Changes in muscle tissue of fresh-frozen salmon, pollock, and hake during storage

The aim of the scientific research was the formation of the structure of semi-finished fish products during freezing and storage. In accordance with the research scheme, the objects were selected as samples of 10-15 fish of the following species: salmon, hake, pollock in a frozen and thawed state. The stiffness indices of muscle tissue of fresh-frozen fish, which were thawed after 2, 4, 5, 8, 10 and 20 hours of storage at -18 °C, were experimentally determined. The elastic modulus was studied for three physical states of fish, which were thawed to -1 °C; 10 °C and 20 °C and then stored for 2, 6 and 10 hours in a thawed state. It was established that repeated changes in the thermal state of muscle tissue (freezing and thawing) of fish leads to a decrease in muscle tissue stiffness. The structure becomes flabby and fibrous. This correlation is particularly evident in fish with significant muscle water content and reduced fat content. Pollock muscle tissue is more susceptible to degradation than salmon. The elastic modulus of salmon muscle tissue thawed and stored for 20 hours at 20°C decreased by 30%, while that of silver hake decreased by 37.8%, while pollock increased by 18.2%. Therefore, for the preparation of semi-finished products (fillets, slices), fish muscle tissue must be portioned while frozen.