“…Consequently, a vital part of quality control is the development of on-line monitoring tech- niques to measure and monitor structural changes that affect product properties during the extrusion process. Currently, measurements of ultrasonic properties are considered as potential tools to describe and monitor these changes (Luan, 1991;Ross, Pyrak-Nolte, & Campanella, 2004), and ultrasound evaluation has been successfully applied to on-line assessment of the processing of polymer melts (Franca, Jen, Nguyen, & Gendron, 2000) and foamed polymer melts (Sahnoune, Tatibouet, Gendron, Hamel, & Piche, 2001), systems that have obvious similarities to extruded food systems. Ultrasound has the advantage of relatively low cost, probes and associated electronics that are relatively robust, and the ability to probe the properties of opaque materials (Povey & McClements, 1988).…”