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Radiation and food preservation

 

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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

By S.M. Alam and M. A. Khan
Nuclear Institute of Agriculture,
 Tandojam, Pakistan.
Jan 29 - Feb 04, 2001

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.

—AsiaNet Feature Serivce