Effect of roasting on rheological and functional properties of sorghum flour

In this study, the effect of grain moisture content (12-20%), temperature (140-180 ℃), and time (5-15 min) of roasting on the quality attributes of sorghum grain was studied. The response functions were rheological attributes of powder flowability, color, water absorption capacity, and sensory acceptability. These response functions could be correlated (r ≥ 0.91, p ≤ 0.01) with the independent variables by second order polynomials. Higher temperature and longer roasting time had a detrimental effect on color and sensory acceptability of product. An increase in moisture content of grain induced lower cohesion characteristics in the flour as evidenced by less energy for compression. Raw sorghum flour exhibited highest peak viscosity of 297 BU compared to only 32-71 BU for roasted samples. Roasted sorghum flour exhibited less shear-thinning phenomenon compared to raw sample, and was more stable towards retrogradation. Optimum condition for maximum sensory acceptability was achieved with a grain moisture content of 16-20% and temperature 161-179 ℃ for 12 min of roasting.