but also to a strong desire to demonstrate that nuclear technology could
offer the human race something other than mass destruction. In partic-
ular, food irradiation has the advantage of being a much more precisely
controlled process than heating, since penetration is deep, instantaneous
and uniform. It also retains the fresh character of the product as low level
irradiation produces no detectable sensory change in most products.
This failure of low doses of radiation to produce appreciable chemical
change in the product has been an obstacle to the development of simple
tests to determine whether a food has been irradiated. Although avail-
ability of such a test is not essential for the control of irradiation, it is
generally accepted that it would facilitate international trade in irradi-
ated food, enhance consumer confidence and help enforce labelling
regulations. A number of methods have been developed that are appli-
cable to specific types of food. Free radicals created by irradiation can be
detected using electron spin resonance when they are trapped in solid
matrices such as bone, seeds and shells. The energy stored in grains of
silicate minerals as a result of irradiation can be measured in foods such
as herbs and spices using thermoluminescence and long chain volatile
hydrocarbons and 2-alkylcyclobutanones produced by irradiation of
fatty foods can be detected using gas chromatography. One microbio-
logical test for irradiated food is based on the ratio between an assess-
ment of total microbial numbers using the DEFT technique (see Chapter
10) and a plate count to determine the number of viable bacteria present.
Food irradiation is not without its disadvantages, but a lot of the
concerns originally voiced have proved to be unfounded. In 1981 an
expert international committee of the FAO/WHO and the International
Atomic Energy Authority recommended general acceptance of food
irradiation up to a level of 10 kGy. They held the view that it ‘constitutes
no toxicological risk. Further toxicological examinations of such treated
foods are therefore not required’.
It had been thought that irradiation could lead to pathogens becoming
more virulent but, apart from one or two exceptions, it has been found
that where virulence is affected it is diminished. In the exceptions noted,
the effect was slight and not sufficient to compensate for the overall
reduction in viable numbers. No example has been found where a non-
pathogenic organism has been converted to a pathogen as a result of
irradiation. Although it has been reported that spores of some my-
cotoxigenic moulds which survive irradiation may yield cultures with
increased mycotoxin production.
Morphological, biochemical and other changes which may impede
isolation and identification and increased radiation resistance have been
noted as a result of repeated cyclic irradiation. However, these experi-
ments were performed under the most favourable conditions and for this
to occur in practice would require extensive microbial regrowth after
88 The Microbiology of Food Preservation