Effect of feed composition, moisture content and extrusion temperature on extrudate characteristics of yam-corn-rice based snack food

Blends of yam, rice and corn flour were processed in a twin-screw extruder. Effects of yam flour (10-40 %), feed moisture content (12-24 %) and extruder barrel temperature (100-140 °C) on the characteristics of the dried extrudates was investigated using a statistical technique response surface methodology (RSM). Radial expansion ratio differed significantly (p ≤ 0.05) with change in all the independent variables. Highest expansion (3.97) was found at lowest moisture content (12 %) and highest barrel temperature (140 °C). Increased yam flour level decreased the expansion ratio significantly. Water absorption index (WAI) increased significantly with increase of all variables. However, water solubility index (WSI) did not change with change in yam flour percent. Hardness of extrudates that varied from 3.86 to 6.94 N was positively correlated with yam flour level and feed moisture content, however it decreased significantly (p ≤ 0.001) with increase of barrel temperature. Yam percent of 15.75 with feed moisture and barrel temperature at 12.00 % and 140 °C respectively gave an optimized product of high desirability (> 0.90) with optimum responses of 3.29 expansion ratio, 5.64 g/g dry solid water absorption index, 30.39 % water solubility index and 3.86 N hardness. The predicted values registered non-significant (p < 0.10) differences from the experimental results. Further study would include the sensory properties enhancement of extruded snacks and little emphasis on the chemistry of interaction between different components.