Fundamental Food Microbiology, Third Edition - Fuad Fathir

512 FUNDAMENTAL FOOD MICROBIOLOGY
microorganisms have been suggested as follows: insects, £1 kGy; molds, yeasts,
bacterial cells, 0.5 to 10 kGy; bacterial spores, 10 to 50 kGy; viruses, 10 to 200
kGy. Thus, at the recommended level of 10 kGy, Clo. botulinum spores are not
destroyed in foods (they need ca. 30 to 60 kGy), although cells of pathogenic (and
spoilage) bacteria are destroyed. The products thus treated should have other barriers
(low pH, low A w, temperature £ 4�C) to control germination and growth of sporeformers.
But some sporeformers (such as Clo. laramie) can germinate and multiply
below 4�C. At present, a low dose level (10 kGy) to destroy
spores are not used in foods except in spices and vegetable seasonings that are used
in very small quantities.
Irradiated foods, such as postheat contamination in heated foods, can be contaminated
later with pathogenic and spoilage microorganisms from various sources
unless proper precautions (such as packaging) are used. 1–4 Also, a food can be
reirradiated and not be detected.
B. Specific Terms
1. Radurization
Radiation pasteurization is mainly intended to destroy spoilage bacteria in highpH–high-A
w foods, especially Gram-negative psychrotrophs in meat and fish and
yeasts and molds in low-pH–low-A w foods. The treatment is generally milder (@1
kGy). The products should be packaged and chilled to prevent growth of pathogens,
which were previously thought to be mesophiles. However, with the recognition of
psychrotrophic pathogens and the importance of psychrotrophic Gram-positive spoilage
bacteria, this treatment may not be effective.
2. Radicidation
This is the radiation of foods to destroy vegetative foodborne pathogens. The
dose level used is ca. 2.5 kGy to 5.0 kGy. Although it is effective against
pathogenic vegetative bacterial cells and molds, spores of the pathogens are not
destroyed. Also, some radiation-resistant strains of pathogens can survive, such
as some Salmonella Typhimurium strains. Irradiated products thus need to be
stored under £4�C, especially to prevent germination and outgrowth of spores of
Clo. botulinum.
3. Radappertization
This method involves radiation of food at a high dose (@30 kGy) to destroy Clo.
botulinum spores in order to get a safety similar to that by 12D heat treatment.
However, this is not recommended for use in food.