**4.4.1 Extracts from vegetables**

Vegetable extracts have shown a good potential when applied under laboratory conditions in culture media. For instance, application of 6% seaweed extract was shown to result in complete inhibition of *S. abony* whereas 3% extract resulted in 93% inhibition (Gupta et al., 2011). In contrast, 2.8% methanolic extract from Irish York cabbage was shown to result in only 64% inhibition of *S. abony* (Jaiswal et al., 2011). Xu et al. (2007) reported a minimal inhibitory concentration (MIC) of 15μl of grapefruit seed extract to

Recent Advances in the Application

of Non Thermal Methods for the Prevention of *Salmonella* in Foods 297

extracts from *S. officinalis* and *S. molle* for over 15 days. In case of *S. molle*, the bacteriostatic effect was seen up to a concentration of 1%. At concentrations higher than 1.5% for *S. officinalis* and 2% for *S. molle*, immediate bactericidal effect was observed with a 2.6 log cfu /g reduction at 1.5% *S. officinalis* and 1 log cfu/g at 2% *S. molle*. However, sensory analysis of meat containing more than 2% of *S. molle* and 1.5% of *S. officinalis* showed a distinguished effect on the flavour and taste. In order to reduce the amount of EO being used, combinations of EO with NaCl were studied. The use of 0.1% or 1.5% *S. officinalis* with 6% or 4% NaCl or 0.1% or 1.5% *S. molle* with 4 or 8% Nacl could effectively eliminate *S. anatum* from refrigerated raw beef (Hayouni et al., 2008). The positive effect of spices on the inactivation of *S*. Typhimurium DT104 was observed when in direct contact, however, the activity reduced when added to food system such as ground beef (Uhart et al., 2006). Utilization of packaging materials containing these antimicrobial compounds is also becoming an attractive option in the food industry. However, a major limitation in using the EO in foods is the effect they have on the sensory properties of foods. At times, the concentration required to show the antimicrobial effect can surpass the

Hurdle approach or the process of using multiple technologies is an effective approach to improve microbial decontamination in comparison to that of a single technology alone. Deliberate and intelligent combination of preservative treatments can help in maintaining the quality of food and delivering almost similar levels of microbial destruction as conventional methods alone. At the same time it warranties to counteract the negative effect of individual technologies on food quality. The choice of hurdles will strongly depend on the type of food it is being applied to in addition to the mode of inactivation. Potential synergistic effects among different technologies have been reported to be more effective than individual technologies applied alone. The outer membrane of gram negative cells prevents the entry of hydrophobic compounds. A combined treatment of heat and irradiation can result in sub-lethal injury to the cells. The sublethally injured cells can be more vulnerable to attack by antimicrobial compounds thereby reducing the dose of each

For instance, combined effect of UV-C (0.5 J/cm2) and potassium lactate, lauric arginate ester and sodium diacetate (FDA approved) resulted in a 3.6-4.1 log reduction of *Salmonella*, *L. monocytogenes* and *Staphylococcus aureus* on the surface of frankfurters (12 weeks storage at 10 °C). In addition, UV-C and antimicrobials had no significant impact on frankfurter color or texture (Sommers et al., 2010). Amiali et al. (2007) studied the synergistic effects of temperature, treatment time and electric field strength on inactivation of *S.* Enteritidis and *Escherichia coli* O157:H7 in egg yolk. A 5 log reduction in the population of *E. coli* O157:H7

Exposure of egg shells contaminated with *S.* Enteritidis with UV radiation (1,500 to 2,500 μW/cm2) followed by ozone (5 lb/in2 gauge for 1 min) resulted in an inactivation of 4.6 logs or more in a total treatment time of 2 min (Roriguez-Romo and Yousef, 2005). Although the individual treatments resulted in similar reductions, however exposure time and pressure were comparatively higher. Combined treatment of lactic and acetic acid with super critical CO2 resulted in 2.33 log cfu/cm2 reduction in *S.* Typhimurium in fresh pork which was higher as compared to these treatments being applied individually (Choi et al., 2009b).

and *S. enteritidis* was observed at an electric field of 30 kV cm−1 and 40 °C.

organoleptically levels resulting in alteration in the flavor of foods.

**5. Hurdle technology or synergism** 

individual technique.

inhibit *Salmonella*. Careaga et al. (2003) reported that a minimum concentration of 1.5 ml of capsicum extract per 100g of meat was needed in order to prevent the growth of *S.*  Typhimurium inoculated in minced beef. Karapinar and Sengun (2007) evaluated the antimicrobial activity of koruk (unripe grape—*Vitis vinifera*) juice against *S*. Typhimurium on cucumber and parsley samples which resulted in 1-1.5 log reduction upon immediate contact with korak juice and the reduction increased as the time of exposure of the vegetables to the juice increased.

The antimicrobial efficacy of plant extracts has been attributed to the presence of phenolic compounds, quinones, alkaloids, flavanols/flavonoids and lectins. Solubility of the extract in the food systems and the pH of the extract are important factors determining their efficacy in foods. Mechanism of action of these phenolic compounds involves alteration in the cell morphology which results in a disruption of the cytoplasmic membrane and leakage of cell constituents. Although the use of vegetable extracts for controlling the growth of *Salmonella* is promising the actual application in foods is in its budding stage.

#### **4.4.2 Extracts of herbs and spices**

In addition to providing flavor and fragrance, spices and herbs have also antimicrobial potential and thus can be used for preventing food deterioration and shelf life extension. Sumac, rosemary, sage, basil and ginger are some of the spices commonly being used for imparting antimicrobial effects on food. The flower, buds, leaf, stem or bark of these plants contains aromatic oily liquid which is the essential oil (EO). These EO are rich in phytochemicals such as terpenoids, polyphenols, flavonoids, antocyanin and organic acids which are responsible for the antimicrobial activity. Compounds such as carvacrol, citral, thymol, eugenol and citric acid have been shown to inhibit the growth of *Salmonella*. Eugenol has been reported to strongly inhibit the growth of *Listeria monocytogenes*, *Salmonella Enteritidis*, *Escherichia coli* and *Staphylococcus aureus.* Carvacrol and thymol are reported to be the principal constituents of EO of certain herbs. Burt et al. (2007) evaluated the antimicrobial activity of carvacrol vapour against *S.* Enteritidis on pieces of raw chicken. UV sterilized chicken pieces treated with carvacrol vapour (2 μl) showed reduced viable numbers of salmonellae at 4, 20 and 37 °C and a concentration of 4 μl resulted in a complete elimination of all viable cells in a minimum of 3 h at 37 °C. Govaris et al. (2010) studied the antimicrobial effect of oregano EO, nisin and their combination against *S.* Enteritidis in minced sheep meat during refrigerated storage (4 or 10 °C) for 12 days. Addition of nisin, at 500 or 1000 IU/g, proved insufficient to inhibit *S.* Enteritidis. The addition of oregano EO at 0.9% caused the population of *S.* Enteritidis to be maintained below 1 log cfu/g whereas a combination of 0.9% oregano EO and nisin at 500 or 1000 IU/g showed a bactericidal effect. The addition of 0.6% or 0.9% EO was found to be organoleptically acceptable also. EOs have also been applied for the elimination of *Salmonella* on fresh tomatoes. Gündüz et al. (2010) tested the antimicrobial potential of essential oil extracts on tomatoes. The tomatoes were inoculated with the nalidixic acid resistant strain of *Salmonella* Typhimurium ATCC 13311 and treated for 5-20 min with water extracts of sumac or oregano oil. Tomatoes treated with 100 ppm oregano or 4% sumac extract resulted in 2.78 and 2.38 log reduction, respectively. Hayouni et al. (2008) studied the antimicrobial effect of extracts from *Salvia officinalis* L. and berries of *Schinus molle* L against *S. anatum* or *S.* Enteritidis inoculated on minced beef meat. Concentrations in the range of 0.02-0.1% showed bacteriostatic effect against both the bacteria by the

inhibit *Salmonella*. Careaga et al. (2003) reported that a minimum concentration of 1.5 ml of capsicum extract per 100g of meat was needed in order to prevent the growth of *S.*  Typhimurium inoculated in minced beef. Karapinar and Sengun (2007) evaluated the antimicrobial activity of koruk (unripe grape—*Vitis vinifera*) juice against *S*. Typhimurium on cucumber and parsley samples which resulted in 1-1.5 log reduction upon immediate contact with korak juice and the reduction increased as the time of exposure of the

The antimicrobial efficacy of plant extracts has been attributed to the presence of phenolic compounds, quinones, alkaloids, flavanols/flavonoids and lectins. Solubility of the extract in the food systems and the pH of the extract are important factors determining their efficacy in foods. Mechanism of action of these phenolic compounds involves alteration in the cell morphology which results in a disruption of the cytoplasmic membrane and leakage of cell constituents. Although the use of vegetable extracts for controlling the growth of

In addition to providing flavor and fragrance, spices and herbs have also antimicrobial potential and thus can be used for preventing food deterioration and shelf life extension. Sumac, rosemary, sage, basil and ginger are some of the spices commonly being used for imparting antimicrobial effects on food. The flower, buds, leaf, stem or bark of these plants contains aromatic oily liquid which is the essential oil (EO). These EO are rich in phytochemicals such as terpenoids, polyphenols, flavonoids, antocyanin and organic acids which are responsible for the antimicrobial activity. Compounds such as carvacrol, citral, thymol, eugenol and citric acid have been shown to inhibit the growth of *Salmonella*. Eugenol has been reported to strongly inhibit the growth of *Listeria monocytogenes*, *Salmonella Enteritidis*, *Escherichia coli* and *Staphylococcus aureus.* Carvacrol and thymol are reported to be the principal constituents of EO of certain herbs. Burt et al. (2007) evaluated the antimicrobial activity of carvacrol vapour against *S.* Enteritidis on pieces of raw chicken. UV sterilized chicken pieces treated with carvacrol vapour (2 μl) showed reduced viable numbers of salmonellae at 4, 20 and 37 °C and a concentration of 4 μl resulted in a complete elimination of all viable cells in a minimum of 3 h at 37 °C. Govaris et al. (2010) studied the antimicrobial effect of oregano EO, nisin and their combination against *S.* Enteritidis in minced sheep meat during refrigerated storage (4 or 10 °C) for 12 days. Addition of nisin, at 500 or 1000 IU/g, proved insufficient to inhibit *S.* Enteritidis. The addition of oregano EO at 0.9% caused the population of *S.* Enteritidis to be maintained below 1 log cfu/g whereas a combination of 0.9% oregano EO and nisin at 500 or 1000 IU/g showed a bactericidal effect. The addition of 0.6% or 0.9% EO was found to be organoleptically acceptable also. EOs have also been applied for the elimination of *Salmonella* on fresh tomatoes. Gündüz et al. (2010) tested the antimicrobial potential of essential oil extracts on tomatoes. The tomatoes were inoculated with the nalidixic acid resistant strain of *Salmonella* Typhimurium ATCC 13311 and treated for 5-20 min with water extracts of sumac or oregano oil. Tomatoes treated with 100 ppm oregano or 4% sumac extract resulted in 2.78 and 2.38 log reduction, respectively. Hayouni et al. (2008) studied the antimicrobial effect of extracts from *Salvia officinalis* L. and berries of *Schinus molle* L against *S. anatum* or *S.* Enteritidis inoculated on minced beef meat. Concentrations in the range of 0.02-0.1% showed bacteriostatic effect against both the bacteria by the

*Salmonella* is promising the actual application in foods is in its budding stage.

vegetables to the juice increased.

**4.4.2 Extracts of herbs and spices** 

extracts from *S. officinalis* and *S. molle* for over 15 days. In case of *S. molle*, the bacteriostatic effect was seen up to a concentration of 1%. At concentrations higher than 1.5% for *S. officinalis* and 2% for *S. molle*, immediate bactericidal effect was observed with a 2.6 log cfu /g reduction at 1.5% *S. officinalis* and 1 log cfu/g at 2% *S. molle*. However, sensory analysis of meat containing more than 2% of *S. molle* and 1.5% of *S. officinalis* showed a distinguished effect on the flavour and taste. In order to reduce the amount of EO being used, combinations of EO with NaCl were studied. The use of 0.1% or 1.5% *S. officinalis* with 6% or 4% NaCl or 0.1% or 1.5% *S. molle* with 4 or 8% Nacl could effectively eliminate *S. anatum* from refrigerated raw beef (Hayouni et al., 2008). The positive effect of spices on the inactivation of *S*. Typhimurium DT104 was observed when in direct contact, however, the activity reduced when added to food system such as ground beef (Uhart et al., 2006). Utilization of packaging materials containing these antimicrobial compounds is also becoming an attractive option in the food industry. However, a major limitation in using the EO in foods is the effect they have on the sensory properties of foods. At times, the concentration required to show the antimicrobial effect can surpass the organoleptically levels resulting in alteration in the flavor of foods.
