Salmonella Survival in Extruded Foods

In the past couple of years, about 25 recalls have occurred due to potential Salmonella contamination in extruded pet foods. Although heat extrusion has proven to be a relatively safe process, the issue may be linked to aspects such as the specific food formulation, process temperature, moisture content, water activity and post-process contamination. Specifically, Salmonella is more heat resistant at low a_w.  Heat resistance of Salmonella can also be altered by the presence of specific ingredients, e.g., fats.  Manufacturers should be equally cautious about post-process contamination, e.g., the unintended microbial contamination of powder or liquid coatings applied after extrusion cooking without further heat treatment.