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Thermal Death Kinetics of Three Representative Salmonella enterica Strains in Toasted Oats Cereal
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2022-08-04
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Chick, M.; Lourenco, A.; Maserati, A.; Fink, R.C.; Diez-Gonzalez, F. Thermal Death Kinetics of Three Representative Salmonella enterica Strains in Toasted Oats Cereal. Microorganisms 2022, 10, 1570. https://doi.org/10.3390/ microorganisms10081570
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, ) 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 aw 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% ofWeibull’s adjusted regression coefficients (R2a
dj) and only 38%
of the linear model’s R2a
dj had values greater than 0.8. For all serovars, both D and values increased
consistently at a 0.11 aw compared to 0.33 and 0.53. At 0.33 aw, the 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 aw. At 100 C, values were 0.9, 5.5 and 2.3 min, respectively,
at 0.11 aw. The addition of sucrose resulted in a consistent reduction of eight out of nine values
determined at 0.11 aw at 85, 95 and 100 C, but this trend was not consistent at 0.33 and 0.53 aw.
The Z values (increase of temperature required to decrease -value one log) were determined with
modified values for a fixed (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 aw, strain or sugar content. These findings
indicated that in TOC, high thermal tolerance was consistent among serovars and thermal tolerance
was inversely dependent on aw.