Impact of variability in protein content of sunflower meal on the extrusion process and physical quality of the extruded salmonid feed

This study aimed to characterize sunflower meal (SFM) with a protein content of ~370 g/kg per dry matter (SFM1) and its two high protein fractions obtained by air classification (SFM2 and SFM3 containing 430 and 490 g/kg of protein per dry matter, respectively) as aqua feed ingredient, based on their functional properties that are important for extrusion processing. A mixture design was applied, varying the levels of SFM1, SFM2 and SFM3 from 88.2 to 267.2 g/kg in dry feed mixes intended for trout. SFM1 presence in the diet caused higher flow resistance of the material in the extruder barrel, and thus higher energy consumption compared to extrusion of diets containing SFM2 and SFM3. SFM1 suppressed the product expansion but induced formation of hollow and brittle pellets with high oil absorption capacity. Increase in protein content of SFM led to more compact structure, resulting in increased hardness, durability, water stability, and decreased oil leakage. Besides better nutritional quality, air classified low fiber SFMs prevail over basic SFM also in terms of their functionality. Still, presence of high fiber SFM could improve physical attributes of pellets in terms of their oil absorption capacity, important characteristic for salmonid feeds. PRACTICAL APPLICATIONS: Identification of functional properties of a certain ingredient is an important task when evaluating a novel ingredient in fish feed industry. This study assessed functionality of dehulled high protein sunflower meals, obtained by air classification, in the aqua feed extrusion process. The inclusion of sunflower meal with protein content higher than 400 g/kg, at level up to 200 g/kg, increased rigidity, water stability and oil retention ability of pellets, while decreased input of mechanical energy during extrusion. The contemporary aqua feed industry is oriented toward low fishmeal/high plant‐based diets. In this respect the outcomes of this study indicate that dehulled sunflower meal could be used as an alternative protein source to fishmeal in aqua feed from technological standpoint with beneficial effects on process parameters and without impaired effects on pellet physical quality.