalence in Foods
Overall, the incidence and prevalence of EHEC strains in meat, milk, poultry, and seafood products
are highly variable. Considerably more positives are found when DNA probes are used to detect for
EHEC strains than when EC O157:H7 is tested alone. The first published study on the prevalence in
meats of EHEC strains was that of Doyle and Schoeni,
22 who tested for EC O157:H7 and found this
strain in 3.7% of 164 beef, 1.5% of 264 pork, 1.5% of 263 poultry, and 2.0% of 205 lamb samples.
In Thailand, EC O157:H7 was recovered from 9% of retail beef, 8–28% of slaughterhouse beef, and
11–84% of cattle fecal specimens.
79 Although EC O157:H7 could not be recovered from sausage in
the United Kingdom, a DNA probe gave positive results on 25% of 184 samples for other EHEC
strains.
77 None were found in 112 samples from 71 chickens.
77 In a study of foods in the Seattle area
following the 1993 outbreak, 17.3% of 294 foods were positive for colonies that contained Stx1 and/or