Thermal Inactivation of Salmonella Surrogate, Enterococcus faecium, in mash broiler feed pelleted in a university pilot feed mill

This study evaluated the thermal inactivation kinetic parameters of a Salmonella surrogate Enterococcus faecium (E. faecium) during feed manufacture in a university pilot feed mill setting. A batch of 227 kg mash broiler feed was pelleted after being inoculated with 1,000 mL of nalidixic acid (NaL) resistant E. faecium (5.4 log₁₀CFU/g) at 70°, 75°, 80°, and 85°C for 0 to 115 s. Bacterial survival cell counts were analyzed by spread plating onto bile esculin agar plus 200 ppm of NaL. Microbial data and thermal kinetic parameters [n=6, Global-Fit and United States Department of Agriculture (USDA)-Integrated-Predictive-Modeling-Program software] were analyzed by R-software (orthogonal polynomial model). Pelleting mash broiler feed at 70°, 75°, 80°, and 85°C decreased (P < 0.05) E. faecium cell counts by 0.81, 1.18, 1.69, and 1.94 log₁₀ CFU/g after 115 s, respectively. D-values of orthogonal polynomial, Linear with Tail, Weibull models for E. faecium at 70°, 75°, 80°, and 85°C were 47.1 to 135.4, 42.1 to 135.2, and 51.4 to 118.8 s, respectively. These results suggest that pelleting at 80 or 85°C reduces E. faecium populations the fastest, and it takes at least 50 s to reduce populations by 1 log₁₀ CFU/g at these temperatures. Thermal inactivation for E. faecium took longer and required higher temperatures in the feed mill than lab estimates, highlighting the importance of testing thermal inactivation temperatures in the field to ensure proper feed hygiene.