Structural properties of protein-stabilized starch-based supercritical fluid extrudates

Supercritical fluid extrusion, a low temperature and low shear process, was used to produce pre-gelatinized corn and potato starch-based extrudates, containing 4-10% thermosetting egg white (EW) or whey protein concentrate (WPC-34), and dried at 22-100 degrees C. Addition of proteins reduced shrinkage of high-moisture extrudates, as indicated by increases in expansion ratio by up to 140 and 341% when the drying temperatures were 22 and 100 degrees C, respectively. Products containing 7% EW or WPC-34 and dried at 85 degrees C expanded best while maintaining an intact structure, with expansion ratio (similar to 12) and bulk density (similar to 0.10 g/cm(3)) comparable to steam extrudates. The products had a unique composite and uniform microcellular structure, with average cell sizes in the range of 50-250 mu m and cell density of the order of 10(6) cells/cm(3). The classical nucleation theory and a qualitative model for cell growth and shrinkage based on glass transition temperature were used to explain the microcellular structure. (C) 1999 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.