Glass Transition of Extruded Wheat,Corn and Rice Starch

Commercial wheat, corn and rice starch were extrusion cooked under a specific mechanical energy input (SME) ranging from 81 to 365 Wh/kg (288 to 1314 kJ/kg). Extrusion cooking at low and high SME resulted in products having significant differences in molecular weight distribution and having crystalline structures of the V‐ and E‐type, as determined by gel permeation chromatography and X‐ray diffraction analysis. Differential scanning calorimetry revealed that the glass transition temperature (T_g) of the extruded starches was independent of the botanical source, the degree of extrusion‐induced molecular fragmentation and the formation of the V‐ and E‐type crystalline structures. The obtained master curve, defined by the relationship between water content and T_g of the amorphous starch, may be used as a predictive tool in modelling the extrusion process of starch or starch containing blends, especially with regard to the formation of the morphological structure and texture attributes of directly expanded products.