FEASIBILITY OF UTILIZING SWEET-POTATO SOLIDS IN EXTRUSION-COOKING

A fractional factorial design of four variables at two levels each was employed to assess the feasibility and best parameter for extruding s weet potato solids (SPS) using a single screw extruder. It was determi ned that a high expansion ratio is a desired quality factor for this t ype of snack food, due to its contribution to textural perception. Pre liminary trials on extrusion of sweet potato solids as the sole compon ent in the feed resulted in brittle, dense, and burnt extrudate. The h igh sugar content (65% total sugar) of the sweet potato solids was cit ed as the cause of these attributes, consequently it was necessary to incorporate wheat flour into the feed to provide a starch matrix for e xpansion and to reduce sugar concentration. The controlled parameters were screw speed, barrel temperature, feed moisture content, and SPS l evel in the feed. Among all possible combinations of controlled parame ters, the highest expansion ratio was obtained at a screw speed of 220 rpm, temperature profile of 110, 105, 115 and 105 degrees C, 13% feed moisture content, 50% sweet potato solids, and 0.5% leavening agent.