Potato starch extrusion exhibits two main differences
when compared to other starches: high melt viscosity
and early melting in the extruder. Both explain the
difficulties usually encountered when processing this
material, characterized by high energy requirements.
Early melting may be due to transition temperatures
lower than the values encountered for cereal
starches. High melt viscosity is linked to the higher
molecular weight of potato starch. Once
macromolecular chains are split and the molecular
weight reduced to the same level as other starches,
under the effect of thermomechanical treatment,
identical melt viscosity is found for the same
moisture content and temperature, whatever the
botanical origin of starch.
These difficulties may be solved by shortening the
screw length in which starch is in a homogeneous
molten phase. This requires a better knowledge of the
melting transition of low water starchy products under
high shear stresses. A better control of these phenomena
would also help in reducing macromolecular
degradation at this stage, which, whatever the origin of
starch, results in a loss of functional properties.