The objective of this study was to develop predictive models that relate extrusion process variables to expansion ratio of five varieties of water yam starch. This was accomplished by varying the feed moisture content (FMC) and extruder parameters which include barrel temperature (BT), screw speed (SS) and determine their effects on resulting expansion ratio using response surface methodology. A single screw extruder (DCE 330, NJ) was used in evaluating the extrudate’s physical property, expansion ratio of the starches that were processed using standard wet milling procedure. The expansion ratios of all the extrudates considered in this study ranged from 1.05 to 1.93. It was observed that changing the feed moisture content, barrel temperature and screw speed significantly (P<0.05) affected the expansion ratio of all the extrudates. Increasing the feed moisture content (18 to 28% db) and screw speed (80 to 180 rpm) resulted in a substantial decrease in expansion ratio of all the extrudates except that of TDa 98/01183. The screw speed and feed moisture content were found to be the major process variables showing significant (P<0.05) linear, quadratic and interaction influences on the expansion ratio.
Key words: Water yam, starch, extrusion variables, extrudate, expansion ratio.
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