IMPACT OF TWIN SCREW EXTRUSION COOKING ON ANTI-NUTRITIONAL AND QUALITY ATTRIBUTES OF SWEET POTATO FLOUR

Effects of barrel temperature (83 – 117°C), feed moisture content (17 – 33% w.b.) and screw speed (60 – 110 rpm) on the trypsin inhibitor activity (TIA), in vitro starch digestibility (IVSD), degree of gelatinization (DG), water absorption and oil absorption indices during the extrusion cooking of sweet potato were studied and optimized using response surface methodology. Results showed that 75 – 97% reduction of trypsin inhibitor was obtained using extrusion cooking; the temperature had a significant effect. Digestibility of sweet potato increased during extrusion cooking. IVSD and DG (ranging from 110.1 to 310.9 mg maltose / g and 40.4 to 85.9% respectively) had a positive correlation with temperature and screw speed. A significant effect of temperature and moisture content on water absorption (WAI) and oil absorption (OAI) indices was observed. Oil absorption index decreased with increase in moisture content. The optimum values of barrel temperature, feed moisture and screw speed for the extrusion cooking of sweet potato were 110ºC, 20% (w.b.) and 100 rpm respectively. At optimum conditions 90% reduction in TIA and gelatinization degree of 75% DG in extruded cooked sweet potato was observed. Extrusion cooking plays an essential role in the reduction of trypsin inhibitors and increases the utilization of sweet potato as a potential ingredient in food formulations.