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