374 Modern Food Microbiology
Figure 15–2 Dose ranges of irradiation for various applications. Source: Adapted from Gr¨ unewald.
28
Some Candida strains have been reported to possess resistance comparable to that of some bacterial
endospores.
Numbers of Organisms
The numbers of organisms have the same effect on the efficacy of radiations as is the case for heat,
chemical disinfection, and certain other phenomena: The larger the number of cells, the less effective
is a given dose.
Composition of Suspending Menstruum (Food)
Microorganisms in general are more sensitive to radiation when suspended in buffer solutions than
in protein-containing media. For example, Midura et al.
52 found radiation D values for a strain of
Clostridium perfringens to be 0.23 in phosphate buffer, whereas in cooked-meat broth, the D value
was 3 kGy. Proteins exert a protective effect against radiations, as well as against certain antimicrobial
chemicals and heat. Several investigators have reported that the presence of nitrites tends to make
bacterial endospores more sensitive to radiation.
Presence or Absence of Oxygen
The radiation resistance of microorganisms is greater in the absence of oxygen than in its presence. Complete removal of oxygen from the cell suspension of Escherichia coli has been reported
to increase its radiation resistance up to threefold.
58 The addition of reducing substances such as
Figure 15–2 Dose ranges of irradiation for various applications. Source: Adapted from Gr¨ unewald.
28
Some Candida strains have been reported to possess resistance comparable to that of some bacterial
endospores.
Numbers of Organisms
The numbers of organisms have the same effect on the efficacy of radiations as is the case for heat,
chemical disinfection, and certain other phenomena: The larger the number of cells, the less effective
is a given dose.
Composition of Suspending Menstruum (Food)
Microorganisms in general are more sensitive to radiation when suspended in buffer solutions than
in protein-containing media. For example, Midura et al.
52 found radiation D values for a strain of
Clostridium perfringens to be 0.23 in phosphate buffer, whereas in cooked-meat broth, the D value
was 3 kGy. Proteins exert a protective effect against radiations, as well as against certain antimicrobial
chemicals and heat. Several investigators have reported that the presence of nitrites tends to make
bacterial endospores more sensitive to radiation.
Presence or Absence of Oxygen
The radiation resistance of microorganisms is greater in the absence of oxygen than in its presence. Complete removal of oxygen from the cell suspension of Escherichia coli has been reported
to increase its radiation resistance up to threefold.
58 The addition of reducing substances such as