High lipid microalgae (Schizochytrium sp.) inclusion as a sustainable source of n-3 long-chain PUFA in fish feed-Effects on the extrusion process and physical pellet quality

The aim of this research was to investigate effects on the extrusion process and physical pellet quality of high lipid microalgae (HL-microalgae) inclusion level as a source of n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) in fish feed. The experiment was based on a 3-component mixture design on commercially relevant feed blends by varying the content of dried HL-microalgae Schizochytrium sp. meal, vital wheat gluten (WG), and soy protein concentrate (SPC). Mixture models with R2 in the range of 0.881-0.998 (P < 0.01) were established for specific mechanical energy (SME), feed melt viscosity and temperature behind die, expansion parameters, and pellet hardness and durability. The mixture components affected SME, melt viscosity and viscous heat dissipation with the highest values observed for SPC followed by WG, and lowest for HL-microalgae rich blends. Increase in viscous heat dissipation and feed melt temperature increased the steam flashing rate and consequently pellet expansion and fat adsorption capacity. Lowest pellet hardness and durability were found for blends high in HL-microalgae or SPC level due to incomplete cooking. HL-microalgae addition up to 132 g/kg DM in SPC rich blends gave favourable processing effects with respect to improved plasticisation and physical pellet quality. This study documents that HL-microalgae has a potential to be used as an alternative and sustainable source of n-3 LC-PUFA in aquaculture feeds without compromising physical pellet attributes.