Hydrogels are a series of soft and wet materials with three dimensions of crosslinked networks. Hydrogels have attracted great attention due to their diverse functional properties, and their wide range of applications, such as in soft robots and actuators, stretched electronic devices, tissue engineering materials, controlled-release drug delivery vehicles, biomedicine materials, food science, and (bio)sensors. In general, there are four core concerns in hydrogel science, including the polymer source, structure fabrication, gel function, and gel applications. According to the logic that the “structure determines function”, it is believed that rational design of structures can effectively regulate the functions and applications of hydrogels. Hence, in the current review, “structure” as the core topic will be highly regarded, and the crosslinking mechanisms and structural diversity of hydrogels are comprehensively summarized. Additionally, hydrogels also show their great application potential in food science. Hence, the current review also pays more attention to the application of hydrogels in food nutrition and health, food engineering and processing, and food safety. It is whished that this review not only serves as a reference for improving the comprehensive understanding of the structural design of hydrogels but also provides a forward-looking idea for hydrogel applications in food science. Graphical abstract Graphical Abstract

Water‐in‐oil (W/O) emulsions can be used to encapsulate and control the release of bioactive compounds for nutrition fortification in fat‐based food products. However, long‐term stabilization of W/O emulsions remains a challenging task in food science and thereby limits their potential application in the food industry. To develop high‐quality emulsion‐based food products, it is essential to better understand the factors that affect the emulsions’ stability. In real food system, the stability situation of W/O emulsions is more complicated by the fact that various additives are contained in the products, such as NaCl, sugar, and other large molecular additives. The potential stability issues of W/O emulsions caused by these encapsulated additives are a current concern, and special attention should be given to the relevant theoretical knowledge. This article presents several commonly used methods for the preparation of W/O emulsions, and the roles of different additives (water‐ and oil‐soluble types) in stabilizing W/O emulsions are mainly discussed and illustrated to gain new insights into the stability mechanism of emulsion systems. In addition, the review provides a comprehensive and state‐of‐art overview of the potential applications of W/O emulsions in food systems, for example, as fat replacers, controlled‐release platforms of nutrients, and delivery carrier systems of water‐soluble bioactive compounds. The information may be useful for optimizing the formulation of W/O emulsions for utilization in commercial functional food products.