Protein serves as a crucial nutritional component in food, offering various functional properties such as emulsification, foaming, and gelation [1]. Protein gel predominantly comprises three-dimensional network structures formed through weak non-covalent crosslinking, such as hydrogen bonding, hydrophobic interactions, electrostatic attraction [2], finding widespread applications in food, biomedicine, and related domains. However, despite their utility, normal protein gels exhibit limited mechanical strength and low stability under high-shear conditions [[2], [3], [4]], thus posing a challenge in meeting evolving societal demands. Moreover, the formation of protein gels necessitates a minimum concentration threshold [5], often requiring high protein concentrations [6,7]. For example, natural whey protein (WP) can only form a gel at concentrations of 10 % or higher [8].

Protein fibrils, also known as amyloid fibrils, initially garnered attention in the study of certain human diseases like Alzheimer's and Parkinson's diseases [9]. Subsequent research revealed that numerous non-disease-related globular proteins, such as WP [10], lysozyme protein [11], egg albumin [12], and soybean protein [13], can also undergo fibrillation. Despite their structural resemblance to the fibrils implicated in amyloidosis, these globular proteins do not possess toxicity [14]. Their discovery opens avenues for innovative applications in biomedicine, food, and other fields.

Protein fibrils are generally prepared under conditions involving high acidity and heat [15], resulting in highly ordered, unbranched nano- or even micro-scale structures formed through hydrophobic interactions, electrostatic forces, hydrogen bonds, and van der Waals forces [16]. Due to their unique architecture, characterized by a high aspect ratio and exposure of multiple active functional groups, along with a more densely hydrogen-bonded network, nanostructured protein fibrils have significant advantages in gel properties. As a result, fibrous protein gels exhibit superior mechanical properties and stability compared to pure protein gels. In addition, the critical concentration required for the formation of fibrous protein gels is lower than that of pure protein gels. For instance, Wu et al. [14] demonstrated that the critical gel concentration for β-lactoglobulin (BLG) fibril gel decreased to 1.16 %, which was lower than that of BLG gel. Therefore, protein fibrils can be produced using fewer starting protein materials, potentially resulting in reduced costs. In addition, the shape and length of protein fibrils largely determine the properties of the resulting gels. If the length of protein fibrils is greater than their persistence length (Lp), they exhibit flexibility, impacting the elasticity of fibril gels. Conversely, fibrils with lengths less than their Lp values assume a rigid, straight-rod configuration devoid of flexibility [17].

Currently, extensive research has been conducted on protein gels, polysaccharide gels, and their compound gels [[18], [19], [20], [21]]. Prior investigations into protein fibrils have also been thorough. For example, Meng et al. [15,16,22,23] systematically reviewed the fibrillation conditions, characteristics, and applications of protein fibrils derived from different food sources, offering valuable insights into fibrillation processes, but they only briefly mentioned the application of protein fibers as gelling agents and did not elaborate on it. Fiber reinforced gel was also reviewed, but the term “fiber” mainly refers to chitosan fiber, chitin microfiber and cellulose microfiber, protein fibers only refer to whey protein fibers and rice bran protein fibers [21]. Or perhaps the content is quite extensive, but lacks comprehensive coverage of existing literature [24]. Therefore, as fibrils are more and more used to form gels, it is necessary to summarize this part in order to comprehensively and systematically grasp the status and progress of research on fibrous protein gels.

This review aims to provide a complete and detailed summary of protein fibril gel, spanning from proteins to protein fibrils and further to protein fibril-based gels. It covers the mechanism of protein fibril formation and the influencing factors in the process, as well as the principle, conditions, performance and discussion of single-component fibril gel, composite gel and fibril reinforced gel. The excellent gel properties of protein fibrils, their mechanisms and applications are mainly introduced. The excellent gel properties of different kinds of protein fibrils in the existing literature were summarized. The prospect and pending problems of fibril-based gels are also prospected, which serve as a resource for further research and the application of fibrous protein gels in diverse fields, especially in the food field.