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The objective of this study was to develop a dynamic model for predicting the growth of Listeria monocytogenes in pasteurized cow milk under fluctuating temperature conditions during storage and temperature abuse. Six dynamic temperature profiles that simulated random fluctuation patterns were designed to change arbitrarily between 4 and 30°C. The growth data collected from 3 independent temperature profiles were used to determine the kinetic parameters and construct a growth model combining the primary and secondary models using a 1-step dynamic analysis method. The results showed that the estimated minimum growth temperature and maximum cell concentration were 0.6 ± 0.2°C and 7.8 ± 0.1 log cfu/mL (mean ± standard error), with the root mean square error (RMSE) only 0.3 log cfu/mL for model development. The model and the associated kinetic parameters were validated using the data collected under both dynamic and isothermal conditions, which were not used for model development, to verify the accuracy of prediction. The RMSE of prediction was approximately 0.3 log cfu/mL for fluctuating temperature profiles, and it was between 0.2 and 1.1 log cfu/mL under certain isothermal temperatures (2-30°C). The resulting model and kinetic parameters were further validated using 3 growth curves at 4, 7, and 10°C arbitrarily selected from ComBase (www.combase.cc). The RMSE of prediction was 0.8, 0.4, and 0.5 log cfu/mL, respectively, for these curves. The validation results indicated the predictive model was reasonably accurate, with relatively small RMSE. The model was then used to simulate the growth of L. monocytogenes under a variety of continuous and square-wave temperature profiles to demonstrate its potential application. The results of this study showed that the model developed in this study can be used to predict the growth of L. monocytogenes in contaminated milk during storage., (Copyright © 2021 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

This study aimed to evaluate the effect of ε-polylysine hydrochloride (ε-PLH) on the growth and thermal inactivation kinetics of Listeria monocytogenes in fish balls. Samples, supplemented with ε-PLH (0, 150, or 300 ppm, w/w), were inoculated with a three-strain cocktail of L. monocytogenes and incubated at constant temperatures of 3.4, 8, 12, or 16 °C for growth studies, or heated at 60, 62.5, 65, or 67.5 °C for thermal inactivation tests. The growth curves were fitted to the Huang primary model, and the Huang and Ratkowsky square-root models (SRM) were used as the secondary models to evaluate the effect of temperature on bacterial growth. The survival during heating was analyzed with a log-linear model. The results showed that, while the lag time of L. monocytogenes was affected by both ε-PLH concentration and temperature, the specific growth rate was unaffected by ε-PLH. Under the same temperature, a 10-time in increase of the lag time would be expected for every 565 ppm in the increase of ε-PLH concentration. Using the Ratkowsky SRM, the estimated nominal minimum growth temperature was -2.04 °C, while the minimum growth temperature was 0.29 °C when estimated with the Huang SRM. Validation at 10 °C showed that the Huang primary model, in combination with either the Huang or Ratkowsky SRM, could accurately predict the growth of L. monocytogenes. On the other hand, the thermal resistance of the pathogen was significantly reduced by increase in temperature or ε-PLH. The thermal z value of L. monocytogenes was 5.78 °C, and the ε-PLH z value was 1642 ppm. The results of this study showed that the combined application of ε-PLH and temperature can be used to control L. monocytogenes in fish balls and to improve food safety and reduce risks to public health., (© 2018 Institute of Food Technologists®.)

Listeria monocytogenes is a potentially fatal foodborne pathogen that can be found in ready-to-eat seafood products, such as fresh salmon roe. Once contaminated, salmon roe must be decontaminated prior to human consumption. This study was conducted to determine the thermal inactivation kinetics of L. monocytogenes in raw salmon roe as affected by bacterial strain, temperature, and salt concentration. Three different strains of L. monocytogenes , including serotype 4b (F2365), 1/2b (F4260), and 1/2a (V7), were individually inoculated to salmon roe supplemented with salt (0–4.5%), and heated under different temperatures (57.5–65.0 °C) to evaluate the survival of the bacterium during heating and determine the D-values. Results showed that the thermal resistance (log D) of L. monocytogenes was significantly affected by bacterial strain, temperature, and salt and by their interactive effects, with strain F2365 being the most heat-resistant among all three strains tested. Salt added to salmon roe significantly increased the thermal resistance of the bacteria. For L. monocytogenes F2365, the z value of the bacterium in salmon roe was 5.99 °C, and its heat resistance increased with the level of salt in a linear manner. The results of kinetic analysis and the models obtained in this study may be used by the seafood industry to develop proper thermal processes to eliminate L. monocytogenes in raw salmon roe and to ensure microbial safety and prevent foodborne illness. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the growth kinetics of Listeria monocytogenes in unsalted and salted (3%) salmon roe. Growth curves, developed using inoculated samples incubated at constant temperatures between 5 and 30 °C, were analyzed by curve-fitting to the Huang and Baranyi models using the USDA IPMP 2013. The experimental results showed that L. monocytogenes in salted samples exhibited approximately 40% longer lag times than the cells in unsalted samples under the same temperature condition, while the rates of bacterial growth were not affected by the addition of salt. The Ratkowsky square-root (RSR) model, Huang square-root (HSR) model, and an Arrhenius-type model were all shown suitable for evaluating the effect of temperature on specific growth rates. The estimated nominal minimum growth temperature in the RSR model was −0.5 °C, whereas the minimum growth temperature in HSR model was 2.57 °C. The HSR models may be more suitable for describing the temperature effect in salted salmon roe. The lag times of L. monocytogenes were found to change log-linearly with the specific growth rates. The mean h 0 in the Baranyi model was 0.742 in unsalted samples and 1.193 in salted samples, and did not appear to change with temperature in a systematic manner. In summary, kinetic models were developed for examining the effect of temperature on growth of L. monocytogenes in unsalted and salted salmon roe samples. The results may be used by the food industry and regulatory agencies to estimate the growth of L. monocytogenes in salmon roe, and to conduct risk assessments of this microorganism. [ABSTRACT FROM AUTHOR]

During preparation stages of ready-to-eat (RTE) foods, they can be cross-contaminated with Listeria monocytogenes which could result to outbreaks of foodborne listeriosis. In this study, the effects of gloves, cutting boards and cleaning methods on the transmission of L. monocytogenes during the processing of salmon sashimi were investigated. Subsequently, an improved particle swarm algorithm optimized BP neural network prediction model (CLPSO-BP) was developed based on Lévy flight and chaotic mapping. After processing contaminated salmons with gloves, we found that the surfaces of the gloves contained a significant amount of L. monocytogenes (5.24 log CFU/g), and 10.69% of the bacteria were subsequently transferred to uninfected salmon after being processed with the same gloves. Contamination of the processing tools with L. monocytogenes was reduced by up to 3 log CFU/g and the transfer rate was reduced by up to 50% after cleaning with room temperature water and detergent. In contrast, no bacteria were found after wiping the surfaces of the tools 70 °C hot water and detergent. The mean squared error (MSE) for the CLPSO-BP modeling tests was 0.1003, indicating accurate predictions. Overall, choosing an appropriate cleaning method and changing gloves regularly can help to avoid cross-contamination when processing RTE foods. • Sufficient independent tests were conducted to determine the range of transfer rates. • CLPSO-BP model has been developed to predict cross-contamination scenarios. • The improved PSO algorithm yields accurate results with small sample sizes. [ABSTRACT FROM AUTHOR]

This study focused on the development of a gaseous ClO 2 treatment system that contained dry ice that was used to form carbon dioxide (CO 2) and an absorbent pad with sodium chlorite (NaClO 2) solution for ClO 2 gas generation. Furthermore, the effects of ClO 2 gas on the populations of Listeria monocytogenes and the quality properties of table grapes during cold storage were evaluated. The system continuously released the sufficient concentrations of ClO 2 gas to treat berries during 30 d of cold storage. After 20 h of ClO 2 gas treatment, the populations of Listeria monocytogenes decreased from 5.88 log CFU/g to a non-detectable (ND) level. There were no significant (p > 0.05) changes in the color parameters (L*, a*, and b*) of table grapes treated with ClO 2 gas. The firmness, weight, total soluble solids (TSS), and titratable acid (TA) losses of table grapes were significantly (p < 0.05) reduced by ClO 2 gas, while Vitamin C was unaffected. Additionally, the residual ClO 2 of table grapes were <0.5 mg/kg, which is considered a safe level. Overall, the novel gaseous ClO 2 treatment system may be used as an effective intervention technology to improve the safety and quality of table grapes during cold storage. • The gaseous ClO 2 treatment system was developed by reacting CO 2 with NaClO 2. • The system released sufficient ClO 2 gas to treat grape samples during cold storage. • The ClO 2 gas effectively killed L. monocytogenes on samples. • The ClO 2 gas also maintained the quality of samples. • The ClO 2 residues of samples reached a safe level. [ABSTRACT FROM AUTHOR]

This study was aimed at investigating the growth of Listeria monocytogenes (L. monocytogenes) in irradiated and raw salmon. Mathematical models were developed to describe the growth of L. monocytogenes with or without the presence of the native microbiota in salmon. At temperatures between 4 and 35 °C, the growth data of L. monocytogenes in sterile salmon were collected to develop the non-competitive growth model, while the observed growth data of both L. monocytogenes and background microflora in raw salmon were analyzed simultaneously to develop the competitive model. The Huang square-root model was used to evaluate the effect of temperature on growth rates and lag times of L. monocytogenes and the native microbiota. A one-step analysis approach was used for model development and the kinetic parameters estimation. The results showed that the background microflora in raw salmon have inhibiting effect on the growth of L. monocytogenes. The lag time of L. monocytogenes in raw salmon was 2.849 times longer than that in sterile salmon, while its specific growth rate was decreased by 78.7% with the presence of the native microbiota. The minimum growth temperature for L. monocytogenes ( T m i n , L m ) in raw salmon estimated by the competitive model was 1.3 °C, which was close to T m i n , L m in sterile salmon (1.2 °C) determined by the non-competitive model. With the relatively low value of RMSE (0.3 Log CFU/g), the non-competitive and competitive models were accurate to describe the growth of L. monocytogenes in sterile salmon and the interaction between L. monocytogenes and the native microflora in raw salmon, respectively. The predictive models and the associated kinetic parameters were validated under isothermal temperature conditions. The validation results indicated that the non-competitive and competitive models were accurate. Overall, the residual errors of predictions of these two models both followed a Laplace distribution. The RMSE values of the models were both 0.4 Log CFU/g and more than 79% of prediction errors were within normal experimental errors (±0.5 Log CFU/g). The results from this study may be useful for the future risk assessments of L. monocytogenes and microbiological shelf-life prediction of salmon. • The growth of L. monocytogenes in sterile and raw salmon were observed. • The growth of L. monocytogenes was interfered by the natural microflora. • The non-competitive and competitive models were developed. • A one-step analysis approach was used to construct models and determine kinetic parameters. [ABSTRACT FROM AUTHOR]