This study aimed to fabricate and characterize β-carotene–loaded filled hydrogel particles (FHPs) produced through complex coacervation between quince seed mucilage (QSM) and whey protein isolate (WPI). A spontaneous β-carotene nanoemulsion (NE) was first prepared by titrating an oil/Tween 80 mixture into a WPI solution, resulting in droplets with a Z-average of 0.1 µm. Incorporation of NE into a QSM solution followed by pH reduction to 4 triggered electrostatic complexation and yielded large FHPs with an average diameter of 29.2 µm and a ζ-potential of −2.37 mV. Microscopy showed that the FHPs exhibited a multinuclear structure in which β-carotene–loaded oil droplets were entrapped within a dense three-dimensional hydrogel matrix. FTIR confirmed the formation of new non-covalent interactions between QSM and WPI, while XRD indicated that β-carotene remained in an amorphous state in both systems. Thermal analysis (TGA/DSC) demonstrated that although initial degradation of FHPs started earlier than that of NE, complete decomposition required higher temperatures, indicating improved thermal stability. Storage tests over 35 days at 4, 25, and 60 °C further revealed that FHPs provided markedly greater chemical stability, with substantially higher β-carotene retention compared to NE (e.g., 32% vs. 4.5% at 25 °C). Weibull kinetic modeling confirmed extended half-lives for β-carotene in FHPs relative to NE (e.g., 81 days vs. 46 days at 4 °C). QSM–WPI coacervate-based hydrogel particles may serve as an efficient delivery system for improving the stability and controlled release of lipophilic bioactives in functional food and pharmaceutical applications.
