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    A new expanded modelling approach for investigating the bioprotective capacity of Latilactobacillus sakei CTC494 against Listeria monocytogenes in ready-to-eat fish products
    (Elsevier, 2021) Bolívar, Araceli; Tarlak, Fatih; Correia Peres Costa, Jean Carlos; Cejudo-Gomez, Manuel; Bover-Cid, Sara; Zurera, Gonzalo; Perez-Rodriguez, Fernando
    Understanding the role of food-related factors on the efficacy of protective cultures is essential to attain optimal results for developing biopreservation-based strategies. The aim of this work was to assess and model growth of Latilactobacillus sakei CTC494 and Listeria monocytogenes CTC1034, and their interaction, in two different ready-to-eat fish products (i.e., surimi-based product and tuna pate) at 2 and 12 degrees C. The existing expanded Jameson-effect and a new expanded Jameson-effect model proposed in this study were evaluated to quantitatively describe the effect of microbial interaction. The inhibiting effect of the selected lactic acid bacteria strain on the pathogen growth was product dependent. In surimi product, a reduction of lag time of both strains was observed when growing in coculture at 2 degrees C, followed by the inhibition of the pathogen when the bioprotective L. sakei CTC494 reached the maximum population density, suggesting a mutualism-antagonism continuum phenomenon between populations. In tuna pate, L. sakei CTC494 exerted a strong inhibition of L. monocytogenes at 2 degrees C (<0.5 log increase) and limited the growth at 12 degrees C (<2 log increase). The goodness-of-fit indexes indicated that the new expanded Jameson-effect model performed better and appropriately described the different competition patterns observed in the tested fish products. The proposed expanded competition model allowed for description of not only antagonistic but also mutualism-based interactions based on their influence on lag time.
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    Development and validation of a one-step modelling approach for the determination of chicken meat shelf-life based on the growth kinetics of Pseudomonas spp
    (Sage Publications Ltd, 2022) Tarlak, Fatih; Perez-Rodriguez, Fernando
    The main objective of the present study was to investigate the effect of storage temperature on aerobically stored chicken meat spoilage using the two-step and one-step modelling approaches involving different primary models namely the modified Gompertz, logistic, Baranyi and Huang models. For this purpose, growth data points of Pseudomonas spp. were collected from published studies conducted in aerobically stored chicken meat product. Temperature-dependent kinetic parameters (maximum specific growth rate 'mu (max) ' and lag phase duration 'lambda') were described as a function of storage temperature through the Ratkowsky model based on the different primary models. Then, the fitting capability of both modelling approaches was compared taking into account root mean square error, adjusted coefficient of determination (adjusted-R-2) and corrected Akaike information criterion. The one-step modelling approach showed considerably improved fitting capability regardless of the used primary model. Finally, models developed from the one-step modelling approach were validated for the maximum growth rate data extracted from independent published literature using the statistical indexes Bias (B-f) and Accuracy (A(f)) factors. The best prediction capability was obtained for the Baranyi model with B-f and A(f) being very close to 1. The shelf-life of chicken meat as a function of storage temperature was predicted using both modelling approaches for the Baranyi model.
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    Inactivation of Salmonella Typhimurium in fresh-cut lettuce during chlorine washing: Assessing the impacts of free chlorine concentrations and exposure times
    (Elsevier, 2023) Possas, Aricia; Posada-Izquierdo, Guiomar Denisse; Tarlak, Fatih; Jimenez-Jimenez, Francisco; Perez-Rodriguez, Fernando
    The aim of this study was to evaluate, quantify and model the inactivation of Salmonella in fresh-cut lettuce during washings with chlorinated water at different free chlorine concentrations (FCC, 0-150 mg/L). Individual fresh-cut lettuce samples (4 cm2) were inoculated with a Salmonella culture (ca. 4 log CFU/cm2) and washed with 100-mL solutions with different FCC for different times (0-150 s). The surviving Salmonella cells recovered from samples were enumerated by plate count methodology. A fast decay on Salmonella counts was marked in the first 20 s of washing, followed by a slowing down on reductions. A maximum of 2.6 log-decrease was observed after 2.5-min washing regardless of FCC. The log-linear with tail primary model coupled with a linear secondary model was fitted to inactivation data obtained at FCC from 50 to 150 mg/L through global regression analysis, yielding a suitable model to describe Salmonella concentrations as a function of FCC and washing times (RMSE = 0.34, R2adj= 0.84). Simulations using the developed model showed inactivation rates varying from 0.17 log CFU/ s at 50 mg/L to 0.86 log CFU/s at 150 mg/L. Disinfection models on lettuce are valuable tools for the validation of control measures in the fresh-cut produce industry and for quantitative risk assessments.
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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.
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    Quantifying and modelling the inactivation of Listeria monocytogenes by electrolyzed water on food contact surfaces
    (Elsevier Sci Ltd, 2021) Possas, Aricia; Perez-Rodriguez, Fernando; Tarlak, Fatih; Maria Garcia-Gimeno, Rosa
    The efficacy of electrolyzed water (EW) to inactivate Listeria monocytogenes on stainless steel surfaces was evaluated and modelled in the present study. L. monocytogenes was inoculated on stainless steel coupons and subsequently subjected to Neutral EW (NEW, pH = 7.0) and Slightly Acid EW (SAEW, pH = 5.0) with different Available Chlorine Concentration (ACC, 50-200 mg/L) for different exposure times (0-6 min). The number of viable cells on coupons decreased as the exposure time increased at all ACC concentrations. Treatments with SAEW resulted in higher reductions of L. monocytogenes, i.e., 2.30 +/- 0.16 to 5.64 +/- 0.11 log cfu/cm(2), in comparison with NEW treatments (1.55 +/- 0.11 to 5.22 +/- 0.12 log cfu/cm(2)), probably due to the synergistic bactericidal effect between the acidic pH, higher oxidation-reduction potential and the effective form of chlorine, reported in previous studies. Since SAEW was the most effective against L. monocytogenes, two approaches were tested to model the survival data: the one- and two-step modelling procedures. The Weibull model was suitable to describe the survival data and both approaches produced suitable survival models (adj-R-2>0.92 and MSE<0.2). EW is effective in reducing bacterial contamination on food-contact surfaces and the survival data and models derived from this study are relevant to optimize its use as an environment-friendly sanitizer in the food industry.