Evaluation of whole soybean as an ingredient in extruded dog diets

Abstract

Soybean use in pet food is low due to undeserved negative perceptions among some marketers and consumers. However, soybean is an excellent ingredient beyond protein for its fat and dietary fiber contribution to dogs. Utilizing internal fat in whole soybeans (WSB) may increase the energy density of dog diets while avoiding production issues, and the oligosaccharides (OS) may perform as prebiotics. The objective of this research was to determine the effects of increasing levels of WSB in dry dog foods. This work elaborated theoretical and practical aspects of extrusion processing, nutrient digestibility, canine in vitro microbial fermentation, palatability, and consumer sensory analysis. Whole soybeans were beneficial at providing elevated fat levels (versus soybean oil) into the extruder without causing critical issues in processing and product stability. The increased inclusion level of WSB did decrease the mechanical energy within the extruder from the intrinsic fat content. In addition, the mechanical energy input did not completely destroy the anti-nutritional factors at increasing WSB levels. The nutrient apparent total tract digestibility in dogs remained high (over 80%), but at higher inclusion of WSB, there was a slight linear decrease which might be attributed to the dietary fibers and residual anti-nutritional factors. The stool quality and palatability were not affected by WSB up to 30% in the formulas in dogs. The WSB diets increased hind-gut fermentation (increased short-chain fatty acids and decreased fecal pH) in dogs, which can be useful in high-fiber diets for geriatric, lower calorie diets for less-active, or gastrointestinal health. The canine in vitro microbial fermentation model further supported the WSB prebiotic effect, wherein greater butyrate production was noted for WSB than for beet pulp due to the fermentation of both oligosaccharides and soluble fiber components in WSB. For overall sensory analysis, WSB could replace proportional levels of brewers' rice, corn gluten meal, and chicken fat for consumers. Subtle differences were noted in increased color and fracturability, and porosity, gritty, oily mouthcoating, and heated oil aftertaste decreased as the WSB inclusion level increased. Only a slight change in color liking was observed from the consumer study, with no effects on overall liking, appearance, size, shape, and aroma liking as the WSB levels increased. In addition, consumers still responded favorably to their dogs' liking scores for the WSB-containing diets. In conclusion, WSB inclusion of 10% in the diets appears to be the optimal level recommended when the diets were produced in the same condition as WSB 0% diet but were feasible in processing and feeding at levels up to 30%.