Radiation Protection of Foods, and Nature of Microbial Radiation Resistance
383
The irradiation of steaks at 1.5 kGy inoculated with ∼10
5 /g of Escherichia coli 0157:H7 resulted in
complete elimination of cells.
21 Yersinia enterocolitica was reduced to undetectable levels under the
same conditions. Irradiation of mechanically deboned chicken meat that was inoculated with ∼400
spores of 20 strains of C. botulinum types A and B at 1.5 or 3.0 kGy resulted in no samples becoming
demonstrably toxic after refrigerated storage for four weeks, but samples that were temperature abused
at 28
◦ C became toxic within 18 hours.
79 In a similar product, an initial level of Salmonella Enteritidis
3.86 log 10 /g was reduced to <10 cfu/g after four weeks at 5
◦ C.
Live oysters were placed in a tank of water to which were added cultures of S. Enteritidis, S. Infantis,
and Vibrio parahaemolyticus, and after 13 hours they contained ca. 4–6 log cfu/g.
33 Irradiation at 3
kGy reduced the two salmonellae by 5 to 6 logs, and 1.0 kGy reduced V. parahaemolyticus by 6
logs.The oysters were not killed by up to 3 kGy.
SEED SPROUTS AND OTHER VEGETABLES
The D values of meat and vegetable isolates of E. coli 0157:H7 on alfalfa and broccoli were found
to be 0.34 and 0.30 kGy, respectively, while a salmonellae cocktail of meat and vegetable isolates
was found to be 0.54 and 0.46 kGy, respectively.
68 No salmonellae were detected on sprouts given a
0.5 kGy or higher dose. The D value for S. Mbandaka on alfalfa seeds was found to be 0.81 ± 0.02
kGy.
81 In this study, an absorbed dose of 4 kGy but not 3 kGy eliminated S. Mbandaka from naturally
contaminated seeds. In another study, an irradiation dose of 2 kGy reduced the APC from 10
5−8 to 10
3−5
cfu/g while coliforms were reduced even more.
67 This treatment extended keeping quality by 10 days
over controls with little adverse effect on seed germination and sprout quality. Although the U.S. Food
and Drug Administration has approved the use of 8 kGy for alfalfa seeds for sprouts, irradiation doses
above 3 kGy lead to a reduction of germination. From a later study of E. coli 0157:H7 and Salmonella
on alfalfa seeds, a 2-kGy dose effected a 3.3-log reduction of E. coli and Salmonella, respectively, with
no significant loss of sprouting.
82 These authors found these organisms to be more radiation resistant
on alfalfa seeds than in meats or poultry. In another study, a nonvegetable isolate of E. coli 0157:H7
had a D value of 1.43 kGy while a vegetable isolate was 1.11.
69 The background biota of broccoli
sprouts was reduced from 10
6 –10
7 to 10
4 –10
5 cfu/g resulting in an increased shelf life of 10 days.
A combination of irradiation and MAP was evaluated for the preservation of fresh-cut lettuce in two
studies. In one, the initial APC of 10
5 –10
6 cfu/g was reduced by ca. 1.5 log 10 cfu/g after 14 days at 4
◦ C
with a dose of 0.35 kGy.
64 This treatment resulted in a 10% loss in product firmness. The Romaine
lettuce was packaged in laminate polyethylene bags with an initial concentration of ca. 1.5% O 2 , 4%
CO 2 , and the remainder N 2 .
64 In the other study, Iceberg lettuce was best with doses of 1–2 kGy,
which reduced the amount of leakage seen in samples exposed to doses >2 kGy.
17 The O 2 content of
the 3
◦ C-stored samples ranged from 1.5 to 3.7% after day 5, and the CO 2 content was higher than in
non-irradiated controls. In a study of the effect of irradiation on the destruction of a 5-strain cocktail of
L. monocytogenes in six different ready-to-eat meats at doses of 2.0 and 4.0 kGy followed by storage
at 4 and 10
◦ C, no cells could be detected when 4.0 kGy was used.
20 With 2.0 kGy and 10
◦ C, survivors
were recovered after the second week but with 2.0 kGy-treated products stored at 4
◦ C, survivors were
recovered after 5 weeks.
Radurization
Irradiation treatments to extend the shelf life of seafoods, vegetables, and fruits have been verified
in many studies. The shelf life of shrimp, crab, haddock, scallops, and clams may be extended from
383
The irradiation of steaks at 1.5 kGy inoculated with ∼10
5 /g of Escherichia coli 0157:H7 resulted in
complete elimination of cells.
21 Yersinia enterocolitica was reduced to undetectable levels under the
same conditions. Irradiation of mechanically deboned chicken meat that was inoculated with ∼400
spores of 20 strains of C. botulinum types A and B at 1.5 or 3.0 kGy resulted in no samples becoming
demonstrably toxic after refrigerated storage for four weeks, but samples that were temperature abused
at 28
◦ C became toxic within 18 hours.
79 In a similar product, an initial level of Salmonella Enteritidis
3.86 log 10 /g was reduced to <10 cfu/g after four weeks at 5
◦ C.
Live oysters were placed in a tank of water to which were added cultures of S. Enteritidis, S. Infantis,
and Vibrio parahaemolyticus, and after 13 hours they contained ca. 4–6 log cfu/g.
33 Irradiation at 3
kGy reduced the two salmonellae by 5 to 6 logs, and 1.0 kGy reduced V. parahaemolyticus by 6
logs.The oysters were not killed by up to 3 kGy.
SEED SPROUTS AND OTHER VEGETABLES
The D values of meat and vegetable isolates of E. coli 0157:H7 on alfalfa and broccoli were found
to be 0.34 and 0.30 kGy, respectively, while a salmonellae cocktail of meat and vegetable isolates
was found to be 0.54 and 0.46 kGy, respectively.
68 No salmonellae were detected on sprouts given a
0.5 kGy or higher dose. The D value for S. Mbandaka on alfalfa seeds was found to be 0.81 ± 0.02
kGy.
81 In this study, an absorbed dose of 4 kGy but not 3 kGy eliminated S. Mbandaka from naturally
contaminated seeds. In another study, an irradiation dose of 2 kGy reduced the APC from 10
5−8 to 10
3−5
cfu/g while coliforms were reduced even more.
67 This treatment extended keeping quality by 10 days
over controls with little adverse effect on seed germination and sprout quality. Although the U.S. Food
and Drug Administration has approved the use of 8 kGy for alfalfa seeds for sprouts, irradiation doses
above 3 kGy lead to a reduction of germination. From a later study of E. coli 0157:H7 and Salmonella
on alfalfa seeds, a 2-kGy dose effected a 3.3-log reduction of E. coli and Salmonella, respectively, with
no significant loss of sprouting.
82 These authors found these organisms to be more radiation resistant
on alfalfa seeds than in meats or poultry. In another study, a nonvegetable isolate of E. coli 0157:H7
had a D value of 1.43 kGy while a vegetable isolate was 1.11.
69 The background biota of broccoli
sprouts was reduced from 10
6 –10
7 to 10
4 –10
5 cfu/g resulting in an increased shelf life of 10 days.
A combination of irradiation and MAP was evaluated for the preservation of fresh-cut lettuce in two
studies. In one, the initial APC of 10
5 –10
6 cfu/g was reduced by ca. 1.5 log 10 cfu/g after 14 days at 4
◦ C
with a dose of 0.35 kGy.
64 This treatment resulted in a 10% loss in product firmness. The Romaine
lettuce was packaged in laminate polyethylene bags with an initial concentration of ca. 1.5% O 2 , 4%
CO 2 , and the remainder N 2 .
64 In the other study, Iceberg lettuce was best with doses of 1–2 kGy,
which reduced the amount of leakage seen in samples exposed to doses >2 kGy.
17 The O 2 content of
the 3
◦ C-stored samples ranged from 1.5 to 3.7% after day 5, and the CO 2 content was higher than in
non-irradiated controls. In a study of the effect of irradiation on the destruction of a 5-strain cocktail of
L. monocytogenes in six different ready-to-eat meats at doses of 2.0 and 4.0 kGy followed by storage
at 4 and 10
◦ C, no cells could be detected when 4.0 kGy was used.
20 With 2.0 kGy and 10
◦ C, survivors
were recovered after the second week but with 2.0 kGy-treated products stored at 4
◦ C, survivors were
recovered after 5 weeks.
Radurization
Irradiation treatments to extend the shelf life of seafoods, vegetables, and fruits have been verified
in many studies. The shelf life of shrimp, crab, haddock, scallops, and clams may be extended from