Engineered nanoparticles from egg and milk proteins: A review of aggregation, gelation, colloidal behaviors and delivery systems.

The development of ideal materials for functional nanostructures remains a central challenge in designing efficient delivery systems for food, nutraceutical, and pharmaceutical applications. Egg and milk proteins are renewable, biodegradable, and biocompatible macromolecules with unique colloidal and structural features. Key proteins such as ovalbumin, ovotransferrin, β-lactoglobulin, α-lactalbumin, and caseins offer excellent gelling, emulsifying, and stabilizing abilities, making them well-suited for engineering diverse nanostructures. This review systematically compares the structural and physicochemical features of egg white and milk proteins, with a focus on their gelation mechanisms, aggregation behavior, and colloidal phase transitions. We examine how environmental factors including pH, ionic strength, temperature and protein concentration, influence solubility and intermolecular interactions, guiding nanoparticle formation. Recent advances in protein nanogels, hybrid nanoparticles, and protein-polysaccharide complexes are discussed, highlighting tuneable size, mucoadhesion, and encapsulation efficiency. Thermodynamic and molecular insights are integrated to reveal how heat-induced gelation, desolvation, and hybrid techniques enable precise nanoengineering. These protein nanoparticles show strong potential for improving solubility, protecting bioactives, enhancing epithelial permeability, and enabling targeted delivery. Challenges remain in immunogenicity and large-scale translation, but with rational design, egg and milk proteins represent promising platforms for biofunctional nanocarriers. This review bridges colloid science and nanoengineering to support the development of next-generation functional delivery systems based on natural proteins.