ApplyingPolymerScienceToUnderstandDrying.docVIP

Applying Polymer Science to Extrusion and Drying of Pet Foods By Brian Plattner, Robert Sunderland and Keith Erdley Introduction Polymer science, the study the glass and melt transitions of polymers, has been developed and used by the synthetic polymer industry for many years. In recent years the principles of polymer science have been applied to the pet food extrusion process to better understand and predict processing effects. Strahm (1998) gives a more complete review of the concepts of glass and melt transitions and their possible applications to extrusion processing. Figure 1: Schematic Diagram of the PTA. There are several instruments that can be used to measure the physical changes associated with the glass transition and melt transition in biopolymers such as starch and protein during thermal processing. Some instruments are not configured to measure a sample’s transition temperatures under typical extrusion conditions. In addition, these instruments are often too sensitive to measure the “controlling” Ts and Tf for a complex blend of raw materials that often include starch, protein, fat, fiber, and ash (Strahm and Plattner 2001). The controlling Ts is the temperature at which a sufficient amount of a sample is softened to allow for particle compaction (Ts) or melted to allow for flow (Tf) through a small orifice. One tool that can measure these transitions is the Phase Transition Analyzer? or PTA (Figure 1). While the PTA does not provide all the answers to questions about how pet foods change under thermal processing, it does provide many unique and potentially useful insights for the pet food extrusion and drying process. Measuring Transition Temperatures Figure 2: Sample Compaction and Flow During Testing in the PTA. To measure the Ts of a pet food sample, a blank die (no orifice) is inserted into the PTA, a two gram sample is loaded, and the pressure is preset to 120 bar and maintained for ten seconds. This initial compaction allows the sample