Simultaneous vacuum ultra violet-amalgam lamp radiation and near-infrared radiation heating for a synergistic bactericidal effect against Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium in black peppercorn

Abstract

This study evaluated the effect of simultaneous irradiation with vacuum ultraviolet (VUV)-amalgam lamp and near-infrared radiation (NIR) to inactivate foodborne pathogens in black peppercorn (Piper nigrum) while monitoring its piperine content and color. NIR treatment for 20 min caused an increase in black peppercorn temperature to 70 °C, and its bactericidal effect showed only 3.14 and 1.88 log reductions of Escherichia coli O157:H7 and Salmonella Typhimurium respectively. Single treatment with a VUV-amalgam lamp for 20 min achieved 2.26 and 1.55 log reductions of E. coli O157:H7 and S. Typhimurium, respectively. However, simultaneous treatment for 15 min produces a greater than 5-log reduction of both foodborne pathogens without changes of black peppercorn quality. The underlying bactericidal mechanism of the VUV-amalgam lamp is 254 nm irradiation with ozone generated by 185 nm irradiation. The ozone concentration was maintained with VUV-amalgam lamp single treatment but decreased during simultaneous treatment. In contrast, due to the drying effect of NIR irradiation, water vapor reacts with 185 nm irradiation or ozone to produce a variety of reactive oxygen species (ROS) such as hydrogen peroxide and hydroxyl radical during simultaneous treatment. The hydrogen peroxide concentration measured by Gastec increased during simultaneous treatment. We also investigated various generated types of ROS that can contribute to a synergistic bactericidal effect. We compared the bactericidal effect of sequential and simultaneous treatments with NIR and VUV-amalgam lamps to black peppercorn. Although sequential treatment showed additional inactivation efficacy, reductions of pathogens were significantly lower than with simultaneous treatment. These findings suggest that simultaneous VUV-amalgam lamp and NIR irradiation treatment via generation of ROS can increase bacterial inactivation efficacy of foodborne pathogens in black peppercorns without quality changes.