With safety being a key focus for petfood manufacturers, especially reducing the potential for and number of incidences of Salmonella contamination, a recent article from All About Feed addresses extrusion temperature as a critical control point in petfood processing. According to Galen J. Rokey, process technology manager, and Doug Baldwin, director of business development, Wenger Manufacturing, a good petfood safety program provides many benefits, including: reduced risks, decreased waste and customer complaints, product traceability, lower product liability, transparency for consumers and brand value.
As part of a comprehensive petfood safety program, extrusion temperature is often chosen as a critical control point since extrusion is the major thermal process used in 95 percent of all petfood production. A correlation between extrusion temperature and moisture and the destruction of pathogenic organisms in an inoculated petfood formula has been shown by recent studies.
The article notes that pilot plant studies are useful in determining expected decontamination with different substrates; resistance of different microbial species to destruction under the same extrusion conditions; and variations in potential for decontamination among various extruders. Necessary revalidation of conditions include presence of new pathogens, extreme contamination levels, severe recipe changes, process parameters outside of the critical control limits, and changes in storage or packaging. However, the question of how to treat retention time in extrusion thermal processing remains.
The importance of accurately measuring and controlling product temperature when extrusion temperature is selected as a critical control point is also noted.
Wenger conducted a series of tests to gauge the impact of temperature sensor location and mounting techniques on the accurate measurement of product temperature. Research found that actual product temperature was less influenced by environmental and other process factors when this measurement was taken in the die cavity after the screw element and before the final die assembly.
The article says that according to the research: "Temperature along the extruder barrel was measured at the highest level in the extrusion process. A cross section of the mass of material in the die cavity can display a flow gradient with higher product velocities in the center of the flow and lower velocities along the die cavity wall.
Occasionally the product flow at the wall of the die cavity can be so low that it may appear to be totally stagnant. It is important to extend the temperature sensor at least 20 mm into the product flow from the side wall of the die cavity to avoid false product temperature readings in the stagnant or low velocity zones.
"Extended tip temperature sensors are subject to abrasive wear from product passing through the die cavity and are often protected by metal sheaths. It is advisable to install two temperature sensors in this location, at 180 degrees from each other.
"Product temperatures can be displayed where they are readily available for production personnel. The process control systems can be configured to alarm when process temperatures drop below the critical limits. Advanced control systems not only monitor and record the extrusion temperature, but can also automatically divert product from the process flow when the temperature is below the critical limit."