Processing–Property Relationships in Fish Protein Hydrolysates: From Controlled Hydrolysis and Peptidomics to Sensory Performance and Translational Readiness

Fish processing generates protein-rich side streams representing 30–70% of whole-fish mass, creating potential for production of fish protein hydrolysates (FPHs). However, their translation into food or nutraceutical ingredients is limited by variable feedstocks, incomplete process reporting and an evidence base dominated by in vitro assays. This review examines how feedstock origin and pre-analytical quality, controlled enzymatic hydrolysis and downstream processing determine peptide composition and techno-functional, sensory and biological performance. It also evaluates peptidomic workflows and grades evidence from chemical assays through randomized human interventions. Across the reviewed literature, FPHs emerge as heterogeneous, lot-defined products rather than a uniform ingredient class. Maximum degree of hydrolysis is not a universally optimal endpoint: extensive proteolysis may improve solubility and assay responses while reducing protein recovery, interfacial functionality and sensory acceptability. Peptide numbers and candidate sequences depend on liquid chromatography–tandem mass spectrometry (LC–MS/MS) acquisition, database selection, search strategy and false-discovery control. In silico predictions therefore require confirmation with synthetic standards, targeted quantification in the hydrolysate and evaluation of gastrointestinal stability and intestinal transport. Human findings remain limited and inconsistent, precluding class-wide health claims. Translation is further constrained by matrix-dependent acceptable doses and product-specific risks related to contaminants, biogenic amines, microbial and oxidative stability, residual protease activity and allergens. This review proposes minimum reporting requirements and an application-driven translational readiness framework linking feedstock qualification, reproducible processing, molecular identity, biological exposure, matrix compatibility, safety, pilot-scale manufacture and human validation. This approach is required to develop standardized FPHs that deliver prespecified benefits at safe, consumer-acceptable doses while remaining economically and environmentally feasible.