Impact of physiochemical properties of protein ingredients on pellet quality and microstructure

Abstract

The objective of this study was to evaluate the effect of different protein ingredients on the physical quality of extruded pellets. Five experimental diets were based on five formulations using fish meal (FM), poultry by-product meal (PBM), and three novel protein ingredients, yellow mealworm (YM), Clostridium ethanolic protein (CAP), and Chlorella variabilis (high protein strain, CV), mixed with wheat flour in a 7:3 ratio. The results showed that the CAP had the highest content of water absorption index and the lowest value of crude lipid. The pellets containing CAP had the lowest water solubility while having the highest expansion ratio. The CV had the highest values of crude lipid and pasting properties (peak viscosity and final viscosity). The feed containing CV had the highest hydration time. The PBM had the highest content of crude lipid and produced pellets with the lowest expansion ratio and floatability. The FM and YM had similar physiochemical properties and the qualities of pellets containing both were also similar. The extruded pellets produced with CAP had the highest pore area and porosity, while extruded pellets containing PBM had a smallest pore area and porosity. Furthermore, the pore area and porosity of extruded pellets containing CV were significantly lower than that of the CAP, FM, and YM groups, and had thicker pore wall structures (P < 0.05). Overall, the comprehensive physical quality score of the extruded pellets, feed containing CAP ranked first, followed by feed formulated with FM, YM, and CV, while PBM ranked last.