*P. R. Davara & V. P. Sangani
Poor post harvest practices including inadequate storage and preservation facilities, as well as adverse climatic conditions, cause heavy losses in India’s agricultural and marine produce. With progressive increase in the quantity of food grains and necessity for longer storage periods, these losses will escalate unless disinfestation measures are improved. Chemical disinfestations methods, such as fumigation, require repeated application, as these do not eliminate insect eggs. They may also leave harmful residues in the treated grains. For ensuring availability of good quality food for people, the post harvesting technology of handling agriculture produce should go hand in hand with increased agricultural output. Food irradiation, as this process is known, is an important milestone in food preservation methodology since the successful development of canning in the 19th century.
Food irradiation promises to offer an effective means for minimizing these losses, thereby increasing their availability, and stimulating exports. In 21st century, it will be one of the important tools which can make Indian agricultural produce globally competitive. Export development authorities, commodity boards, food industry, farmers, traders, and exporters of agricultural commodities can be benefited from the use of radiation processing technology.
Food irradiation is a process by which food is exposed to a controlled source of ionizing radiation to prolong shelf life and reduce food losses, improve microbiologic safety, and/or reduce the use of chemical fumigants and additives. It can be used to reduce insect infestation of grain, dried spices, and dried or fresh fruits and vegetables; inhibit sprouting in tubers and bulbs; retard postharvest ripening of fruits; inactivate parasites in meats and fish; eliminate spoilage microbes from fresh fruits and vegetables; extend shelf life in poultry, meats, fish, and shellfish; decontaminate poultry and beef; and sterilize foods and feeds. One great advantage of irradiation is that it can be accomplished after foods are packaged, preventing recontamination during subsequent handling.
Irradiated food is safe and nutritious and produces no unusual toxicity as long as best management practices are followed. Irradiation is a complement to established techniques that can add to food safety, increase shelf life, reduce loss from spoilage, and increase the diversity of foods available to the population. The technology of food irradiation is the most intensely studied of all food processing techniques.
Irradiation can also be used to overcome fruit fly infestation in fresh fruit. The process brings potentially huge benefits for those countries where fruit flies are endemic and who wish to export to countries that are free of fruit fly. The United States of America has currently accepted irradiation as a quarantine treatment for the control of 11 major species of fruit flies and mango seed weevil.
Food irradiation technique
Irradiation processing of food involves the controlled application of energy from ionizing radiations such as gamma rays, electrons, and X-rays for food preservation. Gamma rays and X-rays are short wavelength radiations of the electromagnetic spectrum. Gamma rays are a part of the electromagnetic spectrum. They can penetrate deep into food materials and bring about desired effects.
Radiation processing of food is carried out inside an irradiation chamber shielded by 1.5 to 1.8 meter thick concrete walls. Food, either pre-packed or in-bulk, placed in suitable containers is sent into the irradiation chamber with the help of an automatic conveyor. When the facility is not in use the radiation source is stored under 6 meter deep water. The water shield does not allow radiation to escape into the irradiation chamber, thus permitting free access to personnel to carry out plant maintenance.
For treating food, the source is brought to the irradiation position above the water level after activation of all safety devices. The goods in aluminium carriers or tote boxes are mechanically positioned around the source rack and are turned round on their own axis, so that contents are irradiated on both sides. Absorbed dose is checked by placing dosimeters at various positions in a tote box or carrier. The quantity of dose is measured in terms of unit, called Gray, abbreviated as Gy. It is the unit of absorbed radiation energy. One gray is equivalent to 1 Joule per kilogram. The old unit of dose is ‘rad’. 1Gray is equivalent to 100 rad.
Table :1 The recommended doses of ionizing radiation for different purposes in food preservation.
|Low dose applications||Less than 1 kGy||
1. Inhibition of sprouting in potato and onion (0.03-0.15 kGy).
2. Delay in fruit ripening (0.25-0.75 kGy).
3. Insect disinfestation in stored grain, pulses and products (0.25-1 kGy).
4. Destruction of parasites in meat and meat products (0.25-1 kGy).
|Medium dose applications||1 to 10 kGy||
1. Elimination of spoilage microbes in fresh fruits, meat, poultry and seafoods (1.5-3 kGy).
2. Elimination of food pathogens in meat, poultry and seafoods (3-7 kGy).
3. Hygienization of spices and herbs (10 kGy).
|High dose applications||Above 10 kGy||
1. Sterilization of food for special requirements which are shelf-stable without refrigeration (25-70 kGy).
2. Elimination of viruses.
3. Sterilization of hospital diets for immune compromised patients (25-70 kGy).
4. Food for astronauts in space.
Low dose irradiation completely kills or sterilizes the common grain pests, and even the eggs deposited inside the grains. Moreover, only a single radiation exposure of grains is sufficient for disinfestations. This, therefore, is ideally suited for large-scale operations, thereby offering substantial economic benefits. Irradiation can also serve as an effective process for disinfestation of certain pre-packed cereal products like atta, soji (rava) and premixes.
Low doses of radiation are effective in delaying the natural processes of ripening in fruits. Thus shelf life of mangoes can be extended by about a week and that of bananas up to two weeks. This could improve the scope for internal trade and augment export of these commercially important fruits of India. Furthermore, gamma radiation can eliminate the seed weevil, an insect that lodges deep inside the stone of the mango.
Fumigation of spices with chemicals like methyl bromide, ethylene oxide and propylene oxide, has inherent disadvantages, especially retention of chemical residues. Single treatment of gamma radiation can make spices free of insect infection and microbial contamination without the loss of flavour components. The treatment can also be used for pre-packed ground spices and curry powders.
The existing inadequate preservation facilities for fish cannot cope up with the rapid spoilage of the catch and thereby limits the availability of seafood in the interior regions. By selective destruction of spoilage bacteria, moderate doses (2 kilo Gray) of radiation can extend the acceptability, and, in turn, marketability of iced fish by about two weeks. Besides, this is the only method of removal of pathogens from pre-packed frozen product. The technology can also be used for hygienization and sterilization of non-food items including cut-flowers, pet food, cattle feed, aqua feed, ayurvedic herbs and medicines and packaging materials.
Over decades of study the FDA and other international organizations such as the International Atomic Energy Agency and the World Health Organization have consistently concluded the following:
- Food does not become radioactive as a result of irradiation.
- The irradiation process is effective in decreasing or eliminating disease-causing microorganisms such as Escherichia coli (E. coli), campylobacter, and salmonella from foods.
- Irradiation reduces spoilage caused by bacteria, insects, and parasites.
- Irradiation inhibits sprouting and delays ripening in some fruits and vegetables.
- Irradiation does not alter in any significant manner the nutritional value of food.
- Alterations in food created by irradiation are like those created by cooking and other processing.
- The irradiation process as regulated by the FDA is safe.
All irradiated food must be clearly labeled with the international irradiation symbol, the Radura (Fig 1) and the words, “treated by irradiation” or “treated with radiation”.
Cost of irradiated Food
Irradiation costs may range from Rs. 0.25 to Rs. 0.50 per kilogram for a low dose application such as sprout inhibition of potato and onion, and insect disinfestation in cereals and pulses. It costs from Rs. 1 to Rs. 3 per kilogram for high dose applications such as treatment of spices for microbial decontamination. The costs could be brought down in a multipurpose facility treating a variety of products around the year.
The safety of irradiated food
The safety of food processed by radiation has been examined carefully, both at the national and international levels. On the basis of extensive studies with laboratory animals carried out in different countries including India, FAO/IAEA/WHO Joint Expert Committee has recommended that the food items irradiated up to an average dose of 10 kilo Gray be accepted as safe from the health angle and do not present any toxicological hazards. In fact, the doses of irradiation required for the treatment of commodities are far below this stipulated limit. The committee has further recognized radiation as a physical process like thermal processing and not as a food additive.
In comparison to other food processing and preservation methods the nutritional value is least affected by irradiation. Extensive scientific studies have shown that irradiation has very little effect on the main nutrients such as proteins, carbohydrates, fats, and minerals.
Vitamins show varied sensitivity to food processing methods including irradiation. For example, vitamin C and B1 (thiamine) are equally sensitive to irradiation as well as to heat processing. Vitamin A, E, C, K, and B1 in foods are relatively sensitive to radiation, while riboflavin, niacin, and vitamin D are much more stable.
The Joint Expert Committee of the Food and Agriculture Organization (FAO), World Health Organization (WHO), and International Atomic Energy Agency (IAEA), in 1980 concluded that irradiation does not induce special nutritional problems in food. The committee also rejected the possibility of development of chromosomal abnormalities by the consumption of irradiated food.
Merits over conventional methods
- Food irradiation technology has unique merits over conventional methods of preservation such as canning, dehydration, salting, etc. as this process does not lead to loss of flavour, odour, texture, and freshness.
- Unlike chemical fumigants, irradiation does not leave any harmful toxic residues in food and is more effective.
- It is efficient and can be used to treat pre-packed commodities. Since gamma rays have high penetrating power, spices can be irradiated after packaging, irrespective of the size of the carton.
Dept. of Processing and Food Engineering
College of Agril. Engg. & Technology
Junagadh Agricultural University
Junagadh – 362001