Recent Advances in 3D-Printed Bigel Systems: Application for Bioactive Delivery, Fat Replacement, and Food Quality Sensing

Bigels are biphasic gel systems formed by combining oleogels and hydrogels. Bigels can encapsulate both hydrophilic and hydrophobic substances and have attracted interest as edible inks in the 3D printing of functional foods and sensors. This review evaluates bigel-based food systems, with emphasis on their applications as edible inks for 3D food printing, from a formulation–process–product perspective. The potential applications of bigel-based systems for bioactive delivery, fat substitution, lipid structuring, and color-responsive freshness indicators are reviewed. Bigels are being used as edible inks in 3D food printing applications, including single-nozzle, multi-material, and coaxial extrusion techniques. The types and ratios of hydrogels and oleogels influence printability by modifying phase organization, interfacial interactions, shear-thinning behavior, and structural recovery. The polysaccharide and/or protein networks in the hydrogel phase can be designed to provide shear-thinning and structural recovery properties, while the wax-, ethylcellulose-, and/or monoglyceride networks in the oleogel phases can be designed to provide mechanical strength. Conventional bigel systems have been investigated for the encapsulation and release of hydrophilic and lipophilic bioactive compounds under simulated gastrointestinal conditions, providing relevant information for the development of 3D-printable delivery systems. Bigel-based formulations have also been investigated for texture-modified foods, personalized nutrition, and plant-based products, with varying levels of evidence for their application in 3D-printed foods. Bigel-based fat replacers can offer improved nutritional profiles while still providing desirable textural and functional attributes of traditional fats. Color-responsive bigels have been investigated as freshness indicators for food quality monitoring, with potential applications in 3D-printed food systems and packaging materials. The limitations of 3D-printed bigels, including scale-up, cost, time, and print performance, are finally reviewed. By distinguishing well-documented applications of conventional bigels from emerging uses in 3D food printing, this review identifies critical research gaps that must be addressed to advance their practical use.