Criteria for the Characterization of Seafood Byproducts to Allow Tracing Their Geographic Origin.

Marine byproducts generated from seafood processing represent valuable reservoirs of structurally and functionally distinct biomolecules, whose composition reflects species, habitat, and processing history. This systematic review identified which marine byproducts have been most extensively studied between 2020 and 2025, with emphasis on their composition, valorisation, and suitability for tracing their geographic origin. Following the PRISMA protocol, 6443 publications were initially retrieved, of which 96 peer-reviewed studies were included for data extraction and analysis. The five most frequently investigated byproducts-skin, bones, scales, shells, and roe-were identified as rich sources of proteins (collagen and gelatin), minerals (hydroxyapatite and calcium carbonate), polysaccharides (chitin), lipids (notably polyunsaturated fatty acids (PUFAs), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA)), and vitamin B12. Collagen properties, particularly imino acid content, hydroxylation degree, crosslinking density, and thermal stability, correlate more strongly with environmental temperature than taxonomy, supporting their potential as markers for tracing geographic origin. The mineral fractions, dominated by hydroxyapatite in bones and scales, or calcium carbonate in shells, provided complementary inorganic fingerprints based on calcium-to-phosphorus ratios, carbonate substitution, trace element composition, and thermal analyses. While the lipid profile alone could not completely discriminate fish roe, proteomic techniques, such as MALDI-TOF MS, make it possible to reliably identify species. Collectively, these byproducts offer complementary organic and inorganic markers that support integrated strategies that allow tracing their origin and fostering their sustainable valorisation, overcoming a key technical bottleneck for their use. However, their large-scale conversion into market-ready products remains limited by technical complexity, process variability, and cost-related constraints.