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    Modeling the Growth of Six Listeria monocytogenes Strains in Smoked Salmon Pate
    (Mdpi, 2023) Bolivar, Araceli; Garrote Achou, Chajira; Tarlak, Fatih; Cantalejo, Maria Jesus; Costa, Jean Carlos Correia Peres; Perez-Rodriguez, Fernando
    In this study, the growth of six L. monocytogenes strains isolated from different fish products was quantified and modeled in smoked salmon pate at a temperature ranging from 2 to 20 degrees C. The experimental data obtained for each strain was fitted to the primary growth model of Baranyi and Roberts to estimate the following kinetic parameters: lag phase (lambda), maximum specific growth rate (mu(max)), and maximum cell density (N-max). Then, the effect of storage temperature on the obtained mu(max) values was modeled by the Ratkowsky secondary model. In general, the six L. monocytogenes strains showed rapid growth in salmon pate at all storage temperatures, with a relatively short lag phase lambda, even at 2 degrees C. The growth behavior among the tested strains was similar at the same storage temperature, although significant differences were found for the parameters lambda and mu(max). Besides, the growth variations among the strains did not follow a regular pattern. The estimated secondary model parameter T-min ranged from -4.25 to -3.19 degrees C. This study provides accurate predictive models for the growth of L. monocytogenes in fish pates that can be used in shelf life and microbial risk assessment studies. In addition, the models generated in this work can be implemented in predictive modeling tools and repositories that can be reliably and easily used by the fish industry and end-users to establish measures aimed at controlling the growth of L. monocytogenes in fish-based pates.
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    Modelling of the Behaviour of Salmonella enterica serovar Reading on Commercial Fresh-Cut Iceberg Lettuce Stored at Different Temperatures
    (Mdpi, 2020) Tarlak, Fatih; Johannessen, Gro; Bascon Villegas, Isabel; Bolivar, Araceli; Posada-Izquierdo, Guiomar Denisse; Perez-Rodriguez, Fernando
    The aim of this study was to model the growth and survival behaviour ofSalmonellaReading and endogenous lactic acid bacteria on fresh pre-cut iceberg lettuce stored under modified atmosphere packaging for 10 days at different temperatures (4, 8 and 15 degrees C). The Baranyi and Weibull models were satisfactorily fitted to describe microbial growth and survival behaviour, respectively. Results indicated that lactic acid bacteria (LAB) could grow at all storage temperatures, whileS. Reading grew only at 15 degrees C. Specific growth rate values (mu(max)) for LAB ranged between 0.080 and 0.168 h(-1)corresponding to the temperatures 4 and 15 degrees C while forS. Reading at 15 degrees C,mu(max)= 0.056 h(-1). This result was compared with published predictive microbiology models for otherSalmonellaserovars in leafy greens, revealing that predictions from specific models could be valid for such a temperature, provided they were developed specifically in lettuce regardless of the type of serovars inoculated. The parameter delta obtained from the Weibull model for the pathogen was found to be 16.03 and 18.81 for 4 and 8 degrees C, respectively, indicating that the pathogen underwent larger reduction levels at lower temperatures (2.8 log(10)decrease at 4 degrees C). These data suggest that thisSalmonellaserovar is especially sensitive to low temperatures, under the assayed conditions, while showcasing that a correct refrigeration could be an effective measure to control microbial risk in commercial packaged lettuce. Finally, the microbiological data and models from this study will be useful to consider more specifically the behaviour ofS. Reading during transport and storage of fresh-cut lettuce, elucidating the contribution of this serovar to the risk bySalmonellain leafy green products.