Impact of High-Pressure Pretreatment on the Structure and Quality of Fish Protein Hydrolysates Extracted from a Mixture of Atlantic Salmon (Salmo salar) and Rainbow Trout (Oncorhynchus mykiss) Rest Raw Material

Abstract Fish protein hydrolysates (FPH), produced via enzymatic hydrolysis, possess functional properties making them suitable for incorporation into functional foods. However, the compact structure of native fish proteins can limit hydrolysis efficiency. To address this, non-thermal technologies, such as high-pressure processing (HPP), may enhance hydrolysis by modifying protein structure. This study investigated the impact of HPP at different pressure–time conditions, applied prior to enzymatic hydrolysis in a mixture of Atlantic salmon ( Salmo salar ) and rainbow trout ( Oncorhynchus mykiss ) rest raw material, on the obtained FPH. HP-induced structural alterations in the peptides were assessed using circular dichroism spectroscopy and intrinsic fluorescence. Over an 8-week storage period, oxidative stability, color, and water-soluble protein content were evaluated, alongside oil-binding capacity, pH solubility, and amino acid composition. The FPH from the sample pretreated at 600 MPa × 8 min exhibited the highest content of water-soluble proteins at the beginning of the storage period (99%), compared to the FPH from the control (91%). However, this content significantly declined by the end of storage across all samples. HPP also improved the lightness ( L* ) of FPH, with the FPH from the 600 MPa × 8 min sample reaching a value of 88.5, compared to 86.3 in the control FPH, with lightness remaining stable during storage. However, oxidative changes were more pronounced in samples pretreated at higher pressures (600 MPa). Oil-binding capacity showed no significant differences between pretreatments, and amino acid profiles remained consistent, indicating preservation of the nutritional quality of the FPH.