Extrusion cooking of a maize/soybean mixture: Factors affecting expanded product characteristics and flour dispersion viscosity

The effects of endosperm hardness and extrusion conditions on expanded product characteristics and flour dispersion viscosity of an extruded maize/soybean (88/12) mixture were studied. Samples were obtained with a Brabender single screw extruder. A factorial experimental design was used to analyze the combined effects on radial expansion of two maize endosperm hardness, extrusion temperature and grits moisture content. Surface response methodology was used to study the effects of extrusion conditions on extrudate properties, taking grits moisture (14–18%) and extrusion temperature (155–185 °C) as factors. Specific mechanical energy consumption, radial expansion, specific volume and product texture were determined on each extrudate sample, and the viscosity of the dispersion from extrudate flour was measured at different solids concentrations. For the 88/12 (maize/soybean) mixture, a softer maize endosperm gives a more expanded product than the harder one. Texture scores were directly related with specific volume. The best extrusion conditions to obtain expanded products and precooked flour from an 88/12 maize/soybean mixture were 170 °C and 14% moisture.