Experimentally Implementing the Linear Nonisothermal Equation for Simultaneously Obtaining D- and z-Values of Salmonella Senftenberg in Skim Milk with a Differential Scanning Calorimeter

• Published in: Journal of food protection 2022-10, Vol.85 (10), p.1410-1417
• Main Authors: Yang, Ren, Fleischman, Gregory J., Shazer, Arlette, Li, Haiping
• Format: Article
• Language: English
• Subjects: Aluminum; Animals; Bacterial inactivation; Capillary tubes; Colony Count, Microbial; Deactivation; Differential scanning calorimeter; Differential scanning calorimetry; Ethanol; Experiments; Food; Food Microbiology; Food safety; Heat resistance; Heating; Heating rate; Hot Temperature; Inactivation; Kinetics; Lethality; Mathematical analysis; Milk - microbiology; Pathogens; Salmonella; Skim milk; Temperature; Temperature lag; Temperature requirements; Thermal kinetics
• ISSN: 0362-028X; 1944-9097
• DOI: 10.4315/JFP-22-009

For bacteria with log-linear thermal inactivation kinetics in food, D-values are obtained in multiple isothermal inactivation experiments at different temperatures, and the z-value is obtained from these D-values. In a previous work, the cumulative lethality integral was mathematically solved in closed form when temperature in the food increased linearly with time. The solution revealed that each nonisothermal experiment could yield both D- and z-values, eliminating the need for getting multiple D-values to get a z-value. The present study reports on the first experimental implementation of this method of obtaining D- and z-values for Salmonella Senftenberg suspended in skim milk for which a differential scanning calorimeter (DSC) provided the required constant heating rate. The resulting D- and z-values were compared with those obtained from an isothermal method with capillary tubes. No significant differences in z-values were found between the two methods. The D-values also agreed but only after correcting the nonisothermal 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. Although D- and z-values should be independent of DSC heating rate, heating rates of 1 and 10 K/min yielded values that were significantly different from the others; therefore, these rates cannot be recommended for use in this nonisothermal method. •D- and z-values were experimentally obtained together for the first time.•A published mathematical analysis was used for the first time to obtain D- and z-values.•An off-the-shelf instrument (DSC) provided the heating protocol stipulated by the analysis.•D- and z-values matched those obtained from the isothermal capillary tube method.•The DSC had limitations for measuring D- and z-values.