Effect of process parameters on the physical quality of low-starch extruded feed containing Clostridium autoethanogenum protein

Clostridium autoethanogenum protein (CAP) is a novel single-cell protein source derived from the inactivated bacterial biomass produced by CO syngas biological fermentation. There has been limited research on the effect of process parameters on the physical quality of aquatic extruded feed containing CAP. A low-starch formula containing 180 g/kg CAP was used to study the effects of preconditioning moisture content (22-30 %), screw speed (240-300 rpm), die temperature (120-150.) and feed rate (56.5-94.5 kg/h) on the physical quality of extruded feed and specific mechanical energy (SME) of the extruder. Preconditioning moisture content had significant effects on the bulk density (P < 0.01), hardness (P < 0.05) and oil absorption capacity (P < 0.01). Screw speed had significant effects on the bulk density (P < 0.05). Die temperature did not have a significant impact on the physical quality of the feed and SME (P > 0.05). Feed rate had significant effects on the bulk density and SME (P < 0.01). The interactions between moisture content and feed rate had significant effects on the bulk density, expansion ratio, hardness, oil absorption capacity and SME (P < 0.01). The quadratic term of moisture content had significant effects on the bulk density, expansion ratio, hardness, oil absorption capacity (P < 0.01) and SME (P < 0.05). The quadratic term of screw speed had significant effects on the oil absorption capacity (P < 0.05). The quadratic term of feed rate had significant effects on the SME (P < 0.01). The water solubility values (WSI; 3.84-5.28 %) and water absorption index (WAI) values (2.61-3.71) of the extruded feeds were distributed within a narrow range. The WSI values decreased with an increase in the feed rate, while the hydration time increased with the increase in moisture content. Based on the Response Surface Methodology results and imposed constraints, the operation window of process parameters for the test diet was obtained.