3D printable fat-mimetic emulsion gels structured by fish gelatin/fucoidan complex coacervates for tunable texture and oxidation resistance

The direct use of fish oil (FO) as a three-dimensional (3D) printing material is hindered by its poor aqueous dispersibility, rapid oxidation, and weak structural integrity. Although high internal phase Pickering emulsions partially address these issues, they rely on solid particles and have rarely been investigated for post-printing performance or multi-material 3D printing applications. We developed 3D printable, fat-mimetic emulsion gels by stabilizing FO with fish gelatin/fucoidan complex coacervates (COA). Polymer-rich liquid microdroplets formed via electrostatic complexation lowered interfacial tension more effectively than either component alone, owing to cooperative adsorption and enhanced penetration and rearrangement. COA-stabilized FO-based emulsion gels (COA–FO) accommodated FO contents exceeding 60 % (v/v) with ∼99.7 % encapsulation efficiencies, exhibiting pronounced shear thinning. Heating from 25 °C to 40 °C reduced the yield stress from 403 to 101 Pa and the consistency index ( K ) from 381 to 60 Pa·s n , enabling smooth extrusion through gelatin-driven thermal softening. Increasing the COA concentration from 25 to 75 mg/mL enhanced thixotropy recovery from 38.4 % to 96.0 %, ensuring structural recovery after shear. 3D-printed scaffolds achieved 86.9 % printing accuracy with minimal deformation and limited oil release, while showing ∼50 % lower lipid oxidation than free oil during 14 d of storage. In dual-nozzle printed tuna-slice analogs, the texture could be tuned by varying the oil content and thermal post-processing. This is the first demonstration of fish gelatin/fucoidan COAs as interfacial stabilizers for printable, oxidation-resistant fat-mimetic inks with thermally enhanced flowability. The post-printing outcomes and multi-material co-printing highlight a versatile platform for structuring non-printable oils and delivering bioactives. • Fish gelatin/fucoidan coacervation (COA) formed liquid microdroplets at pH 3.3. • COA emulsion gels with 60 % fish oil (COA–FO) had >99 % encapsulation efficiency. • COA–FO showed thermal softening and enhanced flowability at 40 °C for extrusion. • 3D-printed COA–FO reduced lipid hydroperoxides to ∼50 % of free oil after 14 d. • Texture of dual-nozzle-printed tuna analogs varied with FO content and pan-cooking.