The Effect of Inoculated Ingredient on the Thermal Resistance of Enterococcus faecium in a Multiingredient Model...

Under the Food Safety Modernization Act, preventive controls must be validated. Process validation is often conducted under worst-case conditions, which requires the adoption of the most conservative inoculation strategies. While inoculation of single-ingredient foods has been widely studied, the impact of inoculation source within a multiingredient food matrix remains unclear. This study evaluated the thermal inactivation kinetics of Enterococcus faecium NRRL B-2354 in a model low-moisture cookie dough with a water activity of 0.25 when contamination was introduced through one of four ingredients (peanut butter, soy protein powder, wheat flour, or milk powder) prior to formulation. Isothermal inactivation was conducted at 95 °C, and a log-linear model was used to estimate D-values. The inoculation source significantly influenced thermal resistance (p < 0.05). D_95 °C values ranged from 3.14 min (milk powder-inoculated cookie dough) to 6.30 min (protein powder-inoculated cookie dough). Notably, the relative order of thermal resistance of E. faecium in the cookie dough differed from that reported for the individual ingredients, indicating that ingredient-level resistance does not directly translate to the behavior observed in a multiingredient matrix. Cookie dough prepared with all four inoculated ingredients exhibited an intermediate D-value (4.43 min) when preequilibrated ingredients were combined. These findings demonstrate that contamination source influences observed thermal resistance in complex low-moisture foods and should be carefully considered when designing validation studies and identifying worst-case scenarios for process validation.