Non-thermal plasma inactivation of Salmonella Typhimurium on different matrices and the effect of selected food components on its bactericidal efficacy

Non-thermal plasma (NTP) is known as an effective source of a variety of reactive species generated in the gas phase. Nowadays, NTP is gaining increasing interest from the food industry as a microbial inactivation technique. In the present study the effect of inoculation method and matrix on inactivation of Salmonella Typhimurium was examined by treating spread plated agar (2.2 log CFU/sample inactivation by NTP), spot inoculated agar (1.9 log CFU inactivation), glass beads (1.3 log CFU inactivation) and peppercorn (0.2 log CFU inactivation). Furthermore, multiple agar matrices supplemented with low and high concentrations of a certain food component (casein, starch, sunflower oil, vitamin C, sodium pyruvate or grinded peppercorns) were inoculated and treated to determine the effect of those components on NTP efficiency. Although starch, vitamin C and sodium pyruvate had no significant influence on the inactivation degree, the presence of 10% casein (2.1 log CFU/sample less inactivation compared to tryptone soy agar (TSA)), 10% pepper (2.1 log CFU less inactivation) or 1% and 10% sunflower oil (1.6 and 2.1 log CFU less inactivation, respectively) in TSA demonstrated the protective effect of these substances for NTP treatment. These experiments led to the conclusion that low inactivation on produce seemed not to arise from the inoculation method nor from the shape of the produce, but is the result of the food matrix.