Polyphenol-protein interactions and changes in functional properties and digestibility

Polyphenols provide extensive health benefits including prevention of certain chronic diseases. Polyphenols form complexes with proteins resulting with functional, nutritional and structural changes in both proteins and polyphenols. There exist a variety of factors that influence protein-phenolic interactions, including type of protein, structure of phenolic compounds, and environmental factors such as temperature, pH, salt concentration and presence of certain reagents. Processing may change the interactions, as well as stability and bioaccesibility of phenolic compounds. Even though the exact mechanism of protein-phenolic interactions is still unknown, their effects on the structural, functional and nutritional properties of proteins and phenolic compounds have been investigated. Although there exist controversial results (due to different analytical techniques used), in general, the published studies reveal that secondary and tertiary structures and solubility of proteins are altered with enhanced thermal stability while antioxidant capacity and bioavailability of phenolic compounds would likely decrease. In this chapter, the chemistry behind protein-phenolic interactions, factors affecting these interactions, and the structural, functional and nutritional changes in proteins and phenolic compounds resulting from the interactions and the characterization methods used are described.