Polymeric nanoparticles (PLGA) have been developed for the encapsulation and controlled release of quercetin and catechin. Nanoparticles were fabricated using a solvent displacement method. Physicochemical properties were measured by light scattering, scanning electron microscopy and ζ‐potential, X‐ray diffraction, infrared spectroscopy and differential scanning calorimetry. Encapsulation efficiency and in vitro release profiles were obtained from differential pulse voltammetry experiments. Antioxidant properties of free and encapsulated flavonoids were determined by TBARS, fluorescence spectroscopy and standard chelating activity methods. Relatively small (d≈ 400 nm) polymeric nanoparticles were obtained containing quercetin or catechin in a non‐crystalline form (EE ≈ 79%) and the main interactions between the polymer and each flavonoid were found to consist of hydrogen bonds. In vitro release profiles were pH‐dependant, the more acidic pH, the faster release of each flavonoid from the polymeric nanoparticles. The inhibition of the action of free radicals and chelating properties, were also enhanced when quercetin and catechin were encapsulated within PLGA nanoparticles. The information obtained from this study will facilitate the design and fabrication of polymeric nanoparticles as possible oral delivery systems for encapsulation, protection and controlled release of flavonoids aimed to prevent oxidative stress in human body or food products.

Many bioactive compounds are hydrophobic materials that are crystalline at ambient and body temperatures, which reduces their bioavailability and poses challenges to their successful incorporation into pharmaceuticals and functional foods. The aim of this study was to determine whether a hydrophobic crystalline bioactive component (quercetin) could be successfully incorporated into nanoemulsion-based delivery systems, and to evaluate the extent to which these delivery systems altered its bioaccessibility. The maximum amount of soluble quercetin that could be loaded into a carrier oil phase (medium chain triglycerides, MCT) at ambient temperature was C_Sat ≈ 0.15 mg mL⁻¹. At quercetin concentrations <C_Sat, nanoemulsions remained stable throughout 30 days storage at 5, 20 and 37 °C, i.e., no droplet growth, droplet creaming, or crystal formation were observed. At quercetin concentrations >C_Sat, nanoemulsions remained physically stable (no droplet growth or creaming), but quercetin crystals formed in the samples during storage. The bioaccessibility of quercetin was determined using an in vitro digestion model simulating the mouth, stomach, and small intestine. A higher percentage of quercetin was solubilized in the micelle phase after small intestine digestion when it was incorporated in nanoemulsions than when it was dispersed in either bulk oil or pure water. The bioaccessibility of crystalline quercetin was less than that of dissolved quercetin. The knowledge gained from this study is valuable for the rational design of delivery systems to incorporate crystalline hydrophobic bioactive compounds into pharmaceuticals and functional foods, and to increase their bioaccessibility.