Control of Porosity and Expansion in Starch Extrusion by Monitoring Pressure at Die Outlet

Abstract

Pore structure of starch extrudates is an important area of study in the food industry. Usually, changes in porosity also results in variations in skeletal material due to influence from degree of cook and type of cook (e.g., pure gelatinization vs. mechanical degradation). However, changing the pressure differential across the extruder die face provides a method by which expansion is controlled without influencing the skeletal material. Results from this study have shown that the volume fraction porosity can be varied from 0.23 to 0.53 with negligible effect on skeletal density. The expansion control method does not control pore sizes with distributions and means having an element of randomness. However, average pore wall thickness is linearly related to the pressure differential across the die face with a reduced pressure differential giving increased pore wall thickness and vice versa. Thus, controlled expansion can be used to produce products/samples that have the same skeletal material but different average pore wall thickness and total porosity.