Synergistic effect of ohmic heating and UV-C irradiation for inactivation of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in buffered peptone water and tomato juice

Hurdle technology, in which preservation techniques are combined, has been of interest to scientists aiming to ensure microbiological food safety. We investigated the synergistic effect of UV-C irradiation and ohmic heating on the inactivation of foodborne pathogens. UV-C irradiation and ohmic heating were applied to buffered peptone water and tomato juice inoculated with pathogens simultaneously or sequentially. A synergistic bactericidal effect of the simultaneous treatment was observed against Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes. For example, the reductions (log CFU/ml) in E. coli O157:117 by UV-C irradiation, ohmic heating and simultaneous treatment in tomato juice were 0.48, 1.84 and 3.83, respectively. Additive effect was observed for cell membrane damage and lipid oxidation values with the simultaneous treatment Therefore, the proposed synergistic bactericidal mechanism by the simultaneous treatment consists of an acceleration of lipid oxidation, which results in an additive effect on cell membrane pore formation. Sequential treatment of UV-C irradiation after ohmic heating showed the least antibacterial effect in buffered peptone water. On the other hand, the reductions levels of all three pathogens in tomato juice were not significantly different between the two treatments regardless of the sequence. The color and lycopene content of tomato juice were not significantly deteriorated by either ohmic heating or the simultaneous treatment. Therefore, the combination treatment of UV-C irradiation and ohmic heating including simultaneous and sequential treatments, and regardless of treatment sequence, can be used as an effective hurdle technology ensuring microbiological safety in juice products.