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International Journal of Multidisciplinary and Current Research ISSN: 2321-3124 Available at: http://ijmcr.com Research Article An Overview of the Principles and Effects of Irradiation on Food Processing & Preservation 1 2 3 4 J.T. Liberty, D.I. Dickson, A.E. Achebe and M.B. Salihu 1 Department of Agricultural & Bioresources Engineering, University of Nigeria, Nsukka 2 Department of Microbiology, University of Nigeria, Nsukka, 3 Department of Home Economics, College of Education, Minna, Niger State 4 Department of Educational Foundation, University of Nigeria, Nsukka, Enugu State, Nigeria Accepted 04 December 2013, Available online 10 December 2013, (Nov/Dec 2013 issue) Abstract When food irradiation is carried out under Good Manufacturing Practice conditions, is commended as an effective, widely applicable food processing method judged to be safe on extensive available evidence, that can reduce the risk of food poisoning, control food spoilage and extend the shelf-life of foods without detriment to health and with minimal effect on nutritional or sensory quality. This view has been endorsed by international bodies such as the World Health Organisation(WHO), the Food and Agricultural Organisation (FAO) and Codex Alimentarius. Food irradiation is the processing of food products by ionising radiation in order to control foodborne pathogens, reduce microbial load and insect infestation, inhibit the germination of root crops, and extend the durable life of perishable produce. The use of irradiation has been approved for about 50 different types of food and at least 33 countries are using the technology commercially. Despite the fact that irradiation has been used for decades for food disinfection that satisfies quarantine requirements in trade, health concerns over the consumption of irradiated food continue to attract attention. This study reviewed the basic principles, applications and the associated potential health risk, if any, posed to consumers as a result of consumption of irradiated food. Review of the available evidence showed that although irradiation processing leads to chemical changes and nutrient losses, the safety and nutrient quality of irradiated foods are comparable to foods that have been treated with other conventional food processing methods such as heating, pasteurisation and canning when the technology is used as recommended and good manufacturing practices are followed. Keywords: chemical changes, food Irradiation, food processing and preservation, shelf-life, spoilage 1.0 Introduction Food irradiation is the processing of food products by There are many processing methods have been ionising radiation in order to control foodborne developed to help prevent food spoilage and improve pathogens, reduce microbial load and insect infestation, safety. The traditional methods of preservation, such as inhibit the germination of root crops, and extend the drying, smoking and salting have been supplemented with durable life of perishable produce (International pasteurisation (by heat), canning (commercial sterilisation Consultative Group, 1991). by heat), refrigeration, freezing and chemical Food irradiation is perhaps the single most studied preservatives. Food irradiation is another technology that food processing technology for toxicological safety in the can be added to the list. It is not new; interest was shown history of food preservation. Studies pertaining to the in Germany in 1896 and it began in the early 1920s, while safety and nutritional adequacy of irradiated foods date in the 1950/60s the US Army Natick Soldier Center back to the 1950s and were frequently associated with (NATICK) experimented with both low dose and high dose the use of radiation to sterilize foods. Hundreds of short- irradiation for military rations (Steward, 2004(a)). In the term and long-term safety studies led to the approval of UK, at the same time, the Low Temperature Research one or more foods for irradiation by presently more than Station programme concentrated on low dose sixty countries. These studies are thoroughly reviewed in pasteurisation (Hannan, 1955). Irradiation is extensively The Safety and Nutritional Adequacy of Irradiated Foods, used in the medical field for sterilising instruments, published by the World Health Organization (WHO 1994). dressings etc. 236|Int. J. of Multidisciplinary and Current research, Nov/Dec 2013 J.T Liberty et al An Overview of the Principles and Effects of Irradiation on Food Processing & Preservation The international symbol showing irradiated food is called to an irradiation chamber. The food is exposed to gamma Radura, showed below. rays from a radioactive source such as cobalt60 (main source for gamma processing of foods) or cesium137 at a controlled rate. The gamma rays evenly penetrate the food product, killing harmful microorganisms, parasites, or insects without altering the nature of the food. These rays do not remain in the food (Roberts et al., 1995). Gamma rays are more powerful than the rays emitted by a microwave oven. Rays from a microwave oven cause food to heat rapidly, whereas gamma rays, with much shorter wavelengths and higher frequencies, penetrate Fig 1: The ‘Radura’, the international symbol for through the food so rapidly that no heat is produced. irradiated food. In the center is an agricultural product, a After food is irradiated, it is stored and may be food, which is in a closed package denoted by the circle, transported back to the processing plant for further and which is irradiated by penetrating rays. handling and packaging. Once the food has been irradiated, it must be handled appropriately to prevent According to the International Atomic Energy Agency recontamination (Roberts et al., 1995). (IAEA), more than 50 countries have approved the use of The irradiation cell (source) consists of cobalt60 or irradiation for about 50 different types of food, and 33 cesium137 rods in stainless steel tubes. These tubes are are using the technology commercially. The positive list of stored in water and raised into a concrete irradiation irradiated products varies between countries but is often chamber to dose the food. Over a period of years the limited to spices, herbs, seasonings, some fresh or dried cobalt60 or cesium137 rods slowly decay to non- fruits and vegetables, seafood, meat and meat products, radioactive nickel and non-radioactive barium, poultry and egg products. Despite the fact that irradiation respectively. No radioactive waste is produced at a food has been used for decades for food disinfection and irradiation facility, and no irradiation facility could have a satisfying quarantine requirements in trade, there is meltdown that could jeopardize the safety and health of considerable debate on the issue of health concerns over plant workers and other citizens of a community. Food the consumption of irradiated food. These include irradiation facilities do not have nuclear reactors. The concerns over the toxicity of the chemicals generated and food is exposed only to the degrading of the cobalt60 or the change in nutritional quality of food products after the cesium137 (Roberts et al., 1995). irradiation. Below is the facility used for irradiation. Foods may be irradiated with electron beams produced from accelerators. This method of irradiation can only be used on foods less than 4 inches thick because of the limited penetrating capacity of the electron beams. This method would be very effective on food such as hamburger patties. Table1: Irradiation Conversion Units 1,000,000 1 megarad (Mrad) 1 gray (Gy) 100 rads 1 kilgray (kGy) 100,000rads 1kGy 100 kilorads (krads) 1kGy 0.1Mrad Fig. 2: Typical food irradiation facility (courtesy Nordian 10kGy 1Mrad International, Ontario, Canada) The irradiation dose applied to a food product is 2.0 Principles of Food Irradiation measured in terms of kilograys (kGy) (Table 1). One kilogray is equivalent to 1,000 grays (Gy), 0.1 megarad Foods such as poultry are processed, packaged with (Mrad), or 100,000 rads. The basic unit is the gray, which oxygen-permeable film, and transported fresh or frozen is the amount of irradiation energy that 1 kilogram of to an irradiation facility. Currently the only commercial food receives. The amount of irradiation applied to a food poultry irradiation facility approved by the U.S. product is carefully controlled and monitored by plant Department of Agriculture (USDA) is Food Technology quality control personnel and USDA inspectors. The Services, Inc., in Mulberry, Florida. At the irradiation irradiation dose applied to a food product will depend facility, the palletized product is transferred by conveyor upon the composition of the food, the degree of 237 | Int. J. of Multidisciplinary and Current research, Nov/Dec 2013 J.T Liberty et al An Overview of the Principles and Effects of Irradiation on Food Processing & Preservation perishability, and the potential to harbor harmful meat and fish products. This triggers the development of microorganisms. The amount of radiation that a food species such as OH−, hydrated electron and H+, which can product absorbs is measured by a dosimeter (Roberts et then induce several chemical reactions with food al., 1995). constituents. Studies show that the quantity of radiolysis products varies as a function of fat content and fat 2.1 Ionising radiation and their sources composition, as well as with the temperature during the irradiation process and the actual dose of radiation used According to the Codex General Standard for Irradiated (Merrit et al., 1979). When fatty acids are exposed to Foods, ionising radiations recommended for use in food high-energy radiation they undergo preferential cleavage processing are: (I) gamma rays produced from the in the ester-carbonyl region giving rise to certain 60 137 radioisotopes cobalt-60 ( Co) and cesium-137 ( Cs), and radiolytic compounds that are specific for each fatty acid (II) machine sources generated electron beams (Nawar et al., 1996). The strong oxidizer ozone is (maximum level of 10 MeV) and X-ray (maximum level of produced from oxygen during food irradiation and can 5 MeV) (CAC,2003). promote the oxidization of lipids and myoglobin (Venugopal et al., 1999). (I) Gamma rays produced from radioisotopes cobalt-60 Many research studies have been carried out in recent and cesium-137 years on meat and fish irradiation and its impact on lipids. Experiments carried out on chicken revealed no Cobalt-60 is produced in a nuclear reactor via neutron significant difference in total saturated and unsaturated bombardment of highly refined cobalt-59 (59Co) pellets, fatty acids between irradiated (1, 3, 6 kGy) and non- while cesium-137 is produced as a result of uranium irradiated frozen (−20°C) chicken muscle (Rady et al., fission. Both cobalt-60 and cesium-137 emit highly 1987). Other studies showed that e-beam irradiation (2.5 penetrating gamma rays that can be used to treat food in kGy) seemed to increase the levels of thiobarbituric acid- bulk or in its final packaging. Cobalt-60 is, at present, the reactive substances (TBARS) in ground beef, but the radioisotope most extensively employed for gamma difference between irradiated and non-irradiated samples irradiation of food (Steward, 2001). was not statistically significant (Nam et al.,2003). The results of Yilmaz and Gecgel (2007) showed that (II) Electron beams and X-ray generated from machine irradiation in ground beef induced the formation of trans sources fatty acids. However, the ratio of total unsaturated fatty acids to total saturated fatty acids was 0.85, 0.86, 0.87, A major advantage of machine-sourced ionising radiation and 0.89 in irradiated ground beef samples (1, 3, 5, and 7 is that no radioactive substance is involved in the whole kGy, respectively) whereas for the control samples it was processing system. Powered by electricity, electron-beam 0.85. Fish lipids are more unsaturated than lipids in red machines use linear accelerators to produce accelerating meats and therefore are more susceptible to oxidation electron beams to near the speed of light. The high- (Khayat et al., 1983). An examination of the effect of energy electron beams have limited penetration power irradiation at 10 kGy on the linoleic and linolenic acid and are suitable only for foods of relatively shallow depth contents of grass prawns found that irradiation resulted (Steward, 2001). Electron beams can be converted into in 16% decrease in linoleic acid content, whereas linolenic various energies of X-rays by the bombardment with a acid was not affected significantly (Hau et al., 1993). In metallic target. Although X-rays have been shown to be the case of Spanish mackerel, C16:0 and C16:1 fatty acids more penetrating than gamma rays from cobalt-60 and decreased when irradiated at 1.5 to 10 kGy. (Al-Kahtani et cesium-137, the efficiency of conversion from electrons al., 1996). No changes were reported in the fatty acid to X-rays is generally less than 10% and this has hindered composition of two species of Australian marine fish the use of machine sourced radiation so far (ICGFI, 1999). irradiated at doses up to 6.0 kGy and the levels of fatty acids in oil remained stable in the irradiated fish samples 3.0 Some Effects of Food Irradiation whereas they decreased in non-irradiated fish (Armstrong et al., 1994). The extent of lipid oxidation was dependent 3.1 Effect of irradiation on lipids on the irradiation dose. An analysis of the literature concluded that when lipids are irradiated under In response to the continuously growing role of conditions which are met in commercial food processing irradiation in food preservation, several reviews and (≤7 kGy), there is no significant loss of nutritional value research studies have been published on the irradiation (Thomas, 1988). of foods of both animal and plant origin over the past years (Arvanitoyannis et al., 2009; Arvanitoyannis et al., 3.2 Effect of irradiation on proteins and amino acids 2010). The application of ionizing radiation results in the radiolysis of water, which is present in most foods such as Damage caused to protein by ionizing radiation includes 238 | Int. J. of Multidisciplinary and Current research, Nov/Dec 2013 J.T Liberty et al An Overview of the Principles and Effects of Irradiation on Food Processing & Preservation deamination, decarboxylation (Diehl, 1990), reduction of are similar to those associated with thermal processing disulfide linkages, oxidation of sulfydryl groups, cleavage (Urbain, 1986). It was found that e-beam irradiated (0 or of peptide bonds and changes of valency states of the 4.5 kGy) raw pork patties produced more volatiles than coordinated metal ions in enzymes (Delincee, 1983). did non-irradiated patties, and the proportion of volatiles Other studies indicated that there was no significant varied with the irradiation conditions (Ahn et al.,1998). destruction of cystine, methionine and tryptophan up to a Irradiation produced many unidentified volatiles that dose of 71 kGy (Josephson et al., 1978). The majority of could be responsible for the off-odor in irradiated raw amino acids in minced lean beef or pork and chicken meat. The results of an experienced testing panel showed breast muscle are stable up to a dose of 5 kGy (Partmann that there was no significant differences in odor and taste et al., 19790. Irradiation does not generally affect the between irradiated (4 kGy) and non-irradiated ground o stability of amino acids and proteins in situ. The stability beef patties (23% fat) during 7 days of storage at 4 C to irradiation at 2 to 45 kGy of tryptophan of shrimp (Giroux et al., 2001) . Irradiation at 2.5 kGy extended the muscle was measured after storage under different shelf life of carp, but at doses above 2.5 kGy, the cooked temperature and moisture conditions. The results meat had an unacceptable odor and flavor. Other studies revealed that the loss of tryptophan was small under all showed that the color of brook char (Salvelinius the conditions applied (Antunes et al., 1977). Essential fontinalis) was affected negatively by irradiation and the amino acids were not affected in electron- beam effect was more pronounced with 3 kGy than with 1 kGy processed (53 kGy) haddock fillets (Lagunas, 1995). Data treatment (Paradis et al., 1996). However, the flavor of obtained from the literature indicate that irradiation of fish was not affected by irradiation. meat at commercial doses (2–7 kGy) has no significant There are several methods that can be employed in effect on the nutritional value of proteins or amino acids order to decrease such detrimental effects of irradiation. (Thayer, 1987). These include oxygen exclusion, the replacement of oxygen with inert gases, the addition of protective agents 3.3 Effect of irradiation on vitamins such as antioxidants, and post-irradiation storage to allow the flavor to return to near-normal levels (Brewer, 2009). Many authors have studied the effect of irradiation on the stability of vitamins in foods (Liu et al., 1991). No loss 3.5 Effect of irradiation on microorganisms of riboflavin is found in pork chops and chicken breasts irradiated at temperatures between −200°C and 200°C at A large amount of data is available on the sensitivity of doses up to 6.6 kGy. Some irradiated samples even microorganisms to irradiation processing; this varies exhibited an increase in riboflavin concentration of up to greatly from micro-organism to micro-organism and is 25% (Kilcast, 1994). Pork chops irradiated at different also dependent on other extrinsic factors. Vegetative cells temperatures with doses up to 5 kGy displayed no loss in are less resistant to irradiation than spores, whereas niacin. A loss of 15% was observed with a dose of 7 kGy moulds have a susceptibility to irradiation similar to that when irradiation was applied at 0°C (Fox et al., 1989). of vegetative cells. However some fungi can be as Furthermore, in the case of pantothenic acid, it has been resistant as bacterial spores (Farkas, 2006). Compared to shown that there is no loss in many foods irradiated at bacteria, viruses generally require higher radiation doses doses of ≥10 kGy (Thayer et al., 1991). The application of for inactivation (Crawford et al., 1996). Studies have gamma irradiation (1, 2, and 6 kGy) on fillets of Black shown that irradiation doses of 2 and 3 kGy destroyed Bream (Acanthopagrus australis) and Redfish Yersinia spp. and Listeria spp., respectively, with the (Centroberyx affinis) resulted in vitamin E loss but this microorganisms being undetectable during storage of could not be correlated with the treatment dosage. All irradiated fish (Montgomery et al., 2003). Irradiation (1, 2, irradiated fillets were found to have vitamin E muscle and 3 kGy) significantly improved the microbiological contents above the levels considered to be desirable for quality of the chicken by reducing the total bacterial human consumption (Armstrong et al., 1994). No loss of count (TBC), with the decrease in TBC being dose- vitamin B12 was observed in haddock fillets irradiated up dependent. In all the irradiated samples, no fecal to 25 kGy. Similarly, there was no loss of niacin in cod coliforms were detected (Kanatt et al., 2005). irradiated at 1 kGy (Murray, 1981). Irradiation of shrimps at 2.5 kGy induced a 15% loss of riboflavin in air, 8% in 4.0 Factors affecting the efficacy of Food Irradiation vacuum, and 20% in nitrogen (Diehl, 1995). The efficacy of ionising radiation for micro-organism 3.4 Effect of irradiation on organoleptic characteristics inactivation depends mainly on the dose of use and the level of resistance of the contaminating organisms. Textural alterations and development of off-flavors are Radiation resistance varies widely among different not considered a problem with irradiation at doses lower species of bacteria, yeast and moulds. Bacterial spores than 2 kGy. Any sensory changes at lower radiation doses are general more resistant than vegetables cells, which is 239 | Int. J. of Multidisciplinary and Current research, Nov/Dec 2013
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