Influence of Product Formulation on D250°F and F250°F Corrected Values of Clostridium sporogenes ATCC 7955

Introduction: The D-value is the time (minutes) required to destroy 90% (1 log) of a given bacterial population at a constant temperature and is inversely related to the rate of destruction. In combination with other variables such as material heat penetration rate, the value is used to define thermal processing conditions necessary to render a specific product microbiologically safe.  D-values are influenced by physiochemical factors such as pH, chemical composition and viscosity, so recalculation may be warranted when product formulations are changed significantly.

Purpose: This study evaluated the impact of product formula modification on the D_250°F and F_250°F corrected values of Clostridium sporogenes ATCC 7955 in order to support thermal process development.

Methods: A 2⁴ factorial experimental design was implemented to determine the D_250°F values for 16 formulations which changed  protein mix (Milk Protein Concentrate (MPC) or Soy Protein Isolate (SPC)/MPC mix), or increased the protein, carbohydrate (Sucrose), and/or vegetable oil level, each by 10%, in a base formulation. The formulations were inoculated with C. sporogenes ATCC 7955 (final concentration of 2.0 x 10⁶ spores/ml) and subjected to 250°F at different intervals using the Joslyn BIER unit. Survivors were enumerated on Modified PA 3679 agar, the D_250°F and F_250°F corrected value calculated.  The statistical analysis evaluated both main effects and two-way interactions.

Results: Increased fat, protein, and soy protein content increased the F_250°F corrected value by 0.5 minutes or more. However, under the conditions of the study, increased carbohydrate did not influence the F_250°Fcorrected values. 

Significance: These results indicate that changing fat and protein content, and protein composition can significantly alter the D_250°F and F_250°F corrected values of C. sporogenes ATCC 7955 potentially influencing heat sensitivity.