**4. Benefits of gamma irradiation**

#### **4.1 Penetrating sterilization**

There has been mounting interest all over the world to utilize gamma irradiation to improve the shelf life of perishable foods as well as to ensure the microbiological safety of the products (Kamat A et al, 2003). According to Chervin and Boisseau, 1994 and Buchanan et al., 1998, ionizing irradiation is a fitting method to control the microorganisms on fruits, fresh fruit juices, fresh-cut vegetables, salads, sprouts, seeds and other, minimally processed

Gamma Irradiation for Fresh Produce 255

that is highly effective against microbial pathogens found in fresh produce. Anu Kamat et al. (2003) reported that a low-dose irradiation (1 kGy) was efficient enough for decontamination and elimination of potential pathogens. Irradiation has been successful in eliminating or greatly reducing the heavy load of spoilage microorganisms in vegetables, herbs, and spices (Satin, 1993). Kim et al. (2005) found that doses of 1.0 to 1.5 kGy reduced total aerobic count on fresh-cut green onions by about 3 logs. According to Lambert and Maxcy,(1984) *Camylobacter jejuni, Aeromonas hydrophila* (Palumbo et al., 1986), and *Yersinia enreocolitica* (El Zawahry and Rowley, 1979) have been found to have a low tolerance for

The potential of gamma irradiation to inactivate foodborne pathogns on fresh produce has been investigated by various scientists. A dose of 5 kGy is reported to reduce a population of *Salmonella serotypes, Staphylococcus aureus, Shigella, E. coli,* and Vibrio species by at least 6 log cycles (Diehl, 1995). This also applies to *E. coli O157:H7* which is reported to be readily inactivated by irradiation (Clavero et al., 1994). Hagenmaier and Baker (1997) have also indicated that normal microflora on lettuce was reduced with a irradiation dose of 0.19 kGy. Irradiation at 0.3 and 0.6 kGy combined with Modified Atmosphere Packaging system MAP is reported to reduce *L. monocytogenes* on endive by 2.5 to 3 logs (Niemira et al. 2005). A 5 log reduction in *E.coli* O157:H7 and lack of adverse effects on sensory attributes was reported (Foley et al, 2002) when lettuce was subjected to 0.55 kGy. Farkas, et al, 1997 also observed a 4-log reduction of *L. monocytogenes* on the surface of sliced bell peppers irradiated at 1.0 kGy. Gamma irradiation is highly effective in inactivating micro-organisms in fresh produce

Safety of irradiated foods involves four aspects: radiological safety, toxicological safety, microbiological safety, and nutritional adequacy. The Bureau of Foods Irradiated Food Committee (BFIFC) of Food and Drug Administration FDA established that more than 90% of all radiolytic compounds in irradiated foods were similar to those found in heating, drying, and freezing of food (Diehl, 1995 and FDA, 1988). Basing its recommendations on radiation chemistry, FDA has concluded that foods irradiated at dose levels up to 1 kGy and foods comprising no more than 0.01 % of daily diet irradiated at 50 kGy or less can be considered safe for human consumption without any toxicological testing (Diehl, 1995). Free radicals are formed when food is irradiated, but they are also formed by exposure to sunlight, frying, baking, grinding, and drying. In wet foods , free radicals disappear within a fraction of a second; in dry foods, the free radicals are much more stable and do not

Irradiated foods are wholesome, nutritious, and nutrient losses are not significantly different from other alternative treatments. The extent of nutritional losses as a result of irradiation is comparable to or less than that of most other processing methods (Josephson and Peterson, 1983; Nawar, 1986). Generally, there is no effect of γ-radiation (up to 10kGy) on the nutrients of irradiated foods. In a previous study, papayas, rambutans, and Kau oranges were acceptable after subjecting to a quarantine level of 0.75kGy (Follet and Sanxter,

and offers a safe alternative as a food decontamination method.

disappear as quickly (ACSH, 1988).

**5.1 Nutrition quality of irradiated fresh produce** 

**5. Effects of gamma irradiation on quality of fresh produce** 

irradiation.

foods. The efficacy of irradiation is not only limited to the surface, but it can penetrate the product and eliminate microorganisms that are present in crevices and creases of vegetables such lettuce (Prakash et al., 2000). According to Takeuchi and Frank 2000, Solomon et al. 2002, bacteria gets inside tissues of leafy vegetables through natural openings or through breakage caused by insect and mechanical in harvesting. Internalization of bacterial pathogens into the edible portions of plants is of particular concern as these microorganisms are unlikely to be detached by washing or surface sanitization methods (USFDA, 1999; Jablasone et al., 2005). Chlorinated water is widely used for disinfection of foods; but it does not completely inactivate bacteria in fresh produce (Seo and Frank, 1998) due to its limited penetrating power into plant tissues. Ionizing radiation is an effective non-thermal means of eliminating pathogenic bacteria in surface, subsurface, and interior regions of fresh produce. Unlike chlorine treatment, low dose irradiation may be effective method of reducing pathogen such as internalized *E. coli O157:H7* in and on the surface of fruits and vegetables. Irradiation technology, due to its ability to penetrate through the food, can be used to effectively control foodborne pathogens in fresh produce. The International Commission on Microbiological Specifications for Foods (ICMSF) in 1980 established that cobalt-60 rays penetrate approximately 20 cm of food (Frazier and Westhoff, 1988). Food irradiation using cobalt-60 is the mostly used method by most processors, because the deeper penetration enables administering treatment to entire industrial pallets, reducing the need for material handling Maurer K.F, 1958). Low dose (0.15-0.5 kGy) irradiation has been reported to be workable dosage range for fresh cut lettuce (Hagenmaier and Baker, 1997). Irradiation thus is potentially more effective than washing or other surface treatments against spoilage organisms and pathogens (Niemira and Fan 2006).

#### **4.2 Gamma irradiation and survival of foodborne pathogens**

In recent years, leafy vegetables and salads are gaining great importance in the human diet, in part due to due to the health concerns. The intake of fruit and vegetable juices are suggested for diverse health effects (Williams, 1995) and are considered a part of a healthy diet and assist in the protection against various diseases. However, fresh produce may harbor potential of foodborne pathogens (Beuchat, 1996; Sumner and Peters, 1997). The food safety regulations on fresh produce set by the Food and Drug Administration are expected for the producers and handlers to reduce the risk of future outbreaks caused by fruits and vegetables (Warner, 1997). Studies have also shown that irradiation as a means of controlling human pathogens such as *E. coli O157:H7* (Thayer and Boyd., 1993) and *Salmonella* (Thayer et al., 1991). Fortunately, the majority of food poisoning pathogens are sensitive to radiation and water is the principal target of ionizing radiation. Water radiolysis generates free radicals, which in turn damage microorganisms deoxyribonucleic acid DNA (Scott J. S, and P. Pillai, 2004). This "ionizing" effect splits water molecules into hydrogen (H+), hydroxyl (OH-) and oxygen (O-2) radicals and deactivate bacterial DNA, proteins, and cell membranes (Niemira and Sommers 2006). The gamma rays hit the double helix of the DNA and cause it to split which results in breaks. The severity and the number of the breaks determine the bacterial cells ability to repair and recover (Jay, 1992). The killing effect of irradiation on microbes is measured in D values. One D value is the amount of irradiation needed to kill 90% of that organism for example, it takes 0.3 kiloGrays to kill 90% of *E. coli* O157: H,7 so the D value of *E. coli* is 0.3 kGy (CAST, 1996). The D-values are different for each organism and change by temperature and the type of food. Irradiation is a treatment

foods. The efficacy of irradiation is not only limited to the surface, but it can penetrate the product and eliminate microorganisms that are present in crevices and creases of vegetables such lettuce (Prakash et al., 2000). According to Takeuchi and Frank 2000, Solomon et al. 2002, bacteria gets inside tissues of leafy vegetables through natural openings or through breakage caused by insect and mechanical in harvesting. Internalization of bacterial pathogens into the edible portions of plants is of particular concern as these microorganisms are unlikely to be detached by washing or surface sanitization methods (USFDA, 1999; Jablasone et al., 2005). Chlorinated water is widely used for disinfection of foods; but it does not completely inactivate bacteria in fresh produce (Seo and Frank, 1998) due to its limited penetrating power into plant tissues. Ionizing radiation is an effective non-thermal means of eliminating pathogenic bacteria in surface, subsurface, and interior regions of fresh produce. Unlike chlorine treatment, low dose irradiation may be effective method of reducing pathogen such as internalized *E. coli O157:H7* in and on the surface of fruits and vegetables. Irradiation technology, due to its ability to penetrate through the food, can be used to effectively control foodborne pathogens in fresh produce. The International Commission on Microbiological Specifications for Foods (ICMSF) in 1980 established that cobalt-60 rays penetrate approximately 20 cm of food (Frazier and Westhoff, 1988). Food irradiation using cobalt-60 is the mostly used method by most processors, because the deeper penetration enables administering treatment to entire industrial pallets, reducing the need for material handling Maurer K.F, 1958). Low dose (0.15-0.5 kGy) irradiation has been reported to be workable dosage range for fresh cut lettuce (Hagenmaier and Baker, 1997). Irradiation thus is potentially more effective than washing or other surface treatments against spoilage

In recent years, leafy vegetables and salads are gaining great importance in the human diet, in part due to due to the health concerns. The intake of fruit and vegetable juices are suggested for diverse health effects (Williams, 1995) and are considered a part of a healthy diet and assist in the protection against various diseases. However, fresh produce may harbor potential of foodborne pathogens (Beuchat, 1996; Sumner and Peters, 1997). The food safety regulations on fresh produce set by the Food and Drug Administration are expected for the producers and handlers to reduce the risk of future outbreaks caused by fruits and vegetables (Warner, 1997). Studies have also shown that irradiation as a means of controlling human pathogens such as *E. coli O157:H7* (Thayer and Boyd., 1993) and *Salmonella* (Thayer et al., 1991). Fortunately, the majority of food poisoning pathogens are sensitive to radiation and water is the principal target of ionizing radiation. Water radiolysis generates free radicals, which in turn damage microorganisms deoxyribonucleic acid DNA (Scott J. S, and P. Pillai, 2004). This "ionizing" effect splits water molecules into hydrogen (H+), hydroxyl (OH-) and oxygen (O-2) radicals and deactivate bacterial DNA, proteins, and cell membranes (Niemira and Sommers 2006). The gamma rays hit the double helix of the DNA and cause it to split which results in breaks. The severity and the number of the breaks determine the bacterial cells ability to repair and recover (Jay, 1992). The killing effect of irradiation on microbes is measured in D values. One D value is the amount of irradiation needed to kill 90% of that organism for example, it takes 0.3 kiloGrays to kill 90% of *E. coli* O157: H,7 so the D value of *E. coli* is 0.3 kGy (CAST, 1996). The D-values are different for each organism and change by temperature and the type of food. Irradiation is a treatment

organisms and pathogens (Niemira and Fan 2006).

**4.2 Gamma irradiation and survival of foodborne pathogens** 

that is highly effective against microbial pathogens found in fresh produce. Anu Kamat et al. (2003) reported that a low-dose irradiation (1 kGy) was efficient enough for decontamination and elimination of potential pathogens. Irradiation has been successful in eliminating or greatly reducing the heavy load of spoilage microorganisms in vegetables, herbs, and spices (Satin, 1993). Kim et al. (2005) found that doses of 1.0 to 1.5 kGy reduced total aerobic count on fresh-cut green onions by about 3 logs. According to Lambert and Maxcy,(1984) *Camylobacter jejuni, Aeromonas hydrophila* (Palumbo et al., 1986), and *Yersinia enreocolitica* (El Zawahry and Rowley, 1979) have been found to have a low tolerance for irradiation.

The potential of gamma irradiation to inactivate foodborne pathogns on fresh produce has been investigated by various scientists. A dose of 5 kGy is reported to reduce a population of *Salmonella serotypes, Staphylococcus aureus, Shigella, E. coli,* and Vibrio species by at least 6 log cycles (Diehl, 1995). This also applies to *E. coli O157:H7* which is reported to be readily inactivated by irradiation (Clavero et al., 1994). Hagenmaier and Baker (1997) have also indicated that normal microflora on lettuce was reduced with a irradiation dose of 0.19 kGy. Irradiation at 0.3 and 0.6 kGy combined with Modified Atmosphere Packaging system MAP is reported to reduce *L. monocytogenes* on endive by 2.5 to 3 logs (Niemira et al. 2005). A 5 log reduction in *E.coli* O157:H7 and lack of adverse effects on sensory attributes was reported (Foley et al, 2002) when lettuce was subjected to 0.55 kGy. Farkas, et al, 1997 also observed a 4-log reduction of *L. monocytogenes* on the surface of sliced bell peppers irradiated at 1.0 kGy. Gamma irradiation is highly effective in inactivating micro-organisms in fresh produce and offers a safe alternative as a food decontamination method.
