Purpose: The objective was to quantify the reproducibility of Salmonella thermal resistance results in oat flour, via multiple-laboratory comparison.
Methods: Four independently operated laboratories, at the Food and Drug Administration (FDA), Illinois Institute of Technology (IIT), Michigan State University (MSU), and Washington State University (WSU), participated in this study. Salmonella Agona lawn cultures were harvested using peptone water and inoculated into three batches of oat flour via liquid addition, which were then equilibrated over 3 days to a water activity of 0.45. Polystyrene bottles containing oat flour samples (100 g) were sent to and subsequently processed by each of the four laboratories using their own isothermal inactivation procedures (80°C). Samples were then serially diluted and plated on trypticase soy agar supplemented with yeast extract. All resultant data were compiled and analyzed collectively.
Results: Average populations of Salmonella Agona in the three oat flour samples before thermal treatment were 7.90±0.20, 7.75±0.25, and 7.75±0.29 log CFU/g. Resultant D80°C-values were 8.15, 10.70, 15.27, and 18.58 min across the four laboratories. Using a one-way ANCOVA, differences in inactivation rates within laboratories were not significantly different (P > 0.05); however, differences in inactivation rates between laboratories were significant (P < 0.05).
Significance: Despite the use of identical inoculated matrices, and similar thermal treatment methods, thermal inactivation rates varied significantly among the four laboratories. Lab- or method-dependent artifacts contributing to such differences may limit the ability to utilize results from separate studies, which also suggests that model validation is critical prior to utilizing single-study results for pasteurization validations or regulatory guidance.