Isothermal inactivation of salmonella, Listeria monocytogenes, and Enterococcus faecium NRRL B-2354 in peanut butter, powder infant formula, and wheat flour

Abstract Pathogens in low water activity foods are an important emerging food safety concern due to notable survival and thermotolerance. Limited but growing data are publicly available to compare the thermotolerance of Listeria monocytogenes, Salmonella spp., and Enterococcus faecium NRRL B-2354 (a Salmonella surrogate). The aims of this study were to determine and assess bacterial thermal inactivation rates of two pathogens and a well-established surrogate across three different low-moisture food matrices containing different levels of fat using a dry inoculation method. Three low-moisture foods (0.11 aw, 45% fat peanut butter; 0.20 aw, 27% fat powder infant formula; and 0.45 aw,  peanut butter > wheat flour for the vast majority of the comparable D-values. While Salmonella is the primary pathogen of concern in low-moisture foods due to survival and outbreaks, these results indicate L. monocytogenes can exhibit similar thermotolerances in low-water activity food matrices including peanut butter and powder infant formula.