Impact of Barrel Temperature, Screw Speed, and Feed Moisture on the Phytate and Tannin Contents of Extruded Snacks from Aerial Yam and Soybean Flour Mixture

This study investigated the impact of barrel temperature, screw speed and feed moisture, as extrusion process parameters, on the phytates and tannins contents of extruded snacks produced from aerial yam and soybean flour mixture, using Response surface methodology. Design Expert (version 11.0.1) was used in the experimental design. A three factor experimental set up at five levels each, with barrel temperature, (X1 = 95, 100, 105, 110, and 115OC), screw speed (X2 = 85, 100, 115, 130, and 145 rpm) and feed moisture levels (X3 = 31, 33, 35, 37, and 39%) as the independent factors was adopted. Coded values for the independent variables used were -2, -1, 0, 1, 2, where -2 represents the lowest, 0 represents the medium (mid-point), and 2 represents highest levels, respectively. The extruded snacks were produced using a laboratory-scale single-screw food extruder, and twenty (20) runs were carried out in the course of the extrusion process. The extruded snacks were subjected to laboratory analysis, using standard equipment and methods. Results of the laboratory analysis for the determination of phytates and tannins contents of the extruded snacks showed that phytates ranged from 12.48 to 32.86 mg/100g, and tannins varied between 0.93 and 5.46 mg/100g sample. Analysis of variance indicated that barrel temperature, screw speed and feed moisture had significant effect (p < 0.05) on the phytates and tannins contents of the extruded snacks. The results obtained for the phytates and tannins contents of the snacks can attest to the fact that it is possible to obtain expanded or ready-to-eat (RTE) products from aerial yam and soybean flour mixture through extrusion processing technology, that possess minimal levels of anti-nutrients/toxicity.