Effect of Lipid Contents and Process Parameters on the Physicochemical, Rheological, Calorimetric and Structural Properties of an Extruded Canine Food

The purpose of this study was to analyze the effect of total lipids content and process parameters on the physicochemical, rheological and structural properties of an extruded canine food that contains discarded beans as protein source. An optimization of temperature (120–150°C), moisture content (1418%), screw speed (120–180 rpm) and total lipids (5–15%) of the extrusion process was performed using surface superimposition methodology. Rheology, calorimetry, X-ray diffraction and scanning electron microscopy studies were performed on the optimal treatment before and after extrusion. Results showed that significant differences (P<0.05) were obtained on physicochemical properties: increasing temperature resulted in decreased expansion index and bulk density, unlike water absorption index, which increased. Also, increasing total lipids decreased hardness and increased color. Finally, the obtained optimal processing conditions were standardized at 150°C, 15.5% moisture, 140 rpm and 10% of total lipids with the resultant characteristics involving hardness: 39.23 N; expansion index: 1.07; bulk density: 1, 021.3 kg/m³; specific mechanical energy: 28.8 kJ/kg; color: 9.27; water absorption index 2.01 g/g; water solubility index: 12.13%; V: 1, 439.61 cP; V: 27, 835 cP; V: 16, 822.4 cP; V: 15, 146.2 cP; and, inimaxminfin V: 1, 676.22 cP. Differential scanning calorimetry showed a high degree of gelatinization in extrudates; retro however, these results are inconsistent with rheological experimentation results. X-ray diffraction showed a decreased crystallinity of the extruded diets. Finally, scanning electron microscopy showed intact starch granules after extrusion, suggesting a partial gelatinization. Results demonstrate the potential use of high lipids content in an extruded food that fulfills nutritional requirements for canine consumption.