Technical Papers and Presentations

Three-dimensional (3D) printing has emerged as a promising technology to produce customized foods tailored to individual sensory preferences and nutritional requirements. Gelled emulsions are particularly attractive as food bioinks due to their soft solid structure and rheological properties. However, the extrusion process subjects the material to high deformation, potentially altering its structure and viscous behavior. In this context, Computational Fluid Dynamics (CFD) is a valuable tool for investigating how processing parameters affect velocity distribution, local shear rates, and extrusion pressure requirements. Nevertheless, modeling these systems remains challenging due to the non-Newtonian nature of food materials and the effects of wall friction and lubrication. In this study, gelled emulsions stabilized with pea protein (20% w/w w.b.) and guar gum (0–1% w/w w.b.) were produced with fixed sunflower oil content (10% w/w w.b.). Rheological properties were evaluated under Small Amplitude Oscillatory Shear and steady shear flow conditions (MCR 702, Anton Paar, Austria). The emulsions were 3D printed using a Foodini food printer (Natural Machines, Spain) at syringe plunger velocities ranging from 0.01 to 0.1 mm/s, while the force applied to the syringe plunger was measured using a texture analyser (TA.HD.Plus, Stable Micro Systems, UK). A finite element mathematical model was developed in COMSOL Multiphysics 5.3a using the PARDISO solver to investigate the extrusion behavior of the materials. A mesh sensitivity analysis was performed to determine the appropriate mesh refinement level. Due to the low extrusion velocities and high viscosities, the flow was modeled as laminar, steady-state, and incompressible, with no-slip boundary conditions and zero pressure at the nozzle outlet. Experimental and simulated pressure values were compared for model validation. Additionally, glycerol was evaluated as a model Newtonian fluid to improve process understanding. Guar gum incorporation increased the consistency coefficient (from 224 to 255 kg/m s) and elastic modulus (from 2432 Pa to 6395 Pa). However, the gum-containing emulsions showed greater structural breakdown under deformation, with larger hysteresis loops and lower structural recovery. Although guar gum increased viscosity, the lower recovery contributed to a higher frequency of printing defects under the same processing conditions. Increasing extrusion velocity increased the pressure applied to the syringe plunger, from 1×10⁴ to 1.8×10⁴ Pa and from 1.5×10⁴ to 2.3×10⁴ Pa for emulsions without and with guar gum, respectively. CFD simulations predicted pressures within the same order of magnitude, ranging from 1×10⁴ to 1.2×10⁴ Pa and from 2.5×10⁴ to 2.7×10⁴ Pa for emulsions without and with guar gum, respectively. For glycerol (0.6 Pa s), the model predicted standard velocity and shear rate profiles, with pressure drops ranging from 2×10³ to 3.8×10³ Pa, whereas experimental values ranged from 1.2×10³ to 1.5×10³ Pa. Although differences between experimental and simulated values were observed, the model successfully captured the order of magnitude and the trends associated with changes in formulation and extrusion velocity. Overall, the CFD model demonstrated good predictive capability for the flow behavior of gelled emulsions during 3D printing. As future work, the effect of friction in the walls will be measured by tribology and considered in simulation.