Thermal energy application on extrusion and nutritional characteristics of dog foods

The aim of this study was to evaluate the effects of specific thermal energy (STE) application at the extrusion preconditioning stage on the processing parameters, starch gelatinization, kibble macrostructure, nutrient digestibility, feces characteristics, and palatability of a dog food formulation. Two experiments were conducted, and both used the same dog food recipe. In the first experiment, six amounts of STE were applied by changing steam infusion in the preconditioner to obtain the following discharge mass temperatures: 45 °C, 55 °C, 65 °C, 75 °C, 85 °C, and 95 °C. After evaluating the processing and kibble characteristics, the diets were fed to 36 dogs (six dogs per diet), and nutrient digestibility was determined by total feces collection. Palatability comparisons were carried out with 36 dogs using the two-pan method. Results were analyzed by analysis of variance (ANOVA), and means evaluated by polynomial contrasts according to the STE application (P < 0.05). In the second experiment, three treatments were produced. The extruder was operated with preconditioner mass temperature of 45 °C, and the amperage documented. On the sequence, the preconditioner mass temperature was increased to 95 °C, and the reduction on amperage was recorded. The extruder feed rate was them increased until a motor amperage equivalent to that of treatment 45 °C was observed but keeping constant preconditioner mass temperature at 95 °C. Processing and kibble characteristics were evaluated. Results were analyzed by ANOVA with means separated by Tukey's test (P < 0.05). In experiment one, a quadratic reduction of specific mechanical energy (SME) implementation with increasing STE was verified (P = 0.004), with a linear increase in total specific energy application to mass (P < 0.001). Regarding the relationship of starch gelatinization with increasing STE, a quadratic increase after preconditioning and a linear increase in kibbles after drying were verified (P < 0.001). Kibble expansion increased (bulk density, expansion rate, specific length), and hardness decreased with increasing STE (P < 0.001). Apparent nutrient digestibility and food palatability did not change according to STE application. Feces dry matter increased (P = 0.003), but pH and fermentation product content did not change. In experiment two, increasing STE was able to substantially elevate the mass production of the extrusion system while keeping the electric energy consumption constant. In conclusion, an increase in STE application decreased the SME required to process the food and increased the kibble expansion, starch gelatinization and in vitro digestibility of organic matter (OM), allowing a substantial increase in extruder productivity without increasing electric energy consumption, an important economic consideration for dog food production efficiency.