Cereal Chem 63:240-246 | VIEW
Extrusion Cooking and Drum Drying of Wheat Starch. II. Rheological Characterization of Starch Pastes.
J. L. Doublier, P. Colonna, and C. Mercier. Copyright 1986 by the American Association of Cereal Chemists, Inc.
Native wheat starch was processed by twin-screw extrusion cooking under five operating conditions, varying feed moisture (19-44%), and barrel temperature (90-180 C). These were compared to two drum- dried starches prepared by industrial processing. Functional properties were assessed from swelling capacities, viscographic patterns, and flow properties, which allowed the cold water behavior, the pasting characteristics, and the paste rheology to be estimated. The cold water behavior and the pasting pattern below 85 C were mainly ascribed to macromolecular entanglements in the solid-phase structure. Extruded samples, except for one processed at pasta-like conditions, exhibited lower cold water swelling and higher solubility than drum-dried starches. This was ascribed to easier disentanglement of macromolecules resulting from starch depolymerization. The hot paste rheology of dispersions heated above 90 C was directly related to the overall macromolecular characteristics as determined by intrinsic viscosity. From viscograms and flow measurements, a transition-like phenomenon was evident within the range 85-90 C. Although extrusion cooking led to much thinner pastes than drum drying, some similar behaviors were observed under specific conditions, for example with high feed moisture and low extrusion temperature.