Review of recent advances in the preparation, properties, and applications of high internal phase emulsions

High internal phase emulsions (HIPEs) have internal phase volume fractions exceeding the close-packing limit (around 74%), which leads to semi-solid characteristics. These soft solids are increasingly being explored for use in food, medical, materials, and cosmetic products due to their unique properties. Nevertheless, a good understanding of the relationship between their composition, structure, and functionality is required. In this review, the formulation and preparation of HIPEs are described. In addition, the impact of the composition and structure of HIPEs on their functional attributes are discussed, such as their rheological properties and gastrointestinal fate. Finally, the application of HIPEs in various fields is described, especially in the food, medical, and material science industries. This review provides valuable information that will stimulate further research into the design and application of HIPEs. HIPEs can be prepared from one-step, two-step, phase inversion, and mold curing methods, which each have their own advantages and limitations for specific applications. Various kinds of bioactive substances can be encapsulated within HIPEs to improve their stability and bioavailability, including probiotics, vitamins, and nutraceuticals. HIPEs can also be used to replace hydrogenated fats in foods, thereby to improve their nutritional profiles. Researchers are currently identifying new methods and stabilizers for preparing HIPEs with enhanced stability and functionality.