Simple Technologies for Converting Rest Raw Materials of Atlantic Salmon (Salmo salar) into High-Quality,Valuable, and Tasty Feed Ingredients

Rest raw materials as viscera, heads, and frames from farmed Atlantic salmon (Salmo salar) were hydrolyzed with the use of endogenous enzymes and the commercial enzymes Protamex and a mixture of Papain and Bromelain. Composition of the prehydrolysis mixture clearly influenced the quality of final hydrolysate and process kinetics. An increased proportion of viscera increased the amount of endogenous enzymes, which influenced hydrolysis kinetics, the extent of hydrolysis, and increased bitterness. Commercial enzymes, in addition to endogenous enzymes, are not always more yield efficient or economically beneficial but can be used to improve the taste and to ease the separation of oil from the hydrolysate fraction. Hydrolysis of denatured proteins in rest raw materials was hardly detectable. Optimum temperature should therefore be selected to avoid protein denaturation and simultaneously maintain high enzymatic activity. Hydrolysates preferably contain a low concentration of oil, and this work shows that high-quality oil can be separated before hydrolysis by mild thermal treatment. The previous separation of oil did not influence hydrolysate yield and decreased the concentration of lipids in the final hydrolysate. The initial separation of oil also increased productivity of the hydrolysis reactor, due to the reduction of hydrolysis volume.