Effect of Extrusion Processing Variables on Finger Millet Flours with Respect to Their Functional Properties Using Response Surface Methodology

Finger millet is fiber rich nutritious food which can be used by diabetic patients and also by healthy persons to maintain body weight owing to their inherent good amount of resistant starch and dietary fiber. Various degrees of structural transformations in the starches can be obtained through wide range of degree of cooking possible through extrusion processing. Response surface methodology was used to study the effect of amylose content (19.42%, 24.19%, 25.74%), moisture (21, 23 and 25%), screw speed (250, 300, 350 rpm) and barrel temperature (160,180 200°C) and their interactive effect on the extrudate properties. Percentage amylose in the finger millet flours was found to have significant effect on the bulk density, sectional expansion index and resistant starch of the extrudates. Expansion of extrudates was negatively correlated to amylose (p=0.022). Barrel temperature was found to be most prominent for modification of RS in finger millet extrudates. Higher amylose content lead to formation of more resistant starch in extrudates of finger millet. The effect of screw speed and barrel temperature was mostly seen on the water absorption index and water solubility index. Quadratic regression model (R2> 0.68) was found appropriate to model the physico-chemical parameters of the exrudates as function of extruder and raw material properties.