An improved physical understanding of the production of extruded fish feed will enable an optimized raw material utilization

Metal or plastic pipes, snackfoods and animal feeds are all products which are possible to manufacture by extrusion. The increased popularity of extruders over the years can be explained by their versatility and productivity (Riaz, 2000; Guy, 2001; Hydraulicsonline.co.uk, 2012). Also, the ability to sell voluminous air- interlarded breakfast products and the low processing costs of the extrudates are properties of interest in terms of marketing and finance (Chessari & Sellahewa, 2001; Guy, 2001). Extruders are characterized by their continuous nature, making it theoretically possible to fabricate infinite solids. However, the production will practically be limited by lack of raw materials or incomplete knowledge of how to adjust the input variables. Even though extrusion is a multivariate phenomenon and the understanding of the interactions between the raw materials, the processing within the barrel of the extruder, and the extrudate have been developed during the recent years, the models are often build on empirical data and confined to specific set-ups (Riaz, 2000; Guy, 2001; Cheng & Friis, 2010). The recipe for fish feed is complex, and the raw materials vary with season and market prices. Changing one ingredient is known to influence important characteristics of the final extrudate (Moraru & Kokini, 2003). Besides the nutritional value of the feed, its physical properties are important as well: An unintended size of the extruded and pelletized feed is known to adversely affect the growth of the fish (Ljungqvist et al., 2011), and uncontrolled feed densities influence its willingness to sink and the amount of lipid possible to add through coating (Kraugerud et al., 2011). Company relevance: Controlling the extrusion process makes intended adjustments of input variables possible. From previous work and the master’s thesis work performed by the candidate in corporation with BioMar A/S, the parameters and mechanisms of importance for description of extrusions are well-known. However, to control and optimize extrusion processes, an understanding and measuring of the involved physical mechanisms and their interplay are crucial. Company relevance: Optimized extrusion processes ensure better utilization of raw materials. Some salmonid species show problems when pellets are dissolve quickly in their stomach and release nutrients in the stomach cavity where muscle activity can force this soup out of the mouth again which is today known as fat belching because the fat part will float to the surface and be very visual. Other salmonid species have the opposite problem where the pellets are difficult to dissolve resulting in malabsorption and poor feed performance. Understanding the underlying physicochemical processes inducing the different degrees of pellet dissolving ensures optimized feed performance. Company relevance: Enhanced pellet quality and feed performance are clear competitive advantages. • References Cheng, H. & A. Friis (2010): Modelling extrudate expansion in a twin-screw food extrusion cooking process through dimensional analysis methodology. Food and Bioproducts Processing. Vol. 88, pp. 188-194. Chessari, C.J. & J.N. Sellahewa (2001): Effective process control. I: R. Guy (ed.) (2001): Exstrusion cooking, Technologies and applications. Woodhead Publishing Limited, Abington Hall, England,  pp. 83-107. ISBN-13: 978-1-8-5573559-0. Guy, R. (2001): Introduction. I: R. Guy (ed.) (2001): Exstrusion cooking, Technologies and applications. Woodhead Publishing Limited, Abington Hall, England, pp. 1-2. ISBN-13: 978-1-8-5573559-0. Hydraulicsonline.co.uk (2012): Joseph Bramah [online]. Hydraulics Online Ltd. [quoted December 5, 2013]. Available on: http://www.hydraulicsonline.com/history-of-hydraulics Kraugerud, O.F., H.Y. Jørgensen & B. Svihus (2011): Physical properties of extruded fish feed with inclusion of different plant (legumes, oilseeds, or cereals) meals. Animal Feed Science and Technology. Vol. 163, pp. 244-254. Ljungqvist, M.G., M.E. Nielsen, B.K. Ersbøll & S. Frosch (2011): Image Analysis of Pellet Size for a Control System in Industrial Feed Production. PLoS One. Vol. 6(10), pp. e26492. Moraru, C.I. & J.L. Kokini (2003): Nucleation and Expansion During Extrusion and Microwave Heating of Cereal Foods. Comprehensive Reviews in Food Science and Food Safety. Vol. 2, pp. 147-165. Riaz, M.N. (2000): Introduction to Extruders and Their Principles. I: M.N. Riaz (ed.) (2000): Extruders in Food Applications. Technomic Publishing Company, Inc., Lancaster, Pennsylvania 17604, USA, pp. 1-23. ISBN-13: 978-1-5-6676779-8.