Pickering oil-in-water emulsions stabilized by hybrid plant protein-flavonoid conjugate particles

Abstract

Protein and polyphenols are often found as self-assembled structures in plants. Inspired by nature, this study looked at controlled engineering of hybrid nanoparticles using plant-based proteins and plant-derived flavonoid crystals. These nanoparticles have been shown to stabilize Pickering emulsions over several months. Potato protein (PoP) and flavonoid quercetin (QC) crystals in mass ratios (PoP:QC) ranging from 100:1 to 5:1, were used to fabricate the hybrid (PoPQC) nanoparticles at pH 7.0. The hydrodynamic diameter (dH), scattering pattern via small angle X-ray scattering (SAXS) and ζ-potential of the PoPQC as well as the protein conformation via circular dichroism (CD) and fluorescence were studied. The oil-in-water (O/W) emulsions stabilized by PoP and PoPQC nanoparticles with degrees of conjugation ranging 0.18–16.55% were analyzed by droplet sizing, ζ-potential measurements, and microscopy across a wide range of length scales. Both CD and SAXS analyses revealed that the conjugation of PoP with QC caused conformational changes in the secondary structure of PoP with the aromatic amino acids interacting with phenolic rings of QC, mainly through hydrophobic interactions. The addition of QC had a considerable impact on both particle size of PoPQC (∼50–∼400 nm) and consequently the droplet size of the corresponding Pickering emulsions stabilized by these spherical particles (d4,3 ∼2–∼35 μm). The droplet size increased significantly (p < 0.05) as the QC content of the particles was increased, whilst the ζ-potential became more negative. Nevertheless, the Pickering emulsions were capable of resisting coalescence over several months, suggesting the application of nature-inspired hybrid nanoparticles.