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A response surface model of Listeria monocytogenes' growth rate was built in this study under different temperatures (10°C, 15°C, 20°C, 25°C and 30°C) and acid concentrations: citric acid (0-0.4%) and ascorbic acid (0-0.4%); two ingredients which are often used in the food industry as preservatives. Mathematical validation was performed with additional samples at different conditions within the range of the model, obtaining acceptable values of root mean square error (0.0466), standard error of prediction (18.84%), bias factor (1.05) and accuracy factor (1.16). The inhibitory effect on growth was more effective with citric acid than ascorbic acid, possibly due to the major dissociation of citric acid occurring inside microbial cells. The different conditions considered in the model will potentially allow L. monocytogenes' response to be predicted in foods having a similar composition to the chemical and physical factors set out in this paper.

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A quantitative risk characterization of Listeria monocytogenes in various ready-to-eat (RTE) food categories (heat-treated meat; smoked and gravad fish; and soft and semi-soft cheeses) in the European Union (EU) was performed; starting from the retail stage. For prevalence and concentration, data from the EU-wide baseline survey was complemented with EU monitoring data and data from other sources. Food serving size and the number of servings per year were estimated from the European food consumption database. Demographical data from Eurostat were also used. Growth of L. monocytogenes considering interaction with lactic acid bacteria was modelled from retail to consumption using temperature-time profiles during transport and storage. This information was combined with the Pouillot dose-response models to estimate the number of listeriosis cases per 10 6 servings as well as the annual number of listeriosis cases in the EU associated with the consumption of the RTE foods. The total number of cases was estimated as 2,318 (95 confidence interval (CI): 1,450-3,612). Cooked meat and sausage presented most cases (median of 863 and 541, respectively). Sliced pâté packaged in normal atmosphere presented the highest listeriosis risk per million servings. With respect to the estimation of the total number of cases per population group, considering each food subcategory separately, the higher risk population group corresponded to elderly, followed, in most cases, by pregnant and healthy, with the exceptions of cooked meat and hot smoked fish in which pregnant presented higher risk than elderly. In the light of results, it seems necessary that educative programs and specific recommendations are specially oriented the most susceptible population groups so as to mitigate the risk. Uncertainty sources for some variables such as initial MAY prevalence should be further elucidated as well as variability in Listeria growth when types of product and populations are compared.

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