An experimental approach to optimize several processing conditions when extruding soybeans

In this experiment involving extrusion of soybeans, a quadratic orthogonal rotary combination design was used to investigate effects of key extrusion conditions, such as bore diameter, temperature, moisture and rotation speed on extrusion efficiencies as indicated by trypsin inhibitor, chymotrypsin inhibitor, urease, lectin, protein solubility and protein digestibility in vitro. As a result, 6 quadratic regression equations of experimental indices under 4 extrusion conditions were separately established. Taking into account the importance of these indices to the nutritional value of soybeans in animal feeding, we propose a set of comprehensive indices to evaluate extrusion efficiency using a fuzzy comprehensive evaluation method. Based on these comprehensive indices, the optimal extrusion conditions for soybeans as a feedstuff can be determined with a single objective quadratic nonlinear programming method.