We live in a naturally radioactive world. Radioactive
polonium and radium are present in our bones; our muscles contain radioactive
carbon and potassium and there are radioactive noble gases and tritium in our
lungs. We are bombarded by cosmic radiation from space and irradiated from
within by the natural and artificial substances, we eat and drink each day.
Until the invention of the X-ray tube in 1895, the only radiation in existence
was natural radiation. In 1896, natural radioactivity was discovered and was
used for medical and research purposes until 1934, when the first artificial
radioactive materials were produced. Since then, many such substances have been
utilized to the beneficial, environmental protection, medicine and a member of
academic and commercial fields.
The use of neutron, X-rays and beta and gamma rays is
described and interpreted with some new data on levels of radiation required to
preserve different foods. Irradiation can be applied for ripening delay,
preservation and extending storage life of various crops, fruits and vegetables.
Some physio-chemical changes may occur after radiation treatment of fresh fruits
and vegetables. The chemical changes brought about by irradiation treatment in
foods have been studied very thoroughly owning to the fears that some of their
changes may produce toxic compounds. Gamma radiation is also used for
decontamination of food items. The technique of food preservation by ionizing
radiation has become established among other technological methods. The main
advantage of these radiation techniques lies in its strong penetrating power.
Gamma and X-rays have germicidal properties and are being exploited in food
industry for preservation. The X-rays are produced by the X-ray tubes, while
gamma rays are emitted from radioactive isotopes such as cobalt-60 and
caesium-137 and these are used for food irradiation. The most commonly employed
unit for measurement of radiation energy absorbed has been the "rad".
A rad is equivalent to 105 Joules (J) of energy absorbed per gram of material
receiving ionizing radiation. Kilorad (Krad) is used when heavy doses are
employed. In accordance with recommendations of the International Organization
for Standardization (ISO), the rad has been replaced by Gray (Gy), which
corresponds to 100 rad. They Gy is the new unit of System International (SI)
system. IAEA, expert committee has permitted irradiation of food materials to
any dose level, whereby the technological properties are not affected.
Initially, the FAO/IAEA/WHO experts committee had allow irradiation of foods
upto a maximum of 10 KGy.
(i) Radiation source: In radiation processing
of food, only gamma rays from cobalt-60 or caesium-137; X-rays generated by a
machine at a maximum energy of five megavolts; or electrons generated by a
machine at a maximum energy of 10 megavolts can be used. Energies from these
radiation sources are too low to induce radioactivity in any material, including
food, exposed to them.
(ii) Radiation dose: The quantity of radiation energy absorbed by a food
as it passes through in processing. Usually measured by a unit called the Gray (Gy)
or (1 Gy = 100 rads). International health and safety authorities have endorsed
the safety of irradiation for all foods up to a dose level of 10 Gray. This
amount of radiation energy equals the amount of heat required to raise the
temperature of water 2.4 degrees Centigrade.
(iii) Electron beams: Streams of electrons (invisible beta particles of
an atom carrying a negative electrical charge) that are accelerated by a machine
in radiation processing. (iv) Gamma rays: Form of electromagnetic
radiation of extremely short wavelength, similar to X-rays. Emitted by
radioactive isotopes such as cobalt-60 that are used as the source of energy in
food irradiation and in medical treatment.
(v) Ionizing radiation: High-energy radiation that can penetrate other
atoms and produce electrically charged particles called ions. Includes gamma
rays, and fastmoving electrons.
(vi) Irradiation: Deliberate treatment of a product by exposing it to
gamma radiation from a radioactive source or to machine-generated X-rays or
electrons under controlled conditions.
(vii) Radioactivity: Property of an atom whose nucleus, or centre, is
physically unstable and spontaneously releases radiation energy. Such atoms can
be natural they include carbon-14 in the environment and potassium-40 in
foods or scientifically produced for industrial, medical, and research purposes.
(viii) X-rays: Form of electromagnetic radiation of a wide variety of
short wavelengths. Usually produced by a machine. Used in heath care for medical
images and in radiation processing of food and other products.
Over many decades, food scientists, chemists,
microbiologists, and other researchers have extensively studied and tested the
use of radiation in food processing. They have identified the process's
benefits, as well as its limitations. Results show that many foods including
fruits, vegetables, seafood, meats, and grains are suitable for radiation
processing, and that some foods such as dairy products are not. Throughout
their studies, scientists have found no substantiated evidence to confirm fears
that irradiated foods are harmful to eat or that they will cause adverse health
effects over time.
A recent book published by the World Health Organization
(WHO) in collaboration with the Food and Agriculture Organization (FAO)
summarizes the results of major studies on the effects of irradiation on food.
Chemical compounds: When low doses of radiation are
applied for example, for disinfestation of grains it is difficult to
detect any chemical change in irradiated food. At higher doses, such as those
required for treatment of meat, many chemical changes occur some vitamins,
sugars, and other nutrients are lost and some different, but not unique,
chemical compounds are formed. Most foods are not noticeably affected by
radiation processing. Some foods, however, (such as milk) are not suitable for
treatment at even low doses of radiation; they develop off-flavours, for
example; or undesirable smells. Irradiation can also cause colour changes in
meats, for example, and softening of some fruits. The extent of these changes is
minor in comparison to changes occur due to other processing methods. It depends
principally on the type of food being irradiated, on the radiation dose, and on
other factors, such as temperature, during radiation processing. At low doses in
radiation processing, the loss of nutrients from food is insignificant. At
higher doses, some vitamin loss occurs but it can be mitigated by controlling
processing and storage conditions. Some vitamins (riboflavin, niacin, and
vitamin D) are fairly insensitive to irradiation. Others (vitamins A, B-1, E,
and K) are more easily lost.
Microbiological changes: Micro-organisms can be injured
and destroyed by irradiation, thereby greatly reducing the number of those that
cause food spoilage or food poisoning. At high doses, microbial cells of
bacteria and other micro-organisms are destroyed, which means the food products
are sterilized and can be sealed and safely stored at room temperatures without
spoilage. Lower doses kill insects or prevent them from reproducing, inactivate
parasites that can cause diseases, and delay growth of food-spoiling organisms
such as moulds and yeasts.
In the 1980s, some 15 countries have approved the use of
radiation processing for specific food products, one key indicator of growing
interest in the technology. Some of them already have commercial irradiation
facilities in place. Interest primarily stems from food irradiation's
endorsement by international health and safety authorities and its ability to
help address serious problems of food supply, health and nutrition, and global
trade and economics. The process has proven capabilities that enables food to be
stored longer and to meet stringent tests of quality and safety when integrated
within an established system for the safe handling and distribution of food.
Many countries are interested in food irradiation as a method to reduce
sometimes staggeringly high food losses. In Africa, for example, post-harvest
food losses are a fundamental cause of food shortages, experts reported at a
recent FAO/IAEA seminar in Dakar, Senegal, attended by delegates from 14 African
countries. Delegates reported production losses of 40 % from infestation of
grains and of more than 50 % from spoilage of yams, a staple product.
The use of irradiation alone as a preservation technique will
not solve problems of post-harvest food losses, which are severe. Worldwide, the
FAO has estimated that about one quarter of all food production is lost after
harvesting, often in storage or transportation, to insects, bacteria, and
rodents. But radiation processing can play an important role in cutting losses
in many cases. In many countries, for example, significant losses of grains
result from insect infestation, moulds, and premature germination. For tuber
crops and onions, sprouting and attack by bacteria and fungi are the major
causes of loss. Several countries, including the Germany, Hungary, and USSR, are
irradiating grains, onions, or other products on an industrial scale.
What scientists know about food-borne disease makes it one of
the most widespread threats to human health and an important cause of reduced
economic productivity. Such was the conclusion of a joint FAO/IAEA expert
committee on food safety in 1983. Each year, for example, more than four million
people in the USA contract serious cases of food poisoning and several thousand
of these victims die. Studies by the US Federal Center for Disease Control show
that in a typical year, foodborne diseases caused by salmonella, campylobacteria,
trichinae, and other parasites, claim an estimated 7000 lives. Moreover, there
are between 24-81 million cases of food-borne diarrhea disease each year. The
relatively low dose of radiation needed to destroy certain bacteria in food can
be very useful in controlling the serious health problems caused by these
organisms. For this reason, irradiation is becoming more widely used in several
countries. Considerable amounts of frozen seafoods, as well as dry food
ingredients, are irradiated in Belgium and the Netherlands. Electron beam
irradiation of blocks of mechanically deponed, frozen poultry products is
carried out industrially in France, Spices are being irradiated in Argentina,
Brazil, Denmark, Finland, France, Hungary, Israel, Norway, United States and
Yugoslavia. Large-scale gamma irradiation of fresh poultry has been evaluated in
Canada. Preservation of foodstuffs through radiation under permissible dose is a
good technique for safe maintenance of food for consumption by human beings. In
spite of the advantages of radiation, many people are afraid of it and its
effects. The public is particularly worried about nuclear accidents in their own
country or in neighbouring countries, that could affect their health and
everyday lives.
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