Trypsin inhibitor and urease activity

Increasing the fat amount of the ration during extrusion can negatively affect product density and product expansion. Ingredients, like whole soybeans (WSB), which are high in fat may increase energy density while avoiding production issues. The objective of this study was to determine the effect of WSB on extrusion and product characteristics of dry expanded dog food. Experimental diets were extruded with 0, 100, 200, and 300 g/kg, as fed WSB. The processing conditions during extrusion were kept constant across all treatments. Processing outputs, trypsin inhibitor, urease, and phytic acid concentrations were analyzed. Single degree of freedom contrasts were used for statistical analysis and significance at α = 0.05. As WSB increased, the extruder load, die pressure and temperature, and specific mechanical energy (SME) decreased linearly (P < 0.05). The bulk density of the products increased linearly (P < 0.05) while the kibble sectional expansion index (SEI) decreased linearly (P < 0.05) as WSB increased. Post-extrusion, trypsin inhibitor and urease activity decreased, but trypsin inhibitor was not eliminated. In conclusion, the increased inclusion level of WSB changed processing conditions and outputs as a result of the intrinsic and intact fat content. Increasing energy input in processing may destroy anti-nutritional factors completely when WSB are included in diets.