A A C C   2 0 0 0   A n n u a l   M e e t i n g

Cereals are often processed in the presence of sugars. This study compares the effects of sucrose on the extrusion of maize and wheat. Cereals of various particle sizes were extruded in a twin screw (Clextral BC 21) at sucrose levels of 0, 5, 10, 15 and 20 percent dry basis. Two types of extrudates were produced, expanded and non-expanded, respectively prepared under severe and mild extrusion cooking conditions. Sucrose addition to maize grits reduced the sectional expansion at higher sucrose levels, whereas, wheat flour was far less susceptible to sucrose incorporation. The degree of starch conversion was measured by Rapid Visco Analyser (RVA), dynamic scanning calorimeter (DSC), x-ray, alkaline soluble viscosity, water absorption and soluble indices. Substantial reduction of starch conversion was observed for maize in presence of sucrose, but there was little effect on wheat. The thermo mechanical behaviour of the non-expanded was evaluated by dynamical mechanical thermo analysis (DMTA). Sucrose plasticizes maize as well as wheat reducing the glass transition temperatures (Tg) to the same extent. The difference between the behaviour appears to be largely related to the particle size.