Abstract
The objective of this study was to investigate the relationships between starch melt transition characteristics, extrusion conditions, and final product properties. Cornstarch was extruded using a corotating twin‐screw extruder at varying moisture content, medium/high screw configuration, and 300/400‐rpm screw speeds. Extrudates were evaluated for bulk density, expansion ratio, cell structure, bending strength, thermal and pasting properties. Temperature change (Δ__T__) was defined as the temperature difference between the native starch melting temperature and its melt temperature just behind the die during extrusion at a given moisture content. Δ__T__ was significantly affected by starch moisture content and mechanical shearing, which controlled the melting behavior of the starch in the barrel. Amylose–lipid complex formation during extrusion increased as Δ__T__ increased and leveled off at Δ__T__ of about 20°C. Pasting peak viscosity of the starch extrudates decreased as Δ__T__ increased and leveled off at Δ__T__ of about 15°C. Within the same range of mechanical shearing intensity, extrudate bulk density and bending strength decreased linearly as Δ__T__ increased. Extrudate expansion was negatively correlated to bulk density. © 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 277–290, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20017