Protein-Based Probiotic Delivery Systems: Structural Basis, Functional Roles, and Food Applications.

Probiotics have considerable potential in regulating gut microbiota, improving metabolic health, and enhancing host immunity. However, during food processing, storage, and gastrointestinal digestion, they are susceptible to stresses including heat, acidity, oxygen exposure, moisture changes, and digestive fluids, leading to reduced viable cell counts and impaired functionality. Developing delivery systems that integrate protective capacity, processing adaptability, and food compatibility is, therefore, an important direction for advancing probiotic applications in foods. Food proteins possess favorable nutritional properties, biocompatibility, and structural design flexibility. They can undergo self-assembly driven by non-covalent interactions and further co-assemble with second components such as polysaccharides and polyphenols, thereby forming diverse delivery materials. Starting from protein assembly behavior, this review summarizes representative formation pathways of protein-based probiotic delivery materials and clarifies how different pathways lead to delivery structures, such as nanoparticles, nanogels, hydrogels, nanofibrils, microcapsule shells, nanocoatings, and nanofibers. On this basis, the three major functional roles of protein materials in probiotic delivery systems are summarized, namely, encapsulation, scaffold construction, and interfacial regulation. Their adaptability to different food matrices in food applications and the safety issues requiring attention are further discussed. This review aims to clarify the structural evolution of protein-based probiotic delivery systems from the origin of material formation, providing a reference for their structure-guided design, processing-pathway optimization, and expanded food applications.