Predictive modelling of Listeria monocytogenes survival and recovery in salmon and pork subjected to sous vide cooking at 55 °C

Mild sous-vide processing is increasingly applied to enhance the sensory and nutritional quality of ready-to-eat foods. However, its microbiological safety remains uncertain, as moderate temperatures may allow survival and recovery of Listeria monocytogenes. This study investigated the behaviour of L. monocytogenes in salmon and pork fillets cooked at 55 °C for 30, 60, or 90 min and subsequently stored at 4 °C or 8 °C for up to 30 days. Two strains, Scott A and CECT 4031, were tested individually and as a cocktail. Outcomes varied according to strain and matrix: complete inactivation occurred only for CECT 4031 in pork, while survival and recovery were consistently detected in other conditions. Slow heating rates (< 2 °C/min) were associated with higher apparent resistance, particularly for Scott A. Inactivation deviated from log-linearity and was best described by the Geeraerd log-linear + tail and Mafart Weibull models, with D-values ranging from 6.8 to 8.3 min. During storage, post-treatment growth occurred in most salmon samples and in pork inoculated with Scott A at 8 °C. Sublethally injured cells recovered, showing maximum growth rates up to 1.0 log CFU g/day and lag phases of 2-14 days. These findings confirm that mild sous-vide treatments at 55 °C do not guarantee complete inactivation of L. monocytogenes, highlighting the need for validation studies that combine lethality and recovery outcomes. Predictive models integrating non-linear inactivation and heterogeneity provide a robust framework for assessing safety in minimally processed foods.