Abstract
The study examined the effect of extrusion process factors on carbohydrate content and energy value of extrudates from aerial yam and soybean composite flour mixes. Laboratory scale single-screw extruder was utilized in extruding blends of aerial yam and soybean flours in the ratio of 1:3. Randomized Central Composite Design (RCCD) was used with a three factor experimental set up at five levels each, with barrel temperature (X1 : 95 ℃, 100 ℃, 105 ℃, 110 ℃, 115 ℃), screw speed (X2 : 85 rpm, 100 rpm, 115 rpm, 130 rpm, 145 rpm) and feed moisture levels (X3 : 31%, 33%, 35%, 37%, 39%) as the independent factors. Response Surface Methodology (RSM) was utilized to analyze the effects of the independent factors on the dependent variables (the responses). Coded values for the independent factors used were -2, -1, 0, 1, 2, where -2 represents the lowest, 0 represents the medium (mid-point), and 2 represents highest levels, respectively. Significant (p < 0.05) regression models describing the effect of the extrusion process conditions on the carbohydrate content and energy value of the extrudates, were utilized. Results obtained from the proximate analysis revealed that carbohydrate contents differed somewhere in the range of 30.11 and 54.15%, while energy value ranged from 398.84 to 529.17 kcal. Carbohydrate contents were significantly (p< 0.05) impacted by barrel temperature, screw speed and feed moisture, while barrel temperature and screw speed showed significant (p< 0.05) impact on energy value. High regression coefficients, R2≥ 0.9 were obtained, showing that the models can be used to navigate the design space. Optimization results based on desirability concept indicated that 112.11 ℃ barrel temperature, 136.49 rpm screw speed and 34.65% feed moisture would produce composite snacks of better carbohydrate content and energy value.