Effect of Enzyme Type and Concentration on Fish Protein Hydrolysates from Gadus morhua Processing Waste

Fish processing waste is a secondary raw material that can be used as part of value-added product systems. Fish protein hydrolysates contain essential amino acids and biologically active peptides that can be included in food formulations. This article introduces an improved enzymatic hydrolysis technology for obtaining protein hydrolysates from secondary fish raw materials. The study featured Central-East Atlantic cod (Gadus morhua) and its processing waste, which included protein-containing backbones, muscle tissue, and fins. Five different enzymes (Pancreatin, Collagenase, Protozyme B, Alcalase 2.4 L FG, and Enzy-Mix U) were applied in a wide range of concentrations. The new technology involved one additional step to improve the sensory properties: protein hydrolysates were treated with an acetic acid solution. The alkaline dissolution stage was also optimized to increase the degree of protein solubility. The resulting hydrolysates underwent a chemical analysis and high-performance liquid chromatography. Other tests made it possible to reveal their amino acid composition and molecular weight distribution. The fish protein hydrolysates demonstrated a high protein content of 85–90% and a high amino acid ratio (110–190%) for virtually all essential amino acids. The product yield ranged from 22 to 55%. As the concentration increased from 1 to 8 g per 1 kg of raw material, the yield of protein hydrolysate and the degree of protein hydrolysis also increased. However, the amount of lowmolecular-weight peptides also grew, which spoilt the sensory profile (bitter taste, strong fishy smell). Only Protozyme proved suitable for the food industry: its concentration could be varied whereas the enzymolysis time could be shortened, if necessary. Pancreatin and Alcalase 2.4 L FG provided high-yield protein hydrolysates for microbiological use.