Thermal Death Kinetics of Three Representative Salmonella enterica Strains in Toasted Oats Cereal

Matthew Chick; Antonio Lourenco; Alice Maserati; Ryan C Fink; Francisco Diez-Gonzalez

doi:10.3390/microorganisms10081570

Thermal Death Kinetics of Three Representative Salmonella enterica Strains in Toasted Oats Cereal

Microorganisms. 2022 Aug 4;10(8):1570. doi: 10.3390/microorganisms10081570.

Authors

Matthew Chick¹, Antonio Lourenco², Alice Maserati¹, Ryan C Fink^{3

4}, Francisco Diez-Gonzalez⁵

Affiliations

¹ Department of Food Science and Nutrition, University of Minnesota, Saint Paul, MN 55455, USA.
² Food Biosciences Department, Teagasc Food Research Centre, Moorepark, P61 C996 Fermoy, Ireland.
³ Faculty of Computer Science, Dalhousie University, Halifax, NS B3H 4R2, Canada.
⁴ Institute for Comparative Genomics, Dalhousie University, Halifax, NS B3H 4R2, Canada.
⁵ Center for Food Safety, University of Georgia, 1100 Experiment St., Griffin, GA 30223, USA.

Abstract

Several reports have indicated that the thermal tolerance of Salmonella at low-water activity increases significantly, but information on the impact of diverse food matrices is still scarce. The goal of this research was to determine the kinetic parameters (decimal reduction time, D; time required for the first decimal reduction, δ) of thermal resistance of Salmonella in a previously cooked low water activity food. Commercial toasted oats cereal (TOC) was used as the food model, with or without sucrose (25%) addition. TOC samples were inoculated with 10⁸ CFU/mL of a single strain of one of three Salmonella serovars (Agona, Tennessee, Typhimurium). TOC samples were ground and equilibrated to a_w values of 0.11, 0.33 and 0.53, respectively. Ground TOC was heated at temperatures between 65 °C and 105 °C and viable counts were determined over time (depending on the temperature for up to 6 h). Death kinetic parameters were determined using linear and Weibull regression models. More than 70% of Weibull's adjusted regression coefficients (Radj2) and only 38% of the linear model's Radj2 had values greater than 0.8. For all serovars, both D and δ values increased consistently at a 0.11 a_w compared to 0.33 and 0.53. At 0.33 a_w, the δ values for Typhimurium, Tennessee and Agona were 0.55, 1.01 and 2.87, respectively, at 85 °C, but these values increased to 65, 105 and 64 min, respectively, at 0.11 a_w. At 100 °C, δ values were 0.9, 5.5 and 2.3 min, respectively, at 0.11 a_w. The addition of sucrose resulted in a consistent reduction of eight out of nine δ values determined at 0.11 a_w at 85, 95 and 100 °C, but this trend was not consistent at 0.33 and 0.53 a_w. The Z values (increase of temperature required to decrease δ-value one log) were determined with modified δ values for a fixed β (a fitting parameter that describes the shape of the curve), and ranged between 8.9 °C and 13.4 °C; they were not influenced by a_w, strain or sugar content. These findings indicated that in TOC, high thermal tolerance was consistent among serovars and thermal tolerance was inversely dependent on a_w.

Keywords: Salmonella; cereal; inactivation; low-water activity; thermal resistance.

Grants and funding

This material is based upon research that was supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2012-67005-19613. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the authors, and do not necessarily reflect the view of the U.S. Department of Agriculture. A.L. is funded by the Research Leaders 2025 postdoctoral funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement number 754380.