Quantitative Evaluation of Thermal Inactivation Kinetics of Free-Floating Versus Surface-Attached Listeria innocua Cells

Abstract

Surface pasteurization is one of the decontamination treatments that can contribute to better preservation of meat products retaining most of their quality characteristics relatively intact if compared with the raw products. The current research compares the kinetics of free-floating and surface attached Listeria innocua cells by using integrated microbial and heat transfer modelling approaches. Surface pasteurization treatments are applied on a (abiotic) Teflon® model system in a novel steam surface decontamination rig. The experimental set-up prevented following four technological aspects to occur, (1) cold purge migration to the surface during the heating process, (2) inactivation kinetics of a cocktail of microbes, (3) protective effect of food components, and (4) physical distribution of bacteria throughout the depth of the product skin. Microbial load predictions are performed based on the inactivation parameters obtained during free-floating cell experiments. These predictions, when compared with the microbial data of the surface treatments, prove that the surface attached cells were much more heat resistant, despite the experimental set-up preventing the aforementioned (technological) events to occur. Indeed, surface attached cells can have different physiological/phenotypical/genetical characteristics, such as cell aggregations, colony formations, presence of flagella. In a final step, three techniques are implemented to evaluate mathematically the kinetics of the surface attached cells. Overall, this research's significance is lying in the quantitative assessment of microbial heat resistance. The technological reasons underlying the increased microbial heat resistance on biotic and abiotic surfaces should be reevaluated, taking into account possible physiological/ phenotypical/genetical characteristics.

The impact of food model system structure on the inactivation of Listeria innocua by cold atmospheric plasma and nisin combined treatments

“…Furthermore, resistance of surface colonies (as compared to planktonic cells) to stresses other than CAP has been demonstrated. For example, Valdramidis et al, (2008) show that L. innocua as surface attached cells on Teflon® were more heat resistant than planktonic cells in liquid medium. Aryani et al, (2016) observed that L. monocytogenes and Lactobacillus plantarum on the surface of ham slices were more resistant to thermal inactivation (65°C or 60°C for each species respectively) than cells in liquid broth.…”

Recent Advances in Minimal Heat Processing of Fish: Effects on Microbiological Activity and Safety

“…A number of efforts have been made to describe the physical parameters and to model the processes, both for dry air (Kondjoyan, Mccann et al 2006a;Kondjoyan, Rouaud et al 2006b;Kondjoyan and Havet 2003;Valdramidis et al 2005) and steam (Kondjoyan and Portanguen 2008;Valdramidis et al 2008). The experimental data typically shows variations way beyond what can be explained by model parameters, thus indicating that the models may be incomplete with respect to parameters.…”