INFLUENCE OF AMYLOSE CONTENT ON THE VISCOUS BEHAVIOR OF LOW HYDRATED MOLTEN STARCHES

Starches with various amylose contents (0%-70%) were processed on a tw in-screw extruder equipped with a special slit die rheometer. Relation ships between thermomechanical treatment and starch macromolecular deg radation are defined, and flow curves are discussed in order to determ ine the role of moisture content, product temperature, and mechanical energy on melt viscosity. The viscous behavior is described by a power -law expression. Viscosity is more sensitive to moisture content and m acromolecular degradation at lower amylose contents. Using multiple re gression analysis, expressions for the different starches are proposed to describe the influence on the viscosity of amylopectin, which is t he macromolecular component with short chain branching. The main diffe rences observed when decreasing the amylose content are a lower viscos ity and less pronounced shear thinning. These effects are interpreted in terms of entanglements. (C) 1996 Society of Rheology.