Effect of the ratio of wheat flour and cassava and process parameters on the pellet qualities in low starch feed recipe extrusion

Abstract

The purpose of the investigation was to study the effects of the ratio of wheat flour and cassava and extrusion process parameters on the physical qualities of low-starch content floating feed in a pilot extrusion plant in order to transfer the production characteristics to scale manufacture. The results show that with an increase of cassava content in formulations, the feed pellet bulk density decreases. When the cassava content is ≥ 54.3 g/kg (wt), the floatability of feed pellet reaches 100 %. The feed pellet hardness depends significantly on the starch sources (P < 0.05). The ratio of wheat flour and cassava in a recipe has significant but irregular impacts on the feed pellet water stability. A wheat flour/cassava ratio (54.3/54.3) was selected as an optimal formulation. For the optimal recipe, a pilot extrusion trial shows that an increase of moisture content and die temperature gives a decrease in the feed pellet bulk density, then an increase in pellet floating possibility. Based on Response Surface Methodology, the optimal parameters for processing the selected recipe are moisture content 32 % (wt), screw speed 247 rpm and die temperature 135 ℃. A theoretical model was also applied to cross-check the results from Response Surface Methodology.