Plant protein-curcumin nanoparticles: How protein traits shape particle properties

Curcumin (Cur) is a hydrophobic nutraceutical with poor water solubility and low oral bioavailability. This study elucidates how plant protein molecular traits shape the assembly, structure, and digestive fate of Cur-loaded nanoparticles. Using a pH-shifting strategy, zein was employed as a hydrophobic core, while soluble legume protein fractions (Sup) or whey protein isolate (WPI, W) served as shell components. The resulting core-shell nanoparticles exhibited tunable particle sizes (40-130 nm), high uniformity (PDI < 0.18), and excellent loading capacity (up to 316.3 μg/mg_protein). Core-shell composition and ratio determined particle size and compactness, while shell protein identity modulated stability and encapsulation efficiency. Proteins with high hydrophobicity and flexible structures promoted stronger interactions with zein, yielding nanoparticles with superior Cur retention during storage (> 93 %) and re-dispersibility after freeze-drying (up to 86.8 %). Under simulated gastric conditions, zein-shell protein co-assemblies protected cleavage sites, reducing proteolysis and enabling delayed Cur release; the complex of zein with mung bean soluble protein at a 1: 4 ratio (4MsupZC) retained 75.1 % of Cur after 1 h of gastric digestion, outperforming other zein-shell protein composites. Peptidomic profiling confirmed that protein interactions modulated both shell and core digestibility. Correlation analysis supported these findings, revealing that zein incorporation attenuated most structure-particle and particle-digestion linkages, consistent with an interaction-masking effect that decouples shell-protein structure from functional outcomes. Collectively, this work establishes a multi-level structure-function relationship between protein molecular traits and nanoparticle performance, providing a mechanistic basis for designing scalable protein-based delivery systems for poorly soluble bioactives.