The motivation is pressing. A rapidly aging global population, together with growing numbers of people living with dysphagia — difficulty swallowing — has created urgent demand for foods that are simultaneously safe, nutritious, and appealing. Such foods must meet strict texture standards to reduce the risk of aspiration, yet they also need to carry meaningful nutrition, particularly lipophilic bioactive compounds, to counter the malnutrition that often accompanies chewing and swallowing disorders. Traditional thickening systems built on starches or hydrocolloids fall short: they struggle to deliver high nutrient density, they cannot structure healthy lipids efficiently, and they tend to break down or separate during long storage.

The team’s starting point was a protein-based Pickering emulsion, a class of systems in which solid particles — rather than synthetic surfactants — adsorb at the oil–water interface and form a protective shell around droplets. The researchers built their interface from ovalbumin, the main protein of egg white, working together with tea polyphenols and hyaluronic acid. Ovalbumin’s amphiphilic character lets it anchor at the interface and form a film, tea polyphenols reinforce the particles through hydrogen bonding and hydrophobic interactions while adding antioxidant capacity, and hyaluronic acid thickens the interfacial layer. When the oil fraction is pushed above 74 percent, the result is a high internal phase emulsion, or HIPE: a material so packed with droplets that it behaves like a soft solid, self-supporting and stable, ideal for loading fat-soluble nutrients.

But stability alone was not enough. A HIPE’s solid-like rheology, the very property that makes it stable, also makes it difficult to process by conventional filling and molding, and even harder to shape with the precision that modern personalized nutrition demands. Enter 3D printing. Extrusion-based food printing promises digital control over both geometry and internal microstructure, which in turn governs how a food breaks apart in the mouth and how nutrients are released. The catch is that a good printing ink must be a rheological paradox: thin and flowing under the high shear of the nozzle, yet instantly stiff and self-supporting the moment extrusion stops.

To resolve that paradox, the researchers turned to the mud–sand analogy. Undissolved gellan gum particles, added at 0.3 percent, played the role of sand: rigid fillers that embed in the droplet network, anchor it physically, and boost mechanical strength. Xanthan gum, tested at 0.2, 0.6, and 1 percent, played the role of mud: its long molecular chains weave a continuous viscoelastic network through the aqueous phase, thickening the system, imparting the shear-thinning behavior needed for smooth extrusion, and reconnecting the gellan particles into a coherent whole. The base formulation — 25 percent composite aqueous phase and 75 percent soybean oil — was homogenized at 12,000 rpm to produce emulsions containing 75 percent oil, well into high internal phase territory.

Spectroscopic and scattering analyses confirmed that the additions were gentle on the protein. Fourier-transform infrared spectra showed that the amide bands of ovalbumin, near 1635 and 1534 per centimeter, remained essentially unchanged across all formulations, meaning the protein’s conformation was barely disturbed. X-ray diffraction revealed a broadly amorphous structure, with xanthan gum actually suppressing the local crystallization of tea polyphenols at higher concentrations, yielding a more uniform composite. Zeta potential measurements told a subtler story: adding gellan gum diluted the system’s net negative charge from about −32 to −26 millivolts, yet the steric hindrance and physical network of the undissolved particles more than compensated, and xanthan gum restored the potential to roughly −35 millivolts at the optimal dose.

Microscopy and stability testing made the synergy vivid. Confocal laser scanning images of the control emulsion showed heterogeneous, flocculated droplets with clear signs of coalescence — the thin interfacial film simply could not withstand the capillary pressures inside a HIPE. Gellan gum alone produced a bipolar droplet distribution, but the combination of gellan and xanthan gum produced small, evenly dispersed droplets locked inside a dense gel matrix. Under centrifugation, the control lost nearly 13 percent of its oil; the best dual-polysaccharide formulation lost none. After 30 days of refrigerated storage, every emulsion remained free of visible phase separation, and heat treatment at 85 degrees Celsius actually strengthened most of the modified systems, as denatured protein formed tougher interfacial films and hydrated gellan molecules tightened the gel network.

The rheological measurements revealed exactly why the material prints so well. All samples showed pronounced shear-thinning, and the storage modulus exceeded the loss modulus throughout, confirming solid-like behavior. As xanthan gum concentration rose, the storage modulus climbed from about 1049 pascals in the control to more than 2500 pascals, while the loss tangent fell — hallmarks of a stronger, more elastic gel. Critically, three-interval thixotropy tests showed that the xanthan-rich formulations recovered roughly 85 percent of their structure after 300 seconds of high shear, thanks to flexible xanthan chains that rapidly re-entangle and bridge the disrupted gellan particles. Yield points shifted to strains above 50 percent, meaning the ink resists deformation during handling yet flows cleanly through the nozzle.

Printing trials put those numbers to the test. The control emulsion exceeded its target dimensions by up to 110 percent, with broken filaments, blurred contours, and collapsed cylinders. Adding gellan gum helped, but deviations still reached 45 percent. The dual-polysaccharide inks, by contrast, achieved near-zero deviation — within a ±3 percent tolerance — producing cylinders and cuboids with crisp edges, uniform layers, and robust interlayer adhesion. The optimal formulation, 0.3 percent gellan gum with 0.6 percent xanthan gum, also proved the most resilient: it survived freeze–thaw cycling better than the 1 percent xanthan version, whose overly rigid network was punctured by growing ice crystals, and it showed the mildest oxidation during a week of storage at −4 degrees Celsius.

Perhaps most importantly for its intended users, the printed foods passed the international standard for dysphagia diets. In fork pressure and spoon tilt tests aligned with the IDDSI framework, the samples deformed under roughly 17 kilopascals — comparable to the force of the tongue during swallowing — broke into small, safe pieces with no large lumps, and held their shape on a tilted spoon, placing them at Levels 6 to 7, soft and bite-sized to easy-to-chew. After steam treatment, the printed constructs retained their form, held water well, and showed a tender texture with reduced adhesiveness, lowering choking risk. The mud–sand design, the authors conclude, offers a generalizable strategy for turning protein-based HIPEs into precision food inks — a step toward printed meals that are simultaneously beautiful, stable, nutrient-dense, and safe for those who need them most.

Subject of Research: Polysaccharide-reinforced protein-based high internal phase emulsions for 3D-printed dysphagia foods

Article Title: “Mud-Sand Structure”-Inspired Synergistic Reinforcement of Gellan Gum and Xanthan Gum on the 3D Printing Properties of Protein-Based High Internal Phase Emulsions

Article References: Xie, Y., He, C., Yu, X., Ma, J., Zhao, E., Liu, M., Zhang, H., Yuan, J., Zhou, Y., Zhu, Q., Cheng, Y., & Liu, Y. (2026). “Mud-Sand Structure”-Inspired Synergistic Reinforcement of Gellan Gum and Xanthan Gum on the 3D Printing Properties of Protein-Based High Internal Phase Emulsions. Current Research in Food Science, Article 101579. https://doi.org/10.1016/j.crfs.2026.101579

Image Credits: AI Generated

DOI: 10.1016/j.crfs.2026.101579

Keywords: 3D food printing, high internal phase emulsion, Pickering emulsion, gellan gum, xanthan gum, ovalbumin, dysphagia, rheology, food ink, IDDSI, tea polyphenols, hyaluronic acid

The central insight running through the collection is that foods rarely sit comfortably on either side of the fluid-solid divide. Instead, they travel continuously through liquid-like, viscoelastic, plastic and solid-like regimes as their internal microstructure evolves. In some materials, a network is born through gelation or crystallization; in others, molecular mobility is frozen out by cooling or a glass transition. In yield-stress materials such as pastes, flow destroys a pre-existing structure that then rebuilds. During drying, cooking and frying, changes in moisture content can simultaneously alter mechanical properties and generate internal stresses and deformation. This continuous, mechanism-dependent journey between states is precisely why food structuring has historically been treated empirically, with process-property relationships assembled through trial and error rather than derived from first principles.

A major theme of the Special Issue is the tight coupling between transport processes, changing material properties and mechanical deformation, particularly during drying. Hu and colleagues present a multiphase, multiscale mechanistic model for hot-air drying of shiitake mushroom, capturing how water removal reshapes the material while it shrinks and stresses. Veser and co-workers predict cabbage-seed drying at laboratory and industrial scales using a non-equilibrium sorption-isotherm approach, while Rizki and colleagues track material-property changes during electrohydrodynamic drying with a close look at the falling-rate period, the stage where moisture loss slows and the material stiffens most dramatically. Shah and Takhar push the coupling even further in microwave frying, combining unsaturated transport based on hybrid mixture theory with electromagnetic equations. Together, these studies make a forceful case that heat and mass transfer cannot be modeled independently of the evolving physical state of the food.

Deformation itself can become a tool rather than a nuisance, and several contributions exploit this deliberately. van der Sman, Curatolo and Teresi investigated buckling during the drying of edible soft matter with a cylindrical core-shell geometry, showing how drying-induced mechanical instabilities generate intricate, predictable deformation patterns. In a companion study, the same team demonstrated programmable shape morphing during drying through symmetry breaking, effectively using moisture gradients to sculpt foods into designed shapes rather than accepting warping as a processing defect. Grasa, Teresi and van der Sman extended the coupled transport-mechanics framework to large-strain anisotropic behavior of meat during cooking using finite-element modeling. These works signal a shift in the field: instead of treating shrinkage, curling and buckling as quality problems to suppress, researchers are beginning to engineer them for structure design.

Underlying this shift is a broader theoretical realignment. Food rheology has traditionally concentrated on materials in their flowing state, while the mechanics of foods undergoing large deformations in a more solid-like condition received comparatively little attention. Meanwhile, advances in soft-matter mechanics and poromechanics now allow deformation, viscoelasticity and moisture transport to be described within thermodynamically consistent frameworks. A particularly striking conceptual bridge is the mathematical correspondence between the configuration tensor used in advanced rheological models and the Cauchy-Green tensor used in large-deformation mechanics. This equivalence offers a common language for materials that alternate between flowing and solid-like states, and its implications for elasto-viscoplastic food materials and stress-driven moisture migration are explored in a recent review by van der Sman in Current Opinion in Food Science. The practical consequence could be a new generation of models that predict, rather than merely reproduce, how foods behave through their whole processing journey.

At the opposite end of the fluid-solid transition lie processes in which a material must first flow in a controlled manner and then preserve its generated shape, and nowhere is this clearer than in three-dimensional food printing. Kim and colleagues examined the printability and structural properties of plant-based scallop adductor-muscle analogues, relating performance to amylose content and the pasting behavior of different rice cultivars. Liu and co-workers studied edible three-dimensionally printed emulsion gels, showing how inulin incorporation modifies both mechanical and sensory properties. Both studies converge on a key conclusion: printability is not simply a question of viscosity. A printable food must respond appropriately during extrusion, then recover or develop enough structural integrity after deposition to hold its printed geometry, a dual requirement that demands careful control across the entire fluid-solid spectrum.

The mechanisms by which foods acquire that structural integrity vary enormously across systems, and the Special Issue maps this diversity down to the molecular scale. Renzetti and colleagues investigated cereal and tuber starches, identifying hydrogen-bond density and glass-transition temperature as governing factors in gelatinization and gel rheology, thereby linking molecular interactions and thermal transitions directly to macroscopic mechanical behavior. On a different front, Holian, Bolton and Wilson explored how structure can be generated in soft solids to produce heat-stable milk chocolate, a formulation challenge that hinges on managing the solid-fat network so the product survives warming without collapsing. Both studies underscore that transitions between fluid-like and solid-like response ultimately originate at smaller length scales, from molecular mobility and intermolecular interactions up to the formation of mesoscopic networks that carry load.

Structured lipid systems offer further illustration of the same soft-matter principle. Shuai and colleagues investigated rice-bran-wax-structured macadamia oleogels and temperature-responsive water-in-oil emulsions, showing how organization of the lipid phase provides a route to tuning mechanical and functional properties, including delivery of bioactive compounds such as astaxanthin. Rasouli Pirouzian and co-workers, in their study of sucrose-free probiotic dark chocolate, addressed formulation optimization in relation to rheological characteristics and the viability of Saccharomyces boulardii. Although oleogels and functional chocolates sit far from drying mushrooms or printed gels on the supermarket shelf, they obey the same underlying rule: macroscopic material behavior emerges from an evolving internal structure whose formation is dictated by composition and processing conditions. This unity of principle is what makes the cross-disciplinary framing of edible soft matter so productive.

Taken together, the contributions point to a future in which food structuring moves from empirical process-property relations toward a genuinely mechanistic and predictive science. Achieving that will require closer integration of experimental characterization and modeling across length and time scales, with rheological and mechanical measurements increasingly combined with techniques that track microstructure, moisture distribution and deformation in real time during processing. Constitutive models, in turn, must evolve beyond reproducing behavior under narrow conditions toward formulations that capture the evolution of internal structure and its coupling to deformation, temperature and moisture transport. The Wageningen symposium and the resulting collection demonstrate the value of bringing food scientists, rheologists, physicists and solid-matter mechanicians to the same table. If that cross-fertilization continues, the next generation of foods may be designed, on paper, from the flow and setting behavior of their molecular ingredients upward.

Subject of Research: The fluid-to-solid state transitions of edible soft matter during food processing

Article Title: Edible soft matter in between fluid and solid states

Article References: Edible soft matter in between fluid and solid states. (n.d.). https://doi.org/10.1016/j.crfs.2026.101561

Image Credits: AI Generated

DOI: 10.1016/j.crfs.2026.101561

Keywords: edible soft matter, food rheology, food drying, 3D food printing, gelatinization, glass transition, oleogels, moisture transport, large-deformation mechanics, food structure, buckling, chocolate structuring