Characterizing the Product Moisture Loss of Selected Starchy Crops during Extrusion

In this study, the effect of extrusion process parameters of a locally developed extruder on the moisture loss of extrudates of the flour and starch of maize and cassava which are grown in Nigeria in large quantity were characterized. These were compared with those of wheat flour which is commonly used for the production of alimentary paste. The parameters considered include feed moisture (30, 40, 50 %), extruder temperature (40, 70, 100 o C) built up by varying the duration of sampling and screw speed (100, 150, 200 rpm). Response Surface Methodology, stepwise regression, correlation and Analysis of Variance were employed to a factorial experiment in completely randomized design. Product moisture varies inversely with duration of operation. An increase in extrusion time decreased moisture content up to a critical value of above which it started to increase again. As feed moisture increased, higher extrudate moisture was obtained. Also, product moisture decreased from 100 to 150 rpm and then increased at 200 rpm. The minimum product moisture of 10.6% indicating maximum moisture loss was attained at 150 rpm and 25% moisture content by maize starch. The equations relating product moisture and the independent variables were established. Generally, the response surface study revealed the range of the extrusion variables for optimum performance. Directions on further experimentation for optimization are suggested. A quadratic coefficient fits the extrusion data very well, better than linear models.