Storage Survival and Thermal Inactivation of Listeria monocytogenes in Peanut Butter and Whole Egg Powders.

Listeria monocytogenes is a concern in low-moisture foods because it can survive prolonged dry storage conditions and exhibit increased heat resistance at low water activity (aw). This study evaluated the survival and thermal resistance of L. monocytogenes in peanut butter powder and whole egg powder equilibrated to approximately 0.25 and 0.45 aw. Inoculated powders were stored at 22 °C for 16 months, followed by thermal treatment at 75 and 80 °C. Log-linear, biphasic, and Weibull models were compared using goodness-of-fit metrics and information criteria. Weibull scale parameters (δ) were calculated from replicate-level fits. During storage, L. monocytogenes persisted longer at 0.25 aw than at 0.45 aw in both matrices. In peanut butter powder, populations declined from 8.48 to 2.70 log CFU/g at 0.45 aw and from 8.89 to 3.64 log CFU/g at 0.25 aw after 16 months. In whole egg powder, populations decreased from 8.25 log CFU/g to nondetectable levels by month 15 at 0.45 aw, whereas 4.62 log CFU/g remained after 16 months at 0.25 aw. Nonlinear models generally outperformed the log-linear model. The largest modeled time to the first 1-log reduction (δ) occurred at 75 °C and 0.25 aw in whole egg powder (18.28 min; 95% CI: 16.34-20.45) and peanut butter powder (13.38 min; 95% CI: 9.18-19.52). Lower aw enhanced both long-term survival and thermal resistance of L. monocytogenes, demonstrating the importance of aw- and matrix-specific validation of thermal processes for low-moisture foods.