Astaxanthin-loaded whey protein/pullulan composite nanodispersions with enhanced stability, bioaccessibility, and antioxidant activity

In this study, a whey protein concentrate (WPC)/pullulan (PUL) nanodispersion system was developed by the emulsification–solvent evaporation method to encapsulate astaxanthin (AST) efficiently, and its physicochemical, structural, stability, and antioxidant properties were systematically evaluated. The nanodispersions exhibited a uniform pink appearance and significantly improved AST dispersibility compared with free AST. The encapsulation efficiency increased with PUL addition and reached a maximum of 73.93 ± 0.24% at 0.8 mg/mL. Spectroscopic analyses (UV–Vis, FTIR, fluorescence) revealed that hydrophobic interactions and hydrogen bonding among WPC, PUL, and AST were responsible for the formation of a stable interfacial structure. Storage stability demonstrated that 0.8 mg/mL PUL improved the 2-month AST retention to 85.06 ± 0.98% at 4 °C, significantly higher than the free AST. During in vitro digestion, WPC/PUL nanodispersions enhanced AST bioaccessibility and provided superior protection against pH- and heat-induced degradation. Antioxidant assays showed that the nanodispersions exhibited stronger DPPH and FRAP activities than free AST, indicating improved radical scavenging and reducing capacity. Overall, WPC/PUL/AST nanodispersions optimized at a pullulan concentration of 0.8 mg/mL exhibited high encapsulation efficiency exceeding 73% along with excellent long-term storage stability characterized by astaxanthin retention above 85% and a controlled release behavior that resulted in bioaccessibility greater than 57%. Prepared from food-grade materials via a simple emulsification–solvent evaporation method, this formulation offers a cost-effective and industrially scalable approach for the delivery of lipophilic bioactives such as astaxanthin in functional foods and nutraceuticals. • Whey protein and pullulan nanodispersions were prepared to encapsulate astaxanthin • Optimal pullulan at 0.8 mg/mL achieved 73.93% encapsulation efficiency and stable core-shell structure • Enhanced storage, pH, thermal, and gastrointestinal stability with highest astaxanthin retention • Nanodispersions improved stability and gastrointestinal bioaccessibility of astaxanthin • Antioxidant activity of astaxanthin was significantly enhanced after encapsulation