**5. Gamma sterilization of food**

Food sterilization by gamma irradiation is the process of exposing food to ionizing radiation to destroy microorganisms, bacteria, viruses, or insects that might be present in the food. Irradiated food does not become radioactive, but in some cases there may be subtle chemical changes.

The treatment of solid food by ionizing radiation can provide an effect similar to heat pasteurization of liquids, such as milk. The use of the term "cold pasteurization" to describe irradiated foods is controversial, since pasteurization and irradiation are fundamentally different processes. Food irradiation is currently permitted by over 50 countries, and the volume of food treated is estimated to exceed 500,000 metric tons annually worldwide. (Farkas & Farkas, 2011).

Sterilization by Gamma Irradiation 185

carotene) may be available to counteract the effects of free radicals generated by normal cell metabolism. When food is irradiated, ionizing radiation reacts with water in the food, causing the release of electrons and the formation of highly reactive free radicals (see Figure 2). The free radicals interact with vitamins in ways that can alter and degrade their structure and/or activity (Murano, 1995). The extent to which vitamin loss occurs can vary based on a number of factors, including the type of food, temperature of irradiation, and availability of oxygen. Nonetheless, vitamin loss almost always increases with increasing doses of radiation. The destruction of vitamins continues beyond the time of irradiation. Therefore, when irradiated food is stored, it will experience greater vitamin loss than food that has not been irradiated. Cooking further accelerates vitamin destruction in irradiated food more

**(kGy) True digestibility Biological value Net proteins** 

0 85.6 80.5 68.9 5 83.6 75.8 63.5 10 86.5 81.7 70.6 25 87.0 78.1 68.0 35 84.8 77.3 65.4 70 85.3 76.4 65.2

Vitamin C, vitamin B1, and, vitamin E are reduced in foods exposed to commercial levels of irradiation (1 kGy – 4.5 kGy). At the low doses of 0.3 to 0.75 kGy, food irradiation has been found to destroy up to 11% of vitamin C in fruit before storage, and up to 79% of vitamin C after three weeks of storage (Mitchell et al, 1992). Additionally, at the limit of its shelf life (270 days) irradiated mango pulp contains 57% less vitamin C than non-irradiated mango pulp at the limit of its shelf life (60 days). Whole grains, beans, and meat are important sources of thiamine (vitamin B1), which helps convert carbohydrates into energy. It is essential for heart, muscle, and nervous system function. Wheat flour irradiated at the low dose of 0.25 kGy lost up to 20 percent of thiamine initially and 62% after three months of storage.25 Beef irradiated at 3.0 kGy, which is below the legal limit, experienced a 19 % loss of thiamine. Oils, corn, nuts, seeds, and green vegetables are important sources of vitamin E, an antioxidant that protects body tissues and cells. It also may improve the immune system and help fight heart disease, cancer, Alzheimer's disease, and cataracts. Hazelnuts irradiated at 1.0 kGy lost 17% of vitamin E upon irradiation, and 58% of vitamin E after three months of storage and 30 minutes of baking. In addition, studies at higher levels of irradiation have demonstrated the destruction of vitamins A and K in food (Stevinson et al, 1959). The question of vitamin K in irradiated diets requires special considerations: i. it is known to be susceptible to destruction by y-irradiation (Ley, 1969); ii. it is synthesized by microbial action in the gut, and animals (particularly those that practice coprophagy) can satisfy part of their requirement by this means. Sterilized diets are usually only fed to specifiedpathogen-free or gnotobiotic animals, i.e. those that have a limited gut microflora or none at all. Thus the organisms responsible for vitamin K synthesis are likely to be absent, and the animal's requirement for dietary vitamin K may be very much higher than that of its conventional counterpart. It is difficult, if not impossible to determine vitamin K chemically

**utilization** 

than in non-irradiated food (Diehl, 1967).

Table 4. Effect of gamma irradiation on the protein of rat diet

**Dose** 

By irradiating food, depending on the dose, some or all of the harmful bacteria and other pathogens present are killed. This prolongs the shelf-life of the food in cases where microbial spoilage is the limiting factor. Some foods, e.g., herbs and spices, are irradiated at sufficient doses (5 kGy) to reduce the microbial counts by several orders of magnitude; such ingredients do not carry over spoilage or pathogen microorganisms into the final product. It has also been shown that irradiation can delay the ripening of fruits or the sprouting of vegetables. Insect pests can be sterilized (be made incapable of proliferation) using irradiation at relatively low doses. The use of low-level irradiation as an alternative treatment to pesticides for fruits and vegetables that are considered hosts to a number of insect pests, including fruit flies and seed weevils. The table 3 showed some use of food irradiation.

Exposure to gamma irradiation doses below 10 kGy is effective in enhancing food safety through the inactivation of pathogenic microorganisms such as *Salmonella* and *Campylobacter* and in extending the shelf-life of the diet by eliminating the microorganisms responsible for food spoilage. Irradiation doses of between 20 to 25 kGy and between 20 to 30 kGy are used most frequently to treat diets intended for specific pathogen-free animals, whereas larger doses of 40 to 50 kGy are recommended for diets intended for gnotobiotic or germ-free animals, where absolute sterility is essential.


Table 3. Food irradiation use

The effects of irradiation on the nutritive value of a product must be established before sterilization by radiation can become an important method for preserving food. The irradiation produces no greater nutrient loss than what occurs in other processing methods. Sample of a rat diet in which the protein 5, 10, 25, 35 and 70 kGy, and the effects on protein quality are given in Table 4. The results indicate no significant effect of irradiation on protein quality. Amino acid composition was similarly very little affected (Ley, 1969). By comparison of the different treatments (different radiation doses) and the control sample (not irradiated) of bean, it was observed that there was no significant alteration in the amino acid contents up to the maximum dose of 10 kGy. Even the more sensitive amino acids, such as the aromatic and basic, under the effect of gamma rays were kept intact in the samples. These results indicate that it is possible to use irradiation to reduce grain losses using different radiation doses without causing significant changes in the amino acid contents.

On the other hand, irradiation reduces the vitamin content of food, the effect of which may be indirect in that inadequate amounts of antioxidant vitamins (such as C, E, and β-

By irradiating food, depending on the dose, some or all of the harmful bacteria and other pathogens present are killed. This prolongs the shelf-life of the food in cases where microbial spoilage is the limiting factor. Some foods, e.g., herbs and spices, are irradiated at sufficient doses (5 kGy) to reduce the microbial counts by several orders of magnitude; such ingredients do not carry over spoilage or pathogen microorganisms into the final product. It has also been shown that irradiation can delay the ripening of fruits or the sprouting of vegetables. Insect pests can be sterilized (be made incapable of proliferation) using irradiation at relatively low doses. The use of low-level irradiation as an alternative treatment to pesticides for fruits and vegetables that are considered hosts to a number of insect pests, including fruit flies and seed

Exposure to gamma irradiation doses below 10 kGy is effective in enhancing food safety through the inactivation of pathogenic microorganisms such as *Salmonella* and *Campylobacter* and in extending the shelf-life of the diet by eliminating the microorganisms responsible for food spoilage. Irradiation doses of between 20 to 25 kGy and between 20 to 30 kGy are used most frequently to treat diets intended for specific pathogen-free animals, whereas larger doses of 40 to 50 kGy are recommended for diets intended for gnotobiotic or germ-free

Meat, poultry Destroys pathogenic fish organisms, such as

Perishable foods Delays spoilage; retards mold growth;

non-citrus fruits Delays ripening avocados, natural juices.

The effects of irradiation on the nutritive value of a product must be established before sterilization by radiation can become an important method for preserving food. The irradiation produces no greater nutrient loss than what occurs in other processing methods. Sample of a rat diet in which the protein 5, 10, 25, 35 and 70 kGy, and the effects on protein quality are given in Table 4. The results indicate no significant effect of irradiation on protein quality. Amino acid composition was similarly very little affected (Ley, 1969). By comparison of the different treatments (different radiation doses) and the control sample (not irradiated) of bean, it was observed that there was no significant alteration in the amino acid contents up to the maximum dose of 10 kGy. Even the more sensitive amino acids, such as the aromatic and basic, under the effect of gamma rays were kept intact in the samples. These results indicate that it is possible to use irradiation to reduce grain losses using different radiation doses without causing significant changes in the amino acid contents.

On the other hand, irradiation reduces the vitamin content of food, the effect of which may be indirect in that inadequate amounts of antioxidant vitamins (such as C, E, and β-

Salmonella, Campylobacter and Trichinae

reduces number of microorganisms

reduces rehydration time

Controls insect vegetables, infestation dehydrated fruit, spices and seasonings and

weevils. The table 3 showed some use of food irradiation.

**Type of food Effect of Irradiation** 

Onions, carrots, potatoes, garlic, ginger Inhibits sprouting

animals, where absolute sterility is essential.

Bananas, mangos,papayas, guavas, other

Table 3. Food irradiation use

Grain, fruit

carotene) may be available to counteract the effects of free radicals generated by normal cell metabolism. When food is irradiated, ionizing radiation reacts with water in the food, causing the release of electrons and the formation of highly reactive free radicals (see Figure 2). The free radicals interact with vitamins in ways that can alter and degrade their structure and/or activity (Murano, 1995). The extent to which vitamin loss occurs can vary based on a number of factors, including the type of food, temperature of irradiation, and availability of oxygen. Nonetheless, vitamin loss almost always increases with increasing doses of radiation. The destruction of vitamins continues beyond the time of irradiation. Therefore, when irradiated food is stored, it will experience greater vitamin loss than food that has not been irradiated. Cooking further accelerates vitamin destruction in irradiated food more than in non-irradiated food (Diehl, 1967).



Vitamin C, vitamin B1, and, vitamin E are reduced in foods exposed to commercial levels of irradiation (1 kGy – 4.5 kGy). At the low doses of 0.3 to 0.75 kGy, food irradiation has been found to destroy up to 11% of vitamin C in fruit before storage, and up to 79% of vitamin C after three weeks of storage (Mitchell et al, 1992). Additionally, at the limit of its shelf life (270 days) irradiated mango pulp contains 57% less vitamin C than non-irradiated mango pulp at the limit of its shelf life (60 days). Whole grains, beans, and meat are important sources of thiamine (vitamin B1), which helps convert carbohydrates into energy. It is essential for heart, muscle, and nervous system function. Wheat flour irradiated at the low dose of 0.25 kGy lost up to 20 percent of thiamine initially and 62% after three months of storage.25 Beef irradiated at 3.0 kGy, which is below the legal limit, experienced a 19 % loss of thiamine. Oils, corn, nuts, seeds, and green vegetables are important sources of vitamin E, an antioxidant that protects body tissues and cells. It also may improve the immune system and help fight heart disease, cancer, Alzheimer's disease, and cataracts. Hazelnuts irradiated at 1.0 kGy lost 17% of vitamin E upon irradiation, and 58% of vitamin E after three months of storage and 30 minutes of baking. In addition, studies at higher levels of irradiation have demonstrated the destruction of vitamins A and K in food (Stevinson et al, 1959). The question of vitamin K in irradiated diets requires special considerations: i. it is known to be susceptible to destruction by y-irradiation (Ley, 1969); ii. it is synthesized by microbial action in the gut, and animals (particularly those that practice coprophagy) can satisfy part of their requirement by this means. Sterilized diets are usually only fed to specifiedpathogen-free or gnotobiotic animals, i.e. those that have a limited gut microflora or none at all. Thus the organisms responsible for vitamin K synthesis are likely to be absent, and the animal's requirement for dietary vitamin K may be very much higher than that of its conventional counterpart. It is difficult, if not impossible to determine vitamin K chemically

Sterilization by Gamma Irradiation 187

palmitileic (C16:1) fatty acids decreased when irradiated at 1.5–10 kGy. Contents of total saturated fatty acids in the muscle of non-irradiated sea bream was respectively lower than in 2.5 kGy irradiated sea bream and higher than in 5 kGy irradiated sea bream. There was significant difference in the content of total unsaturated fatty acids , mono unsaturated fatty acids between 2.5 kGy and 5kGy irradiated sea bream and no significant difference was determined in the content of unsaturated fatty acids, mono unsaturated fatty acids between non-irradiated and irradiated fish. On the other hand, the content of poly unsaturated fatty acids in the muscle of 5 kGy irradiated sea bream was significantly lower than in nonirradiated and 2.5 kGy irradiated sea bream (Erkan & Özden, 2007). All at same, the total saturated and total monounsaturated fatty acid contents were 27.97% and 24.72% for nonirradiated for sea bass, respectively. The amounts of these two fatty acids in irradiated samples increased to 28.18 and 25.75% for 2.5 kGy and 29.08 and 28.54% for 5 kGy. Significant difference also was found in the content of total unsaturated fatty acids, mono unsaturated fatty acids between 2.5 kGy (25.75%) and 5 kGy (28.54%) irradiated sea bass

Irradiated ground beef samples with 7 kGy had the highest total trans fatty acids, total monounsaturated and total unsaturated fatty acids than the other samples. Results showed an increase in trans fatty acids related to the increase on irradiation dose in ground beef and irradiation dose changed fatty acids composition especially trans fatty acids in ground beef (Ylmaz & Gecgel, 2007). Total saturated fatty acids and unsaturated fatty acids, mono unsaturated fatty acids of beef lipid increased with irradiation (1.13, 2.09 and 3.17 kGy), but ratios of unsaturated fatty acids, mono unsaturated fatty acids to saturated fatty acids did not change. Whilst, total poly unsaturated fatty acids reduced with irradiation, which

When radiation is used for the sterilization of medical devices, the compatibility of all of the components has to be considered. Ionizing radiation not only kills microorganisms but also affects material properties. Medical devices are made of many different materials, some of which are metals, but most are non-metals, such as formed polymers, composite structures and even ceramics. Radiation itself does not directly affect metals since sterilization energies are safely below any activation thresholds. Metals, such as those used in orthopaedic implants, are virtually unchanged by the radiation sterilization process. Nevertheless, it has to be kept in mind that some types of polymers when irradiated in contact with a metal can cause some corrosion of the metal or surface discolouration. This is generally caused from

Polymer devices subjected to irradiation sterilization will inevitably be affected by the radiation and the environment used during sterilization, and will experience changes in the polymer structure such as chain scission and crosslinking (Schnabel, 1981). For some polymers both processes coexist and either one may be predominant depending not only upon the chemical structure of the polymer, but also upon the conditions of irradiation is performed like temperature, environment, dose rate, etc. The crosslinking and main scissions that take place during irradiation may lead to sharp changes in physical properties of the polymers. These effects will lead to changes in the tensile strength, elongation at break and impact strength. The exact changes seen will depend both on the basic polymer and any

and between non-irradiated and irradiated fish. (Özden & Erkan, 2010).

resulted in poly unsaturated fatty acids to saturated fatty acids ratio decrease.

**6. Gamma sterilization of medical devices** 

by products released by some polymers during irradiation.


in animal diets because other components react as vitamin K to the assay procedure. Assessment of the vitamin K content of a diet must therefore depend on the response of the animals receiving it. The Table 5 gives the doses, which the some food vitamins lost.

Table 5. Vitamins lost after gamma irradiation of some food

A study of the vitamin contents of diets for guinea-pigs (RGP), chicks (SCM) and cats after irradiation at doses ranging from 20 to 50 kGy has been made (Coates et al., 1969). At doses of the order of 20 to 30 kGy, vitamin losses from the guinea-pig and chick diets were very small indeed, but a severe loss of vitamin A from the cat diet was observed after treatment at 25 kGy. The losses were such that they could have been compensated for by addition of about twice the usual supplement of the vitamins affected. Stability decreased markedly with increased moisture content of the diet.

Poly unsaturated fatty acids were reported to have beneficial effects on human health and also are susceptible to peroxidation damage (Haghparast et al., 2010). Therefore, stability of these components needs to be considered for the standardization of the radiation process (Erkan and Özden, 2007). Ionizing radiation causes the radiolysis of water which is present to a great extent in food. This generates free radicals (see Figure 2) all of which react with the food constituents. The most susceptible site for free radical attack in a lipid molecule is adjacent to the double bonds. The most affected lipids during irradiation are thus the polyunsaturated fatty acids that bear two or more double bonds (Brewer, 2009).

Study on chicken showed no significant difference in total saturated and unsaturated fatty acids between irradiated (1, 3, 6 kGy) and non-irradiated frozen chicken muscle (Rady et al.,1988), however Katta et al. (1991) found significant decrease in the amount of palmitic acid and increase in oleic acid as irradiation dose level increased (0.5-3 kGy) in chicken meat.

Changes in the palmitic (C16:0), oleic (C18:1) and linoleic (C18:2) fatty acids of soybeans at different radiation doses (1, 5, 10, 20, 40, 60, 80 and 100 kGy) were no found (Hafez et al.,1985). The irradiation at 10 kGy also changes the linoleic and linolenic acid contents of grass prawns. Irradiation caused a 16% decrease in linoleic acid content, whereas linolenic acid was not affected significantly (Hau and Liew, 1993).

The irradiation of fish no changes fatty acid compositions of two species of Australian marine fish irradiated at doses of up to 6 kGy (Armstrong et al., 1994), but chemical components of tilapia and Spanish mackerel has been reported (Al- Kahtani et al., 1996). Irradiation of tilapia at 1.5–10 kGy caused a decrease in myristic (C14:0), palmitic (C16:0) and palmitileic (C16:1) fatty acids. In the case of Spanish mackerel, palmitic (C16:0) and

in animal diets because other components react as vitamin K to the assay procedure. Assessment of the vitamin K content of a diet must therefore depend on the response of the

Mango 10 Vitamin C Youssef et al., 2002 Grapefruit 10 Vitamin C Patil et al., 2004 Pork 10 Thiamin Fox et al., 1997

Beef 45 Thiamin Fox et al., 1995

A study of the vitamin contents of diets for guinea-pigs (RGP), chicks (SCM) and cats after irradiation at doses ranging from 20 to 50 kGy has been made (Coates et al., 1969). At doses of the order of 20 to 30 kGy, vitamin losses from the guinea-pig and chick diets were very small indeed, but a severe loss of vitamin A from the cat diet was observed after treatment at 25 kGy. The losses were such that they could have been compensated for by addition of about twice the usual supplement of the vitamins affected. Stability decreased markedly

Poly unsaturated fatty acids were reported to have beneficial effects on human health and also are susceptible to peroxidation damage (Haghparast et al., 2010). Therefore, stability of these components needs to be considered for the standardization of the radiation process (Erkan and Özden, 2007). Ionizing radiation causes the radiolysis of water which is present to a great extent in food. This generates free radicals (see Figure 2) all of which react with the food constituents. The most susceptible site for free radical attack in a lipid molecule is adjacent to the double bonds. The most affected lipids during irradiation are thus the

Study on chicken showed no significant difference in total saturated and unsaturated fatty acids between irradiated (1, 3, 6 kGy) and non-irradiated frozen chicken muscle (Rady et al.,1988), however Katta et al. (1991) found significant decrease in the amount of palmitic acid and increase in oleic acid as irradiation dose level increased (0.5-3 kGy) in chicken

Changes in the palmitic (C16:0), oleic (C18:1) and linoleic (C18:2) fatty acids of soybeans at different radiation doses (1, 5, 10, 20, 40, 60, 80 and 100 kGy) were no found (Hafez et al.,1985). The irradiation at 10 kGy also changes the linoleic and linolenic acid contents of grass prawns. Irradiation caused a 16% decrease in linoleic acid content, whereas linolenic

The irradiation of fish no changes fatty acid compositions of two species of Australian marine fish irradiated at doses of up to 6 kGy (Armstrong et al., 1994), but chemical components of tilapia and Spanish mackerel has been reported (Al- Kahtani et al., 1996). Irradiation of tilapia at 1.5–10 kGy caused a decrease in myristic (C14:0), palmitic (C16:0) and palmitileic (C16:1) fatty acids. In the case of Spanish mackerel, palmitic (C16:0) and

polyunsaturated fatty acids that bear two or more double bonds (Brewer, 2009).

**(kGy) Vitamins lost reference** 

Thiamin

Lakritz and Thayer, 1992

animals receiving it. The Table 5 gives the doses, which the some food vitamins lost.

Chicken 30 Vitamin E and

Table 5. Vitamins lost after gamma irradiation of some food

acid was not affected significantly (Hau and Liew, 1993).

with increased moisture content of the diet.

meat.

**Food Dose of sterilization** 

palmitileic (C16:1) fatty acids decreased when irradiated at 1.5–10 kGy. Contents of total saturated fatty acids in the muscle of non-irradiated sea bream was respectively lower than in 2.5 kGy irradiated sea bream and higher than in 5 kGy irradiated sea bream. There was significant difference in the content of total unsaturated fatty acids , mono unsaturated fatty acids between 2.5 kGy and 5kGy irradiated sea bream and no significant difference was determined in the content of unsaturated fatty acids, mono unsaturated fatty acids between non-irradiated and irradiated fish. On the other hand, the content of poly unsaturated fatty acids in the muscle of 5 kGy irradiated sea bream was significantly lower than in nonirradiated and 2.5 kGy irradiated sea bream (Erkan & Özden, 2007). All at same, the total saturated and total monounsaturated fatty acid contents were 27.97% and 24.72% for nonirradiated for sea bass, respectively. The amounts of these two fatty acids in irradiated samples increased to 28.18 and 25.75% for 2.5 kGy and 29.08 and 28.54% for 5 kGy. Significant difference also was found in the content of total unsaturated fatty acids, mono unsaturated fatty acids between 2.5 kGy (25.75%) and 5 kGy (28.54%) irradiated sea bass and between non-irradiated and irradiated fish. (Özden & Erkan, 2010).

Irradiated ground beef samples with 7 kGy had the highest total trans fatty acids, total monounsaturated and total unsaturated fatty acids than the other samples. Results showed an increase in trans fatty acids related to the increase on irradiation dose in ground beef and irradiation dose changed fatty acids composition especially trans fatty acids in ground beef (Ylmaz & Gecgel, 2007). Total saturated fatty acids and unsaturated fatty acids, mono unsaturated fatty acids of beef lipid increased with irradiation (1.13, 2.09 and 3.17 kGy), but ratios of unsaturated fatty acids, mono unsaturated fatty acids to saturated fatty acids did not change. Whilst, total poly unsaturated fatty acids reduced with irradiation, which resulted in poly unsaturated fatty acids to saturated fatty acids ratio decrease.
