INFORM February 2025 Volume 36 (2)

20 • inform February 2025, Vol. 36 (2)

How different phases of the bigel organize depends on the ingredients, such as the structuring agents and the emulsi fier used, and on processing conditions, such as temperature and shear forces. These parameters affect the dispersed phase particle size, distribution, and morphology and, in turn, the mechanical and physical properties, like melting behavior and viscoelasticity. For example, Jiang and team found the oleogel-hydro gel ratio significantly impacts the bigel microstructure and mechanical properties of gelatin/ethylcellulose-glycerol monostearate (GMS) type bigels. They discovered phase inver sion from oil-in water, to bicontinuous, to a final water-in oil phase caused by an increase in the oil ratio (https://doi. org/10.1016/j.foodhyd.2021.107461). Moreover, our group found that with glycerol monostearate oleogel and gelatin hydrogel using a sucrose ester emulsifier with hydrophilic–lipo philic balance value (HLB) between one and six, the droplet size and mechanical stability of the bigel was directly affected by HLB value (https://www.mdpi.com/2304-8158/9/12/1857). Previous studies explored key process factors, such as the type and concentration of oleo- and hydro-gelators, the hydro gel-to-oleogel ratio, and emulsifier type and concentration and found they all play a crucial role in determining the texture, stability, and even nutritional value of food-grade bigels. The choice of structuring agent used in each phase, such as mono glycerides, natural waxes, stearic acid, and fatty alcohols for

oleogels, and sodium alginate, agar, carrageenan, pectin, and other polysaccharides for hydrogels, further defines the bigel’s spreadability and mechanical properties. In particular, add ing polysaccharides improves texture, as their large molecular weight and linear or branched structures can stabilize the gel network and strengthen the overall gel. For example, researchers reported creating 3D-printable fat analogs using vegetable oils, potato starch, and inulin that exhibited qualities similar to beef and pork fat, while main taining structure during cooking ( https://doi.org/10.1016/j. carbpol.2021.118285). In another study, researchers used ethylcellulose as an oleogelator and wheat starch as a hydro gelator to develop a food-grade bigel system as a fat sub stitute. It showed no significant difference during sensory analysis when tested in low-fat burgers compared to ani mal-fat burgers and displayed better cooking properties ( https://doi.org/10.1016/j.ifset.2022.103028). Additionally, a smooth, firm, margarine-like bigel formulated with can delilla wax and Xanthan gum demonstrated how increas ing hydrogel droplets as active fillers strengthens the bigel matrix when the dominant oleogel phase decreases ( https:// doi.org/10.1039/D3FO00002H). All these examples show how polysaccharides are effective as bigel hydrogelators; however, we found that substituting them with proteins can enhance their nutritional profile and make them even more attractive for food applications.

Examples of the overall appearance and confocal images of raw and cooked bigels with and without the addition of transglutaminase, along with Cryo-HR-SEM micrographs of TG-crosslinked bigel. In the confocal images (left, middle) the oil phase is in red (Nile red) and the water phase is in blue (Nile Blue A) (Scale bar 50 µm). Source: Davidovich-Pinhas lab