Development of protein-Polyphenol conjugates via free radical grafting method: Evaluation of physico-chemical and functional properties.

Lipid oxidation is a common phenomenon in emulsions that can be controlled by different techniques. Since proteins are beneficial emulsifiers but with low antioxidant ability, they are used in combination with an antioxidant compound such as polyphenols. Strong interaction between the protein and the polyphenol makes this combination more effective. In this study, soluble fraction of faba protein concentrate (FPC) was conjugated with tannic acid via the free radical grafting, and the structural and functional characteristics of the conjugates were determined in comparison with the mixture of the protein and tannic acid, and the pure protein. After dialysis, the amount of protein and polyphenol from the conjugated materials was significantly reduced, indicating that the unreacted peptides and polyphenol left the solutions. The reduction of the free amino and thiol groups in the protein specified the establishment of a strong interaction between the protein and tannic acid remaining in the solution. Moreover, the conjugate showed high ABTS, hydroxyl radical scavenging activity and ferric reducing power than the protein alone. As the purpose of making the conjugate was to be used as a multilayer film around the oil droplets, the film formation ability of the conjugates was investigated using Langmuir-Blodgett technique. Depending on the size of the trough and the nature of the compounds being used, the concentration and surface pressure required to form a strong film will vary. All samples showed an extended gas state of the film that changed abruptly and directly into a solid state below a critical surface area. Such LB film of the protein-tannic acid conjugate will be used to test its free radical scavenging ability so that its ability to prevent lipid oxidation in emulsions can be predicted.