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gives an idea of the quantity of radiation recommended to eliminate a microbial population giving
the high margin of safety which is desirable.
This radiation process has been operated by industry now for several years. As many as 70
million plastic hypodermic syringes alone are radiation-sterilized each year in this country. The
radiation plants operate within the factories, demonstrating that there has been no difficulty
concerning the safety of operation of plants of this kind.
In addition to the four commercial plants mentioned, at the well known Wantage Research
Laboratory which houses the Isotope Research Division of Harwell a fully commercial plant was
constructed in 1960 to demonstrate the process to industry, using a 350,000 curies cobalt 60
source.
A plant in Australia to eliminate anthrax spores from imported hair has operated successfully
since 1960.
These plants are designed with the necessary safety features and operate by press-button
control, not requiring a large number of expert staff.
Operation and Construction of a Commercial Plant
These plants have been constructed by engineering firms which have licensing agreements
with the United Kingdom Atomic Energy Authority in regard to design and construction. The
cobalt is supplied by the UKAEA through the Radiochemical Centre at Amersham.
In essence the plant consists of a concrete shielding which encloses the chamber in which
the isotope source is suspended. A conveyor-belt system carries the goods to be irradiated round
the isotope source at a certain speed which ensures that the required dose is received. The
isotope source can be lowered into a pond of water 20 feet deep (or into a slit in the ground
where it is safe), so that personnel can enter the chamber when required for maintenance. In the
operation of these plants small indicator discs are applied to each carton before entering the
radiation plant. These discs are yellow in colour before irradiation and change to a red colour
during the treatment. This is one of the methods used to distinguish between the untreated and
treated cartons.
The Application of this Process in the Treatment of Food
The possibility of applying this radiation process to food has been studied for many years. A
great deal of work was carried out in the USA by the US Army who saw the advantage of this
process to meet certain army requirements. Work in the United Kingdom began as early as 1953
at the Low Temperature Research Station at Cambridge in relation to the preservation of meat.
The subject was also taken up in 1958 at Wantage Research Laboratory, a UKAEA establishment,
where a wide range of radiation facilities were established including the commercial scale
radiation plant previously referred to. Other research establishments and some industrial concerns
have been involved in various aspects of the subject.
A wide variety of potential processes for radiation have been investigated. These include
in descending order of dose required the following: —
(1) Sterilization of fresh meat in order to allow storage at room temperature. The dosage
required was about 5 megarad in order to deal effectively with the possible Clostridium
botulinus hazard as dealt with efficiently in the canning process. Unfortunately at this dose of
radiation flavour and odour changes occur which are generally regarded as objectionable. In fact
the amount of chemical change is very small but our sensory perception is so discriminating
that these changes can be detected subjectively. In addition even this high dosage of radiation
will not inhibit enzyme activity so that autolysis will continue during room temperature storage,
resulting in loss of texture.
(2) To extend the refrigeration life (0° — 4°C.) of fresh meat and fish by eliminating those
micro-organisms responsible for spoilage within this temperature range, the dose required is
between 0.1 and 0.5 megarad, depending upon the particular commodity to be considered. With
this treatment the effect on the quality of the food is small and the refrigeration life can be
extended considerably. An extra few days can readily be achieved. This can assist in the problem
of distribution through the wholesale and retail trade. These processes are of current interest,
and possibilities in regard to fish treatment are being looked at by the White Fish Authority in
collaboration with the Torry Research Station, Aberdeen, and the UKAEA.
(3) Radiation is being looked at for its use in eliminating certain pathogens from food, in
particular salmonellae. The range of dose needed is 0.1 to 1 megarad depending on the commodity
in which salmonella is present, because research has demonstrated that the same serotype can
vary in resistance according to the food environment in which it is present.
(4) Moulds can be eliminated from fruit. The dose required is about 0.25 megarad without
affecting the quality especially of soft fruit, e.g. strawberries and cherries.
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