Radiation Protection of Foods, and Nature of Microbial Radiation Resistance
387
With regard to B vitamins, Liuzzo et al.
46 found that levels of
60 Co irradiation between 2 and 6 kGy
effected partial destruction of the following B vitamins in oysters: thiamine, niacin, pyridoxine, biotin,
and B 12 . Riboflavin, pantothenic acid, and folic acid reportedly increased by irradiation, probably
owing to the release of bound vitamins. Overall, the reported effects on water-soluble vitamins are not
striking.
84
In addition to flavor and odor changes produced in certain foods by irradiation, certain detrimental
effects have been reported for irradiated fruits and vegetables. One of the most serious is the softening
of these products caused by the irradiation–degradation of pectin and cellulose, the structural polysaccharides of plants. This effect was shown by Massey and Bourke
49 to be caused by radappertization
doses of irradiation. Ethylene synthesis in apples is affected by irradiation so that this fruit fails to mature as rapidly as nonirradiated controls.
49 In green lemons, however, ethylene synthesis is stimulated
upon irradiation, resulting in a faster ripening than in controls.
50
Among radiolytic products that develop upon irradiation are some that are antibacterial when
exposed in culture media. When 15 kGy were applied to meats, however, no antimicrobial activity
was found in the meats.
12 The overall wholesomeness and toxicology of irradiated foods have been
reviewed.
76,85
STORAGE STABILITY OF IRRADIATED FOODS
Foods subjected to radappertization doses of ionizing radiation may be expected to be as shelf stable
as commercially heat-sterilized foods. There are, however, two differences between foods processed
by these two methods that affect storage stability: Radappertization does not destroy inherent enzymes,
which may continue to act, and some postirradiation changes may be expected to occur. Employing
45 kGy and enzyme-inactivated chicken, bacon, and fresh and barbecued pork, Heiligman
31 found the
products to be acceptable after storage for up to 24 months. Those stored at 70
◦ F were more acceptable
than those stored at 100
◦ F. Licciardello et al. reported the effect of irradiation on beefsteak, ground
beef, and pork sausage held at refrigerator temperatures for 12 years.
45 These foods were packed with
flavor preservatives and treated with 10.8 kGy. The investigators described the appearance of the meats
as excellent after 12 years of storage. A slight irradiation odor was perceptible, but was not considered
objectionable. The meats were reported to have a sharp, bitter taste, which was presumed to be caused
by the crystallization of the amino acid tyrosine. The free amino nitrogen content of the beefsteak was
75 and 175 mg%, respectively, before and after irradiation storage; and 67 and 160 mg% before and
after storage, respectively, for hamburger.
Foods subjected to radurization ultimately undergo spoilage from the surviving biota if stored at
temperatures suitable for growth of the organisms in question. The normal spoilage biota of seafoods
is so sensitive to ionizing radiations that 99% of the total biota of these products is generally destroyed
by doses on the order of 2.5 kGy. Ultimate spoilage of radurized products is the property of the few
microorganisms that survive the radiation treatment. For further information on all aspects of food
irradiation, see references 66 and 89.
NATURE OF RADIATION RESISTANCE OF MICROORGANISMS
The most sensitive bacteria to ionizing radiation are Gram-negative rods such as the pseudomonads; the coccobacillary-shaped Gram-negative cells of moraxellae and acinetobacters are among the
387
With regard to B vitamins, Liuzzo et al.
46 found that levels of
60 Co irradiation between 2 and 6 kGy
effected partial destruction of the following B vitamins in oysters: thiamine, niacin, pyridoxine, biotin,
and B 12 . Riboflavin, pantothenic acid, and folic acid reportedly increased by irradiation, probably
owing to the release of bound vitamins. Overall, the reported effects on water-soluble vitamins are not
striking.
84
In addition to flavor and odor changes produced in certain foods by irradiation, certain detrimental
effects have been reported for irradiated fruits and vegetables. One of the most serious is the softening
of these products caused by the irradiation–degradation of pectin and cellulose, the structural polysaccharides of plants. This effect was shown by Massey and Bourke
49 to be caused by radappertization
doses of irradiation. Ethylene synthesis in apples is affected by irradiation so that this fruit fails to mature as rapidly as nonirradiated controls.
49 In green lemons, however, ethylene synthesis is stimulated
upon irradiation, resulting in a faster ripening than in controls.
50
Among radiolytic products that develop upon irradiation are some that are antibacterial when
exposed in culture media. When 15 kGy were applied to meats, however, no antimicrobial activity
was found in the meats.
12 The overall wholesomeness and toxicology of irradiated foods have been
reviewed.
76,85
STORAGE STABILITY OF IRRADIATED FOODS
Foods subjected to radappertization doses of ionizing radiation may be expected to be as shelf stable
as commercially heat-sterilized foods. There are, however, two differences between foods processed
by these two methods that affect storage stability: Radappertization does not destroy inherent enzymes,
which may continue to act, and some postirradiation changes may be expected to occur. Employing
45 kGy and enzyme-inactivated chicken, bacon, and fresh and barbecued pork, Heiligman
31 found the
products to be acceptable after storage for up to 24 months. Those stored at 70
◦ F were more acceptable
than those stored at 100
◦ F. Licciardello et al. reported the effect of irradiation on beefsteak, ground
beef, and pork sausage held at refrigerator temperatures for 12 years.
45 These foods were packed with
flavor preservatives and treated with 10.8 kGy. The investigators described the appearance of the meats
as excellent after 12 years of storage. A slight irradiation odor was perceptible, but was not considered
objectionable. The meats were reported to have a sharp, bitter taste, which was presumed to be caused
by the crystallization of the amino acid tyrosine. The free amino nitrogen content of the beefsteak was
75 and 175 mg%, respectively, before and after irradiation storage; and 67 and 160 mg% before and
after storage, respectively, for hamburger.
Foods subjected to radurization ultimately undergo spoilage from the surviving biota if stored at
temperatures suitable for growth of the organisms in question. The normal spoilage biota of seafoods
is so sensitive to ionizing radiations that 99% of the total biota of these products is generally destroyed
by doses on the order of 2.5 kGy. Ultimate spoilage of radurized products is the property of the few
microorganisms that survive the radiation treatment. For further information on all aspects of food
irradiation, see references 66 and 89.
NATURE OF RADIATION RESISTANCE OF MICROORGANISMS
The most sensitive bacteria to ionizing radiation are Gram-negative rods such as the pseudomonads; the coccobacillary-shaped Gram-negative cells of moraxellae and acinetobacters are among the