Beyond Protein Yield: Biochemical Constraints, Extraction Strategies, and Recovery of Proteins from Brown Macroalgae

Brown macroalgae are potential sources of proteinaceous ingredients for marine biorefineries, but extraction yield does not necessarily predict final recovery or product suitability. This critical narrative review examines three linked dimensions of processing: protein accessibility within algal biomass, retention across successive recovery operations, and requirements of the intended product. Primary studies show that substantial protein solubilization may be followed by much lower precipitation recovery and that pretreatments can affect solubilization, precipitation, and iodine content differently. Interactions with alginates and phlorotannins are plausible contributors to recovery losses, although their quantitative effects remain insufficiently established. Reported “protein yields” also represent different analytical endpoints, including nitrogen, colorimetric protein equivalents, amino acids, dry-extract mass, and final-product recovery, frequently with incompatible denominators. We examine these distinctions across extraction technologies, downstream separations, integrated biorefineries, and peptide production. Protein-enriched solids, soluble concentrates, mixed ingredients, and peptide precursors have distinct recovery targets. A product-defined framework is proposed to guide selection of recovery streams and evaluation of proteinaceous recovery, product composition, safety, functionality, and resource requirements. Progress requires compatible measurements across processing stages and experimental tests of whether improved release translates into greater recovery of suitable final products.