**4.1.1 Irradiation**

The use of ionizing radiation as a means of food preservation is being extensively researched and is approved in many countries such as the United States, France, Netherlands and Canada. The use of radiation dose up to 7 kiloGray (kGy) has been sanctioned by WHO as safe. The critical target of ionizing radiation is the bacterial DNA. Gamma rays, X-rays and electron beam are the most common types of ionizing radiation. Gamma radiation is generated using radioactive isotopes such as cobalt-60 or Cesium-137 (FDA approved) whereas for electron beam high speed electrons are generated using electricity. Generation of X-rays involves interposition of a metal target between the food and the electron beam. The choice of use between e-beam and X-ray is typically made as an exchange between efficiency and product penetration depth. Unlike gamma radiation, the

**Food Product Strain Condition Reduction Reference Technique** 

100 Hz 4.27 log

175 Hz 3.75 log

Sliced Ham *S.* Typhimurium 2 kGy 3.78 Song et al., 2011 Electron

Sliced Ham *S.* Typhimurium 8000 J/ m2 2.02 logs Chun et al., 2009 UV-C

Table 2. Inactivation of *Salmonella* spp. achieved by application of non-thermal techniques in

The use of ionizing radiation as a means of food preservation is being extensively researched and is approved in many countries such as the United States, France, Netherlands and Canada. The use of radiation dose up to 7 kiloGray (kGy) has been sanctioned by WHO as safe. The critical target of ionizing radiation is the bacterial DNA. Gamma rays, X-rays and electron beam are the most common types of ionizing radiation. Gamma radiation is generated using radioactive isotopes such as cobalt-60 or Cesium-137 (FDA approved) whereas for electron beam high speed electrons are generated using electricity. Generation of X-rays involves interposition of a metal target between the food and the electron beam. The choice of use between e-beam and X-ray is typically made as an exchange between efficiency and product penetration depth. Unlike gamma radiation, the

600 MPa for 10 min and 21.5 °C

35 °C , 2 h 94-98% Wei et al., 1991 *hpcd* 

36 °C , 15 min 0.83 log Meurehg, 2006 *hpcd* 

36 °C , 15 min 1.23 log Meurehg, 2006 *hpcd* 

Karaman 2001 *hpcd* 

<sup>2005</sup>*hpcd* 

(2002) PEF

PEF

PEF

beam

Mosqueda-Melgar et al.,

Mosqueda-Melgar et al.,

6.5-8.2 log Chen et al., 2006 HPP

2007

2007

20 °C 7 log Bull et al., 2004 HPP

15 min 7 log Erkmen and

10 min 6 log Kincal et al.,

55 °C 5.0 log Liang et al.,

Chicken meat *S.* Typhimurium 13.7 MPa,

Trimmings *Salmonella spp.* 10.3 MPa,

Ground beef *Salmonella spp.* 10.3 MPa,

saline *S*. Typhimurium 6 MPa, 35 °C ,

Orange juice *S*. Typhimurium 38 MPa, 25 °C ,

Melon juice *S.* Enteritidis 2000 μs and

juice *S.* Enteritidis 1250 μs and

Orange juice *S*. Typhimurium 90 kV/cm and

Orange juice *Salmonella spp.* 600 MPa and

UHT Milk *Salmonella spp.* 

**4. Non thermal approaches 4.1 Application of radiation** 

Beef

Physiological

Watermelon

foods

**4.1.1 Irradiation** 

processing time using electron beam is very short and the technique does not produce radioactive waste. The effect of both techniques on the quality is minimal as no heat is generated during the process. However, electron beam can penetrate only up to 8 cm in foods which is its major limitation. Nonetheless both these techniques are being studied for eliminating *Salmonella*. Irradiation in the range of 2-3 kGy has been used for the elimination of *Salmonella* in meat products. Park et al. (2010) reported lower total aerobic counts in gamma rays treated beef sausage patties as compared to electron beam treated samples. Reduction of 3.78 and 2.04 logs has been reported using electron beam irradiation (2 kGy) for *S.* Typhimurium inoculated in sliced ham (Song et al., 2011) and powdered weaning foods (Hong et al., 2008), respectively whereas Martins et al., (2004) reported a 4 log reduction in a cocktail of *Salmonella* strains using 1.7 kGy in watercress thereby showing the applicability of gamma radiation in salad vegetables. Application of 3 kGy electron beam resulted in a reduction of 6.75 and 4.85 logs of *S*. Tennessee and *S*. Typhimurium inoculated in Peanut butter (Hvizdzak et al., 2010). In contrast, irradiation by electron beam was found to be an unacceptable method for destroying *Salmonella* on raw almonds (Prakash et al., 2010). A dose of 5 kGy was reported to be required for achieving a 4 log reduction whereas radiation intensity higher than 2.98 kGy induced significant sensory changes in raw almonds (Prakash et al., 2010). Mahmoud (2010) reported 3.7 logs reduction in *S*. enterica per tomato upon the application of 0.75 kGy X-rays. Increasing the dose to more than 1 kGy resulted in more than 5 logs reduction. X-ray has shown to result in more than 6 logs reduction in ready to eat shrimps (Mahmoud, 2009) and spinach leaves and shredded iceberg lettuce (Mahmoud et al., 2010). However, several adverse effects (lipid oxidation, textural degradation) caused by ionizing radiation have prevented this technology from being extended. Especially, lipid oxidation of meat products by irradiation is the most important factor for quality decline. An increase in the off-odors of irradiated ground pork and pork chops upon refrigerated storage were observed (Ohene-Adjei et al., 2004). The negative effects of gamma radiation on the appearance and color of chicken breasts, pork loin and beef loin, has also been reported (Kim et al., 2002). Additionally just like other inactivation techniques, *S*. Typhimurium has been reported to develop resistance against the radiation if the cells are repeatedly processed with electron beam at sub-lethal doses (Tesfai et al., 2011). Although irradiation has a high potential to be used for food preservation, its use is limited by an uncorroborated view that irradiated foods are not well accepted by the public as safe and desirable.
