Extrusion Cooking of Rice Flour and Amaranth Blends

Response surface methodology was used to investigate the extrusion cooking and product properties of rice flour and amaranth blends in a CM45-F conical, counter-rotating twin-screw extruder. Three mixtures at a level of 20, 40 and 60 g/100 g amaranth were extrusion cooked using a central composite design with varied barrel temperature (150-190 °C), feed moisture (11-16 g/100 g wb), feed rate (15-35 kg/h), and screw speed (58-82 rpm). Pressure, torque, specific mechanical energy (SME), Brabender pasting properties, expansion of extrudate characterised by sectional (SEI) and longitudinal expansion (LEI), product density, breaking strength, and total colour change were determined. Increasing amaranth content in the blends increased die pressure, but decreased torque and SME. Increasing amaranth content caused an enormous decrease in the sectional expansion index (SEI) and increase in the breaking strength of extrudate. Well expanded rice-amaranth products with acceptable soft texture were at amaranth levels of 20-40 g/100 g. Optimal extrusion cooking conditions most likely to produce rice-amaranth products suitable for a puffed snack food were at high barrel temperature, low moisture, high screw speed, and feed rates in the range of 25-35 kg/h.