Effect of Shear Energy on Size Reduction of Starch Granules in Extrusion

Abstract

AbstractThe changes of size and size distribution of starch granules under extrusion conditions have been investigated by using a single screw extruder and an optical microscope coupled with an image analysis system. The mechanical energy input and material processing time were key factors influencing the degree of starch granular size reduction. In a high shear extrusion process (T=40°C), the weight average granular size of extrudate was reduced from ˜12.4μ (raw waxy corn starch) to 1˜2μ, whereas in a low shear extrusion (T=90°C), and granular size was reduced to ˜7μ. Fine particles (±0.5μ) were observed in both extrusion processes. They were 76% (w/w) under a high shear and long processing time conditions and 5% in a low shear and short time process. During the size reduction process, the peaks of size distribution of starch granules shifted from the large size region toward the medium size region and finally to a rather narrowed peak at the small size region when extensive size reduction measures were applied. Extrusion processes can be used to reduce starch granular size effectively.