Microbiology and Biotechnology Research: An Overview Vol. 9

Global fish processing generates enormous volumes of by-products, including heads, viscera, skin, bones, scales and trimmings, that historically have been discarded or reduced to low-value fishmeal despite constituting a rich reservoir of catalytically active proteins. This review critically synthesises recent literature on the recovery, biochemical characterisation and commercial exploitation of enzymes derived from fish-processing residues, with particular attention to proteases, lipases, chitinolytic enzymes and collagen-modifying biocatalysts. The composition and enzymatic potential of major by-product fractions are examined alongside conventional and emerging recovery strategies, ranging from salting-out and chromatographic purification to aqueous two-phase partitioning and membrane-based fractionation. Particular emphasis is placed on the cold-adapted kinetic and structural properties that distinguish fish-derived enzymes from their mammalian and microbial counterparts, and on how these properties translate into practical advantages for low-temperature food processing, detergent formulation, leather manufacture and nutraceutical peptide production. The review further considers the use of fish by-products as low-cost fermentation substrates for microbial enzyme production and evaluates techno-economic and environmental assessments of enzymatic valorisation relative to chemical alternatives. Across the literature examined, enzymatic bioconversion consistently emerges as a milder, more selective and more sustainable route to recovering protein hydrolysates, collagen peptides, chitin derivatives and lipid fractions than acid or alkaline hydrolysis, although industrial uptake remains constrained by raw-material variability, enzyme cost and regulatory heterogeneity. The review concludes by identifying priority research directions, summarising the principal contributions of the field, and outlining the methodological limitations inherent to a narrative synthesis of a rapidly evolving literature.