The research team, led by Evangelia Pasidi, Nikolaos Stratis and Patroklos Vareltzis, prepared sunflower-oil emulsions fortified with five different concentrations of vitamin D3, ranging from 10 to 100 micrograms per milliliter. The droplets were homogenized by ultrasound into a consistent coarse emulsion with a mean droplet diameter of roughly 2.3 to 2.5 micrometers, a size deliberately held constant across batches so that any differences in digestion behavior could be attributed to vitamin loading rather than to physical structure. The emulsions were then run through the INFOGEST protocol, the internationally standardized in vitro digestion method that mimics the oral, gastric and intestinal phases with realistic enzymes, bile salts, pH values and 37-degree incubation.

The critical action takes place in the intestinal phase, where pancreatin and bile salts are added and the pH is raised to 7. The researchers sampled independent digestion tubes every five minutes for two hours, isolated the micellar fraction by high-speed centrifugation and filtration, saponified the samples to liberate the vitamin from its lipid carriers, and quantified cholecalciferol by high-performance liquid chromatography with ultraviolet detection. The resulting time courses revealed a striking pattern: micellar vitamin D3 climbed rapidly during the first thirty minutes of intestinal digestion and then settled onto a plateau that persisted for the remainder of the two-hour experiment, with only small, statistically insignificant fluctuations.

Speed, it turns out, depends on dose. During the rising phase, micellar vitamin concentration grew at 0.093 micrograms per milliliter per minute for the most dilute emulsion, 0.323 for the intermediate one, and 1.112 for the most concentrated, differences that were statistically significant. But when the data were normalized to each emulsion’s initial vitamin load, the rates converged to statistically indistinguishable values between 0.006 and 0.01 per minute. In other words, the shape of the incorporation curve is an intrinsic property of the digestion system, not of how much vitamin was poured in at the start.

Concentration did matter, however, for efficiency. Within just five minutes of the intestinal phase, the dilute 10 microgram-per-milliliter emulsion had already delivered 60 percent of its initial vitamin into the micellar phase, while the richer formulations managed only 36 and 32 percent. By the plateau, the lowest dose retained a bioaccessibility index of 0.69, the highest of the series, whereas the intermediate concentrations plateaued near 0.53 to 0.56 and the highest dose recovered to 0.61. The authors attribute this inverse relationship to a finite pool of mixed micelles: bile salts are added once at a fixed concentration in the static protocol, fatty acid release is similar across samples because the oil-to-water ratio is constant, and so the micellar carrying capacity is capped. At low vitamin loads, nearly every encounter between a micelle and a dissolved vitamin molecule succeeds; at high loads, the micelles saturate and excess vitamin is left behind, possibly forming self-aggregates that never make it into the absorptive fraction.

To describe these dynamics quantitatively, the team built two competing mechanistic models, each partitioning the vitamin into an unreleased pool trapped in the lipid phase, a released pool in the bulk aqueous phase, and the micellar destination. Model 1 uses first-order kinetics throughout, with the release and micellization rates multiplied by a lipolysis-progress term, the running ratio of free fatty acids produced to the maximum producible, plus a loss term accounting for precipitation or degradation that prevents bioaccessibility from ever reaching 100 percent. Gastric lipolysis was measured separately by titration and proved minimal, reaching only 1.68 percent hydrolysis, a result consistent with the known ability of the Tween 80 emulsifier to displace gastric lipase from droplet surfaces.

Model 2 goes further, introducing an explicit population of micelles with a maximum number constrained by bile salt availability, a vitamin formation flux that slows as micellar capacity fills, and a dynamic loading term describing how much vitamin each individual micelle can carry. That loading follows Michaelis-Menten-style saturation in the released vitamin concentration and includes a swelling factor, reflecting prior evidence that solubilizing hydrophobic molecules physically enlarges micelles. Parameters were estimated with an Enhanced Scatter Search optimizer in MATLAB, and both models were rigorously validated using leave-one-out cross validation across the five concentrations, a fitting discipline that tests whether the equations genuinely generalize rather than merely memorize the training data.

Model 2 emerged as the stronger performer. Its mean absolute percentage error on training data was 12.3 percent versus 17.7 percent for Model 1, a statistically significant improvement, and its test-set error of 16.9 percent came with nearly 30 percent less variability than its rival. Perhaps most tellingly, both models independently converged on a lipolysis rate constant of 0.04 per minute with essentially zero variance across folds, indicating that the fat-hydrolysis machinery of the system was captured with high confidence. The micellization constants were consistently higher than every other rate constant in both models, supporting a key physiological conclusion: micellar incorporation is rapid and is not the rate-limiting step in making vitamin D3 bioaccessible. Instead, the bottleneck lies upstream, in the pace at which lipolysis frees fatty acids to build the micellar ferry in the first place.

The authors are candid about the model’s soft spots. Several parameters, notably the maximum micelle number and the intrinsic per-micelle loading capacity in Model 2, are structurally meaningful but practically unidentifiable from the current data, because they enter the equations as a product whose factors trade off against each other. They propose that future work directly measure micelle counts during digestion and track whole-digesta vitamin concentrations to close the mass balance, which would tighten these estimates. The study is also limited to a single coarse sunflower-oil emulsion under static conditions, whereas real digestion involves dynamic pH regulation and gallbladder bile delivered gradually rather than as a single bolus.

Even so, the implications for food and supplement design are considerable. Because bioaccessibility peaks at low doses and saturates beyond roughly 25 micrograms per milliliter, simply fortifying foods with more vitamin D3 yields diminishing returns once micellar capacity is exhausted; smarter strategies such as nanoemulsion carriers, which previous work has shown to boost D3 bioaccessibility relative to coarse emulsions, may achieve more. The integrated ODE framework itself is arguably the study’s most transferable product: by coupling release, lipolysis and micellization into one predictive engine, it offers supplement manufacturers and fortified-food formulators a computational tool for engineering release profiles in silico before committing to bench trials, and a foundation for embedding digestion chemistry into physiologically based models of nutrient delivery.

Subject of Research: Kinetic modelling of vitamin D3 bioaccessibility during simulated intestinal digestion

Article Title: Vitamin D 3 concentration behavior during intestinal in vitro digestion: an experimental and kinetic modelling approach

Article References: Vitamin D 3 concentration behavior during intestinal in vitro digestion: an experimental and kinetic modelling approach. (n.d.). https://doi.org/10.1016/j.jafr.2026.103310

Image Credits: AI Generated

DOI: 10.1016/j.jafr.2026.103310

Keywords: vitamin D3, bioaccessibility, in vitro digestion, INFOGEST, mixed micelles, lipolysis, kinetic modelling, ordinary differential equations, emulsions, HPLC, nutrient delivery, food fortification

Bigels are biphasic gel systems in which an oleogel—a network of structuring agents that traps liquid oil without any solid fat—meets a hydrogel, a water-based gel built from proteins or polysaccharides. Unlike conventional emulsions, both phases in a bigel are already solid-like on their own. When they are blended together, the result is a hybrid material whose architecture can be tuned continuously between two extremes: droplets of oleogel suspended in a continuous hydrogel, droplets of hydrogel dispersed in a continuous oleogel, or a bicontinuous structure in which both networks interpenetrate.

The review, authored by Bing Li, Mingyu Qi, Hengpeng Wang, Hui Zhang, and Xiangren Meng of Yangzhou University together with Bimal Chitrakar of Hebei Agricultural University, synthesizes a rapidly growing body of literature on how composition and processing govern the phase structure and interfacial properties of these systems. According to the authors, the choice of gelling agents, the ratio of hydrogel to oleogel, and fabrication variables such as mixing speed and temperature all shift the balance between the two phases. That shift, in turn, determines whether the finished bigel behaves as a firm, sliceable solid or a soft, spreadable cream—a degree of control that is crucial when a fat substitute must adapt to wildly different food matrices, from cookie dough to mayonnaise.

The rheological fingerprint of a bigel is central to its utility. Studies summarized in the review show that as the oleogel fraction increases, bigels generally display higher storage modulus, greater firmness, and more pronounced solid-like behavior, while hydrogel-dominated formulations yield softer, more elastic textures. Phase inversion—where increasing the concentration of structuring proteins such as soy protein isolate flips the continuous phase from water-continuous to oil-continuous—offers another powerful lever. By understanding these structure-property relationships, formulators can dial in the exact mechanical response a given product demands, whether that is the plasticity of butter, the cohesiveness of sausage fat, or the flow of a cake batter.

On the fat-substitution front, the review catalogues impressive progress. Bigels built from candelilla wax oleogels and guar gum hydrogels, gelatin and kappa-carrageenan hydrogels paired with monoglyceride olive oil oleogels, and rice bran wax systems with gums and monoglycerides have all been deployed to replace saturated or trans fats in cookies, shortbread, sausages, and fermented meat products. In semi-dry sausages, bigel systems partially replaced pork backfat while preserving physicochemical and sensory characteristics. Fish oil-based bigels have been formulated into low-fat mayonnaise with outstanding sensory and antioxidant properties, effectively converting a reformulation challenge into a vehicle for omega-3 fatty acids. Plant-based bigels have even been 3D-printed into meat analogues, exploiting whole soybean particles as Pickering stabilizers.

The mechanism behind this success is structural mimicry. Animal fats and commercial shortenings are, at the microstructural level, assemblies of fat crystals surrounding liquid oil. A bigel reproduces this hierarchy using two mutually immiscible gel networks instead: the oleogel phase supplies the lipid body and lubrication, while the hydrogel phase contributes water-holding capacity, elasticity, and a creamy particle-like sensation on the tongue. Research on konjac glucomannan-gelatin binary hydrogel bigels has shown that composition and phase ratio can even be tuned to adjust oral sensation—how the material melts, coats, and breaks down during chewing—bringing reformulated products closer to the sensory benchmark of the full-fat originals.

Where bigels arguably shine even brighter is in nutrient delivery. Because the two phases are chemically distinct, a single bigel can load hydrophobic bioactives such as curcumin, lycopene, beta-carotene, or lutein into the oleogel network while simultaneously hosting hydrophilic compounds like riboflavin, epigallocatechin gallate, or N-acetylneuraminate in the hydrogel phase. This co-delivery capability addresses a chronic problem in functional food design: many nutraceuticals are either poorly soluble in water or unstable in oil, but rarely can a single carrier accommodate both classes at once. Bigel systems produced through whey protein isolate cold-set gelation have demonstrated simultaneous vehiculation of curcumin and riboflavin, while glycerol monostearate-modified bigels have improved the co-delivery of curcumin and catechins from tea.

Controlled release is the second half of the delivery story. The review highlights bigel formulations that protect sensitive cargo through the harsh acidic environment of the stomach and release it further down the gastrointestinal tract. Lycopene carried in monoglyceride-beeswax oleogel paired with gellan gum hydrogel survived delivery far better than in simpler systems, and lutein in a bigel matrix showed superior gastric protection with controlled release and an enhanced antioxidant profile. Probiotics have benefited as well: lecithin-stearic acid and whey protein bigels boosted the survival of beneficial bacteria during simulated digestion, and Lactobacillus plantarum encapsulated in soy lecithin-beeswax oleogel with flaxseed gum hydrogel showed enhanced survival during both storage and gastrointestinal transit—findings with obvious implications for functional yogurts and spreads.

Heat-triggered release adds another dimension. Bigels based on candelilla wax oleogels and guar gum hydrogels have been engineered to remain stable during storage but release their payload when heated during cooking or consumption, a property that could allow flavor or nutrient release precisely at the moment of eating. Interface engineering pushes this further: modifying the boundary between oleogel and hydrogel phases in bigel beads has enhanced stability and prolonged the release of encapsulated bioactives, effectively turning each bead into a programmable microcapsule.

The authors frame their synthesis as a roadmap rather than a victory lap. Mapping structure-property-application relationships across oleogel-in-hydrogel, hydrogel-in-oleogel, and bicontinuous bigel types, they identify actionable levers—oleogelator selection, hydrogel composition, phase ratio, and processing—for improving texture and nutritional performance in low-fat formulations. Challenges remain, including oxidation of unsaturated oils within oleogel networks, scale-up of fabrication processes, and long-term storage stability. But with global burden of disease data pointing to persistent malnutrition and obesity across 204 countries, a technology that lets manufacturers remove the worst fats while adding protective nutrients in the same structural gesture is the kind of quietly elegant solution that could reshape the supermarket shelf.

Subject of Research: Bigel biphasic gel systems for fat substitution and nutrient delivery in foods

Article Title: Bigel with tailored functional characteristics: applications in fat substitution and nutrient delivery

Article References: Li, B., Qi, M., Wang, H., Zhang, H., Chitrakar, B., & Meng, X. (2026). Bigel with tailored functional characteristics: applications in fat substitution and nutrient delivery. Food Science and Biotechnology. https://doi.org/10.1007/s10068-026-02292-9

Image Credits: AI Generated

DOI: 10.1007/s10068-026-02292-9

Keywords: bigels, oleogel, hydrogel, fat substitute, nutrient delivery, rheology, food structure, bioactive compounds, controlled release, low-fat foods, probiotics, food science