**5. Hurdle technology or synergism**

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 individual technique.

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

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).

Recent Advances in the Application

0308-8146

0362-028X

515, ISSN 0266-8254.

of Non Thermal Methods for the Prevention of *Salmonella* in Foods 299

Amiali, M., Ngadi, M.O., Smith, J.P., & Raghavan, G.S.V. (2007). Synergistic effect of

Angsupanich K., & Ledward, D.A. (1998). High pressure treatment effects on cod (*Gadus* 

Barbosa-Canovas, G.V., Pierson, M.D., Zhang, Q.H., & Schaffner, D.W. (2001). Pulsed electric fields. *Journal of Food Science*, pp. 65–79 Supplement, ISSN 1750-3841 Bouwknegt, M., Dam-Deisz, W.D.C., Schouten, J.M., Wannet, W.J.B., Van Pelt, W., Visser,

Bull, M.K., Zerdin, K., Howe, E., Goicoechea, D., Paramanandhan, P., Stockman, R.,

Burt, S.A., Fledderman, M.J., Haagsman, H.P., van Knapen, F., & Veldhuizen, E.J.A. (2007).

Careaga, M., Fernández, E., Dorantes, L., Mota, L., Jaramillo, M.E., & Hernandez-Sanchez,

Choi, Y.M., Bae, Y.Y., Kim, K.H., Kim, B.C., & Rhee, M.S. (2009a). Effects of supercritical

*Meat Science*, Vol. 82, No. 4, (August 2009), pp. 419–424, ISSN 0309-1740 Choi, Y.M., Kim, O.Y., Kim, K.H., Kim, B.C., & Rhee, M.S. (2009b). Combined effect of

Chun, H.H., Kim, J.Y., Chung, K.S., Won, M., & Song, K.B. (2009). Inactivation kinetics of

*Microbiology*, Vol. 83, No. 3, (June 2003), pp. 331-335, ISSN 0168-1605 Cheah, P.B., & Ledward, D.A. (1996). High pressure effects on lipid oxidation in minced pork. *Meat Science*, Vol. 43, No. 2, (June 1996), pp. 123–134, ISSN 0309-1740 Chen, H., Guan, D., & Hoover, D.G. (2006). Sensitivities of food-borne pathogens to pressure

http://www.rivm.nl/bibliotheek/rapporten/285859013.pdf

No. 2, (June 2004), pp. 135-149, ISSN 1466-8564

(November 2007), pp. 346-350, ISSN 0168-1605

(March 2007), pp. 689-694, ISSN 0260-8774.

temperature and pulsed electric field on inactivation of *Escherichia coli* O157:H7 and *Salmonella enteritidis* in liquid egg yolk. *Journal of Food Engineering*, Vol. 79, No. 2,

*morhua*) muscle. *Food Chemistry,* Vol. 63, No. 1, (September 1998), pp. 39–50, ISSN

G., van de Giessen, A. W., *Surveillance of zoonotic bacteria in farm animals in the Netherlands* (2003) Results from January 1998 until December 2000. (RIVM report 285859013, available from *www.rivm.nl*) Accessed on 2 July 2011,

Sellahewa, J., Szabo, S.A., Johnson, R.L., & Stewart, C.M. (2004). The effect of high pressure processing on the microbial, physical and chemical properties of Valencia and Navel orange juice. *Innovative Food Science and Emerging Technologies*, Vol. 5,

Inhibition of *Salmonella enterica* serotype Enteritidis on agar and raw chicken by carvacrol vapour. *International Journal of Food Microbiology*, Vol. 119, No. 3,

H. (2003). Antibacterial activity of *Capsicum* extract against Salmonella *typhimurium* and *Pseudomonas aeruginosa* inoculated in raw beef meat. *International Journal of Food* 

changes. *Journal of Food Protection*, Vol. 69, No. 1, (January 2006), pp. 130–136, ISSN

carbon dioxide treatment against generic *Escherichia coli, Listeria monocytogenes, Salmonella typhimurium*, and *E. coli* O157:H7 in marinades and marinated pork.

organic acids and supercritical carbon dioxide treatments against nonpathogenic *Escherichia coli*, *Listeria monocytogenes*, *Salmonella typhimurium* and *E. coli* O157:H7 in fresh pork. *Letters in Applied Microbiology*, Vol. 49, No. 4, (October 2009), pp. 510-

*Listeria monocytogenes*, *Salmonella enterica* serovar Typhimurium, and *Campylobacter* 

Application of PEF (25kV/cm, 250 μs in pulses of 2.12 μs) followed by heat treatment at 55 °C for 3.5 min increased the inactivation of *Salmonella* Enteritidis inoculated into liquid whole egg from 1 logs to 4.3 logs (Hermawan et al., 2004). The combination treatment had no effect on the color, pH, viscosity and brix of the treated samples and had a longer shelf life in comparison to heat treated samples.

High pressure applied in combination with other agents such as heat or antimicrobial agents can be effectively used to increase microbial inactivation. Individual and combined effects of HPP and nisin treatment on relative resistance, viability and cellular components on *S.* Enteritidis (strains: FDA and OSU 799) was evaluated in culture media. High pressure up to 200MPa and nisin (200 IU/ml) when applied separately did not have any effect on the viability of either strain. However, application of high pressure (500 MPa) or a combination of nisin with a pressure of 350MPa (OSU 799 strain) and 400 MPa (FDA strain) resulted in an 8 log reduction (Lee and Kaletunç, 2010). Penetration of nisin into the cells was assisted by the pressure and thereafter the additive effect of two hurdles resulted in inactivation to be achieved at a lower value than when the technique was applied separately. Viedma et al. (2008) studied the synergistic effects of antimicrobial peptide enterocin AS-48 and high-intensity-PEF treatment (35 kV/cm, 150 Hz, 4 μs and bipolar mode) on the inhibition of *S. enterica* CECT 915 in apple juice. A combination of high intensity PEF (1000 μs) and AS-48 (60 μg/ml) and a treatment temperature of 40 °C resulted in 4.5 log reduction. The sequence of the synergistic treatments was an important factor as the inhibition was observed only when HIPEF was applied in the presence of previously-added bacteriocin. Since both, enterocin AS-48 and high pressure PEF, act on the bacterial cytoplasmic membrane, synergism between them could be a result of enhanced permeability of bacterial cytoplasmic membrane.
