Improved aqueous solubility, bioaccessibility and cellular uptake of quercetin following pH‐driven encapsulation in whey protein isolate

Summary The purpose of this study was to increase the water solubility and potential bioavailability of quercetin by encapsulation in whey protein isolate (WPI) based on a green, efficient pH‐driven method. According to the results, the water solubility of quercetin increased by 346.9: times after loading into WPI nanoparticles. When the initial quercetin concentration was 0.25 mg mL −1 and WPI was 2% w/v, the encapsulation efficiency reached 94.1%, the Z‐average diameter was 36.63 nm, and the zeta potential was −36.4 mV at pH 7.0. The fluorescence spectroscopy assay suggested the molecular complexation of quercetin and WPI at pH 12.0. X‐ray diffraction assay indicated the enclosure of amorphous quercetin in WPI. Correspondingly, the bioaccessibility increased from 2.76% to 31.23% and the Caco‐2 cell monolayer uptake increased from 0% to 2.12% after nanoencapsulation. This work confirmed that the pH‐driven method is an effective approach to prepare WPI–quercetin nanocapsules to improve physical and potentially biological properties of quercetin.