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Influence of Graded Levels of Microbially Enhanced Protein on Processing and Expansion of Extruded Dog Foods

Chen, Y. and G. Aldrich

Dry expanded kibbles with ingredients that bring extra nutrition and health benefits are much better received than those which are simply an economic choice by manufacturers. Microbially enhanced protein (MEP) from soybeans, a fermented ingredient, may promote utilization. The objective of this study was to determine the influence of increasing levels of MEP on extrusion processing parameters and kibble characteristics. Four dietary treatments were evaluated which differed by level of MEP in exchange for soybean meal (15%; SBM) at 5, 10 and 15% (5MEP, 10MEP and 15MEP, respectively). The four diets were produced on a single-screw extruder with processing data and samples collected every 15 minutes. Results were analyzed as a completely randomized design by one-way ANOVA and treatment means were separated by Tukeys test using R open-source software. Feed rate and extruder waterflow rate were not different among treatments. However, motor power, shaft speed and specific mechanical energy (SME) was least for 5MEP (P< 0.05, 30.1 KW, 322.5 rpm and 38.4 kW hr/ton, respectively). The SME for SBM was also less (P< 0.05) than 10MEP and 15 MEP (43.72, vs 47.4 and 47.0 kW hr/ton, respectively), but shaft speed did not differ among these treatments. Both kibble diameter and sectional expansion index (SEI) of 5MEP (11.9 mm and 10.0 mm2, respectively) were greater (P< 0.05) than SBM (11.0 mm and 7.6 mm2, respectively), 10 MEP (11.4 mm and 8.6 mm2, respectively) and 15MEP (11.5 mm and 8.9 mm2, respectively). While thickness of 5MEP was thinner (P< 0.05) than SBM, 10MEP and 15MEP (5.73 vs average 6.20 mm, respectively). Bulk density was greater (P< 0.05) for SBM than 5MEP (408.7 vs 374.0 kg/m-3, respectively), while10MEP and 15MEP (388.8 and 392.7 kg/m-3, respectively) were similar to both extremes. 

Addition of MEP in extruded dog diets improved expansion and reduced energy requirement, but the benefits may be less at greater inclusion levels.