Physical bonding between sunflower proteins and phenols : Impact on interfacial properties

The complexation of proteins with phenolic compounds has been recently considered a promising route to improve the oxidative stability of food dispersions, such as oil-in-water (O/W) emulsions. However, the effect of such a complexation on the functional properties of proteins, such as their emulsifying and interfacial properties, has not been deeply studied yet. To gain insight on this matter, non-covalently bonded protein-phenol complexes were formed in aqueous dispersions. Highly pure sunflower protein isolate (SFPI, 94 wt%) and the polar phenolic compound chlorogenic acid (CGA) were mixed at neutral pH and the resulting complexes were characterised regarding their size and interfacial properties. Larger amounts of CGA led to more extensive complexation, therefore larger complexes, and reduction of free protein molecules. Hydrogen bonding was indicated as the main form of interaction between the elements. Sunflower proteins were able to adsorb at the oil-water interface and thereby to decrease the interfacial tension. The latter was further decreased when the complexes were used instead of the sole SFPI. Furthermore, O/W emulsion droplets stabilized by the complexes exhibited high stability against coalesence. These results indicate that the physical interactions between SFPI and CGA positively affected the interfacial and emulsifying properties of sunflower proteins. This is an intriguing bottom line regarding the challenges (e.g discoloration, loss of solubility and nutritional value) associated with full valorization of sunflower oil extraction residues and in general protein fractions rich in phenolic compounds