3D printability of engineered high internal phase Pickering emulsions for lipophilic bioactive delivery: rheology, stability and retention of β-carotene in zein-guar gum based colloidal networks.

This work introduces a zein-guar gum (ZNP-GG) food-grade stabilizing system for high internal phase Pickering emulsions (HIPPEs) designed for lipophilic bioactive encapsulation and 3D printing. Zein nanoparticles exhibited strong positive surface charge (+41.7 ± 2.8 mV), progressively neutralized through hydrogen bonding and hydrophobic association with guar gum, forming stable, non-covalent complexes with nearly neutral ζ-potential. Compared to emulsions stabilized solely by ZNPs, ZNP-GG complexes retained comparable emulsifying activity (≈16-17 m2/g) but showed markedly higher emulsifying stability due to steric and viscoelastic reinforcement from GG. HIPPEs (defined by an internal oil volume fraction (ϕint) > 0.74) fabricated using these complexes showed physical stability (TSI = 2.31) after 14 days of storage at ambient temperature and fine droplet size (∼17 μm), forming highly elastic, shear-thinning, and partially thixotropic networks suited for extrusion printing. Increasing GG concentration from 0.3% to 0.7% (w/v) enhanced structural rigidity, with hardness (110.8 g) and gumminess (86.4 g) rising significantly. The emulsions demonstrated environmental resistance to temperature (20-80 °C), ionic strength (0-500 mM NaCl), pH (2.00-10.00), and three freeze-thaw cycles. To demonstrate encapsulation potential, β-carotene was used as a model lipophilic compound, achieving 94-98% efficiency and 85% and 68% retention after 14 days at 5 °C and 20 °C, respectively. All formulations achieved printing accuracies above 97%, maintaining geometry for over 24 h. This study establishes ZNP-GG HIPPEs as a clean-label, 3D-printable biocolloidal platform bridging interfacial engineering and digital food design for advanced nutraceutical delivery.