Influence of Extrusion Variables on the Residence Time and Throughput of a Single Screw Extruder

Aims: The influence of extrusion cooking variables on the residence time and throughput of a single screw extruder were investigated using blends of African yam bean (AYB) and cassava flour. The main purpose was to optimize the throughput and residence time of AYB/cassava extrusion using three operating variables (screw speed (SS), feed moisture content (MC) and feed composition (FC)).
Study Design: African yam bean and cassava tubers were processed into flours. A central composite design (CCD) was used to determine the feed moisture content, feed composition and the screw speed used in the operation.
Place and Duration of Study: The cassava tubers were obtained from National Research Institute, Umudike Abia State, the AYB from a local market in Abia State Nigeria and the extrusion work was done at Federal Polytechnic Mubi Adamawa State Nigeria.
Methodology: Twenty extrusion runs were conducted with eight (23) factorial, six star points and six central points. The throughput (TP) and residence time (RT) were determined using standard procedures. Data obtained were subjected to response surface analysis (RSA) and ANOVA.
Results: The results of the response surface regression of TP showed that SS was highly significant in the linear, quadratic and interactive effects. The critical throughput values were 0.098Kg/min for combination of screw speed and moisture content and 0.084Kg/min for combination of feed composition and moisture content variables. The residence time increased as the moisture content and screw speed decreased. The critical residence time values of 59.94s and 28.63s were obtained.
Conclusion: The results confirmed that residence time was inversely proportional to screw speed and moisture content. The data obtained from the study could be used for control of product characteristics and possible projection for the commercial production of extruded blends of African yam bean and cassava flour using a single screw extruder.