Structure formation by carbon dioxide injection in extrusion cooking

Twin-screw extrusion at low temperature with carbon dioxide injection to assist expansion: extrudate characteristics

“…It is also a function of extent of dextrinization of starch. Our results agree with those of Ferdinand et al (1990). Higher CO 2 injection pressure resulted in more starch fragmentation during the extrusion process than at lower CO 2 injection pressure.…”

“…The cell size, cells per unit area and expansion ratio of extrudates were more easily controlled in the supercritical fluid extrusion process as compared to traditional extrusion (Bladwin, Park, & Suh, 1996). One dividend of keeping the product temperature below 100°C and preventing formation of steam during extrusion is to permit the use of melts with high moisture content wherein the viscous dissipation of heat is minimal (Ferdinand, Clark, & Smith, 1992;Ferdinand et al, 1990;Sokhey, Rizvi, & Mulvaney, 1996). Sodium bicarbonate was used by Lai, Guetzlaff, and Hoseney (1989) to generate CO 2 in extrusion cooking.…”

Microcellular Starch-Based Foams

“…The low density in watensteam blown extrudate may be attributed to the starch melt being better able to stabilize bubbles at the higher temperatures achieved in a water\steam blown extrudate. The cells of the C0 2 blown extrudate were fairly uniform in size but had thick walls and were much larger than 10 μπι (34). Small cell size may be possible by better defining the critical processing parameters and improving processing methods.…”

“…The moisture within the barrel is thoroughly dispersed throughout the melt and becomes superheated under the conditions of high heat and pressure that are generated. As the starch melt exits the barrel through the die, the pressure drops to atmospheric converting superheated moisture to steam and causing the melt to expand into a foam (33)(34). This foam process occurs in three steps the first of which is the nucleation step where vapor filled bubbles form within the melt (33).…”

“…Ferdinand et al (34) used a temperature profile that kept the starch extrudate below 100 °C and injected C0 2 into the extruder barrel. The starch extrudate had a higher density using C0 2 versus water/steam as the blowing agent.…”