Effect of extrusion operating conditions on the physical and sensory properties of tef (Eragrostis tef [Zucc.] Trotter) flour extrudates

Abstract

Effect of extrusion variables including barrel temperature (110, 130 and 150°C), feed
moisture content (17, 21 and 26 % wwb) and screw speed (100 and 140 rpm) on the
physical and sensory properties of an extruded product was investigated using two tef
cultivars (DZ 01-99 and 196, red and white coloured, respectively). Increased barrel
temperature, reduced feed moisture content and a higher screw speed showed a
significantly (p < 0.01) higher radial expansion (2.11 and 2.35), reduced bulk density (0.54
and 0.48 g/cm 3 ) and less compression resistance extrudate (64.16 and 60.83 N) with
minimum moisture retention after extrusion respectively, for white and red tef varieties.
Water absorbing and water solubility indices more attained the characteristics of a typical
gelatinized product at these severe processing conditions. The study showed significant
differences (p<0.05) in hedonic rating for colour texture and overall acceptance between
products as evaluated by the sensory panels. In general, extrusion variables induced
significant changes in the product quality attributes evaluated.