Complexation between flaxseed protein isolate and phenolic compounds: Effects on interfacial, emulsifying and antioxidant properties of emulsions

Interfacial and emulsifying properties of flaxseed protein isolate (FPI) and its phenolic complexes were studied, aiming to develop plant-based natural emulsifiers with improved interfacial and oxidative activity and adding value to the by-product of flaxseed oil production. Flaxseed polyphenols (FPP) and hydroxytyrosol (HT) were used as model phenolic compounds. The stability of emulsions produced using FPI, FPI-FPP and FPI-HT as emulsifiers was measured and correlated with their solubility and surface charge. The dynamic interfacial tension (DIT) and dilatational elasticity (E′) and viscosity (E”) were measured at flaxseed oil/water interface. The diffusion and penetration rate constants were calculated using DIT data. The complexation of FPI with FPP and HT significantly increased the diffusion rate constant at low FPI concentration (0.1 mg mL−1). At higher FPI concentration (from 1 to 10 mg mL−1), the DIT and penetration rate constant of FPI, FPI-FPP and FPI-HT were not different. The E’ of interfacial layer of FPI was lower than that of FPI-HT interfacial layer but was higher than that of FPI-FPP interfacial layer. The E” of FPI-FPP and FPI-HT complexes was lower than that of FPI. FPI-stabilised emulsion with higher charge density had higher physical stability compared to the emulsions stabilised by FPI-phenolic complexes which had lower charge density. The emulsions stabilised by FPI-FPP and FPI-HT complexes had higher antioxidative stability compared to that of FPI stabilised emulsion. The emulsions stabilised by FPI-FPP and FPI-HT complexes had higher red and yellow hue than the emulsion stabilised by FPI.