The effect of sugars on the extrusion of maize grits: II. Starch conversion

Differential scanning calorimetry (DSC), X-ray diffraction and rheological studies have revealed that the conversion of A-type starch during the extrusion of mixtures of maize grits with sugars depends on sugar type and concentration. Sugars inhibited the starch conversion (fructose more than sucrose) by reducing the specific mechanical energy input. Addition of sugars led to changes in the packing of amylose–lipid complexes in the extrudate from an E-type to V-type. It is postulated that the complexes pack initially in the less stable E-form and then rearrange to the more stable V-form, a process which is accelerated by the addition of sugars because of the enhanced molecular mobility resulting from the reduction in the glass transition temperature. This rearrangement is also seen when extrudates containing no sugar are equilibrated at ambient temperature at moisture contents between 14.5% and 18% (w.b.).