Effect of extrusion on trypsin inhibitor contents of soy-sweet potato mixtures

Mixtures of soy and sweet potato (Ipomoea batatas) (L.) Lam), flours contai ning 18%, 25% and 30% moisture, respectively, were extruded in a single scr ew extruder. Results showed that inactivation of trypsin inhibitor was enha nced by both reductions in feed moisture and soy flour contents of sample m ixtures. Hence subsequent extrusion was carried at 18% feed moisture with v ariable feed ratio, screw rotation speed and die diameter, using a central composite rotatable, near orthogonal experimental design. Results further s howed that the effect of increasing the ratio of soy in the mixture was lin early significant (p>0.05). Optimum Trypsin Inhibitor (TI) inactivation val ue of 3.40 mg/g was predicted at a feed composition of 80% sweet potato, 9 mm die diameter and 154 Ipm, respectively.