Chapter 15
Radiation Protection of Foods,
and Nature of Microbial
Radiation Resistance
Although a patent was issued in 1929 for the use of radiation as a means of preserving or protecting
foods, it was not until shortly after World War II that this method of food protection received any
serious consideration. While the application of radiation has been somewhat slow in reaching its
maximum potential use, the full application of this method presents some interesting challenges to
food microbiologists and other food scientists.
Radiation may be defined as the emission and propagation of energy through space or through
a material medium. The type of radiation of primary interest in food preservation is electromagnetic. The electromagnetic spectrum is presented in Figure 15–1. The various radiations are separated
on the basis of their wavelengths, with the shorter wavelengths being the most damaging to microorganisms. The electromagnetic spectrum may be further divided as follows with respect to the
radiations of interest in food preservation: microwaves, ultraviolet rays, X-rays, and gamma rays.
The radiations of primary interest in food preservation are ionizing radiations, defined as those radiations that have wavelengths of 2000 ˚
A or less—for example, alpha particles, beta rays, gamma
rays, and X-rays. Their quanta contain enough energy to ionize molecules in their paths. Because
they destroy microorganisms without appreciably raising the temperature, the process is termed cold
sterilization.
In considering the application of radiation to foods, there are several useful concepts that should be
clarified. A Roentgen is a unit of measure used for expressing an exposure dose of X-ray or gamma
radiation. A milliroentgen is equal to 1/1,000 of a roentgen. A Curie is a quantity of radioactive
substance in which 3.7 × 10
10 radioactive disintegrations occur per second. For practical purposes,
1 g of pure radium possesses the radioactivity of 1 curie of radium. The unit for a curie is the Becquerel
(Bq). A rad is a unit equivalent to the absorption of 100 ergs/g of matter. A kilorad (krad) is equal to
1,000 rads, and a megarad (Mrad) is equal to 1 million rads. The newer unit of absorbed dose is the
Gray (1 Gy = 100 rads = 11 joule/kg; 1 kGy = 10
5 rads). The energy gained by an electron in moving
through 1 V is designated eV (electron volt). An meV is equal to 1 million electron volts. Both the
rad and eV are measurements of the intensity of irradiation.
371
Radiation Protection of Foods,
and Nature of Microbial
Radiation Resistance
Although a patent was issued in 1929 for the use of radiation as a means of preserving or protecting
foods, it was not until shortly after World War II that this method of food protection received any
serious consideration. While the application of radiation has been somewhat slow in reaching its
maximum potential use, the full application of this method presents some interesting challenges to
food microbiologists and other food scientists.
Radiation may be defined as the emission and propagation of energy through space or through
a material medium. The type of radiation of primary interest in food preservation is electromagnetic. The electromagnetic spectrum is presented in Figure 15–1. The various radiations are separated
on the basis of their wavelengths, with the shorter wavelengths being the most damaging to microorganisms. The electromagnetic spectrum may be further divided as follows with respect to the
radiations of interest in food preservation: microwaves, ultraviolet rays, X-rays, and gamma rays.
The radiations of primary interest in food preservation are ionizing radiations, defined as those radiations that have wavelengths of 2000 ˚
A or less—for example, alpha particles, beta rays, gamma
rays, and X-rays. Their quanta contain enough energy to ionize molecules in their paths. Because
they destroy microorganisms without appreciably raising the temperature, the process is termed cold
sterilization.
In considering the application of radiation to foods, there are several useful concepts that should be
clarified. A Roentgen is a unit of measure used for expressing an exposure dose of X-ray or gamma
radiation. A milliroentgen is equal to 1/1,000 of a roentgen. A Curie is a quantity of radioactive
substance in which 3.7 × 10
10 radioactive disintegrations occur per second. For practical purposes,
1 g of pure radium possesses the radioactivity of 1 curie of radium. The unit for a curie is the Becquerel
(Bq). A rad is a unit equivalent to the absorption of 100 ergs/g of matter. A kilorad (krad) is equal to
1,000 rads, and a megarad (Mrad) is equal to 1 million rads. The newer unit of absorbed dose is the
Gray (1 Gy = 100 rads = 11 joule/kg; 1 kGy = 10
5 rads). The energy gained by an electron in moving
through 1 V is designated eV (electron volt). An meV is equal to 1 million electron volts. Both the
rad and eV are measurements of the intensity of irradiation.
371