384 Modern Food Microbiology
twofold to sixfold by radurization with doses from 1 to 4 kGy. Similar results can be achieved for fish
and shellfish under various conditions of packaging.
59 In one study, scallops stored at 0
◦ C had a shelf
life of 13 days, but after irradiation doses of 0.5, 1.5, and 3.0 kGy, shelf life was 18, 23, and 42 days,
respectively.
63 The Gram-negative non-spore-forming rods are among the most radiosensitive of all
bacteria, and they are the principal spoilage organisms for these foods. Following the irradiation of
vacuum-packaged ground pork at 1.0 kGy and storage at 5
◦ C for 9 days, 97% of the irradiated biota
consisted of Gram-positive bacteria, with most being coryneforms.
15 The Gram-negative coccobacillary rods belonging to the genera Moraxella and Acinetobacter have been found to possess degrees of
radiation resistance higher than for all other Gram negatives. In studies on ground beef subjected to
doses of 272 krad, Tiwari and Maxcy
86 found that 73–75% of the surviving biota consisted of these
related genera. In unirradiated meat, they constituted only around 8% of the biota. Of the two genera,
the Moraxella spp. appeared to be more resistant than Acinetobacter spp., with D 10 values of 0.539
and 0.583 kGy, whereas the D 10 for M. osloensis strains was 477 up to 1,000 krad (0.477–1.0 kGy).
In comparing the radiosensitivity of some non–spore-forming bacteria in phosphate buffer at −80
◦ C,
Anellis et al.
2 found that Deinococcus radiodurans survived 18 kGy, Enterococcus faecium strains
survived 9–15 kGy, E. faecalis survived 6–9 kGy, and Lactococcus lactis did not survive 6 kGy.
Staphylococcus aureus, Lactobacillus casei, and Lactobacillus arabinosus did not survive 3-kGy
exposures. It was shown that radiation sensitivity decreased as the temperature of irradiation was
lowered, as is the case for endospores.
The ultimate spoilage of radurized, low-temperature-stored foods is invariably caused by one or
more of the Acinetobacter-Moraxella or lactic acid types noted above. The application of 2.5 kGy to
ground beef destroyed all pseudomonads, Enterobacteriaceae, and Brochothrix thermosphacta; and
reduced aerobic plate counts (APCs) from 6.18/g to 1.78 log 10 /g, but reduced lactic acid bacteria only
by 3.4 log/g.
57
Radurization of fruits with doses of 2–3 kGy brings about an extension of shelf life of at least 14
days. Radurization of fresh fruits is permitted by at least six countries, with some meats, poultry, and
seafood permitted by several others (Table 15–5). In general, shelf-life extension is not as great for
radurized fruits as for meats and seafood because molds are generally more resistant to irradiation
than the Gram-negative bacteria that cause spoilage of the latter products. When ground beef patties
were subjected to 2.0 kGy under vacuum, they remained unspoiled after 60 days in the refrigerator.
55
In another study, unirradiated ground beef patties that originally contained 10
6 APC/g contained 10
8 /g
after 8 days at 4
◦ C, but the samples that were irradiated at 2 kGy (range 1.9–2.4) reached only 10
6 /g
after 55 days at 4
◦ C.
56 In regards to pathogens in ground beef, it was concluded that an applied
dose of 2.5 kGy would be sufficient to destroy 10
8.1 E. coli. 0157:H7, 10
3.1 salmonellae, and 10
10.6
Campylobacter jejuni.
7
Insect eggs and larvae can be destroyed by 1 kGy, and cysticerci of the pork tapeworm (Taenia solium)
and the beef tapeworm (T. saginata) can be destroyed with even lower doses, with cysticercosis-infested
meat being rendered free of parasites by exposure to 0.2–0.5 kGy.
92
LEGAL STATUS OF FOOD IRRADIATION
At least 40 countries had approved the irradiation of some foods as of mid-1989.
47 At least 20
different food–packaging materials have been approved by the U.S. Food and Drug Administration
(FDA) at levels of 10 or 60 kGy. In 1983, the FDA permitted spices and vegetable seasonings to be
irradiated up to 10 kGy (U.S. Federal Register, July 15, 1983). In 1985 the FDA granted permission
for the irradiation of pork at up to 1 kGy to control Trichinella spiralis (U.S. Federal Register, July 22,
twofold to sixfold by radurization with doses from 1 to 4 kGy. Similar results can be achieved for fish
and shellfish under various conditions of packaging.
59 In one study, scallops stored at 0
◦ C had a shelf
life of 13 days, but after irradiation doses of 0.5, 1.5, and 3.0 kGy, shelf life was 18, 23, and 42 days,
respectively.
63 The Gram-negative non-spore-forming rods are among the most radiosensitive of all
bacteria, and they are the principal spoilage organisms for these foods. Following the irradiation of
vacuum-packaged ground pork at 1.0 kGy and storage at 5
◦ C for 9 days, 97% of the irradiated biota
consisted of Gram-positive bacteria, with most being coryneforms.
15 The Gram-negative coccobacillary rods belonging to the genera Moraxella and Acinetobacter have been found to possess degrees of
radiation resistance higher than for all other Gram negatives. In studies on ground beef subjected to
doses of 272 krad, Tiwari and Maxcy
86 found that 73–75% of the surviving biota consisted of these
related genera. In unirradiated meat, they constituted only around 8% of the biota. Of the two genera,
the Moraxella spp. appeared to be more resistant than Acinetobacter spp., with D 10 values of 0.539
and 0.583 kGy, whereas the D 10 for M. osloensis strains was 477 up to 1,000 krad (0.477–1.0 kGy).
In comparing the radiosensitivity of some non–spore-forming bacteria in phosphate buffer at −80
◦ C,
Anellis et al.
2 found that Deinococcus radiodurans survived 18 kGy, Enterococcus faecium strains
survived 9–15 kGy, E. faecalis survived 6–9 kGy, and Lactococcus lactis did not survive 6 kGy.
Staphylococcus aureus, Lactobacillus casei, and Lactobacillus arabinosus did not survive 3-kGy
exposures. It was shown that radiation sensitivity decreased as the temperature of irradiation was
lowered, as is the case for endospores.
The ultimate spoilage of radurized, low-temperature-stored foods is invariably caused by one or
more of the Acinetobacter-Moraxella or lactic acid types noted above. The application of 2.5 kGy to
ground beef destroyed all pseudomonads, Enterobacteriaceae, and Brochothrix thermosphacta; and
reduced aerobic plate counts (APCs) from 6.18/g to 1.78 log 10 /g, but reduced lactic acid bacteria only
by 3.4 log/g.
57
Radurization of fruits with doses of 2–3 kGy brings about an extension of shelf life of at least 14
days. Radurization of fresh fruits is permitted by at least six countries, with some meats, poultry, and
seafood permitted by several others (Table 15–5). In general, shelf-life extension is not as great for
radurized fruits as for meats and seafood because molds are generally more resistant to irradiation
than the Gram-negative bacteria that cause spoilage of the latter products. When ground beef patties
were subjected to 2.0 kGy under vacuum, they remained unspoiled after 60 days in the refrigerator.
55
In another study, unirradiated ground beef patties that originally contained 10
6 APC/g contained 10
8 /g
after 8 days at 4
◦ C, but the samples that were irradiated at 2 kGy (range 1.9–2.4) reached only 10
6 /g
after 55 days at 4
◦ C.
56 In regards to pathogens in ground beef, it was concluded that an applied
dose of 2.5 kGy would be sufficient to destroy 10
8.1 E. coli. 0157:H7, 10
3.1 salmonellae, and 10
10.6
Campylobacter jejuni.
7
Insect eggs and larvae can be destroyed by 1 kGy, and cysticerci of the pork tapeworm (Taenia solium)
and the beef tapeworm (T. saginata) can be destroyed with even lower doses, with cysticercosis-infested
meat being rendered free of parasites by exposure to 0.2–0.5 kGy.
92
LEGAL STATUS OF FOOD IRRADIATION
At least 40 countries had approved the irradiation of some foods as of mid-1989.
47 At least 20
different food–packaging materials have been approved by the U.S. Food and Drug Administration
(FDA) at levels of 10 or 60 kGy. In 1983, the FDA permitted spices and vegetable seasonings to be
irradiated up to 10 kGy (U.S. Federal Register, July 15, 1983). In 1985 the FDA granted permission
for the irradiation of pork at up to 1 kGy to control Trichinella spiralis (U.S. Federal Register, July 22,