Physicochemical Properties of Quinoa Extrudates

Abstract

Response surface methodology (RSM) was used to analyse the effect of temperature, screw speed, and feed moisture content on physicochemical properties of quinoa extrudates. A three-level, three-variable, Box-Behnken design of experiments was used. The experiments were run at 16-24% feed moisture content, 130-170°C temperature, and 250-500 rpm screw speed with a fixed feed rate of 300 g/min. Second order polynomials were used to model the extruder response and extrudate properties as a function of process variables. Responses were most affected by changes in feed moisture content and temperature, and to a lesser extent by screw speed. Calculated specific mechanical energy (SME) values ranged between 170-402 kJ/kg which were lower than those observed for other cereals, most likely due to high (7.2%) fat content of quinoa. High levels of feed moisture alone, and in combination with high temperature, resulted in poor expansion. The best product, characterised by maximum expansion, minimum density, high degree of gelatinization and low water solubility index, was obtained at 16% feed moisture content, 130°C die temperature, and 375 rpm screw speed, which corresponds to high SME input. It was demonstrated that the pseudo-cereal quinoa can be used to make novel, healthy, extruded, snack-type food products.