The manufacturing of aquafeed through extrusion has been an attractive process due to the continuous nature of production, the scalability of equipment, and the tunability of processing conditions to achieve specific product properties. In addition, extrusion processing can handle a wide range of formulation matrices, which allows the extruded feed to be tailored to specific fish species and their feeding preferences, in addition to satisfying their nutritional requirements. However, a practical limitation currently exists with regard to understanding the mechanisms governing material transformation throughout the extrusion device, which leads to difficulty in innovating, predicting, and controlling product quality. A nascent body of literature is emerging in an attempt to address inefficiencies in aquafeed product development and process optimisation, yet significant challenges remain unexplored within the literature. This study investigates the current state-of-the-art in aquafeed extrusion via a literature review, outlining the type of studies performed, the typical characterisation metrics covered, an overview of the key results, and the challenges and opportunities remaining within the field.
In the first section, the study investigates the ingredient matrices used to generate feed products, including alternative protein sources (besides fishmeal) such as insect meals, plant proteins, and microalgae products, in addition to the effect that different ingredients have on pellet quality. The second section outlines the influence of various processing parameters (e.g. barrel temperature, moisture content, screw speed) on the extrusion response variables (e.g. specific mechanical energy) and extrudate physical properties. The third section presents the subsequent impact of extrudate physical properties (e.g. texture, density, solubility) on the performance of aquaculture research trials, including feed conversion/utilization, nutrient digestibility, and animal health. Lastly, the fourth section addresses key challenges facing feed extrusion in the aquaculture industry, such as feed availability and variability, animal health and nutrition, and economic feasibility, in addition to outlining opportunities for innovation and improvement, such as digital tools for quality control and by-product utilization. Overall, this review outlines the state-of-the-art in extrusion technology for producing high-quality aquafeed, while highlighting barriers and gaps to efficient and cost-effective aquafeed manufacturing.