THE EFFECT OF SUGARS ON THE EXTRUSION OF MAIZE GRITS .2. STARCH CONVERSION

Differential scanning calorimetry (DSC), X-ray diffraction and rheolog ical 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 (fruct ose more than sucrose) by reducing the specific mechanical energy inpu t. Addition of sugars led to changes in the packing of amylose-lipid c omplexes in the extrudate from an E-type to V-type. It is postulated t hat the complexes pack initially in the less stable E-form and then re arrange to the more stable V-form, a process which is accelerated by t he addition of sugars because of the enhanced molecular mobility resul ting from the reduction in the glass transition temperature. This rear rangement is also seen when extrudates containing no sugar are equilib rated at ambient temperature at moisture contents between 14.5% and 18 % (w.b.).