**3. Thermal processing**

Heating of food is the most common and effective method for eliminating pathogens. Thermal pasteurization, involving the reduction or inactivation of micro-organisms, was traditionally the most common method for the production of microbiologically safe food products. The method involves generation of heat outside the food which gets transferred into the food through conduction or convection. Although the method is inexpensive, preservative free and environmental friendly, it does result in undesirable changes related to the nutritional and organoleptical properties of foods. At the same time, the content or bioavailability of some bioactive compounds such as ascorbic acid, phenolic compounds or carotenoids may be severely diminished. The case becomes even worse if the food product is heat sensitive. Nonetheless the extent of destruction depends on the temperature used for processing in addition to the time for which it is applied. In order to circumvent the shortcomings of thermal processing, several non-thermal methods such as the use of radiation, high pressure processing and natural antimicrobials are receiving considerable attention (table 2).

Recent Advances in the Application

public as safe and desirable.

**4.1.2 Ultravoilet radiation** 

reproduce.

of Non Thermal Methods for the Prevention of *Salmonella* in Foods 291

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

Irradiation using non-ionizing rays, especially ultraviolet (UV)-C (wavelengths of 220–300 nm with 90% emission at 253.7 nm) has been approved as a non thermal method by the U.S. Food and Drug Administration (FDA) for surface sterilization (US Food and Drug Administration (2007)). This technique has been used extensively to decontaminate food surfaces directly or other materials which come in contact with food surfaces. The main industrial application of UV is its use in disinfection of drinking water. The mechanism of action of UV light involves the interruption of bacterial replication due to the formation of thymine dimers in the bacterial chromosome either killing them or making them unable to

Chun et al., (2009) reported a reduction of 2.02 logs of *S*. Typhimurium in sliced ham upon the application of 8000 J/m2 of UV-C whereas in the case of chicken breasts a reduction of only 1.19 logs were observed upon the application of 5 kJ/m2 UV-C radiation (Chun et al.,


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