Rheological characterization of akamu, a semi-liquid food made from maize, millet and sorghum

Abstract

Viscosity-rotational speed (shear rate) relationships were determined for sweetened and unsweetened akamu, a cooked starchy extract prepared from fermented maize, millet and sorghum, at temperatures between 10 and 70 °C. The rotational speeds were between 10 and 100 rev/min. Akamu exhibited pseudoplastic behaviour at all temperatures. Akamu from maize had the highest viscosity and millet-akamu the lowest. A power-law equation adequately described the relationship, and correlation coefficients were from –1·0000 to –0·9915. Power-law indices were not affected by temperature, sugar and grain type, and were between 0·33 and 0·37 for all the samples. Consistency indices decreased with temperature, and the Arrhenius equation was used to describe the dependence. Activation energies varied from 3·3 to 11·6 MJ/mol. Sweetened samples had slightly lower activation energies. Sorghum-akamu showed the least sensitivity to temperature and maize-akamu the highest.