Development of Thermal Surrogate Cultures for In-plant Validation Studies of Pet Food Products

Introduction: Outbreaks of Salmonella have been associated with dry pet food products. Low-moisture pet food products do not support the growth of Salmonella. However, the pathogen can persist for prolonged periods of time in dry products. In-plant HACCP programs commonly identify preconditioning, extrusion, baking and drying processes as kill steps for pet food products. An appropriate surrogate can be used in the plant setting to validate the safety of multi-variable thermal processes.

Purpose: The objective of this study was to determine if a biosafety level I Pediococcus acidilactici could be utilized as a surrogate microorganism for in-plant thermal processing validation studies for pet food products.

 Methods: A generic preservative-free dry pet food product (kibbles) was used to compare the thermal death time kinetics of P. acidilactici (ATCC 8042) to that of a cocktail of seven Salmonella strains associated with low moisture products. The test product was inoculated with lyophilized cultures and heat treated at 170°F to190°F.

 Results: The D-values were determined by least squares linear regression.  Test results showed that P. acidilactici was slightly more heat resistant than the Salmonella cocktail.

 Significance: These data suggest that inactivation characteristics (D- and z-values) of P. acidilactici could be utilized to predict the response of Salmonella.