Change of organoleptic and physical characteristics of pikeperch skin during its processing in natural juices

Studies have been conducted on the effect of natural vegetable and fruit juices (pumpkin, tomato, apple) and their mixtures containing weak organic acids and used as a liquid medium for hydration of pre-treated walleye fish skin (Sander lucioperca) on the degree of its softening, which occurs as a result of hydration of collagen molecules of fish raw materials in the mixture with natural juices, accompanied by an increase in its mass and thickness). It was determined that the initial fish skin with a thickness of 0.18-1.00 mm at the end of the hydrolysis process had a thickness of 2.6-6.3 mm (apple juice), 2.12-4.01 mm (dried) and 0.69-2.08 mm (tomato), and the skin weight increased by 400, 257.5 and 230%, respectively. It was noted that, despite significant swelling (increase in volume), the skin retained its shape during the entire hydrolysis process (up to 30 days in tomato juice), which indicates a weak degree of hydrolysis of raw materials and preservation of the natural shape of the fish collagen molecule. It is shown that the hydrolyzed mixture is easily homogenized to obtain a homogeneous mass, which is a juice-containing hydrate of fish collagen (food additive). The dynamics of pH changes in various juices and their mixtures is presented depending on the duration of the hydrolysis process with fish skin, which depends on the type of juice used and has a general tendency to deoxidation of the resulting final product compared with the juice used. The values of peak loads for needle puncture and rupture of fish skin were determined, which showed a significant decrease in their hydrolysis process, compared with raw skin.