Quantifying variability on thermal resistance of Listeria monocytogenes

• Variability factors for thermal inactivation of Listeria monocytogenes were quantified.
• Higher strain variability was observed in comparison to biological and experimental variabilities.
• The effect of growth history on thermal resistance variability was in the same order of magnitude as strain variability.
• The effect of growth history on variability was mainly determined by the growth phase.
• Strain variability and the effect of growth history explain almost all variabilities found in literature.

Knowledge of the impact of strain variability and growth history on thermal resistance is needed to provide a realistic prediction and an adequate design of thermal treatments. In the present study, apart from quantifying strain variability on thermal resistance of Listeria monocytogenes, also biological variability and experimental variability were determined to prioritize their importance. Experimental variability was defined as the repeatability of parallel experimental replicates and biological variability was defined as the reproducibility of biologically independent reproductions. Furthermore, the effect of growth history was quantified. The thermal inactivation curves of 20 L. monocytogenes strains were fitted using the modified Weibull model, resulting in total 360 D-value estimates. The D-value ranged from 9 to 30 min at 55 °C; from 0.6 to 4 min at 60 °C; and from 0.08 to 0.6 min at 65 °C. The estimated z-values of all strains ranged from 4.4 to 5.7 °C. The strain variability was ten times higher than the experimental variability and four times higher than the biological variability. Furthermore, the effect of growth history on thermal resistance variability was not significantly different from that of strain variability and was mainly determined by the growth phase.