Rheological, Mechanical, and Structural Properties of Thermo-Reversible Gelatine Hydrogels Incorporating Unrefined Beeswax-Structured Oil-in-Water Emulsions for Additive Manufacturing

This study reports on the design and characterisation of thermo-reversible gelatine hydrogels incorporating beeswax-structured oil-in-water emulsions as novel 3D-printable food inks. Beeswax oil-in-gel emulsions (BOGEs) were prepared by varying the sunflower oil to beeswax (SFO:BW) mass fraction (1:0, 3:1, 1:1, 1:3 and 0:1) at a fixed lipid loading (10% wt.) within a 4% wt. gelatine matrix. The BOGEs were evaluated in terms of microstructure, thermophysical properties, small and large amplitude oscillatory shear rheological behaviour, instrumental hardness, and 3D printability. CLSM images revealed a progressive transition from an emulsion-filled to a bigel-like microstructure with increasing beeswax content, driven by partial crystallisation and percolation of lipid droplets. Differential scanning calorimetry confirmed that beeswax incorporation progressively suppressed the gelatine hydrogel fusion enthalpy, indicating that wax crystal lattices govern the supramolecular organisation of the gelatine network. SAOS tests showed that BW enhanced the elastic modulus, with a critical solid fat content threshold (Φc = 0.294) above which lipid droplet percolation provided an additional structural reinforcement. LAOS characterisation revealed a type III nonlinear viscoelastic response, with delayed yielding and enhanced structural integrity at higher BW fractions. Instrumental hardness measurements confirmed the active filler role of BW at mass fractions ≥0.5. 3D printing assessment demonstrated that intermediate SFO:BW ratios (3:1 and 1:1) afforded the highest printing fidelity, combining favourable extrusion flow with adequate post-deposition shape retention. Overall, the results demonstrate that beeswax-structured emulsions can effectively tailor the structure–function properties of gelatine hydrogels, enabling the development of clean-label, multiphase food inks suitable for extrusion-based 3D printing applications.