Modeling the growth rate and lag time of different strains of Salmonella enterica and Listeria monocytogenes in ready-to-eat lettuce

• Published in: Food microbiology 2012-05, Vol.30 (1), p.267-273
• Main Authors: Sant’Ana, Anderson S., Franco, Bernadette D.G.M., Schaffner, Donald W.
• Format: Article
• Language: English
• Subjects: atmosphere; Biological and medical sciences; carbon dioxide; Colony Count, Microbial; Consumer Product Safety; equations; Fast Foods - microbiology; Food Contamination - analysis; Food industries; Food Microbiology; Food Packaging - methods; food pathogens; Food Storage - methods; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology; growth models; Lactuca - microbiology; Lettuce; Linear Models; Listeria monocytogenes; Listeria monocytogenes - growth & development; Listeria monocytogenes - isolation & purification; microbiological risk assessment; Models, Biological; Predictive modeling; Ready-to-eat vegetables; Salmonella; Salmonella enterica; Salmonella enterica - growth & development; Salmonella enterica - isolation & purification; Temperature; Time Factors; Variability
• ISSN: 0740-0020; 1095-9998
• DOI: 10.1016/j.fm.2011.11.003

The growth parameters (growth rate, μ and lag time, λ) of three different strains each of Salmonella enterica and Listeria monocytogenes in minimally processed lettuce (MPL) and their changes as a function of temperature were modeled. MPL were packed under modified atmosphere (5% O2, 15% CO2 and 80% N2), stored at 7–30 °C and samples collected at different time intervals were enumerated for S. enterica and L. monocytogenes. Growth curves and equations describing the relationship between μ and λ as a function of temperature were constructed using the DMFit Excel add-in and through linear regression, respectively. The predicted growth parameters for the pathogens observed in this study were compared to ComBase, Pathogen modeling program (PMP) and data from the literature. High R2 values (0.97 and 0.93) were observed for average growth curves of different strains of pathogens grown on MPL. Secondary models of μ and λ for both pathogens followed a linear trend with high R2 values (>0.90). Root mean square error (RMSE) showed that the models obtained are accurate and suitable for modeling the growth of S. enterica and L. monocytogenes in MP lettuce. The current study provides growth models for these foodborne pathogens that can be used in microbial risk assessment. ► Modeling the growth of three different strains of Salmonella and L. monocytogenes. ► Primary and secondary modeling of growth rate and lag time in mix of lettuces. ► Salmonella grew faster than L. monocytogenes in the temperatures tested (7–30 °C). ► L. monocytogenes showed higher lag times at 7 and 10 °C than Salmonella enterica. ► Secondary modeling for both pathogens showed a linear trend with R2 values >0.90.