PROPERTIES OF CROSS-LINKED STARCH PRODUCED IN A SINGLE SCREW EXTRUDER WITH AND WITHOUT A MIXING ELEMENT

摘要

Starch was extruded with sodium hydroxide and sodium trimetaphosphate in order to cross-link it in a single-screw extruder with and without a mixing element at constant screw speed of 90 rpm in the first set of experiments and at similar mean residence time controlled by screw speed in the second set of experiments. For the screw without mixing element in the second set of experiments, screw speed was adjusted to give the similar residence time as the single-screw extruder with mixing element at 220 rpm. Phosphorus content and pasting curves of extrudates showed that starch was cross-linked during extrusion. Replacing the screw without mixing element by the screw with mixing element increased specific mechanical energy dissipation into starch, but there was not significant difference between water solubility and absorption indices of starch cross-linked in the single-screw extruder with and without the mixing element at constant screw speed in the first set of experiments and at similar mean residence time in the second set of experiments.