**2. Fresh produce and foodborne pathogens**

Consumption of fresh produce in many countries has increased substantially in recent years, in part due to an increased awareness of the health benefits that fresh produce provides.

Gamma Irradiation for Fresh Produce 253

also been associated with several produce recalls *(*Faber and Peterkin. 1991; Leverentz, 2004*),* including red bell peppers, romaine lettuce, sprouts, and apple slices. Presence of this pathogen has also been reported in potatoes, radishes, cabbage, cucumbers, and mushrooms

Many outbreaks have been traced to produce, and this will continue to occur until fresh produce growers, processing plants, retail stores, and consumers increase their knowledge and awareness of the risks and consequences of foodborne pathogens. Given that fresh produce is ready to eat, and is not subjected to further microbial killing steps, there is a call for produce industry to use effective methods to eliminate or reduce the risk of foodborne pathogens. Gamma irradiation could be applied as a control measures to help minimize

Gamma rays use irradiation given off by Cobolt-60, a radioisotope of cobalt (Steele and Engel, 1992). It is reported that all radiation facilities in the world use Cobalt-60 rather than Cesium-137 (WHO, 1987). Cobalt-60 is derived from cobalt-59 which is placed in a nuclear reactor and bombarded with neutrons until an extra neutron is absorbed forming the unstable radioisotope cobalt-60. Over 80% of the cobalt-60 available on the world market is being produced in Canada (Diehl, 1995). For use as a radiation source the activated cobalt pellets are encapsulated in a stainless steel linear in form of pin or pencil to minimize absorption of the cobalt and to minimize heat build up. The stainless rods are placed on racks which are stored in approximately 25 feet of water and raised into concrete irradiation chamber to dose the food (Jones, 1992). As the food go through the chamber, the stainless steel linears are raised above the water so that it is exposed to gamma rays. The irradiation dose applied to food is measured in terms of kiloGyray (kGy) and is usually measured in a unit called the Gray, abbreviated Gy. The newer unit,1 Gy = 100 rads; 1 kGy = 1,000 Grays). The practical working range of food irradiation is generally from 50 Gy to as high as 10,000 Gy, depending upon the food in question and the effect desired (Satin, 1993). There are three general application and dose categories that are referred to when foods are treated with ionizing radiation (Urbain, 1986): (1) Low dose (radurization) up to approximately 1 kGy for sprout inhibition, delay of ripening, and insect disinfection, (2) Medium dose (radicidation)- 1 to 10 kGy for reduction of non-spore forming pathogens, delay of ripening, and reduction of spoilage microorganisms, and (3) High dose (radappertization)-10 to 50 kGy for reduction of microorganisms to the point of sterility. In the United States, the amount of irradiation dose applied to food is controlled by plant quality personnel and United States Department

obtained from the market *(*Heisick, et al 1989*).*

**3. Gamma irradiation** 

food safety risks associated with foodborne pathogens.

of Agriculture (USDA) and inspectors (Giddings and Marcotte, 1991).

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

**4. Benefits of gamma irradiation** 

**4.1 Penetrating sterilization** 

However, foodborne illness outbreaks linked to fresh produce are becoming more frequent and widespread (Warriner et al, 2009; Harris et al., 2003; Sivapalasingam et al, 2004). Foodborne illness outbreaks associated to leafy vegetables is an indication that increased consumption of fresh produce could present new challenges with regard to fresh produce safety (FDA, 2008). Recent outbreaks of foodborne illness linked with produce have raised concerns and underline the challenges to the public health as well as to fresh produce industry. The increased concern of fresh produce and its relation to food borne illness has been indicated by several surveillance studies (Ilic, Odomeru, & LeJeune, 2008; little & Gillespie, 2008). Other countries together with the United States of America have targeted foodborne pathogens in fresh produce as emerging issue in food safety and one of the most pressing public health needs. Fresh fruits and vegetables are frequently contaminated since they are grown in open fields with potential exposure to enteric pathogens from animals, soil, irrigation water, and manure. Cross contamination of fresh produce with foodborne pathogens may occur during the production cycle and can originate from soil, insects, equipment, animals or humans (Tracy and Harris, 2003; Liao and Fett, 2001; Ukuku and Sapers, 2001). It is indicated that pathogen contaminated water or surface run-off waters can lead to cross-contamination of fruits and vegetables in the field (Beuchat and Ryu, 1997). Similarly, the application of raw animal manure for fertilizer increases the threat of contamination on fruits and vegetables ( Brackett, 1992). Direct or indirect pathogen contamination of fresh produce can occur at many points in the production chain during growth and processing *(*Fenlon, et al, 1996*;* Beuchat and Ryu. 1997)*,* thus presenting a food safety challenge to consumers.

Pathogenic microorganisms, such as Cyclospora *cayetanensis, Escherichia coli* O157:H7, Hepatitis A, *Listeria monocytogenes,* Norovirus, *Salmonella* spp., and *Shigella* spp. are the major foodborne microbial pathogens associated with fresh produce. *Salmonella, Escherichia coli* O157:H7, and *Listeria monocytogenes* have been associated with fresh produce over the past two decades. *E. coli* O157:H7 illnesses have also been linked to the consumption of fresh fruits and vegetables (Tauxe, et al 2000). *E. coli* O157:H7 is capable of causing hemorrhagic colitis and hemolytic uremic syndrome (HUS) and thus has gained attention from public health agencies and institutions. Proximity of domestic or wild animals to irrigation water systems may result *E. coli* O157:H7 (Wachtel, et al 2002) and other pathogenic bacteria being washed from manure to production fields. *E. coli* O157:H7 contaminated manure may get into the water system, and once present, can be applied to growing crops (Institute of Food Technologists, 2002). Foodborne pathogens in the fresh produce indicate a weakness in the fresh produce industry has was demonstrated by recent multi-state (Unites States) outbreaks in produce, including *E. coli* OH7:H7 outbreak from spinach that lead to 183 cases of illness, 29 cases of Hemolytic Uremic Syndrome (HUS), 95 hospitalizations, and one death (http://www.cdc. gov/foodborne/ecolispinach) ; *Salmonella* Typhimurium outbreak from tomatoes that involved 183 cases of illnesses http://www.fda.gov/bbs/topics/ NEWS/ 2006/NEW01504. html); and in December 2006, Taco Bell restaurants in the Northeast were also associated with *E. coli* O157:H7 and iceberg lettuce was considered to be the single most likely source of the outbreak, 8 cases of Hemolytic Uremic Syndrome (HUS), and 53 hospitalizations were reported to Center of Disease Control (http://www.cfsan.fda.gov/~news/whatsnew.html. *Salmonella enteritidis, S. infantis,* and *S. typhimurium* have also been reported to be capable of growth in chopped cherry tomatoes (Asplund, K., and E. Nurmi.1991). *Listeria monocytogenes* is a common contaminant and has

However, foodborne illness outbreaks linked to fresh produce are becoming more frequent and widespread (Warriner et al, 2009; Harris et al., 2003; Sivapalasingam et al, 2004). Foodborne illness outbreaks associated to leafy vegetables is an indication that increased consumption of fresh produce could present new challenges with regard to fresh produce safety (FDA, 2008). Recent outbreaks of foodborne illness linked with produce have raised concerns and underline the challenges to the public health as well as to fresh produce industry. The increased concern of fresh produce and its relation to food borne illness has been indicated by several surveillance studies (Ilic, Odomeru, & LeJeune, 2008; little & Gillespie, 2008). Other countries together with the United States of America have targeted foodborne pathogens in fresh produce as emerging issue in food safety and one of the most pressing public health needs. Fresh fruits and vegetables are frequently contaminated since they are grown in open fields with potential exposure to enteric pathogens from animals, soil, irrigation water, and manure. Cross contamination of fresh produce with foodborne pathogens may occur during the production cycle and can originate from soil, insects, equipment, animals or humans (Tracy and Harris, 2003; Liao and Fett, 2001; Ukuku and Sapers, 2001). It is indicated that pathogen contaminated water or surface run-off waters can lead to cross-contamination of fruits and vegetables in the field (Beuchat and Ryu, 1997). Similarly, the application of raw animal manure for fertilizer increases the threat of contamination on fruits and vegetables ( Brackett, 1992). Direct or indirect pathogen contamination of fresh produce can occur at many points in the production chain during growth and processing *(*Fenlon, et al, 1996*;* Beuchat and Ryu. 1997)*,* thus presenting a food

Pathogenic microorganisms, such as Cyclospora *cayetanensis, Escherichia coli* O157:H7, Hepatitis A, *Listeria monocytogenes,* Norovirus, *Salmonella* spp., and *Shigella* spp. are the major foodborne microbial pathogens associated with fresh produce. *Salmonella, Escherichia coli* O157:H7, and *Listeria monocytogenes* have been associated with fresh produce over the past two decades. *E. coli* O157:H7 illnesses have also been linked to the consumption of fresh fruits and vegetables (Tauxe, et al 2000). *E. coli* O157:H7 is capable of causing hemorrhagic colitis and hemolytic uremic syndrome (HUS) and thus has gained attention from public health agencies and institutions. Proximity of domestic or wild animals to irrigation water systems may result *E. coli* O157:H7 (Wachtel, et al 2002) and other pathogenic bacteria being washed from manure to production fields. *E. coli* O157:H7 contaminated manure may get into the water system, and once present, can be applied to growing crops (Institute of Food Technologists, 2002). Foodborne pathogens in the fresh produce indicate a weakness in the fresh produce industry has was demonstrated by recent multi-state (Unites States) outbreaks in produce, including *E. coli* OH7:H7 outbreak from spinach that lead to 183 cases of illness, 29 cases of Hemolytic Uremic Syndrome (HUS), 95 hospitalizations, and one death (http://www.cdc. gov/foodborne/ecolispinach) ; *Salmonella* Typhimurium outbreak from tomatoes that involved 183 cases of illnesses http://www.fda.gov/bbs/topics/ NEWS/ 2006/NEW01504. html); and in December 2006, Taco Bell restaurants in the Northeast were also associated with *E. coli* O157:H7 and iceberg lettuce was considered to be the single most likely source of the outbreak, 8 cases of Hemolytic Uremic Syndrome (HUS), and 53 hospitalizations were reported to Center of Disease Control (http://www.cfsan.fda.gov/~news/whatsnew.html. *Salmonella enteritidis, S. infantis,* and *S. typhimurium* have also been reported to be capable of growth in chopped cherry tomatoes (Asplund, K., and E. Nurmi.1991). *Listeria monocytogenes* is a common contaminant and has

safety challenge to consumers.

also been associated with several produce recalls *(*Faber and Peterkin. 1991; Leverentz, 2004*),* including red bell peppers, romaine lettuce, sprouts, and apple slices. Presence of this pathogen has also been reported in potatoes, radishes, cabbage, cucumbers, and mushrooms obtained from the market *(*Heisick, et al 1989*).*

Many outbreaks have been traced to produce, and this will continue to occur until fresh produce growers, processing plants, retail stores, and consumers increase their knowledge and awareness of the risks and consequences of foodborne pathogens. Given that fresh produce is ready to eat, and is not subjected to further microbial killing steps, there is a call for produce industry to use effective methods to eliminate or reduce the risk of foodborne pathogens. Gamma irradiation could be applied as a control measures to help minimize food safety risks associated with foodborne pathogens.
