Design of multi-functional protein-based emulsifiers by conjugation and complexation for improved performance

Oil-in-water emulsions are widely employed as delivery systems for bioactive compounds in food and medical applications. However, their practical utility is often limited by susceptibility to physical and chemical degradation during processing and storage. To address these challenges, the functional properties of protein-based emulsifiers can be enhanced through complexation (non-covalent interactions) or conjugation (covalent binding of proteins to polysaccharides or polyphenols, including adducts formed in Maillard-type reactions) with polysaccharides or polyphenols. These strategies have shown promise in improving emulsion stability, environmental stress tolerance, and bioactivity. This review provides a comprehensive overview of recent advances in the development of protein-polysaccharide and protein-polyphenol complexes and conjugates, with a focus on their application in improving the stability of oil-in-water emulsions. Key topics include the mechanisms and methods of complexation and conjugation, techniques for their physicochemical and structural characterization, and their functional performance under varying conditions such as pH, ionic strength, temperature, freeze-thaw cycles, dehydration, oxidative stress, and gastrointestinal environments. The potential applications of these systems in the food industry are also highlighted, along with current challenges and future research directions.