For bacteria that follow log-linear thermal inactivation in food, D values are obtained in multiple isothermal inactivation experiments at different temperatures, and the z value obtained from them. In a previous work, it was shown mathematically that the cumulative lethality integral can be solved in closed-form if temperature in the food increases linearly with time. Moreover, the solution showed that each non-isothermal experiment could yield both D and z values, eliminating the need for getting multiple D values to get z . This paper reports on the first experimental implementation of this method of obtaining D and z for Salmonella Senftenberg suspended in skim milk where a differential scanning calorimeter (DSC) provided the required constant heating rate. The resulting D and z values were compared with those obtained from the isothermal method using capillary tubes. The results showed no statistical difference between the z values from the two methods. The D values also agreed, but after correcting the non-isothermal value for temperature lag in the DSC caused by the large sample size required. A 5 K/min heating rate was used in this comparison. Other rates were also investigated; 1, 3, 7.5 and 10 K/min. While D and z values should be independent of DSC heating rate, it was nevertheless found that heating rates of 1 and 10 K/min yielded values that were statistically different from the others and therefore, cannot be recommended for use in this non-isothermal method.
Experimentally Implementing the Linear Non-Isothermal Equation for Simultaneously Obtaining D and z Values of Salmonella Senftenberg in Skim Milk Using a Differential Scanning Calorimeter
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Ren Yang, Gregory Fleischman, Arlette Shazer, Haiping Li; Experimentally Implementing the Linear Non-Isothermal Equation for Simultaneously Obtaining D and z Values of Salmonella Senftenberg in Skim Milk Using a Differential Scanning Calorimeter. J Food Prot 2022; doi: https://doi.org/10.4315/JFP-22-009
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