Multivariate modelling of extruded fish feed pellet quality
Physical quality of extruded fish feed has become more important due to the use of bulk transport and pneumatic feed delivery systems. The complexity of the extrusion process, and limitations in basic knowledge on protein properties and protein/starch-interaction, make it a demanding task to obtain consistent product quality based on different types of raw materials. Changes in feed mash properties might lead to large quantities of feed pellets that are not consistent with product specifications and give increased production costs due to reprocessing needs or customer complaints.
Fishmeal at high inclusion level is a critical protein ingredient with respect to aquafeed processing and has a significant impact on pellet physical quality. Fishmeal is produced by use of heat coagulation combined with a mechanical and thermal dewatering process.
Tor Andreas Samuelsen of Nofima Ingrediens and colleagues from epartment of Chemistry, University of Bergen, Norway, have studied the impact on pellet hardness and durability of commercial fishmeal parcels combined with low, medium and high water and steam input levels in the extrusion process. Commercial fish meal parcels with a large variation in chemical composition and physical properties were produced from high quality herring at three different fishmeal factories in Norway. The experimental feed mixtures were processed on a Wenger TX-52 extruder at three moisture levels. The fishmeal quality was assessed based on 18 quality parameters and prediction models for pellet hardness, specific mechanical energy (SME) and starch gelatinization established based on partial least squares regression (PLSR) modeling. The study documented the possibility to develop a model explaining pellet hardness based on chemical and physical properties of fish meal and steam/water level in the process. The work also demonstrated that fishmeal physicochemical properties and added moisture had a significant effect on the melt viscosity and thereby dissipation of mechanical energy in the extruder barrel.
The information can be used by the aquafeed industry to better understand and correct the observed variance in extrusion properties and pellet quality and to improve the product specifications used by fish meal producers and purchasers. Examples on how the knowledge can be used to solve problems in the extrusion process will be discussed at Aquafeed Horizons, May 3, 2011 in Cologne Germany.
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