Radiation Protection of Foods, and Nature of Microbial Radiation Resistance
375
sulfhydryl compounds generally has the same effect in increasing radiation resistance as an anaerobic
environment has.
Physical State of Food
The radiation resistance of dried cells is, in general, considerably higher than that for moist cells.
This is most likely a direct consequence of the radiolysis of water by ionizing radiations, which is
discussed later in this chapter. Radiation resistance of frozen cells is greater than that of nonfrozen
cells. Grecz et al.
26 found that the lethal effects of gamma radiation decreased by 47% when ground
beef was irradiated at −196
◦ C as compared to 0
◦ C.
Age of Organisms
Bacteria tend to be most resistant to radiation in the lag phase just prior to active cell division. The
cells become more radiation sensitive as they enter and progress through the log phase and reach their
minimum at the end of this phase.
PROCESSING OF FOODS FOR IRRADIATION
Prior to being exposed to ionizing radiations, several processing steps must be carried out in much
the same manner as for the freezing or canning of foods.
Selection of Foods
Foods to be irradiated should be carefully selected for freshness and overall desirable quality.
Especially to be avoided are foods that are already in incipient spoilage.
Cleaning of Foods
All visible debris and dirt should be removed. This will reduce the numbers of microorganisms to
be destroyed by the radiation treatment.
Packaging
Foods to be irradiated should be packed in containers that will afford protection against post irradiation contamination. Clear glass containers undergo color changes when exposed to doses of radiation
of around 10 kGy, and the subsequent color may be undesirable.
Blanching or Heat Treatment
Sterilizing doses of radiation are insufficient to destroy the natural enzymes of foods (Figure 15–2).
In order to avoid undesirable postirradiation changes, it is necessary to destroy these enzymes. The
best method is a heat treatment—that is, the blanching of vegetables and mild heat treatment of meats
prior to irradiation.
375
sulfhydryl compounds generally has the same effect in increasing radiation resistance as an anaerobic
environment has.
Physical State of Food
The radiation resistance of dried cells is, in general, considerably higher than that for moist cells.
This is most likely a direct consequence of the radiolysis of water by ionizing radiations, which is
discussed later in this chapter. Radiation resistance of frozen cells is greater than that of nonfrozen
cells. Grecz et al.
26 found that the lethal effects of gamma radiation decreased by 47% when ground
beef was irradiated at −196
◦ C as compared to 0
◦ C.
Age of Organisms
Bacteria tend to be most resistant to radiation in the lag phase just prior to active cell division. The
cells become more radiation sensitive as they enter and progress through the log phase and reach their
minimum at the end of this phase.
PROCESSING OF FOODS FOR IRRADIATION
Prior to being exposed to ionizing radiations, several processing steps must be carried out in much
the same manner as for the freezing or canning of foods.
Selection of Foods
Foods to be irradiated should be carefully selected for freshness and overall desirable quality.
Especially to be avoided are foods that are already in incipient spoilage.
Cleaning of Foods
All visible debris and dirt should be removed. This will reduce the numbers of microorganisms to
be destroyed by the radiation treatment.
Packaging
Foods to be irradiated should be packed in containers that will afford protection against post irradiation contamination. Clear glass containers undergo color changes when exposed to doses of radiation
of around 10 kGy, and the subsequent color may be undesirable.
Blanching or Heat Treatment
Sterilizing doses of radiation are insufficient to destroy the natural enzymes of foods (Figure 15–2).
In order to avoid undesirable postirradiation changes, it is necessary to destroy these enzymes. The
best method is a heat treatment—that is, the blanching of vegetables and mild heat treatment of meats
prior to irradiation.