Medium/low internal phase Pickering emulsion gels stabilized by biopolymer: Stability mechanism, material design, and application.

Pickering emulsion gels have garnered significant attention due to their advantageous properties, including good stability, surfactant-free nature, and gel-like characteristics. Most prior research has focused on high internal phase Pickering emulsions. In recent years, however, medium/low internal phase (internal phase volume fraction <74%) Pickering emulsion gel (M/LIPPEG) has emerged as a new focus, primarily driven by the need to reduce the use of fats and irritating internal-phase solvents in food and pharmaceutical applications. This review emphasizes the interfacial behavior and gelation mechanisms of M/LIPPEGs. It compares their correlation and difference with the conventional emulsion gels and high internal Pickering emulsion gels, revealing that their stability stems from three interconnected and coexisting factors in real systems: the formation of free particle networks in the continuous phase, droplet aggregation, and jamming effects. The size and spatial presence of free particles were incorporated into the discussion on the jamming effect in emulsion gels and quantitatively analyzed, thereby clarifying the synergistic relationships among the three stabilization mechanisms. Subsequently, this review summarizes the advantages and limitations of M/LIPPEGs stabilized by various biopolymers, and suggests that hybrid particles represent a promising future research direction. Furthermore, strategies for the moderate addition of additional gelators to develop various types of M/LIPPEGs, such as filled Pickering emulsion gels, multiple Pickering emulsion gels, and Pickering bigels, are summarized. Finally, the current state of research and challenges of M/LIPPEGs are discussed across diverse applications, including fat substitutes, delivery systems, dysphagia diets, 3D/4D printing inks, and wound dressings. Currently, the research and development of M/LIPPEGs are still in the initial stage, and there are few examples of semi-solid and liquid emulsion gels with long-term stability. This paper will provide valuable information for the development of M/LIPPEGs and their applications in the food and pharmaceutical sectors.