Effects of extrusion conditions on quality of cassava bran/cassava starch extrudates

Blends of cassava bran and cassava starch were processed in a single-screw extruder. Response surface methodology was used to determine the effect of the concentration of cassava bran (10-50%), barrel temperature (150-210 degreesC), feed moisture (16-20%) and screw speed (120-180 r.p.m.) on the characteristics of the dried extrudates. All the independent variables were significant (P < 0.05) for radial expansion. The water absorption index (WAI) and water solubility index (WSI) were affected by bran level, screw speed and temperature, while only moisture and temperature influenced specific volume. The maximum radial expansion was found when all the independent variables were at their lowest levels. Lowest-density extrudates (highest specific volume) were obtained at 16-18% moisture and 180-200 °C. An increase in bran level increased the WAI but decreased the WSI when the temperature was higher than 170 °C. Screw speed had a slight effect on those responses, decreasing water absorption and increasing water solubility when changed from 120 to 180 r.p.m.