Aquafeed extrusion (review)

Extrusion is one of the most important technological operations in aquafeed production. Indeed, the digestibility of feed nutrients considerably increases as a result of extrusion. The review deals with the issues of vegetable and animal raw materials processing for aquafeed production through extrusion. The analysis of scientific publications discussing the monitoring subject showed that extrusion of multicomponent mixtures (compound feed) had been studied insufficiently. Research objectives were to generalize and analyze English-language scientific publications containing information on the technologies of compound fish feed extrusion, to clarify the information on the rational parameters of their implementation and the effects on the properties of finished extruded feed. Search, selection, as well as systematic review of highly cited English-language scientific articles on the research subject for the period 2000–2020, were carried out. In the course of the analysis of literary sources, it was detected that the properties of the finished extruded feed were mostly affected by the extrusion temperature, raw material moisture and screw speed. The regularities of changes in the properties of ready-extruded feed granules, as a result of changes in extrusion parameters, have been determined. The results of the analyzed scientific articles made it possible to establish the peculiarities of the extrusion of compound feed for aquaculture based on plant raw materials, in particular starch. We defined the regularities of compound fish feed extrusion containing raw materials with a considerable amount of protein of animal origin, in particular its new type: insects’ biomass. This new type of protein-containing raw materials of animal origin can successfully replace expensive fish meal in the fish feed composition. The essential factor, limiting the application of animal raw materials in fish feed, in particular insects, is its moisture, which should not exceed 30% so that the extrusion process was fully effective. Reducing the feed mixture moisture is possible when combining various types of animal and plant raw materials with high and low moisture. This will ensure the acceptable moisture of the mixture and get the high-quality extruded feed. Aquafeed extrusion is a promising trend. However, it requires additional research to determine the parameters of the extrusion process common to all types of both plant and animal raw materials and their mixtures.