Relationship Between Extrusion Conditions and System Parameters of Extrusion Cooking of Cassava and Soybean Blends: Application of Response Surface Analysis

Abstract

Blends of cassava flour and partially defatted soybean four were processed in a single-screw extruder. Experimental design with feed moisture (FM)(16, 20, 24 gwater/100g flour), amount of soybean (10–30 gsoybean/100g flour) and barrel temperature (120, 145, 170 ^oC) as independent variables produced 17 different combinations that were studied using Box-Behnken Design of response surface methodology to investigate the effect of these variables on extruder system parameters, namely, product temperature (PT), residence time (RT), machine throughput (MT) and specific mechanical energy (SME). The recorded values for all responses varied from 121 to 175 ^oC, 42.34 to 65.11 seconds, 3.65 to 4.56 and 159.01 to 213.63kJ/kg, respectively.  Second-order polynomials were used to model the extruder responses as a function of process variables. All three variables affected responses significantly especially their linear terms (P<0.05) and all the fitted models were all significant (P<0.05) and correlated with experimental data (R² ³ 0.934).

Keywords: Cassava flour, Soybean flour, Product temperature, Residence time, Machine throughput, Specific mechanical energy.