Nanocomplexes of whey protein fibrillar aggregates and quercetin as novel multi-functional biopolymeric ingredients: interaction, chemical structure, and bio-functionality

Abstract

This study aimed to use whey protein fibril (WPF) as a solubility enhancer for the quercetin at an acidic condition (pH 3.5) similar to the food beverages. The fibrillar aggregates formed by 6.0 h heating of whey protein solution showed the highest ability to form the soluble complexes with quercetin due to their high surface hydrophobicity. The sedimentation of quercetin during the storage was considerably decreased by binding to WPF. The association between WPF and quercetin through hydrophobic interactions and hydrogen bonding was detected by intrinsic tryptophan fluorescence and Fourier transform infrared spectroscopy. The morphology of complexes was investigated using atomic force microscopy. The surface charge density, apparent viscosity, surface tension, and foaming properties (foaming capacity and foam stability) of WPF were affected by binding to quercetin. The bound quercetin endowed whey protein nanofibrils with a strong radical scavenging activity and reducing power. The release of quercetin from WPF-quercetin complex was investigated under simulated gastrointestinal conditions. The results of this study revealed that whey protein nanofibril is an ideal natural nanoscale carrier for improving the water solubility of quercetin, and the resulting complexes can be used as novel multi-functional ingredients in the formulation of food products especially acidic beverages.