Evaluación de la inocuidad microbiológica del lomo de salmón (Salmo salar) tras la aplicación del tratamiento de cocción al vacío a temperaturas moderadas

Abstract

Sous Vide is a cooking technique where a raw or partially cooked food is cooked under vacuum conditions while controlling time and temperature to obtain consistent results and a high-quality product, particularly when mild heat treatments are applied during a prolonged period that varies according to the type of food. However, the application of mild and prolonged heat treatments may favor the generation of adaptation phenomena to stress or the sublethal damage to bacterial cells which may not be sufficiently effective to eliminate or reduce significantly pathogenic microorganisms such as Listeria monocytogenes and Salmonella spp. For this reason, there is concern about the risks associated with this type of product among those that use this technique. _x000D_ _x000D_ _x000D_ _x000D_ The objective of this doctoral dissertation was to evaluate the lethal effect of cooking under a vacuum with isothermal conditions using a vapor-convection oven in mild temperatures (55 and 60 ºC) during 30, 60 and 90 minutes among inoculated, individually and in combination, samples of salmon loin with two strains of Listeria monocytogenes (CECT 4031 y Scott A) and two serovars of Salmonella enterica subsp. enterica (serovar Enteritidis CECT 4300 and Senftenberg CECT 4565), and their possibility of recovery and growth after conservation for 30 days at optimal temperature (4 ºC) and abuse temperature (8 ºC). The program Bioinactivation FE was used for data modelling of non-isothermal inactivation while the DMFit feature of the program Combase allowed to adjust the models of growth. In addition, to incorporate the observed variability in the predictive models, the Monte Carlo simulation was used. _x000D_ _x000D_ _x000D_ _x000D_ After thermic treatment at 55 ºC, the survival curve of Listeria monocytogenes and Salmonella spp. were adjusted to a non-lineal model, while at 60 ºC, due to the increased intensity of the treatment, could not be modelled. During the conservation of the salmon loin samples in refrigeration, the behavior of damaged cells of Listeria monocytogenes and Salmonella spp. were divided in three scenarios: total inactivation, growth/no growth, and viability. Total inactivation was observed only in S. Enteritidis in treatment at 60 ºC for 90 minutes, conserved at 4 ºC and that after 30 days there were no viable cells detected. Growth/no growth, where a combination of viable cells and non-viable cells may be present simultaneously, was observed in most of the treatments at 60 ºC for both pathogens. While the viability scenario, in which bacterial counts were over the quantification limit (5 UFC/g), was observed primarily in thermic treatments at 55 ºC. _x000D_ The recovery and growth of Listeria monocytogenes and Salmonella spp. was determined by the heterogeneity of the individual cell response. In addition, other factors may have favor adaptation phenomena to sublethal stress and the recovery of cellular damage such as: low rate of heat treatment, application of mild heat treatment, long periods of conservation in refrigeration as well as those associated with the experimental design. The results obtained in this dissertation make it difficult to establish a microbiological safety margin of salmon loin when cooked under a vacuum with mild heat treatments.

Date of Award	9 Jul 2021
Original language	Spanish
Supervisor	Montserrat Vila Brugalla (Director)