Purpose: The objective of this study was to utilize non-pathogenic E. coli strains as surrogates for E. coli O157:H7 to perform an in-plant validation for multiple pet food formulations.
Methods: Six E. coli strains were selected as surrogates and combined in equal portions to create 109 CFU/ml culture cocktails to inoculate four 907 kg batches of pet food. For each batch, 1 l of cocktail was added in the initial mixing step. Samples were collected after completion of mixing, post-extrusion, and post-drying for each batch. Samples were enumerated with 3 M Coliform/E. coli petrifilm. Surface swabs were taken following post-production equipment cleaning and sanitizing and analyzed for the presence of Salmonella using the BAX system.
Results: The samples from the mixer resulted in a 103 to 104 CFU/g inoculation level. The temperature of the extruded pet food reached 117.2°C, 91°C, 101.7°C, and 107.8°C for pet food batches 1, 2, 3, and 4, respectively. After extrusion, no growth was detected across all batches. Pet food batches 1 and 2 were combined in the drying step; likewise, batches 3 and 4 were combined with all post-drying samples showing no growth. Post-sanitation swabs taken of the equipment were negative for Salmonella.
Significance: This in-plant validation of pet food processing demonstrates the use of non-pathogenic surrogate organisms that have been selected for their behavior which mimics their pathogenic counterparts. Validations for processing and the destruction of pathogens are an important practice to fulfill the more rigorous requirements being developed for pet food regulations.