Advances in the formation mechanism, influencing factors and applications of egg white gels: A review

Gels are extensively studied and used in various fields, including food, beverages, medicine, and daily living products. Egg white gels are particularly noteworthy due to their low cost, broad applications, and outstanding potential. However, a lack of comprehensive understanding of natural and modified egg white gels has limited their applications. Based on the introduction of the main protein components in egg white and their physicochemical properties, an overview of five typical categories of egg white gels produced by heat, alkalis, enzymes, ions, and acids treatments, respectively, was presented. Then the formation mechanisms of these gels and their main influencing factors as well were elaborated. Finally, their current applications and prospects in foods and materials were illustrated on the basis of their main characteristics. The five typical egg white gels share a common gel formation pattern, in which the proteins denature first and then coalesce into a gel driven by intermolecular forces. However, the mechanisms and processes of denaturation of egg white proteins differ significantly when treated with different ways, and therefore gels with various properties will be formed driven by different intermolecular forces. Egg white proteins undergo denaturation and structural unfolding after heat treatment and then form stiff gels driven by disulfide bonds and hydrophobic interactions, which are commonly found in steamed, boiled, and fried eggs. After denaturing and unfolding under alkali treatment, proteins can coalesce into transparent gels with high elasticity and strength driven by disulfide bonds, typically represented by preserved eggs. Egg white proteins denatured by heat and alkali treatment can also form peptide bond crosslinks catalyzed by enzymes (e.g., transglutaminase), or aggregated by electrostatic and hydrophobic interactions in the presence of ions (Ca2+, Zn2+, etc.), or coalesced in the presence of acids, resulting in the formation of enzymes, ions, and acid-induced gels, respectively. However, their strength is generally weak, and therefore the synergy of other factors is usually needed in applications. In conclusion, due to the wide-ranging application prospects and significant value of egg white gels in various fields such as foods and materials, it is of crucial importance to gain a deeper understanding of the gelation mechanisms and influencing factors, which is essential for improving the quality of gel products and developing novel egg-based gel products.