Protein–polyphenol conjugates: Antioxidant property, functionalities and their applications

Proteins from different sources serve as primary food components, while polyphenols, as secondary metabolites, are abundantly present in plant. Both components play an important role in functional properties and quality of food products. Interaction between proteins and polyphenols, yielding “protein-polyphenol conjugate”, spontaneously occurs in most of food systems, and is known to have an impact on sensorial, functional, and nutraceutical properties of the food products. Protein-polyphenol conjugate can be implemented for improvement of food quality. In this article, mechanism and factors affecting protein-polyphenol interactions as well as the functionalities of protein-polyphenol conjugates, especially solubility, thermal stability, emulsifying, gelling and antioxidant properties, are revisited. The information on potential applications of protein-polyphenol conjugates in emulsions, protein-based films, and protein gels, as well as conjugates-based delivery systems is also discussed and reviewed. The interaction of proteins and polyphenols mainly results from non-covalent (H-bonding, electrostatic interactions) or covalent bonds taking place mostly based on the oxidation of proteins or polyphenol by enzymatic or non-enzymatic pathways. Moreover, protein-polyphenol interaction greatly depends on environmental conditions such as temperature and pH as well as on the conformation or type of proteins and polyphenols. The protein-polyphenol conjugates with higher thermal stability, antioxidant activities, better emulsifying properties and enhanced gelling property can be used as novel food additives for improvement of functionalities and quality of food products.