Relationship between viscosity and expansion properties of variously extrusion-cooked corn grain components

Normal corn flour and starch were extrusion-cooked at different die L/D ratios (extrusion pressure), screw speeds and moisture contents. Apparent viscosity, shear rate, expansion volume and molecular degradation of starch during or after extrusion-cooking were determined and the interrelationships among these properties were studied. Overall, the apparent viscosity of the extrusion-cooked starch or flour affected expansion more than did the extrusion pressure. The maximum expansion volume of 13.8 for starch was obtained at an apparent viscosity of 3 kPa-s.