Effect of extrusion variables on physical, structure and sensory properties of wheat germ-corn grits extrudates

ABSTRACT

Yellow corn grits were replaced using 15% defatted wheat germ [DWG] and extruded with a single-screw extruder. The variables studied were moisture content of raw material [14, 18 and 22%], extrusion temperature [140, 160 and 180°C] and extruder screw speed [180, 210 and 240 rpm]. Functional properties, scanning electron microscopy [SEM] and sensory attributes of the products were evaluated. Extrudate made of 100% corn grits was also prepared for comparison. Extruded blends had lower expansion, Water absorption index, water solubility index and breaking strength, higher bulk density than extruded corn. Moisture content, temperature and screw speed had significant effects on sensory properties of extrudates. Moisture content of 14%, extrusion temperature 160°C and screw speed of 240 rpm were the best extrusion conditions for yellow corn grits or corn grits containing 15% DWG. Scanning electron microscopy showed that extrusion variables had pronounced influence on microstructure and size of air cells of extrudates. The photomicrographs supported some of the previous findings: