Twin-screw extrusion of cassava starch and isolated soybean protein blends

The effects of the extrusion parameters on isolated soybean protein (ISP) a nd cassava starch (CS) blends were studied. Extruded samples were prepared by using a ZSK-30 Werner and Pfleiderer twin-screw extruder. The study was carried out using Response Surface Methodology. The ISP followed by the moi sture content were the most important linear variables significantly affect ing axial expansion, specific volume, water solubility index and colour dif ference. The radial and axial expansion ranged from 2.30 to 3.77 and from 1 .02 to 2.62, respectively. The highest ISP concentrations in the blends res ulted in the highest specific volumes of the extrudates. Simultaneous incre ases of the barrel temperature and ISP level increased the water absorption index and lowered the water solubility index of the extrudates. Extruded p roducts were softer at higher barrel temperature. The greatest difference i n colour values was for the blends with the highest ISP concentration.