Cryoextrusion in technology of fish feed production

The process of grinding the frozen fish raw materials using the useful model of a piston-type extruder with cooled working bodies has been investigated. A new feed product – cryo minced fish feed – has been obtained. The possibility of replacing the standard manufacturing operations of the defrosting and subsequent grinding of raw materials by one operation of cryoextrusion has been justified. Planning of the experimental part has been performed by the method of combination squares. During the experiment, the volume of samples, their specific surface area, mass, initial and final temperatures of the working chamber, the temperature of raw materials, the temperature of the resulting minced meat, the pressure force, the time of the experiment, the mass of waste have been determined. The rational shape and size of the die holes for the extrusion of raw materials have been determined. It has been found that when using a nozzle with the "hourglass" shape of holes with a diameter of 4.5 mm and 7 mm, the duration of the extrusion process for the studied fish species is 47 to 130 s. The finished product – cryo minced fish feed – has a fairly homogeneous structure and juicy texture, the temperature in the thickness of the product is equal to the temperature of the raw material before its processing (–18 °C). The granulometric composition of the cryo minced fish feed using the sieve analysis has been determined. The statistical processing of the results of experiments to determine the pressure of frozen fish raw material by the method of nonlinear regression has been carried out using the program DataFit version 9.1.32. The regression equation describing the influence of the complex parameter – the coefficient of the hole shape, taking into account the diameter and shape of the matrix hole, and the degree of grinding of raw materials on the force of extrusion has been obtained. The expediency of using the matrix "hourglass" which allows to obtain the lowest pressure force for bony fish of the North Sea basin has been proved.