Coassembly of Casein and Xanthan Gum as Nanocarriers for Lutein: Characterization, Interaction Mechanism, pH-Responsive Behavior, and Sustained-Release Potential

Oral delivery of lutein-based nutraceuticals is often limited by enzymatic degradation and structural instability in gastrointestinal environments, underscoring the need for nanocarriers with enhanced stability and tailored release profiles. Herein, casein (CA) and xanthan gum (XG) coassembled to form CA/XG nanocarriers via hydrogen bonding, hydrophobic interactions, and electrostatic complexation, which provided optimal microenvironments for lutein (Lut) encapsulation and delivery. At a CA:XG:Lut mass ratio of 1:1:1, the system achieved a 90.44% encapsulation efficiency and 20.91% loading capacity. CX@Lut nanocomplexes exhibited excellent redispersibility and superior physicochemical stability across a broad pH range, thermal conditions, and electrolyte concentrations. In in vitro simulated digestion, CA/XG nanocarriers effectively suppressed Lut premature release in gastric fluid while enabling controlled delivery to intestinal absorption sites with sustained release in intestinal and colonic environments. This work provides a theoretical foundation for designing biopolymer-based nanocarriers to enhance the stability and functional performance of hydrophobic bioactive compounds in food applications.