MODELING THE SPECIFIC MECHANICAL ENERGY OF EXTRUDED WATER YAM (Dioscorea alata) FLOURS USING RESPONSE SURFACE ANALYSIS

The objective of this study was to develop predictive models that relate extrusion process variables to specific mechanical energy of flours produced from five (5) varieties of water yam. This was accomplished by varying the feed moisture content (FMC) and other extruder parameters which include barrel temperature (BT), screw speed (SS) and determine their effects on resulting specific mechanical energy using response surface methodology (RSM). The water yam (D. alata) flours produced were extruded using a single screw extruder (DCE 330, NJ). The specific mechanical energy of all the extrudates considered in this study ranged from 12290.32 to 86113.96 Jg-1. It was observed that changing the feed moisture content, barrel temperature and screw speed significantly (P < 0.05) affected specific mechanical energy of all the extrudates studied. Increasing the feed moisture content (18-28 % db) and screw speed (80-180 rpm) resulted in a substantial decrease in specific mechanical energy (85.73 %). The screw speed and feed moisture content were found to be the major process variables showing significant (P < 0.05) linear and quadratic influences only on the specific mechanical energy of the flour extrudates considered. Most of the interactions between independent variables were significant for all the varieties considered except TDa 297 flour extrudates that had R2 = 0.506.