Kraugerud and Svihus of the Norwegian University of Life Sciences studied the effects of online pre-treatment of plant ingredients on processing responses and physical properties in extruded fish feed.
A feed processing study was conducted to evaluate the influence of plant ingredient (soybean meal, rapeseed meal, field peas and faba beans), pre-treatment of the mash (water addition of 400 g/kg total moisture to the plant meal fraction of the mash for 45 min at 45 °C) and conditions applied during the extrusion process (screw speed of 325 or 225 rpm) on quality of fish feeds.
Pre-treatment of the plant ingredients increased the extrusion temperature and the steam pressure in the barrel and reduced the specific mechanical energy, resulting in a decrease in hardness in the diets subjected to the pre-treatment.
Pre-treatment of the feed also resulted in a decrease in bulk density that was lowest for the rapeseed meal diet.
There was an effect of plant ingredient on temperature in the extruder, but only in the third section, while no effect was observed on pressure.
Diets with field peas and faba beans resulted in increased pellet hardness.
Increased screw speed reduced both pellet hardness and bulk density.
The novel pre-treatment method can be implemented online in an extrusion line, if desired, for nutritional purposes. However for regular ingredients it does not affect physical quality.