Inactivation of Listeria Monocytogenes at various growth temperatures by ultrasound pretreatment and cold plasma

Abstract

Effects of ultrasound pretreatments and dielectric barrier discharge (DBD) cold plasma on the inactivation of Listeria monocytogenes (L. monocytogenes) under various growth temperatures were investigated, and membrane fatty acid profiles of L. monocytogenes were also determined. Fatty acids anteiso-C15:0, anteiso-C17:0 and C15:0 were the most abundant fatty acids at any given growth temperature (10, 25, 37 and 42 °C). Principal components analysis (PCA) and redundancy analysis (RDA) displayed that preconditioning growth temperatures induced noticeable modifications in membrane fatty acid profile, which could be separated from each other and classified roughly into four groups. In addition, growth temperature-mediated alterations in fatty acid profile and membrane fluidity of L. monocytogenes were associated with cell viability, with a significant increase in intracellular reactive oxygen species (ROS) levels (P < 0.01) and a significant reduction in the resistance to DBD plasma exposure (P < 0.01). For inactivation kinetics, the sigmoidal-like model (RMSE10 °C = 0.037; RMSE25 °C = 0.055; RMSE37 °C = 0.073; RMSE42 °C = 0.192) with three phases (shoulder region, log-linear phase and tailing phase) was the most appropriate model that could describe the inactivation curves of L. monocytogenes. Survival assays and scanning electron microscopy (SEM) indicated that ultrasound pretreatments caused a weakening effect on the membrane. In general, this study provided new insights on correlating growth temperature-mediated alterations in fatty acid profile with intracellular ROS levels and inactivation efficiency.