Physical and Molecular Properties of Re‐extruded Starches as Affected by Extruder Screw Configuration

Abstract

ABSTRACT Amylomaize V, amylomaize VII, wheat and rice starches were extrusion cooked in a single‐screw extruder at 140°C barrel temperature and 140 rpm screw speed. Extrudates were ground and re‐extruded through a 3 mm cylindrical die nozzle using screws with no mixing (NM), 1 mixing (1M) or two mixing (2M) elements. Overall expansions were the highest and bulk densities were lowest with 1M. Radial expansions for amylomaize V, amylomaize VII, and wheat starches were the highest with 1M and lowest with 2M. Amylopectin contents of starches decreased with corresponding increases of gel permeation chromatograph peak II fractions when number of mixing elements was increased. λ max values of peak I and peak II decreased upon re‐extrusion of starches with increasing number of mixing elements.