Evaluation of different starch sources in extruded feed for Atlantic salmon

The aim of the experiment was to investigate the effect of partial or total substitution of wheat flour with oat meal and tapioca starch in extruded salmon feed. A mixture design (simplex centroid mixture design) was used to analyse the effect of starch source on physical quality of extruded feed. Physical quality of the extruded feed was evaluated as cohesiveness, pellet density, axial and radial expansion, durability, hardness, strain at rupture and elastic modulus. Starch sources affected behaviour of the diet formulations during extrusion and caused changes in the physical properties of the extruded products. Significant correlations (P < 0.05) between physical properties and weight fraction of the starch sources allowed the establishment of predictive models. The inclusion of oat meal and tapioca starch in the diet gave extruded feed with a higher porosity and lower oil absorption capacity. The mechanical properties of the extruded feeds were significantly different from each other, most likely due to the complex nature of texture formation with respect to process parameters and properties of ingredients.