Microbiological safety evaluation of sous-vide treatments at mild temperatures applied to pork loin
- Autores: Montserrat Vila Brugalla
- Directores de la Tesis: María Manuela Hernández Herrero (dir. tes.), Artur Xavier Roig Sagués (dir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: Esther Sendra Nadal (presid.), Alicia Subires Orenes (secret.), Sílvia de Lamo Castellví (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia de los Alimentos por la Universidad Autónoma de Barcelona
- Materias:
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- Resumen
A raising interest has been detected nowadays in relation to the use of cooking techniques at moderate temperatures like sous-vide cooking. Given the possibility of using these techniques to prepare food in advance, and considering that data on behaviour of bacteria in the range of 40 to 60 °C is scarce, there is great concern in accurately define the microbiological safety of this food. The aim of this doctoral thesis was to characterize the effect of mild temperature vacuum cooking treatments on two main food pathogens, L. monocytogenes and Salmonella spp. inoculated in raw pork meat.
Challenge studies were conducted using two bacterial strains of Salmonella (S. enterica subsp. enterica serovar Enteritidis CECT 4300 and Senftenberg CECT 4565), and Listeria monocytogenes (CECT 4031 and Scott A), inoculated either individually or in combination. Pork loin pieces were inoculated, vacuum packed and cooked in a steam oven at two different temperatures (55 and 60 ºC) during 30, 60 or 90 minutes. Lethality caused by each treatment was determined just after cooking. Further recovery of injured cells was evaluated during storage at 4 and 8 ºC until the 30th day after treatments. Evolution of microbial counts were modelled using the predictive tools Bioinactivation FE for thermal inactivation and DMFit for growth through the storage time. The Monte Carlo method was applied in order to incorporate the variability observed between replicates in the predictive models of inactivation and growth.
The heterogeneity of results was important. One source of this variability was probably the steam oven performance between 55 and 60 ºC. At these cooking temperatures, Salmonella spp. was more heat resistant than L. monocytogenes, but it was less able to growth during cold storage. Microbiological safety evaluation of sous-vide mild heat treatments must be based both on lethality and on the capability of recovery during storage. Considering both factors, three different scenarios were obtained: complete inactivation, presence of viable cells and a growth/no growth interface. In case of a complete inactivation (S. Enteritidis and L. monocytogenes Scott A and CECT 4031 cooked at 60 ºC), inoculated strains were not detected in any replicate during all the storage period. In case of viability, all replicates showed counts above the quantification limit (5 CFU/g), whether growth was observed or not (S. Senftenberg, L. monocytogenes Scott A, cocktail of L. monocytogenes strains at 55 ºC, and cocktail of Salmonella spp. strains at 55 ºC during 30 min). Finally, in some experimental conditions a “growth/no growth” behaviour, with different proportions of death, viable and injured cells, was observed. This circumstance took place in inoculated samples cooked at 60 ºC (S. Senftenberg, cocktail of L. monocytogenes) and 55 ºC (cocktail of Salmonella spp. and L. monocytogenes CECT 4031).
In conclusion, the microbiological safety of sous-vide mild heat processes have to be accurately assessed on a case-by-case basis. Heat treatments at 60 ºC for 90 min applied to pork loin could be considered reasonably safe and suitable for “cook-chill” systems in relation to Salmonella spp. and L. monocytogenes strains included in the essay, as long as no temperature abuse occurs during shelf-life. Treatments at 60 ºC during 30 and 60 minutes must be used only for “cook-serve” systems. Sous-vide cooking of pork loin at 55 ºC during 30, 60 and 90 minutes cannot be considered safe in relation to S. Senftenberg and L. monocytogenes Scott A due to the presence of survivor cells that can growth at 8 ºC. This treatment must be used only for “cook-serve” systems. This study provides useful data for future risk assessment studies applied to meat sous-vide cooked at mild temperatures.
