Biophysical, Rheological, and Functional Properties of Complex of Sodium Caseinate and Olive Leaf Aqueous Polyphenolic Extract Obtained Using Ultrasound-Assisted Extraction

Abstract

This study demonstrated the use of ultrasound-assisted extraction to render aqueous extract polyphenolic compounds from olive leaves. Sodium caseinate-olive leaf extract complexes were produced using different amounts of olive leaf extract (0, 0.5, 1, 1.5, and 2% w/v). Turbidity, solubility, antioxidant activity (DPPH and ABTS assays), foaming capacity and stability and surface hydrophobicity tests were done on each sample. To study the interaction mechanisms and structural changes, fluorescence, and Fourier-transform infrared were performed. Oil-in-water emulsions of the complexes were prepared and analyzed for their emulsifying properties (emulsifying activity index and emulsifying stability index), rheological properties and viscosity. Addition of olive leaf extract at higher amounts (1.5 and 2%) enhanced the turbidity, water solubility, antioxidant activity, and foam capacity/stability of protein-polyphenol complexes. Moreover, it was found that non-covalent interactions mainly hydrogen bonds were the main interaction mechanism of sodium caseinate/ olive leaf extract complexes. Surface hydrophobicity of complexes decreased with increasing amount of olive leaf extract. In terms of emulsion formation, the activity and stability increased with increasing the concentration of olive leaf extract. Addition of olive leaf extract also slightly increased the viscosity and viscoelastic parameters (storage and loss modulus).