Whey Protein-Based Micro- and Nanocapsules Loaded with Quercetin: Design and Functional Properties

Whey–quercetin-loaded microspheres were synthesized using the solid/organic phase/water phase (S/O/W) method, whereas nanocapsules were prepared by interfacial polymerization. The resulting systems noted that Q1, Q2, and Q3 were characterized by polarized light microscopy (PLM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), high-performance liquid chromatography (HPLC), and antioxidant activity assays. Structural and spectroscopic analyses confirmed the successful encapsulation of whey and quercetin within both microsphere and nanocapsule systems. Q2 exhibited the highest encapsulation efficiency (51.79 ± 1.03%) and loading capacity (5.78 ± 0.71%), demonstrating its superior quercetin encapsulation performance. However, measurable antioxidant activity was detected exclusively in the nanocapsule formulations, whereas microspheres showed no detectable activity under the experimental conditions. Although the antioxidant activity of encapsulated quercetin was lower than that of free quercetin, the nanocapsules retained a radical-scavenging capacity, supporting their potential as effective delivery systems.