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-r otating twin-screw extruder. The effects of fiber, sugar and screw spe ed on water absorption index (WAI) and water solubility index (WSI) co rrelated well with hulk density and specific volume of extrudates. Inc reasing 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 th at 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 conte nts and was negatively correlated with the radial expansion of extruda tes. Salt (0-2%) had no significant effects on the WAI, WSI, and micro structure of extrudates. (C) 1995 Academic Press Limited