Purpose: This study validates the efficacy of a high-intensity-preconditioner (HIP) for controlling Enterococcus faecium, a nonpathogenic surrogate for Salmonella spp. in heat treatment validations, in a generic dog food formulation.
Methods: Dry pet food ingredients (~227 kg) were spray inoculated with E. faecium (~5.8 log CFU/g; 30 min attachment period). Batches of pet food were treated through a HIP system using three different treatment parameters: A) 68°C for 154 s, B) 68°C for 65 s, or C) 90°C for 65 s. Enterococcus faecium populations were enumerated by direct plating onto selective and injury-recovery agars, before and after HIP treatments, to quantify process lethality.
Results: Treatment B resulted in the least microbial lethality (P≤0.05), achieving approximately a 1.5 log CFU E. faecium/g reduction. Treatments A and C were statistically different when comparing selective media counts, achieving 3.9 and 5.1 log CFU/g reductions, respectively. However, these two treatments were similar (P>0.05) when comparing injury recovery counts (3.4 and 3.5 log CFU/g reductions, respectively), indicating the presence of a higher population level of sub-lethally injured cells resulting from the higher temperature, shorter exposure time provided by treatment C.
Significance: Preconditioning of raw ingredient formulations is a common thermal treatment prior to extrusion processes in the generation of kibble-style pet foods. The present study validated the efficacy of three HIP processes for reducing E. faecium. This study was indicative of the lethality effect expected for Salmonella spp. since E. faecium was used as a surrogate organism in similar heat treatment validations of foods, and generally is slightly higher in its thermal tolerance. Pet food processors can use this information to help define critical control points when using an HIP system.