EFFECTS OF SOY FIBER, SALT, SUGAR AND SCREW SPEED ON PHYSICAL-PROPERTIES AND MICROSTRUCTURE OF CORN MEAL EXTRUDATE

The physical properties and microstructure of corn meal extruded with soy fiber, salt, and sugar were studied using an intermeshing and co-rotating twin-screw extruder. The effects of fiber, sugar and screw speed on water absorption index (WAI) and water solubility index (WSI) correlated well with hulk density and specific volume of extrudates. Increasing screw speed decreased WAI but increased WSI. Increasing fiber content from 0-20% lowered the WAI, but increased the WSI. The trends were reversed with further increases in fiber content. An increase in the sugar content reduced WSI. Scanning electronmicroscopy revealed that increasing fiber, sugar contents, and screw speed resulted in less expanded extrudates with smaller air cell size and thicker cell walls. The breaking strength increased with increasing sugar and fiber contents and was negatively correlated with the radial expansion of extrudates. Salt (0-2%) had no significant effects on the WAI, WSI, and microstructure of extrudates. (C) 1995 Academic Press Limited