Hydroxyl group regulates self-assembly of hydroxybenzoic acid derivatives-diacylglycerol-β-cyclodextrin particles and formation of Pickering emulsions stabilized by these complexes : a combined experimental and simulation study

Abstract

This work combined multi-scale characterization with molecular dynamics (MD) simulations to investigate how hydroxyl group number of polyphenol molecules regulate self-assembly of polyphenol-diacylglycerol (DAG)-β-cyclodextrin (β-CD) ternary complexes and formation of resulting oil-in-water (O/W) Pickering emulsions using p-hydroxybenzoic acid (PHBA), protocatechuic acid (PCA), and gallic acid (GA) as models. XRD and ATR-FTIR confirmed hydrogen bonding dominated the complex process. Increasing hydroxyl groups reduced particle size and induced β-CD transition from cage- to channel-type structure in the complexes. Interfacial rheology and SAXS revealed that PCA-DAG-β-CD emulsions exhibited the fastest self-assembly rate with excellent resistance of interface layer to deformation. MD simulations confirmed weak hydrogen bonding and poor interfacial adsorption for PHBA-DAG-β-CD, while GA preferred to form GA-β-CD complexes in aqueous phase due to high hydrophilicity. PCA showed the most favorable self-assembly dynamics and strongest interfacial adsorption. PCA-50 % DAG-β-CD emulsion had the smallest oil droplets (3.9 ± 1.2 μm), the highest stability and excellent oxidative stability. This study highlights that stable Pickering emulsions require balancing hydrogen-bonding strength with polyphenol partitioning at the interface, providing mechanistic insight for designing DAG-based emulsions with polyphenols.