Processing traits and digestibility of extruded dog foods with soy protein concentrate

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Abstract
Summary: Soya bean protein concentrate (SPC) with two particle sizes were evaluated on extrusion parameters, kibble formation, digestibility and palatability of dog foods. Eight diets were extruded:PBM—control diet based on poultry by‐product meal (PBM);GM—a diet in which corn gluten meal (GM) replaced 45% of the diet protein;cSPC15%,cSPC30% andcSPC45%—diets in whichSPCof coarse particle size (600 μm) replaced 15%, 30% and 45% of the diet protein; andsSPC15%,sSPC30% andsSPC45%—diets in whichSPCof small particle size (200 μm) replaced 15%, 30% and 45% of the diet protein. The digestibility of nutrients was evaluated for thePBM,GM,cSPC45% andsSPC45% diets, using six dogs per food. ThePBM,GMandcSPC45% diets were compared for palatability. Data were submitted for analysis of variance, and the means were compared by polynomial contrasts or Tukey's test (p < .05). ThecSPCincreased the specific mechanical energy (SME) application, extrusion temperature and pressure linearly, resulting in lower kibble density and higher expansion and starch gelatinization (SG) (p < .01). When comparing thePBM,GM,cSPC45% andsSPC45% diets, higherSME, extrusion temperature and pressure,SGand kibble expansion were verified for thecSPC45% diet (p < .05). TheDM, fat and crude protein digestibility were similar among diets. FaecalpH, ammonia and lactate did not differ, demonstrating that the removal of oligosaccharides and soluble non‐starch polysaccharides ofSPCproduces an ingredient with mostly non‐fermentable fibre. Dogs preferred thePBMto theGMdiet (p < .05), but consumed thePBMandcSPC45% foods equally. In conclusion,SPCexhibited good extrusion functionality, favouring kibble expansion andSG, with high digestibility, similar to that ofPBM. The removal of soluble compounds from soya beans resulted in an ingredient with low fermentable fibre content, which did not alter faecal formation or characteristics.

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