Partial replacement of fish meal by cottonseed protein concentrate and the effects of preconditioning water content and die temperature on pellet physical quality of extruded floating fish feed

Abstract

A two-factorial central composite design was performed to investigate the effects of preconditioning water content (PCwater: 21, 22.5, 26, 29.5 or 31%) and die temperature (Dtemp: 115, 119.4, 130, 140.6 or 145 ℃) on the physical properties of extruded floating fish feed. This design was applied to two separate diet formulas to study the effect of cottonseed protein concentrate (CPC) inclusion (replacing 67% of fish meal-FM in the diet). A total of 26 batches of diets were prepared. Response surface methodology was used for regression and parameter optimization. Averaged over all PCwater and Dtemp combinations, CPC-pellets had a lower bulk density, oil leakage, higher expansion rate, oil absorption, hardness, pellet durability index and a longer hydration time than FM-pellets. A negative correlation between oil absorption and oil leakage was presented in the CPC-pellets but not in the FM-pellets. Moreover, the influence of PCwater on the PPQ was uniform across both formulas except for oil leakage. However, the effect of Dtemp on the PPQ differed between the formulas. For oil leakage, it was maximal at both the highest PCwater and Dtemp combination in the FM-pellets, while it was maximized at both the lowest PCwater and Dtemp combination in the CPC-pellets. Furthermore, exchanging fish meal with CPC improved the optimal processing conditions and enlarged the operating window to produce the desired feed. This reduces water and energy consumption in feed production.