**4.1.2 Ultravoilet radiation**

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 reproduce.

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.,

Recent Advances in the Application

carotene concentrations (Bull et al., 2004).

**4.2.2 High pressure carbon dioxide (HPCD)** 

cost is obtained.

of Non Thermal Methods for the Prevention of *Salmonella* in Foods 293

directly suspended in water and then given the treatment. The effect was attributed to the fact that low water activity provided a protective effect to the bacterial cells. Application of HPP to orange juice resulted in 7-log inactivation of *Salmonella* at 600 MPa and 20 °C (Bull et al., 2004) and 615MPa and 15 °C (Teo et al., 2001) for 60 s. At the same time, HPP was reported not to have any significant effect on the quality parameters of orange juice such as titratable acid content, °Brix, viscosity, alcohol insoluble acids, color, ascorbic acid and β-

However, the application of high pressure at high temperatures may result in undesirable changes in the quality of many foods. Moreover, in the case of meat products, high pressure can increase the susceptibility of meat products to attack by oxygen thus resulting in increased lipid oxidation. For instance, Ma et al. (2007) reported almost 5-fold increase in TBARS values after 7 days storage at 4 °C in beef exposed to a pressure ≥400MPa. In other studies, pressures higher than 300 or 400 MPa (at ambient temperatures) caused increased rate of oxidation in pork (Cheah and Ledward, 1996) and cod muscles (Angsupanich and Ledward, 1998), respectively. McArdle et al. (2011) reported detrimental effect of HPP at 600MPa on texture, oxidation and water binding properties of beef. However lower TBARS and cook loss for beef processed by HPP were obtained as compared to raw or conventional heat processed samples. Besides, HPP carried out at high temperatures can cause cell wall breakdown and result in loss of cell turgidity. In addition, large-scale industrial application will only be possible if the technique becomes economical. The treatment time and the pressures applied are the major factors involved in deciding the cost and in achieving the desirable microbial inactivation. Hence, it is important to optimize conditions wherein minimal pressure is applied for the shortest time so that a food product with a reasonable

High pressure carbon dioxide (HPCD) is another upcoming treatment that is being extensively used as a non-thermal technique for food pasteurization. The process is not only environmentally friendly due to the non-toxic nature of carbon dioxide but also involves application of lower CO2 pressure as compared to those employed for HPP. The use of lower pressures makes this technique an energy-saving process. The major factor involved in the destruction is CO2 although pressure helps in greater penetration of CO2 in the cells. Lethality imparted by pressurized CO2 is a result of disassociation of CO2 (in foods with high water content) into reactive ions such as carbonates (CO32-), bicarbonates (HCO3-

hydrogen (H+). These reactive ionic species can then have an effect on the permeability of the cell membrane and properties of cell constituents. In addition, generation of carbonic acid (H2CO3) in the water present in food products further results in a reduction in the pH

Studies involving the use of HPCD for the inactivation of *S.* Typhimurium (Kim et al., 2007; Erkmen and Karaman, 2001; Erkmen 2000; Wei et al., 1991) have clearly reported the microbial strain, pressure applied, pH of the medium, type of medium and temperature to be important factors for the inactivation. *S.* Typhimurium in orange juice was effectively reduced by 5-6 logs when subjected to continuous dense phase carbon dioxide (DPCD) for 10 min at 21–107 MPa and 25 °C (Kincal et al., 2005) whereas in another study reduction as high as 8 logs was achieved when the growth media was changed to physiological saline (PS) or phosphate buffer solution (Kim et al., 2007). Kim et al. (2007) also analyzed the structural changes in *S.* Typhimurium cells upon the application of super-critical CO2. A

of the food products enhancing the penetration of CO2 (Wei et al., 1991).

) and

2010). At the same time, storage of UV-C treated chicken breasts resulted in an increase in the TBARS values and a negligible change in the Hunter L, a and b values for the product. The effects of UV-C on the quality attributes and decontamination efficiency against *Salmonella* Enteritidis were evaluated in different egg fractions (de Souza and Fernández, 2011). In terms of quality attributes, UV-C did not affect the viscosity and the pH however, browning due to maillard reaction was detectable in egg yolk and whole egg at low UV-C doses. The TBARS value was not significantly different to untreated samples. At the same time, a reduction of 5.3, 3.3 and 3.8 log was achieved under dynamic conditions (9.22 J/cm2, 39 min) in egg white, egg yolk and whole egg, respectively.

The main drawback of UV irradiation is that it is a surface sterilization method. The efficiency of the treatment will strongly depend on the actual location of the bacterial contaminant as well as the composition, surface topography and transmissivity of the food (Allende et al., 2006). Moreover, the penetration of UV in liquid foods will strongly depend on the characteristics of the liquid product. The presence of solid particles and other components can seriously hinder the penetration. In addition the actual physical arrangement, power and wavelength of the UV source will also play a significant role. Besides, care has to be taken while using short wave UV regarding the damage that it can cause to human eyes in addition to being a cause of skin cancers and burns in humans upon excessive exposure.

#### **4.2 Application of pressure**

#### **4.2.1 High pressure processing (HPP)**

High pressure processing (HPP) is a food processing method involving the application of pressure throughout the food. The technique is independent of the shape of food and can be used for both solid and liquid samples. Pressures in the range of 100-800 MPa are generally applied with temperatures ranging from 0-100 °C. The main target for HPP is the bacterial cytoplasmic membrane. In addition to the loss of solute, enzyme inactivation and protein coagulation might also occur as a result of excess pressure. HPP technique has been used for reducing or eliminating *Salmonella* in foods or culture media. Reduction of 6.5-8.2 logs in *Salmonella* inoculated in UHT whole milk was achieved at a pressure of 600 MPa for 10 min and 21.5 °C (Chen et al., 2006). Several instances regarding the growth of *Salmonella* spp. on the surface of tomatoes have been reported. HPP has been applied for the removal of this bacterium from the tomatoes surface. Application of pressures in the range of 350-550 MPa has been reported to result in 0.46-3.67 log reduction in *S. enterica* serovar Braenderup inoculated on diced and whole tomatoes (Maitland et al., 2011). Exposure to a pressure of 550 MPa for 2 min resulted in a reduction of several *S. enterica* serovars (Baildon, Gaminara, Michigan and Typhimurium) in the range of 4 log cfu/ml or greater for broth, water and apple juice (Whitney et al., 2007). Time did not seem to be an important factor when HPP was applied in a chicken meat model system. Treatment at 400 MPa for 2 min and 20 °C resulted in an inactivation between 3.26 and 4.35 log in a chicken meat model system (Escriu and Mor-Mur, 2009). The applicability of HPP as a preservation method against *Salmonella* has also been evaluated for products with lower water activity such as raw almonds. Goodridge et al. (2006) studied the effect of continuous and oscillatory HPP treatment on the viability of two *Salmonella* Enteriditis strains (FDA and PT30) inoculated onto raw almonds. Continuous pressurization of raw almonds resulted in less than one log reduction whereas the oscillatory process provided 1.27 and 1.16 log reduction for FDA and PT30 strains, respectively. However, a reduction of 3.37 logs was achieved when the almonds were

2010). At the same time, storage of UV-C treated chicken breasts resulted in an increase in the TBARS values and a negligible change in the Hunter L, a and b values for the product. The effects of UV-C on the quality attributes and decontamination efficiency against *Salmonella* Enteritidis were evaluated in different egg fractions (de Souza and Fernández, 2011). In terms of quality attributes, UV-C did not affect the viscosity and the pH however, browning due to maillard reaction was detectable in egg yolk and whole egg at low UV-C doses. The TBARS value was not significantly different to untreated samples. At the same time, a reduction of 5.3, 3.3 and 3.8 log was achieved under dynamic conditions (9.22 J/cm2,

The main drawback of UV irradiation is that it is a surface sterilization method. The efficiency of the treatment will strongly depend on the actual location of the bacterial contaminant as well as the composition, surface topography and transmissivity of the food (Allende et al., 2006). Moreover, the penetration of UV in liquid foods will strongly depend on the characteristics of the liquid product. The presence of solid particles and other components can seriously hinder the penetration. In addition the actual physical arrangement, power and wavelength of the UV source will also play a significant role. Besides, care has to be taken while using short wave UV regarding the damage that it can cause to human eyes in addition to being a cause of skin cancers and burns in humans upon

High pressure processing (HPP) is a food processing method involving the application of pressure throughout the food. The technique is independent of the shape of food and can be used for both solid and liquid samples. Pressures in the range of 100-800 MPa are generally applied with temperatures ranging from 0-100 °C. The main target for HPP is the bacterial cytoplasmic membrane. In addition to the loss of solute, enzyme inactivation and protein coagulation might also occur as a result of excess pressure. HPP technique has been used for reducing or eliminating *Salmonella* in foods or culture media. Reduction of 6.5-8.2 logs in *Salmonella* inoculated in UHT whole milk was achieved at a pressure of 600 MPa for 10 min and 21.5 °C (Chen et al., 2006). Several instances regarding the growth of *Salmonella* spp. on the surface of tomatoes have been reported. HPP has been applied for the removal of this bacterium from the tomatoes surface. Application of pressures in the range of 350-550 MPa has been reported to result in 0.46-3.67 log reduction in *S. enterica* serovar Braenderup inoculated on diced and whole tomatoes (Maitland et al., 2011). Exposure to a pressure of 550 MPa for 2 min resulted in a reduction of several *S. enterica* serovars (Baildon, Gaminara, Michigan and Typhimurium) in the range of 4 log cfu/ml or greater for broth, water and apple juice (Whitney et al., 2007). Time did not seem to be an important factor when HPP was applied in a chicken meat model system. Treatment at 400 MPa for 2 min and 20 °C resulted in an inactivation between 3.26 and 4.35 log in a chicken meat model system (Escriu and Mor-Mur, 2009). The applicability of HPP as a preservation method against *Salmonella* has also been evaluated for products with lower water activity such as raw almonds. Goodridge et al. (2006) studied the effect of continuous and oscillatory HPP treatment on the viability of two *Salmonella* Enteriditis strains (FDA and PT30) inoculated onto raw almonds. Continuous pressurization of raw almonds resulted in less than one log reduction whereas the oscillatory process provided 1.27 and 1.16 log reduction for FDA and PT30 strains, respectively. However, a reduction of 3.37 logs was achieved when the almonds were

39 min) in egg white, egg yolk and whole egg, respectively.

excessive exposure.

**4.2 Application of pressure** 

**4.2.1 High pressure processing (HPP)** 

directly suspended in water and then given the treatment. The effect was attributed to the fact that low water activity provided a protective effect to the bacterial cells. Application of HPP to orange juice resulted in 7-log inactivation of *Salmonella* at 600 MPa and 20 °C (Bull et al., 2004) and 615MPa and 15 °C (Teo et al., 2001) for 60 s. At the same time, HPP was reported not to have any significant effect on the quality parameters of orange juice such as titratable acid content, °Brix, viscosity, alcohol insoluble acids, color, ascorbic acid and βcarotene concentrations (Bull et al., 2004).

However, the application of high pressure at high temperatures may result in undesirable changes in the quality of many foods. Moreover, in the case of meat products, high pressure can increase the susceptibility of meat products to attack by oxygen thus resulting in increased lipid oxidation. For instance, Ma et al. (2007) reported almost 5-fold increase in TBARS values after 7 days storage at 4 °C in beef exposed to a pressure ≥400MPa. In other studies, pressures higher than 300 or 400 MPa (at ambient temperatures) caused increased rate of oxidation in pork (Cheah and Ledward, 1996) and cod muscles (Angsupanich and Ledward, 1998), respectively. McArdle et al. (2011) reported detrimental effect of HPP at 600MPa on texture, oxidation and water binding properties of beef. However lower TBARS and cook loss for beef processed by HPP were obtained as compared to raw or conventional heat processed samples. Besides, HPP carried out at high temperatures can cause cell wall breakdown and result in loss of cell turgidity. In addition, large-scale industrial application will only be possible if the technique becomes economical. The treatment time and the pressures applied are the major factors involved in deciding the cost and in achieving the desirable microbial inactivation. Hence, it is important to optimize conditions wherein minimal pressure is applied for the shortest time so that a food product with a reasonable cost is obtained.
