Thermal and rheological properties of protein feed ingredients- Impact on the fish feed extrusion process and pellet quality

For sustainable and cost effective aquaculture production, fishmeal levels have been reduced and several new plant protein sources have been introduced in feed formulation. The new recipes based on plant proteins have increased the complexity in the extrusion process. The scale of the salmon production have also resulted in use of bulk transport and highly automated feed deliveries to the cages which have resulted in much more impact on the feed pellet and thereby focus on the physical quality of the feed. Production of high-energy fish feed based on plant proteins ingredients demands high moisture and thermomechanical energy for homogeneous transformation, in addition to high starch contents for network formation and expansion parameters. The use of high moisture increases the energy consumption during drying process and consequently high drying cost and environmental impact. The plant proteins concentrates are derived after initial processing which alters the physicochemical properties and water absorption kinetics of different as well as similar types of proteins. The results are that the thermal and rheological behaviour or the ingredients are changed and should be explored at wide range of moisture contents in order to determine the required properties. The main objective of the project was to determine the physicochemical, thermal and rheological properties of various feed protein ingredients used in salmon feed formulation with impact on extrusion process conditions and end product physical properties. This work has provided new understanding of the chemical, thermal and rheological properties of various fish feed ingredients with the impact on melt transition behaviour and final physical extrudate quality. The work has documented that different plant proteins need different moisture and temperature for homogeneous plasticisation. Critical moisture levels with increased effect of temperature on the viscosity reduction in the rubbery phase are defined. The experimental work has also provided new analytical and experimental tools to examine feed ingredients which can be used by the feed manufacturing industry to better understand how to impact and control physical pellet quality.

Title: Thermal and rheological properties of protein feed ingredients - Impact on the fish feed extrusion process and pellet quality (TPEX) The supply and cost of feed ingredients of marine origin are becoming a key limiting factor for the production of salmonid fish. The fishmeal level has been reduced and exchanged with several new vegetable protein sources. This development has increased the complexity of the extrusion process and given new challenges in the manufacture of a consistent physical pellet quality. The project aims to quantify effects of protein thermal and rheological properties on the fish feed manufacturing process (extrusion cooking) and physical pellet quality. The fish feed process is a complex multivariate system involving both phy sical and chemical variables. To understand the interaction between these variables and their impact on the final pellet quality demands development of new knowledge on how the feed ingredients is transformed in the extrusion process and how they interact in the extrusion process and in the final expanded pellet product. Our approach will be to combine physical and chemical analyses with thermal and rheological measurements both on the individual protein ingredients and the final feed pellet. The research tasks will give challenges on selection of analytical tools, method development, interpretation and application of the results. Improved understanding of the effect of protein ingredient physicochemical properties on the extrusion cooking process and ph ysical pellet properties will enable the feed producers to improve their processing control and product quality. This will be of importance in the development of new cost effective diets for salmonids and improve our flexibility in the use of alternative protein raw materials.