Extrusion cooking on pasting properties and relative viscosity of selected starch crops

Abstract
Rheological properties of food are very important indicators of the quality and texture of food products. In this study, the relative viscosity and pasting characteristics (cold and hot paste viscosity) of extrudates from a locally developed extruder (L/D 12:1, CR 4.4:1, 4 KW) were determined. The extrudates were processed from the flour and starch of cassava and maize and wheat flour. Stepwise regression and other follow up tests were employed to a factorial experiment in completely randomized design. Relative viscosity increased positively with duration of operation for cassava products and negatively for cereal products. For Hot Paste Viscosities (HPV) and Cold Paste Viscosities (CPV) however, both products decreased negatively with extrusion. The most stable of the products is Cassava Starch at 40% moisture content. Also, retrogradation decreased with increasing extrusion time and moisture content. The equations relating the various dependent and independent variables were established to predict the quality of the products. Quadratic coefficients fitted the extrusion data very well than linear models.

Key words: Extrusion, hot and cold paste viscosities