Deamidated Zein Peptide Nanoparticles for Enhanced Quercetin Delivery: Structural Analysis, Stability, and Antioxidant Properties

To address the poor solubility, instability, and low oral bioavailability of quercetin (Q), Q-loaded nanoparticles (Q@DDZ) were fabricated using deamidated zein peptide (DDZ) via a pH-driven method. As a food-grade hydrophilic colloid, DDZ effectively improves the colloidal stability of the delivery system. Deamidation increased hydrophilic amino acids and surface negative charge. DDZ bound Q via static quenching with a higher binding constant (Ka = 2.25 × 103 L/mol) and more binding sites (n = 1.7561) than zein, along with stronger hydrogen bonding and hydrophobic interactions. Q@DDZ exhibited higher encapsulation efficiency (45.36–87.32%) and loading capacity (1.82–12.27%) than Q@zein, with a smaller particle size and better dispersibility. At 50.0 μg/mL Q, Q@DDZ showed 41.06% (DPPH) and 46.62% (ABTS) higher scavenging rates than free Q. It displayed excellent stability under acidic, high ionic strength, and thermal conditions (80 °C, 180 min). In simulated digestion, Q@DDZ delayed Q release in the oral and gastric phases and prolonged intestinal release, which indicated potentially improved bioavailability. This study provides mechanistic insights into deamidation-modified plant protein delivery systems for hydrophobic bioactives, offering new perspectives for the development of functional biopolymer gel materials.