Effect of Blending ratio and operating conditions

Effect of blend ratio (soybean-teff proportion), feed moisture (9.5-12.5%) and barrel temperature (122-138°C) on physicochemical and sensory properties of an extruded product from brown teff [Eragrostis teff (Zucc.) Trotter] (DZ 01-99 variety) and full fat soybean (Glycine max) (AFGAT variety) were investigated. The extrusion experiment was conducted using a pilot scale co-rotating twin screw food extruder using Central Composite experimental Design (CCD). Second degree polynomial models for the responses as a function of the independent variables were generated. Soybean flour addition to teff flour resulted in increased protein, lipid and total ash content but reduced crude fiber and total carbohydrate content. Blend ratio showed a dominant effect on physicochemical and sensory properties of products. Increased soybean proportion resulted in increased bulk density, hardness, specific length, moisture content, WAI, WSI and WHC but reduced diametric expansion of extruded product. Increased feed moisture increased diametric expansion and specific length but reduced WSI of extrudates.