Researchers from the Serbian Institute of Food Technology, together with Skretting and Biomin, performed a study to characterize sunflower meal with a protein content of ~370 g/kg per dry matter and its two high-protein fractions (430 and 490 g/kg) as an aquafeed ingredient, based on their functional properties that are important for extrusion processing. A mixture design was applied, varying the levels of sunflower meal from 88.2 to 267.2 g/kg in dry trout feed mixes. 

Sunflower meal with low protein content caused higher flow resistance of the material in the extruder barrel, and thus higher energy consumption compared to extrusion of diets containing higher protein fractions. Moreover, low-protein sunflower meal suppressed the product expansion but induced the formation of hollow and brittle pellets with high oil absorption capacity. 

An increase in protein content of sunflower meal led to a more compact structure, resulting in increased hardness, durability, water stability and decreased oil leakage. Besides better nutritional quality, air-classified low fiber sunflower meals prevail over basic meals also in terms of their functionality. Still, the presence of high-fiber sunflower meal could improve the physical attributes of pellets in terms of their oil absorption capacity, an important characteristic for salmonid feeds.

Practical applications

The identification of functional properties of a certain ingredient is an important task when evaluating a novel ingredient in the fish feed industry. This study assessed the functionality of dehulled high protein sunflower meals, obtained by air classification, in the aquafeed 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 aquafeed 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 aquafeed from a technological standpoint with beneficial effects on process parameters and without impaired effects on pellet physical quality.

Check out the study here.