Formation of soluble starch or thermoplastic starch requires disruption of starch granules
and their supramolecular structures, dissociation of complexes with lipids and melting of
crystals with the assistance of added water. Figure 4 shows an environmental scanning
electron microscope (SEM) image of corn starch granules. Though there is bound water
within starch that varies with ambient humidity, water is typically added. A water
concentration of 25 %·w/w will give a gelatinisation temperature with a range of 60-70 °C.
Gelatinisation is assisted by shear. An extruder, either a twin-screw or single-screw, is
suitable for continuous shear processing. Alternatively batch mixers with a wiping action
can be used.